3.5.2 Effects of salinity on ROS production in sorghum

Under salinity stress, the production of reactive oxygen species (ROS) and an increase in the antioxidant enzymatic activity is a vital component of salt tolerance capacity of the plant. Salinity stress is linked with associated with enhanced antioxidant activity. Salinity decreased superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POX), and glutathione reductase (GR), and total antioxidant and phenol contents of tissues in sorghum cultivars [93]. The stem yield and soluble carbohydrate contents decreased as salinity level increased in sweet sorghums cultivars such as Keller and Sofra, and in one-grain sorghum cultivar Kimia, whereas it is also reported that at the higher salinity stress the sorghum cultivar 'Keller'showed high sucrose contents and stem yield [90].

### 3.5.3 Salinity and ion toxicity in sorghum

The large aggregation of toxic ions such as Na+ and Cl causes unsettling influence in ion uptake and K+ status of plant tissues. In this manner, it is the high K+ / Na+ perception and the conservation of low Na+ /K+ ratio in plant tissues, which describe as salt-tolerant genotypes [94]. The Na+ content in sorghum plant's tissue enhanced with excessive Na+ contents, and as a result of significant contrasts in Na+ contents of root and shoot among genotypes. Lesser accumulation of Na+ in the shoot might be due to lower Na+ uptake by the root or from the variation in the Na+ transfer rate to the shoot. For example, salt-tolerant sorghum variety (Jambo) amassed less Na+ concentration in the root and shoot tissues than the salt-sensitive

### Salinity Stress in Arid and Semi-Arid Climates: Effects and Management in Field Crops DOI: http://dx.doi.org/10.5772/intechopen.87982

genotypes and kept up lower Na+ /K+ ratios both in the root and shoot [95]. Particular testimony of Na+ ions in the shoot depends on leaf base [96], and enhancing levels of Ca2+ in the control condition increased plant growth and brought down Na+ take-up of sorghum plants [97]. The high Ca2+ accumulation in leaf and root tissues were observed in the salt-tolerant genotype Jambo than the salt sensitive varieties, Payam and Kimia [98].

## 3.6 Effects of salinity on sugarcane (Saccharum sp.)

Sugarcane is a key commercial and irrigated crop of the tropical and subtropical areas of the world [99]. Sugarcane is propagated further by setts from the stem cuttings of mature plants (one-year-old crop). Sugarcane is an important source of sugar in Asia and Europe. It also supplied the basic raw material for the production of jaggery (Gur), white sugar, and khandsari. Further, sugarcane juice is widely being used for drinking and beverage purposes.

#### 3.6.1 Salinity and sugarcane production

However, salinity during the flowering season imposed no detrimental impacts on

Sorghum is monocot species, and C4 plant with high photosynthetic capability and productivity has a spot with Poaceae family. The most of the sorghum species found in Australia and the rest of the world (Asia, Africa, Mesoamerica, India, and Pacific Oceans). Sorghum is the extremely beneficial yield, which can be used for essentialness source, human sustenance (grain), domesticated animals feed (grain and biomass), and mechanical reason (fiber or paper and treatment of natural sideeffect). The sorghum biomass is used as fuel (ethanol generation) and sugar sub-

The sorghum plant has an extraordinary adjustment potential to abiotic stresses,

), and the reduction reaches

/K+ ratio in plant tissues, which

/

particularly high salinity, which is significant for genotypes developing in an extreme environment [89, 90]. By and large, sorghum is considered as a respectable salinity tolerant species with genotypic varies from cultivar to cultivar. The thresh-

25% and 50% at 7 and 10 dSm1 respectively [34]. Salinity also influences the sorghum plant's physiological procedures, for example, seed germination rate, K+ take-up, net photosynthesis rate (Pn), biomass amassing, and biochemical qualities (chlorophyll substance or electrolyte leakage). In sorghum plants, a notable salinity induced phenotype of plant growth was observed after 4 days of exposure of 200 mM NaCl salinity stress [91]. Similarly, in sweet sorghum, salinity increase the

Under salinity stress, the production of reactive oxygen species (ROS) and an increase in the antioxidant enzymatic activity is a vital component of salt tolerance capacity of the plant. Salinity stress is linked with associated with enhanced antioxidant activity. Salinity decreased superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POX), and glutathione reductase (GR), and total antioxidant and phenol contents of tissues in sorghum cultivars [93]. The stem yield and soluble carbohydrate contents decreased as salinity level increased in sweet sorghums cultivars such as Keller and Sofra, and in one-grain sorghum cultivar Kimia, whereas it is also reported that at the higher salinity stress the sorghum

The large aggregation of toxic ions such as Na+ and Cl causes unsettling influence in ion uptake and K+ status of plant tissues. In this manner, it is the high K+

describe as salt-tolerant genotypes [94]. The Na+ content in sorghum plant's tissue enhanced with excessive Na+ contents, and as a result of significant contrasts in Na+ contents of root and shoot among genotypes. Lesser accumulation of Na+ in the shoot might be due to lower Na+ uptake by the root or from the variation in the Na+ transfer rate to the shoot. For example, salt-tolerant sorghum variety (Jambo) amassed less Na+ concentration in the root and shoot tissues than the salt-sensitive

duration of germination and reduced germination percentage [92].

cultivar 'Keller'showed high sucrose contents and stem yield [90].

fiber quality, but salinity after flowering resulted in reduced fiber quality.

