*2.9.2 Function*

Plant roots create a class of chemicals known as strigolactones. Strigolactone encourages the growth of parasitic plants like Strigalutea and other members of the genus Striga that grow in the roots of the host plant. Because they form a mutualistic connection with these plants and offer phosphate and other soil nutrients,

strigolactone plays a crucial part in the symbiotic fungi's ability to identify the plant. Strigolactone has a function in the enhancement of lateral root development and root hair elongation, as well as the inhibition of shoot branching in plants [36].

## **3. Role of phytohormone in stress**

Due to their effects on hormonal and nutritional imbalances, stress conditions have a significant negative impact on crop productivity. Some common stresses that have a negative impact on plant growth and development include salinity, drought, heavy metals, nutrient deficiency, and pathogens. These stresses have an impact on plant growth in one way or another. A single stress can negatively impact several plant functions in a variety of ways. For instance, salt reduces plant development by generating hormonal abnormalities, ion toxicity, oxidative stress, nutritional problems, and water stress. Plants adapt specific defence systems to deal with biotic and abiotic challenges in their native soil environments. To each given stimulus, several cellular signalling pathways are triggered [37]. The synthesis of phytohormones is accelerated by these signals. Signalling molecules called phytohormones control physiological and developmental processes in plants. There are several biotic and abiotic factors that influence hormone production, which substantially varies These hormones may have a significant impact on plant growth and development even at very low concentrations. Plant defence against environmental stresses depend heavily on hormonal signalling. The primary function of phytohormone production in plants is resistance to stress. Auxin, cytokinins, ethylene, gibberellins, and abscisic acid are the five main groups of phytohormones. Brassinosteroids, jasmonic acid, salicylic acid, and nitric acid have also been found as chemical messengers present in trace amounts in plants in addition to these well-known plant hormones. These hormones move throughout the plant body via the xylem or phloem transport stream.

The most investigated stress-responsive hormone among them is abscisic acid (ABA), which has a role in a variety of conditions include osmotic, drought, and cold stress. Plant processes including organogenesis, embryogenesis, and the development of vascular tissue are all regulated by auxin. A new class of plant hormones known as brassinosteroids affects processes such as flowering, senescence, and seed germination [38].


**5. Using transgenic approaches to develop cold tolerance**

Biotechnology offers new strategies that can be used to develop transgenic canola plants with improved tolerance to cold stress. Rapid advancement in recombinant DNA technology and development of precise and efficient gene transfer protocols have resulted in transformation and regeneration of transgenic lines in canola and other plant species (Wani *et al.,* 2008; Gosal *et al.,* 2009; Wani *et al.,* 2011). Genes that respond to freezing stress have been isolated and characterized, and studies suggest that they contribute to chilling tolerance and cold acclimation (Knight *et al*., 1999; Hsieh *et al.*, 2002). Therefore, the transgenic approach should be pursued actively in canola breeding to improve cold tolerance. Efforts have been made to generate transgenic lines, which have shown improved tolerance to cold stress (Savitch, *et al.,* 2005).

Transgenic technology has the ability to improve cold stress in plants by introducing or down-regulating genes that regulate specific trait (Kumar, 2006). In the last few years, several efforts have been made to identify and characterize cold-responsive (*COR*) genes. Homologous components of the *Arabidopsis CBF* cold response pathway have also been found in many plants (Yamagachi-Shinozaki and Shinozaki, 2006). Some of these putative orthologs have been analyzed, and functionally tested. Most of the studies indicate that the expressions of *CBFs* and *CORs* in response to cold stress are similar in many plant species. Thus, they involve rapid cold induced expression of the *CBFs* followed by expression of *CBF*-targeted genes that increase freezing tolerance. It is important to note that as we aspire

treatment. Sumoylation/desumoylation of proteins has been shown to have a pivotal role in cold acclimation (Miura *et al*., 2007). Sumoylation is a post-translational protein modification where small ubiquitin-related modifier (SUMO) proteins are conjugated to protein substrates in a process dependent on SUMO E3 ligases, whereas desumoylation is the removal of SUMO proteins from their target proteins by SUMO proteases. It might protect target proteins from proteasomal degradation because sumoylation prevents ubiquitination (Ulrich, 2005). SIZ1, an *Arabidopsis* SUMO E3 ligase is shown to be required for the