3.5 Effects of salinity on sorghum [(Sorghum bicolor L.) Moench]

strate through aging (methane creation) [88].

old level of salinity for grain sorghum is (6.8 dS m1

3.5.2 Effects of salinity on ROS production in sorghum

3.5.3 Salinity and ion toxicity in sorghum

208

Na+ perception and the conservation of low Na+

3.5.1 Effects of salinity on sorghum

Climate Change and Agriculture

The salinity is a major environmental concern, responsible for a significant decline in sugarcane yield [100]. The sugarcane production is low under less fertile soil caused by salinity stress. This plant is categorized as a moderately salt sensitive species which can withstand the ECe up to 1.7 dS m1 . But, a further increase in EC could induce the adverse effects on its production. The detrimental impacts of salinity at germination or bud emergence stage mainly varied across the different species. Akhta et al. [101] reported a significant reduction in sprout emergence at different days after sowing under moderate and severe salinity stress depends on the nature of cultivars.

Under severe salinity stress conditions, growth could be significantly influenced by the accumulation of active oxygen species [102]. Vasantha et al. [103] observed the reduced leaf area index (LAI) of sugarcane by 36% during Formative Growth

Figure 2. Classification of field crops subjected to salinity stress. Extracted from Maas and Grattan [105].

Phase (FGP) and by 21% during Grand Growth Period (GGP). Additionally, they observed it decreased in biomass accumulation by 44% during FGP and 32% during GGP. The significant reduction in shoot and root biomass accumulation in sugarcane sprouts with increasing salinity level from normal to 120 mM NaCl [101]. Similarly, the increasing NaCl level resulted in a reduction of the shoot, root length, root volume, and leaf area of sugarcane seedlings by 36–41, 29–42, and 52–66%, and chlorophyll contents by 20.0–45.0% respectively [104]. The other factors which directly reflect the depletion of growth of sugarcane are linked with alterations in gas exchange parameters, and reduced transpiration and photosynthetic rates due to stomatal closure. As concern sugarcane yield and related traits, the sucrose juice (6%) of sugarcane was significantly reduced induced during Grand Growth Period (GGP) and so also the brix [103]. Similar to the millable canes (MC) and cane yield were reduced drastically under salinity. The MC decreased by 8.0–100% by exposing under salinity. Additionally, salinity caused negative impacts on cane yield, cane length, and single cane weight. Hence, the different field crops showed a different level of response to salinity stress depends on their genetic nature and as EC increased from 32 dS m1 , the yield is unacceptable from the most of the field crops (Figure 2) [105].

4.1.2 Closure of stomata

DOI: http://dx.doi.org/10.5772/intechopen.87982

of salt presented in soil environment [115].

4.2 Agronomic practices to cope salinity

input use efficiency (IUE) under salinity [116].

4.2.1 Water and nutrient management strategies

scheduling [119].

211

The ultimate response of plant subjected to salt stress is the closure of stomata [110]. The carbon dioxide assimilation decrease, as EC level increase (0–20 dS m1

Salinity occurs because of excessive accumulation of soluble salts via soil chemical properties and irrigated water. As a result of salinity stress and ion (Na+ and Cl) toxicity, the disturbance of ion imbalance occurs. By adopting some measures, these problems can manage plant growth by adopting some agronomic strategies such as water and nutrient management to improve soil health, plant growth, and

Irrigation water with high electrical conductivity (EC), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), and pH value also causes of salinity stress and plant growth reduction [117]. For the better survival of plant against salinity stress, a wise water management strategy is indispensable. Availability of good quality irrigated water is very vital for the survival of crop plant and yield [118]. The usage of good quality water is a good option to drain or leeched down the soluble salts from the root zone for better soil management and plant growth [118]. The canal water is a good replacement of brackish underground water for irrigation of field crops. If canal water is unavailable, the use of gypsum with brackish underground water is the best option, and it increased 25–294% rice yield and 182% wheat production under salinity [119]. Similarly application of canal water with 100% gypsum help to lower the ECe, pH value, and SAR of soil at 0–30 cm depths than saline water with 100% gypsum in field crops [120]. In case of less availability of good quality water, then the 25% gypsum amendment with unfit irrigating water is the best option. The wise use of less good quality is than never mix up with the unfit underground water or tub well water, and follows the irrigation

The management of salinity stress by nutrient management is the wise use of calcium (Ca2+) source in the form of gypsum (CaSO42H2O) and to improve soil water infiltration and better plant growth. Application of gypsum (100%), a

which results in plant growth reduction as well as the closure of stomata. This closure of stomata decreased the intracellular (Ci) CO2 partial pressure leading to hampering the Pn [5]. High salinity stress in rhizosphere decrease the transpiration rate (Tr), reduce the root water potential. Salinity stress enhances the biosynthesis of abscisic acid (ABA) and closes the stomata after reaching the guard cells. ABA passage from root to shoot causes closure of stomata and save the leave tissue from dehydration [54, 111]. Mostly, salinity hinders Pn in various crop plants. However, the sound reasons for lower Pn are stomatal closure, lower sink activity, reduced efficiency of rubisco, dislocation of vital cations from the membrane structure of leaf which lead to changes in permeability, and swelling and inefficiency of the grana [112], or might be due to the direct effects of salinity on conductance of stomata through a decrease in guard cell turgidity and CO2 partial pressure within plant cell [113]. Closure of stomata plays a vital role to survive with salinity stress. Chen and Gallie [114] studied that the ascorbate or ascorbic acid (AsA) redox state controls the transpiration rate and conductance of stomata. Stomatal guard cells control through Na+ which control transpiration rate according to the concentration

Salinity Stress in Arid and Semi-Arid Climates: Effects and Management in Field Crops

)

### 4. Management strategies

There are two groups of management strategies against salinity, first one natural adaptation responses towards salinity, and second are human-made management strategies to handle the salinity stress in field crops or plants. Tolerance or resistance of rice plant to salt stress involves many adaptive responses at molecular, cellular, and physiological levels. Among the natural management strategies by the plants to salinity stress based on three strategies: (i) exclusion of Na+ from the cytoplasm due to low uptake, or pumping out of the ion from the cell by active mechanisms, (ii) requisitioning of Na+ into the vacuole and (iii) preferential accumulation in the leaf tissues. However, the genotypes with high leaf Na contents proved to be generally salt sensitive, and only those can tolerate high tissue concentrations, which can sequester Na+ into the vacuoles of leaf cells. The essential processes leading to plant adaptation to high salinity include ionic, metabolic, and osmotic adjustments. The salt-resistant genotypes can successfully cope with osmotic and ionic stresses caused by the excess of NaCl; they can effectively reduce the oxidative damage and can detoxify the harmful metabolites [106].

#### 4.1 Natural adaptation responses towards salinity by plant

#### 4.1.1 Osmotic adjustment

Osmotic adjustment is the best and favorable plant physiological strategy to endure concentration of toxic ion (Na+ and Cl) in cytoplasm and compartmentalization in vacuoles, and define the salinity tolerance limits for plant [107]. Under osmotic stress, accumulation of free sugar, glycine betaine, organic solutes, and the proline in the plant's cytoplasm is also an important strategy to cope with the salinity stress [108]. This phenomenon is important to handle the antagonistic abiotic stresses, including salinity and maintain the homeostasis in osmotic or ionic signaling [17]. Similarly, leaf area or leaf architecture is also an important trait of the plant, which can reduce the excessive amount of Na+ in leaves through dilution effects and the transpiration force [109].

Salinity Stress in Arid and Semi-Arid Climates: Effects and Management in Field Crops DOI: http://dx.doi.org/10.5772/intechopen.87982

#### 4.1.2 Closure of stomata

Phase (FGP) and by 21% during Grand Growth Period (GGP). Additionally, they observed it decreased in biomass accumulation by 44% during FGP and 32% during GGP. The significant reduction in shoot and root biomass accumulation in sugarcane sprouts with increasing salinity level from normal to 120 mM NaCl [101]. Similarly, the increasing NaCl level resulted in a reduction of the shoot, root length, root volume, and leaf area of sugarcane seedlings by 36–41, 29–42, and 52–66%, and chlorophyll contents by 20.0–45.0% respectively [104]. The other factors which directly reflect the depletion of growth of sugarcane are linked with alterations in gas exchange parameters, and reduced transpiration and photosynthetic rates due to stomatal closure. As concern sugarcane yield and related traits, the sucrose juice (6%) of sugarcane was significantly reduced induced during Grand Growth Period (GGP) and so also the brix [103]. Similar to the millable canes (MC) and cane yield were reduced drastically under salinity. The MC decreased by 8.0–100% by exposing under salinity. Additionally, salinity caused negative impacts on cane yield, cane length, and single cane weight. Hence, the different field crops showed a different level of response to salinity stress depends on their genetic nature and as EC

, the yield is unacceptable from the most of the field crops

There are two groups of management strategies against salinity, first one natural adaptation responses towards salinity, and second are human-made management strategies to handle the salinity stress in field crops or plants. Tolerance or resistance of rice plant to salt stress involves many adaptive responses at molecular, cellular, and physiological levels. Among the natural management strategies by the plants to salinity stress based on three strategies: (i) exclusion of Na+ from the cytoplasm due to low uptake, or pumping out of the ion from the cell by active mechanisms, (ii) requisitioning of Na+ into the vacuole and (iii) preferential accumulation in the leaf tissues. However, the genotypes with high leaf Na contents proved to be generally salt sensitive, and only those can tolerate high tissue concentrations, which can sequester Na+ into the vacuoles of leaf cells. The essential processes leading to plant adaptation to high salinity include ionic, metabolic, and osmotic adjustments. The salt-resistant genotypes can successfully cope with osmotic and ionic stresses caused by the excess of NaCl; they can effectively reduce the oxidative damage and can

increased from 32 dS m1

Climate Change and Agriculture

4. Management strategies

detoxify the harmful metabolites [106].

effects and the transpiration force [109].

4.1.1 Osmotic adjustment

210

4.1 Natural adaptation responses towards salinity by plant

Osmotic adjustment is the best and favorable plant physiological strategy to endure concentration of toxic ion (Na+ and Cl) in cytoplasm and compartmentalization in vacuoles, and define the salinity tolerance limits for plant [107]. Under osmotic stress, accumulation of free sugar, glycine betaine, organic solutes, and the proline in the plant's cytoplasm is also an important strategy to cope with the salinity stress [108]. This phenomenon is important to handle the antagonistic abiotic stresses, including salinity and maintain the homeostasis in osmotic or ionic signaling [17]. Similarly, leaf area or leaf architecture is also an important trait of the plant, which can reduce the excessive amount of Na+ in leaves through dilution

(Figure 2) [105].

The ultimate response of plant subjected to salt stress is the closure of stomata [110]. The carbon dioxide assimilation decrease, as EC level increase (0–20 dS m1 ) which results in plant growth reduction as well as the closure of stomata. This closure of stomata decreased the intracellular (Ci) CO2 partial pressure leading to hampering the Pn [5]. High salinity stress in rhizosphere decrease the transpiration rate (Tr), reduce the root water potential. Salinity stress enhances the biosynthesis of abscisic acid (ABA) and closes the stomata after reaching the guard cells. ABA passage from root to shoot causes closure of stomata and save the leave tissue from dehydration [54, 111]. Mostly, salinity hinders Pn in various crop plants. However, the sound reasons for lower Pn are stomatal closure, lower sink activity, reduced efficiency of rubisco, dislocation of vital cations from the membrane structure of leaf which lead to changes in permeability, and swelling and inefficiency of the grana [112], or might be due to the direct effects of salinity on conductance of stomata through a decrease in guard cell turgidity and CO2 partial pressure within plant cell [113]. Closure of stomata plays a vital role to survive with salinity stress. Chen and Gallie [114] studied that the ascorbate or ascorbic acid (AsA) redox state controls the transpiration rate and conductance of stomata. Stomatal guard cells control through Na+ which control transpiration rate according to the concentration of salt presented in soil environment [115].