Transgenic attempts with many structural genes have also been made with a moderate degree of success. The overexpression of genes encoding LEA proteins can improve the stress tolerance of transgenic plants. Expression of the citrus gene encoding a LEA protein, CuCOR19 increased the cold tolerance of transgenic tobacco (Hara *et al.,* 2003). Likewise, the freezing tolerance of *Arabidopsis* was increased by the ectopic expression of the wheat gene WCS19 (Dong *et al.,* 2002), the *Arabidopsis* gene COR15A (Artus *et al.,* 1996), and the coexpression of the genes RAB18 and COR47, and XERO2 and ERD10 (Puhakainen *et al*., 2004). The freezing tolerance of strawberry leaves was enhanced by expression of the wheat dehydrin gene WCOR410 (Houde *et al.,* 2004). On the other hand, the expression of two cold-induced LEA proteins from spinach (Kaye *et al.,* 1998) and three desiccation-induced LEA proteins from *C. plantagineum* (Iturriaga *et al.,* 1992) in tobacco did not induce any significant changes in the freezing or drought tolerance of the respective transgenic plants. This may indicate either that not all LEA proteins make a significant contribution to plant stress tolerance, or that they need a particular background to function in, as suggested for

Biotechnology offers new strategies that can be used to develop transgenic canola plants with improved tolerance to cold stress. Rapid advancement in recombinant DNA technology and development of precise and efficient gene transfer protocols have resulted in transformation and regeneration of transgenic lines in canola and other plant species (Wani *et al.,* 2008; Gosal *et al.,* 2009; Wani *et al.,* 2011). Genes that respond to freezing stress have been isolated and characterized, and studies suggest that they contribute to chilling tolerance and cold acclimation (Knight *et al*., 1999; Hsieh *et al.*, 2002). Therefore, the transgenic approach should be pursued actively in canola breeding to improve cold tolerance. Efforts have been made to generate transgenic lines, which have shown improved

Transgenic technology has the ability to improve cold stress in plants by introducing or down-regulating genes that regulate specific trait (Kumar, 2006). In the last few years, several efforts have been made to identify and characterize cold-responsive (*COR*) genes. Homologous components of the *Arabidopsis CBF* cold response pathway have also been found in many plants (Yamagachi-Shinozaki and Shinozaki, 2006). Some of these putative orthologs have been analyzed, and functionally tested. Most of the studies indicate that the expressions of *CBFs* and *CORs* in response to cold stress are similar in many plant species. Thus, they involve rapid cold induced expression of the *CBFs* followed by expression of *CBF*-targeted genes that increase freezing tolerance. It is important to note that as we aspire

accumulation of SUMO conjugates during cold stress.

transgenic strawberry plants (Houde *et al.,* 2004).

tolerance to cold stress (Savitch, *et al.,* 2005).

**5. Using transgenic approaches to develop cold tolerance**

to engineer cold stress in Canola, the contitutive expression of *Arabidopsis CBF* genes in other plants resulted in increasing freezing tolerance (Yamagachi-Shinozaki and Shinozaki, 2006). There are also other structural genes that have been used to engineer cold tolerance in some plants with amoderate degree of success. An example is tobacco that was engineered by over-expressing chloroplast glycerol-3-phosphate acyltransferase (*GPAT*) gene from squash and *Arabidopsis* (Murata *et al.,* 1992). The transgenic tobacco showed enhanced cold tolerance and an increase in the number of unsaturated fatty acids present in the plant cell wall. In another study, Pennycooke *et al.,* (2003) down-regulated α-Gal (α –Galactosidase) in petunia, and this resulted in transgenic plants with an increased freezing tolerance. This suggested that transformation with α-Gal is another way in which freezing tolerance of plants can be genetically improved. The genes encoding *LEA* proteins can also improve tolerance to cold stress if they are overexpressed in other plants. Citrus gene encoding a *LEA* protein, *CuCOR19* was over-expressed in tobacco and an increased cold tolerance of transgenic tobacco was achieved (Hara *et al.,* 2003). The expression of the wheat dehydrin gene WCOR410, in strawberry leaves also enhanced freezing tolerance (Houde *et al*., 2004). In a separate study, Kim *et al*., (2007) engineered tobacco with ring zinc finger protein (RDCPt) from hot pepper and their results indicated that the expression of this gene improved cold tolerance in transgenic plants when compared to wild type. In another study Su *et al.,* (2010), determined that *MYBS3* was critical in cold adaptation in rice and it enhanced cold tolerance. Their report indicated that transgenic rice constitutively overexpressing *MYBS3* tolerated 4°C for at least 1 week and there were no interferences with the yield. All these studies demonstrate that the relationships among different pathways regulated by cold acclimation are complex. Therefore, it is important to understand the mechanism regulating cold-regulated genes in order to engineer cold tolerant canola. In developing transgenic canola, one can study the genes aforementioned with the aim of over-expressing or down-regulating them in Canola plants. The advent of molecular genetics and biotechnology offers a possibility to genetically engineer Canola to be more tolerant to cold. The technology has been modified to significantly improve breeding efficiency, thus resulting in rapid and accurate incorporation of cold tolerant genes into Canola plants.

#### **5.1 ABA-independent gene regulation to cold stress**

Environmental stresses induce the expression of many genes that can be classified into two groups. The first group corresponds to proteins involved in transduction pathways, such as transcription factors, whereas the second group includes effector proteins like the enzymes of osmolyte biosynthesis. Many studies have been focused on transcription factors involved in gene expression regulation. For each signal (salt, drought, and cold), several pathways can be distinguished depending on ABA dependent and ABA independent. ABAindependent expression of stress-responsive genes can occur through dehydrationresponsive element (DRE)/C-repeat (CRT) cis-acting elements. The binding factors CBF/DREB1 (CRT-binding factor/DRE-binding factor 1) and DREB2 mediate gene expression in response to cold and drought/salinity, respectively). Interestingly, the CBF4 protein seems to mediate drought response unlike the other CBFs (Haake *et al*., 2002). A particular feature of CBF proteins is their early and transient cold induction, which precedes

Prospects for Transgenic and Molecular

through molecular genetics.

element in molecular plant breeding in canola.

Available from:

**7. Conclusions**

**8. References**

Breeding for Cold Tolerance in Canola (*Brassica napus* L.) 23

polymorphisms for many agronomically important candidate genes for cold tolerance. It is also possible to elucidate the genetic control of cold tolerance through allele-trait association studies. This can be implemented by combining SNP haplotype data for *Brassica* candidate genes with pedigree and quantitative trait information. DNA-chip and high-throughput SNP genotyping technologies will accelerate our understanding of cold tolerance in canola

Cold is an environmental factor that adversely affects the productivity and oil quality and limits the geographical distribution and growing season of canola. Although significant progress has been made to elucidate the genetic mechanisms underlying cold tolerance in Canola, our current understanding is limited to single and shallow temperature stress. In cold regions such as Canada, canola plants are subjected to intense levels of cold stresses, and hence, the response of canola to a combination of different cold temperatures deserves more attention. Newly developed varieties offer an opportunity to test the effects of multiple cold temperatures, and to perform extensive field studies under diverse environments to assess their tolerance. Discoveries in cold stress response in model species such as *Arabidopsis thaliana* can be adapted to canola to identify candidate genes, a key

Andrews, J., & Morrison, J. (1992). Freezing and ice tolerance tests for Winter *Brassica*. *Journal of the American Society of Agronomy,* Vol. 84, No. 6, pp. 960-962. Angadi, V. (2000). Response of three *Brassica* species to high temperature stress during

Aroca, R.; Irigoyen, J. & Sanchezdiaz, M. (2003). Drought enhances maize chilling

Artus, N., Uemura, M., Steponkus, L., Gilmour, J., Lin, C., & Thomashow, F. (1996).

Blackshaw, E. (1991). Soil temperature and moisture effects on downy brome vs. winter

Boyles, M. (2011). Oklahoma State University. Herbicide foliar and residual injury. Cold

Brzostowicz, A., & Barcikowska, V. (1987). Possibility of frost resistance testing of *Brassica napus* with the help of delayed luminescence intensity. *Cruciferae Newsletter*, pp. 12, 27. Canola Connection. (2011). The Canola Council of Canada, markets & statistics. Available

canola, wheat and rye emergence. *Crop Sci*. Vol. 31, pp. 1034-1040.

 http://www.canola.okstate.edu/herbicides/foliarresidualinjury/index.htm Brule-Babel, L., & Fowler, D. (1988). Genetic control of cold hardiness and vernalization

tolerance.II. Photosynthetic traits and protective mechanisms against oxidative

Constitutive expression of the cold regulated *Arabidopsis thaliana* COR15a gene affects both chloroplast and protoplast freezing tolerance. *Proceedings of National*

temperatures symptoms. Symptoms similar to herbicide carryover injury.

reproductive growth. *Can. J. Plant Sci*., Vol. 80, pp.693-701.

stress. *Physiologia Plantarum*, Vol. 117, pp. 540-549.

requirement in wheat. *Crop Sci*. vol. 28, pp. 879–884.

from: http://www.canolacouncil.org/acreageyields.aspx

*Academy of Sciences,* Vol. 93, pp. 13404–13409.

the expression of cold-responsive genes. This requires the involvement of a constitutively expressed CBF-transcriptional inducer, which would be activated by cold treatment.