#### 4.2 Agronomic practices to cope salinity

Salinity occurs because of excessive accumulation of soluble salts via soil chemical properties and irrigated water. As a result of salinity stress and ion (Na+ and Cl) toxicity, the disturbance of ion imbalance occurs. By adopting some measures, these problems can manage plant growth by adopting some agronomic strategies such as water and nutrient management to improve soil health, plant growth, and input use efficiency (IUE) under salinity [116].

#### 4.2.1 Water and nutrient management strategies

Irrigation water with high electrical conductivity (EC), sodium adsorption ratio (SAR), residual sodium carbonate (RSC), and pH value also causes of salinity stress and plant growth reduction [117]. For the better survival of plant against salinity stress, a wise water management strategy is indispensable. Availability of good quality irrigated water is very vital for the survival of crop plant and yield [118]. The usage of good quality water is a good option to drain or leeched down the soluble salts from the root zone for better soil management and plant growth [118]. The canal water is a good replacement of brackish underground water for irrigation of field crops. If canal water is unavailable, the use of gypsum with brackish underground water is the best option, and it increased 25–294% rice yield and 182% wheat production under salinity [119]. Similarly application of canal water with 100% gypsum help to lower the ECe, pH value, and SAR of soil at 0–30 cm depths than saline water with 100% gypsum in field crops [120]. In case of less availability of good quality water, then the 25% gypsum amendment with unfit irrigating water is the best option. The wise use of less good quality is than never mix up with the unfit underground water or tub well water, and follows the irrigation scheduling [119].

The management of salinity stress by nutrient management is the wise use of calcium (Ca2+) source in the form of gypsum (CaSO42H2O) and to improve soil water infiltration and better plant growth. Application of gypsum (100%), a

combination of gypsum + farmyard manure (FYM) + H2SO4, CaSO42H2O + FYM + chiseling, pyrite, and humic acid (HA), in rice, wheat, sorghum crop improved soil properties, plant biomass, and yield [118, 121]. Application of N, P, K, S, Zn, B, and Mn separately or with different combination increased rice total above ground biomass and grain production under salt-affected soils [122, 123]. Humic acid improves nutrients availability by chelating with unavailable nutrients (P, K, Ca, Fe, Zn, and Cu) and buffered pH value, and enhanced soil microbial, enzymatic and physiological activities, and plant growth under salinity [121, 124]. The combined effect of humic acid (HA) with gypsum (24 and 48 kg/ha) in rice was higher than the alone effect of HA on ECe and SAR due to its chelating effect with other nutrients subjected to salinity [125]. The use by-product of sugarcane (press-mud), green manure, poultry manure, and Sesbania as a cover crop for amendment of soil to reduce the effect of salinity which is a source of macro and micronutrients especially Zn and S in crops are also good options [126]. There are some other useful agronomic practices to reduce the effect of salt stress on the plant are periodic use of fresh water, subsoiling, deep tillage, sanding, and application of organic and inorganic fertilizers, and adopting crop rotation [118].

collective application of advanced molecular mapping, genomics, transcriptomics,

Salinity Stress in Arid and Semi-Arid Climates: Effects and Management in Field Crops

Many salt tolerance genes have been discovered by using traditional breeding techniques, such as subtractive hybridization, differential hybridization, and through genetic information from the model organism. Furthermore, protein crystallography, a proteomic study has enabled researchers to the exploration of the protein's structure and function for salt tolerant genes. After salt tolerance gene identification, many latest techniques for foreign gene transformation to the desired plant can help to improve field crop production. Such as CRISPR CAS9, PEGmediated gene transfer, electroporation, partial or the micro projectile bombardment, microinjection, and Agrobacterium-mediated gene transfer. These tech-

Salinity stress is the one of the key growth hampering agents for field crops. Salinity not only effects the plant growth but also affect yield by creating osmotic, ionic, and oxidative stresses. From this chapter, it is concluded that, the rice (sensitive), sugarcane and maize (moderately sensitive, wheat and sorghum (moderately tolerant), and cotton (tolerant) subjected to salinity. There are many

management strategies, including traditional soil, water, and nutrient management strategies as well as genetic modification and by using molecular breeding, tools are suitable for producing salt tolerance cultivars. The bunch of information in this chapter wills able the scientific community to understand the role of salinity stress

Sajid Hussain is thankful to China National Rice Research Institute for the necessary facilities and to Chinese Academy of Agricultural Sciences, China for the award of Postdoctoral Fellowships. SH is giving special thanks to Prf. Dr. Qianyu Jin and Junhua Zhang for motivated me to write this chapter and provided my friendly environment to complete this task. We are also highly thankful to Dr. M. Ashraf and M. Shaukat, for contributing in chapter write up and providing us supporting

and proteomics approaches.

niques are available for many crops.

5. Conclusions and future perspectives

in field crops and their management options [115].

Acknowledgements

material.

213

4.2.4 Molecular breeding to improve salt tolerance

DOI: http://dx.doi.org/10.5772/intechopen.87982

### 4.2.2 Application of hormones regulators

The hormonal imbalance is one of the salinity effects on plants. There are many plant growth regulators being used as hormones regulator or plant growth regulators such as aminoethoxyvinylglycine (AVG), ethephon, and 1-methylcyclopropene (1-MCP) for ethylene inhibitor under salt stress and enhance the boles and spikelets development in rice and cotton respectively [4]. Similarly, exogenous applications of abscisic acid (ABA), brassinosteroids (BRs) or their analogs (D-31, D-100, etc.) are good option to improve plant performance under salinity [127, 128].

#### 4.2.3 Traditional breeding for salt tolerance

To meet the demand for food and livelihood of the increasing population on the globe, the increase in the agriculture production is indispensable. Therefore, many efforts have been made to improve salinity tolerance capacity of the crops through conventional plant breeding and biotechnology [129]. Salinity tolerance is a complex trait both at the genetic and physiological level and controlled by polygenes. It has been speculated that salinity tolerance seems to be regulated by independent genes at different growth stages [130]. Traditional breeding has been considered as a more promising and efficient approach to improve the salt tolerance. Conventional breeding involves identification of QTLs using closely linked markers along with their phenotypic evaluation. One of the best-studied QTL for salt tolerance; saltol was identified by the conventional breeding approach in rice [131]. This QTL was found to control shoot Na+ /K+ ratio at the seedling stage. So, the identification of new QTLs and later pyramiding of these QTLs would lead to the development of the more promising salt tolerant line. Marker-assisted backcrossing (MAB), which is one of the best traditional breeding approaches that involve the transfer of the specific allele at target locus from donor to recipient parent, can be used for this purpose. Traditional breeding mainly relied on the use of diverse germplasm resources to identify the landraces showing salt tolerance and then map the locus responsible for salt tolerance. This can be seen as an advantage as well as a disadvantage. Salt tolerance is an outcome of involvement of diverse cellular processes like ion transport and homeostasis, osmoregulation, and oxidative stress protection. Identification and characterization of key genes for salt tolerance would need the

collective application of advanced molecular mapping, genomics, transcriptomics, and proteomics approaches.


**2. Control of microbial virulence and resistance**

### **2.1 Quorum sensing inhibition**

Quorum sensing (QS) is a cellular signaling system, which is developed in response to population cell density [3, 4]. QS cascade relays on the release of signaling molecules called QS autoinducers/signals. The QS signals are produced at low levels with the start of microbial growth and accumulate upon increase in the cell density. Quorum sensing signals coordinate the microbial virulence behaviors such as secretion of toxins, secretion of exoenzymes, microbial motility, adhesion and biofilm assembly [11]. Furthermore, microbial communication systems have been assigned in fungi [12] and viruses [13]. Studies of QS provide significant insights into different mechanisms that control the interactions in microbial communities and how these interactions affect microbial pathogenesis. Several QS systems are well understood including Gram-negative bacteria that produce acyl-homoserine lactone (AHL) signals, including *Pseudomonas aeruginosa*, *Vibrio* sp., *Acinetobacter baumannii* and *Serratia marcescens* [5, 14, 15]. Alternatively, Gram-positive species such as *Staphylococcus aureus* utilize autoinducer peptide (AIP)-based QS systems [16].

Various strategies for quorum sensing inhibition have been explored. The quorum sensing inhibition approaches could be accomplished via interference with the synthesis of QS signals, elimination of the signal accumulation and disruption of signal-receptor interaction [17–19].

#### *2.1.1 Interference with the synthesis of the autoinducing signals*

One of the main quorum sensing inhibiting approaches is the interference with the synthesis of the autoinducing signals [20]. AI-2 compounds are considered as "universal" signal molecules of Gram-negative and Gram-positive bacteria [14, 21]. Moreover, they are encountered in species communications. The biosynthesis of AI-2 requires two main enzymes: methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTA/SAH nucleosidase) and LuxS. AI-2 molecules contribute in various virulence behaviors, biofilm formation and host-pathogen interaction. Therefore, targeting AI-2 elaborates broad spectrum quorum sensing inhibition [22, 23]. In this instance, Gutierrez group have identified the transition analogs, 5′-methylthio- (MT-), 5′-ethylthio-(EtT-) and 5′-butylthio- (BuT) DADMeimmucillin, which specifically bind and inhibit MTA enzymes in *Escherichia coli* O157:H7. Also, 4,5-dihydroxy-2,3-pentanedioneS-ribosyl-homocysteine analogs have been developed as competitive inhibitor of LuxS [24–26].

On other instance, inhibiting AHL-synthesis has been extensively studied, for instance, triclosan inhibited both N-3-oxo-dodecanoyl-l-homoserine lactone and N-butyryl-l-homoserine lactone [27, 28], anthranilate derivatives are a *Pseudomonas* quinolone signal inhibitors [28], and proanthocyanidins have been approved as inhibitor of LasI/RhlI AHL synthases expression [29]. Furthermore, precursors of *Pseudomonas* quinolone signals (PQS) such anthranilatic acid derivatives reduced the pathogenicity of *P. aeruginosa* in lung-infected mice [15].

#### *2.1.2 Elimination of the QS signals accumulation*

Other common strategy is eliminating the accumulation of the QS signals, which have been attained by degrading the QS signal using enzymes or through sequestering the signal by synthetic polymers [30, 31] or utilizing antibodies that bind with the signals. Synthesized monoclonal antibodies (AP4-24H11) by Park group provoke high binding affinity for sequestering AIP-IV and decrease α-hemolysin

**195**

*New Approaches for Competing Microbial Resistance and Virulence*

production in *S. aureus* with relief of abscess formation in the infected murine model [32]. Kaufmann and coauthors inhibited the *P. aeruginosa* QS cascade via development of AHL-specific monoclonal antibodies. Synthetic polymers such as itaconic acid sequester the signaling molecules AHL and attenuate QS in *V. fischeri*

Moreover, disturbing enzymes responsible for biosynthesis of QS signals is a chief method, which affects both production and accumulation of different signals and perturb quorum sensing circuit [30]. Acylases, lactonases and oxidoreductases are the widely identified enzymes that target AHLs. AHL lactonases are broad AHL degrading enzymes, which produce its effect via hydrolyzing the ester bond of the AHL ring [34]. Lactonases have been isolated from various *Bacillus* sp., which harbor *aiiA* (autoinducer inactivation gene) [35, 36]. Ulrich study showed that, the heterologous expression of *aiiA* in *Burkholderia thailandensis* and *P. aeruginosa* lowered the levels of AHL and QS-related virulence factors [37]. Other important AHL lactonases are AttM and AiiB, which have been isolated from *Agrobacterium* sp. [38], AhlD from *Arthrobacterium*, AhlK from *Klebsiella* [39] and AidC from *Chryseobacterium* [40], QsdA from *Rhodococcus erythropolis* strain W2 [41], AiiM of *Microbacterium testaceum* [42], AidH of *Ochrobactrum* sp. T63 [43] and QsdH of *Pseudoalteromonas yunnanensis* [44]. Furthermore, paraoxonases 1, 2 and 3 (PON1 to −3) are mammalian lactonases were identified in the airway epithelia and mam-

AHL acylases enzymes (*aiiD)* and homologs were found in *Ralstonia* [46], *Actinoplanes utahensis* and *Pseudomonas* sp. The purified AiiD protein has the ability to degrade 3OC10HSL into HSL and 3-oxodecanoic acid. In addition, PvdQ, QuiP and HacB are specific AHL acylases of *P. aeruginosa*, in addition, HacA and HacB acylases of *Pseudomonas syringae* [47, 48]. Furthermore, the broader substrate specificity of AHL acylase (AhlM) was detected in *Streptomyces* sp. strain M664

Oxidoreductases from *Rhodococcus erythropolis* inactivates AHLs (oxidation or reduction) with subsequent elimination of bacterial virulence *in vivo. Rhizobium* strain NGR234 possess diverse AHL-inactivation loci: *dhlR*, *qsdR1* and *qsdR2*, with lactonases activity, *aldR*, and *hydR-hitR* [50]. Enzymatic degradation of other QS autoinducers have been described: *carA* and *carB* from *Bacillus*, *E. coli* DH10B, *Staphylococcus* and *Pseudomonas* as the genes responsible for inhibition of DSF signaling [51]. Hod (3-hydroxy-2-methyl-4(1*H*)-quinolone 2,4-dioxygenase) stimulates the cleavage of PQS and attenuates PQS-regulated virulence factors. Roy and coauthors elicit the AI-2 activation activity of endogenous LsrK in *E. coli*, however, exogenously phosphorylation of AI-2 by LsrK eliminates its intracellular transport

Interference with signal detection through eliminating the QS signal-receptor binding represents a successful approach [53, 54]. Various synthetic and natural AHL analogs have been reported to block the binding of the signal with specific receptors in *P. aeruginosa* and *Vibrio* sp. The prototype signal inhibitors, halogenated furanones, which are produced from *Delisea pulchra* represent a good example [55, 56]. Natural analogs have been also isolated with signal-receptor interference including ajoene [57], eugenol [58], flavonoids [59], iberin [60], furocoumarins [61], ellagic acid, penicillanic acid and patulin [62], phenethyl amide [63] and

The synthetic furanone derivative C-30 interferes and hinders the interaction of AHLs with the receptors [65]. Other furanone analogs have been developed

with activity towards medium- and long-chain AHLs [49].

and hinders subsequent activation of AI-2 [52].

1H-pyrrole-2-carboxylic acid [64].

*2.1.3 Elimination of the QS signal-receptor interaction*

*DOI: http://dx.doi.org/10.5772/intechopen.90388*

[31, 33].

malian sera [45].

*Microorganisms*

**2.1 Quorum sensing inhibition**

of signal-receptor interaction [17–19].

*2.1.1 Interference with the synthesis of the autoinducing signals*

have been developed as competitive inhibitor of LuxS [24–26].

the pathogenicity of *P. aeruginosa* in lung-infected mice [15].

*2.1.2 Elimination of the QS signals accumulation*

One of the main quorum sensing inhibiting approaches is the interference with the synthesis of the autoinducing signals [20]. AI-2 compounds are considered as "universal" signal molecules of Gram-negative and Gram-positive bacteria [14, 21]. Moreover, they are encountered in species communications. The biosynthesis of AI-2 requires two main enzymes: methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTA/SAH nucleosidase) and LuxS. AI-2 molecules contribute in various virulence behaviors, biofilm formation and host-pathogen interaction. Therefore, targeting AI-2 elaborates broad spectrum quorum sensing inhibition [22, 23]. In this instance, Gutierrez group have identified the transition analogs, 5′-methylthio- (MT-), 5′-ethylthio-(EtT-) and 5′-butylthio- (BuT) DADMeimmucillin, which specifically bind and inhibit MTA enzymes in *Escherichia coli* O157:H7. Also, 4,5-dihydroxy-2,3-pentanedioneS-ribosyl-homocysteine analogs

On other instance, inhibiting AHL-synthesis has been extensively studied, for instance, triclosan inhibited both N-3-oxo-dodecanoyl-l-homoserine lactone and N-butyryl-l-homoserine lactone [27, 28], anthranilate derivatives are a *Pseudomonas* quinolone signal inhibitors [28], and proanthocyanidins have been approved as inhibitor of LasI/RhlI AHL synthases expression [29]. Furthermore, precursors of *Pseudomonas* quinolone signals (PQS) such anthranilatic acid derivatives reduced

Other common strategy is eliminating the accumulation of the QS signals, which have been attained by degrading the QS signal using enzymes or through sequestering the signal by synthetic polymers [30, 31] or utilizing antibodies that bind with the signals. Synthesized monoclonal antibodies (AP4-24H11) by Park group provoke high binding affinity for sequestering AIP-IV and decrease α-hemolysin

**2. Control of microbial virulence and resistance**

Quorum sensing (QS) is a cellular signaling system, which is developed in response to population cell density [3, 4]. QS cascade relays on the release of signaling molecules called QS autoinducers/signals. The QS signals are produced at low levels with the start of microbial growth and accumulate upon increase in the cell density. Quorum sensing signals coordinate the microbial virulence behaviors such as secretion of toxins, secretion of exoenzymes, microbial motility, adhesion and biofilm assembly [11]. Furthermore, microbial communication systems have been assigned in fungi [12] and viruses [13]. Studies of QS provide significant insights into different mechanisms that control the interactions in microbial communities and how these interactions affect microbial pathogenesis. Several QS systems are well understood including Gram-negative bacteria that produce acyl-homoserine lactone (AHL) signals, including *Pseudomonas aeruginosa*, *Vibrio* sp., *Acinetobacter baumannii* and *Serratia marcescens* [5, 14, 15]. Alternatively, Gram-positive species such as *Staphylococcus aureus* utilize autoinducer peptide (AIP)-based QS systems [16]. Various strategies for quorum sensing inhibition have been explored. The quorum sensing inhibition approaches could be accomplished via interference with the synthesis of QS signals, elimination of the signal accumulation and disruption

**194**

production in *S. aureus* with relief of abscess formation in the infected murine model [32]. Kaufmann and coauthors inhibited the *P. aeruginosa* QS cascade via development of AHL-specific monoclonal antibodies. Synthetic polymers such as itaconic acid sequester the signaling molecules AHL and attenuate QS in *V. fischeri* [31, 33].

Moreover, disturbing enzymes responsible for biosynthesis of QS signals is a chief method, which affects both production and accumulation of different signals and perturb quorum sensing circuit [30]. Acylases, lactonases and oxidoreductases are the widely identified enzymes that target AHLs. AHL lactonases are broad AHL degrading enzymes, which produce its effect via hydrolyzing the ester bond of the AHL ring [34]. Lactonases have been isolated from various *Bacillus* sp., which harbor *aiiA* (autoinducer inactivation gene) [35, 36]. Ulrich study showed that, the heterologous expression of *aiiA* in *Burkholderia thailandensis* and *P. aeruginosa* lowered the levels of AHL and QS-related virulence factors [37]. Other important AHL lactonases are AttM and AiiB, which have been isolated from *Agrobacterium* sp. [38], AhlD from *Arthrobacterium*, AhlK from *Klebsiella* [39] and AidC from *Chryseobacterium* [40], QsdA from *Rhodococcus erythropolis* strain W2 [41], AiiM of *Microbacterium testaceum* [42], AidH of *Ochrobactrum* sp. T63 [43] and QsdH of *Pseudoalteromonas yunnanensis* [44]. Furthermore, paraoxonases 1, 2 and 3 (PON1 to −3) are mammalian lactonases were identified in the airway epithelia and mammalian sera [45].

AHL acylases enzymes (*aiiD)* and homologs were found in *Ralstonia* [46], *Actinoplanes utahensis* and *Pseudomonas* sp. The purified AiiD protein has the ability to degrade 3OC10HSL into HSL and 3-oxodecanoic acid. In addition, PvdQ, QuiP and HacB are specific AHL acylases of *P. aeruginosa*, in addition, HacA and HacB acylases of *Pseudomonas syringae* [47, 48]. Furthermore, the broader substrate specificity of AHL acylase (AhlM) was detected in *Streptomyces* sp. strain M664 with activity towards medium- and long-chain AHLs [49].

Oxidoreductases from *Rhodococcus erythropolis* inactivates AHLs (oxidation or reduction) with subsequent elimination of bacterial virulence *in vivo. Rhizobium* strain NGR234 possess diverse AHL-inactivation loci: *dhlR*, *qsdR1* and *qsdR2*, with lactonases activity, *aldR*, and *hydR-hitR* [50]. Enzymatic degradation of other QS autoinducers have been described: *carA* and *carB* from *Bacillus*, *E. coli* DH10B, *Staphylococcus* and *Pseudomonas* as the genes responsible for inhibition of DSF signaling [51]. Hod (3-hydroxy-2-methyl-4(1*H*)-quinolone 2,4-dioxygenase) stimulates the cleavage of PQS and attenuates PQS-regulated virulence factors. Roy and coauthors elicit the AI-2 activation activity of endogenous LsrK in *E. coli*, however, exogenously phosphorylation of AI-2 by LsrK eliminates its intracellular transport and hinders subsequent activation of AI-2 [52].

#### *2.1.3 Elimination of the QS signal-receptor interaction*

Interference with signal detection through eliminating the QS signal-receptor binding represents a successful approach [53, 54]. Various synthetic and natural AHL analogs have been reported to block the binding of the signal with specific receptors in *P. aeruginosa* and *Vibrio* sp. The prototype signal inhibitors, halogenated furanones, which are produced from *Delisea pulchra* represent a good example [55, 56]. Natural analogs have been also isolated with signal-receptor interference including ajoene [57], eugenol [58], flavonoids [59], iberin [60], furocoumarins [61], ellagic acid, penicillanic acid and patulin [62], phenethyl amide [63] and 1H-pyrrole-2-carboxylic acid [64].

The synthetic furanone derivative C-30 interferes and hinders the interaction of AHLs with the receptors [65]. Other furanone analogs have been developed

including S-phenyl-l-cysteine sulfoxide and diphenyl disulfide [66] and tetrazole derivatives [67]. Furthermore, synthetic LasR derivatives have been developed such as indole derivatives, non-AHL-like antagonists [68], the synthesized azines derivatives, 4-(alkyloxy)-6-methyl-2H-pyran-2-one [69] and aspirin [70]. Triphenyl hybridγ-butyrolactones and cyclopentanones derivatives are potent inhibitors of LuxR [71]. Putative LasI inhibitors have been identified using molecular docking methods including the trans-cinnamaldehyde [72], (z)-5-octylidenethiazolidine-2, 4-dione [73] and fatty acyl purified from marine *Streptomyces* sp. [74]. Additionally, meta-bromo-thiolactone is a potent inhibitor of RhiI and subsequent PQS cascade [11].

In *S. aureus*, the interference with agr system has been accomplished using solonamide A and B that are cyclodepsipeptides derivatives, which purified from marine *Photobacterium* and reduced the expression of *hla* and RNAIII. Solonamide can act through competitive inhibition of agr system such as *S. aureus* agr system via structure similarity to the AIPs [75]. Other *S. aureus* quorum-sensing inhibitors have been identified including linear peptidomimetics as competitive inhibitors to AgrC [76], savirin as potent inhibitor of AgrA [77] and the polyhydroxy anthraquinone ω-hydroxyemodin as inhibitor of AgrA [78].


3.2.3. Synthesis of Na2[Pd(*cis*-CyHSS)]

According to Section 3.2.1, 116.77 mg (0.24 mmol) of *cis*-CyHSS and 73.9 mg (0.26 mmol) of (NH4)2[PdCl4] yielded 121 mg (0.19 mmol), 79%, yellow solid.

1H-NMR (D2O, 298 K, 360 MHz, δ): 1.39–2.21 (m, 8H, CH2–CH2), 3.59–3.69 (m, 4H, CH2–NH), 4.44–4.47 (m, 2H CH–CH), 6.89–6.91 (m, 2H, CHarom), 7.53–7.57 (m, 4H, CHarom).

1H-NMR (D2O, 268 K, 360 MHz, δ): 1.19–2.01 (m, 8H, CH2–CH2*),* 3.14 (d, *J* = 13.4, 1H, CH2–N),

3.41 (d, *J*2 = 12.9 Hz, 2H, CH–CH), 3.47 (d, *J* = 13.4, 1H, CH2–N), 3.89 (d, *J* = 13.4, 1H, CH2–N), 4.24 (d, *J* = 13.4, 1H, CH2–N), 6.70 (d, *J* = 8.4 Hz, 2H, CHarom), 7.32–7.38 (m, 4H, CHarom).

13C{1H} NMR (D2O, 90 MHz), δ: 165.52, 129.41, 127.70, 123.60, 118.70, 65.11, 51.49, 24.26, 20.61. IR (ATR), ν/cm−1: 596.1, 634.3, 707.9, 1028.4, 1107.2, 1170.8, 1301.2, 1475.2, 1592.5

ESI-MS for C20H22Na2N2O8S2Pd (*m*/*z*): calcd for [M + Na]+ 656.954; found 656.956.

#### 3.2.4. Synthesis of [Pd(*trans*-CyHSS)]

According to Section 3.2.1, 116.77 mg (0.24 mmol) of *trans*-CyHSS and 73.9 mg (0.26 mmol) of (NH4)2[PdCl4] yielded 132 mg (0.21 mmol), 88%, yellow solid.

1H-NMR (D2O, 298 K, 360 MHz, δ): 1.25 (s, 4H, CH2–CH2), 1.80 (s, 2H, CH2–CH2), 2.51 (s, 2H CH2–CH2), 2.79 (s, 2H, CH2–CH2), 3.74 (d, *J* = 13.3 Hz, 2H, CH2–NH), 4.17 (d, *J* = 13.3 Hz, 2H, CH–NH), 6.87–6.90 (m, 2H, CHarom), 7.52–7.55 (m, 4H, CHarom).

1H-NMR (D2O, 268 K, 360 MHz, δ): 0.75 (s, 4H, CH2–CH2), 1.30 (s, 2H, CH2–CH2), 2.04 (s, 2H CH2–CH2), 2.30 (s, 2H, CH–CH), 3.28 (d, *J* = 13.3 Hz, 2H, CH2–NH), 3.68 (d, *J* = 13.3 Hz, 2H, CH–NH), 6.38 (d, *J* = 8.3 Hz, 2H, CHarom), 7.01–7.04 (m, 4H, CHarom).

13C{1H} NMR (D2O, 90 MHz, δ): 16.54, 129.40, 128.29, 127.72, 123.53, 118.74, 67.34, 50.29, 29.44, 24.14. IR (ATR), ν/cm−1: 606.7, 708.8, 1033.3, 1105.3, 1165.3, 1298.4, 1473.3, 1590.4

ESI-MS for C20H22Na2N2O8S2Pd (*m*/*z*): calcd for [M + Na]+ 656.954; found 656.956.

#### 3.2.5. Preparation of Pd–Salan Stock Solutions

In water (10 mL), 0.1 mmol of the appropriate salan and 28.4 mg (0.1 mmol) of (NH4)2[PdCl4] were dissolved. The pH was set to 7.5 with 5 M NaOH, and the solution was stirred at 60 ◦C for 10 h. With time, the light brown solution turned bright yellow. Aliquots of such stock solutions of the catalysts were added to the C–C cross-coupling reaction mixtures. 1H-NMR spectra of these stock solutions are identical to those prepared by dissolution of isolated complexes (Figures S110 and S111).