Four orthologues of the *Arabidopsis* CBF/DREB transcriptional activator genes were identified from the winter *Brassica napus*, cv. Jet neuf (Gao *et al.,* 2002). All four BNCBF clones encode a putative DRE/CRT (LTRE)-binding protein with an AP2 DNA-binding domain, a putative nuclear localization signal and a possible acidic activation domain. Deduced amino acid sequences suggested that BNCBFs 5, 7, and 16 are very similar to the *Arabidopsis* CBFI whereas BNCBF17 is different in that it contains two extra regions of 16 and 21 amino acids in the acidic domain. Transcripts hybridizing specifically to BNCBF17 and to one or more of the other BNCBFs accumulated in leaves within 30 min of cold exposure of the *Brassica* seedlings and preceded transcript accumulation of the coldinducible BN28 gene, a *Brassica* orthologue of the cor6.6 or KIN gene from *Arabidopsis*. Coldinduced accumulation of BNCBF17 mRNA was rapid but was short-lived compared to transcripts hybridizing to BNCBF5/7/16. Transcripts hybridizing to one or more of BNCBF5/7/16 accumulated at low levels after the plants were subjected to prolonged exposure to salt stress. BNCBF17 was not responsive to salt stress. BNCBF transcript accumulation was similar in both spring and winter *Brassica* but the persistence of the transcripts in the cold were generally shorter in the spring than in the winter type. BNCBF5 and 17 proteins bind in vitro to the LTRE domains of the cold-inducible BN115 (cor15a orthologue) or BN28 promoters. Differential binding preferences, however, to LTREs between BNI 15 and BN28 were observed. Mutation of the core CCGAC sequence of the LTRE indicated that BNCBF17 had a lower sequence binding specificity than BNCBF5. Furthermore, experiments indicated that the LTREs were able to drive BNCBF5 and 17 trans-activation of the Lac-Z reporter gene in yeast. We conclude that the BNCBFs reported here could function as trans-acting factors in low-temperature responses in *Brassica*, controlling the expression of cold-induced genes through an ABA-independent pathway. Chen *et al.* (2011) indicated that BnCOR25 protein expression was up-regulated by cold, dehydration, and exogenous ABA treatment, suggesting this gene may be activated via ABA-dependent signal pathway. In this study, the data revealed that BnCOR25 was localized on cell periphery, at which the BnCOR25 protein may bind to cell membrane. In addition, BnCOR25 protein also displays a number of dehyrins' features. Thus, BnCOR25 protein may play a role in cold resistance in a similar manner. It can be concluded, however, that DRE/CRT element, Bn CBFs and Bn COR25 are capable of mediating the cold induced expression of genes in *Brassica napus* via an ABA-independent pathway.

#### **6. Future research**

The development of genetically engineered cold tolerant Canola plants by introducing or overexpressing selected genes is a viable option for producing an elite plant. It is also the only option if genes of interest originate from different species or distant relatives. However, the increasing availability of data related to large-scale genome homology between *Arabidopsis* and *Brassica* species means that canola is well-positioned to be among the first major crop species to benefit from continuous progress in plant biotechnology and molecular marker technologies. The sequencing of *B. napus* genome and the emergence of detailed physical maps are of great importance towards engineering cold tolerant canola. The availability of complete gene sequences for *Brassica* can enhance advances in detecting polymorphisms for many agronomically important candidate genes for cold tolerance. It is also possible to elucidate the genetic control of cold tolerance through allele-trait association studies. This can be implemented by combining SNP haplotype data for *Brassica* candidate genes with pedigree and quantitative trait information. DNA-chip and high-throughput SNP genotyping technologies will accelerate our understanding of cold tolerance in canola through molecular genetics.


**3. Reasons for variations**

#### **3.1. Climatic driving**

The retreat or advance of a glacier is attributed to the amount of snow accumulation and ablation and is a result of an integrated response to climate. Temperature, precipitation, or a composite of climate inputs acts as the major driving force on glacial fluctuations: increased snowfalls or decreased temperature could favour a positive mass balance, making a glacier grow; otherwise, glaciers may recede. Although it is well known that glaciers are a sensitive indicator of climate change, the complexity of the glacier-climate relationship is not an easy puzzle to solve because glaciers are a component linked with many other components in the natural systems and the forcings that influence glacier distribution and changes operate at different scales. It can take several decades for a glacier to respond to some change in climate, and this time lag varies non-linearly and due to many other non-climatic factors such as glacier types and topography [60, 61].

Like in many mountain ranges around the world, the Tian Shan glaciers are retreating or disappearing in response to the increasing atmospheric temperature in the past a few decades. Almost all meteorological stations have observed a warming trend since the 1970s in central Asia [23]. The IPCC Fifth Assessment Report AR5 [62] noted that the warming was particularly strong in winter (November to March), with a rate of 2.4°C per 50 years, in the semi-arid area of Asia. The estimate of the increase in mean annual temperature is about 0.1–0.2°C per decade [62]. Such changes in temperature cause less persistent snow accumulation and prolonged melting season for glaciers. This is likely associated with a weakening or spatial shift of the Siberian high pressure further to the east over the continental Asia in the past century [20, 23].

Precipitation changes driven by the zonal and meridional atmospheric circulation patterns do not show spatially coherent trends in central Asia [28, 63]. Instrumental data of recent decades revealed that the mean annual precipitation generally shows an increasing trend in both northern ranges of the Kyrgyz Tian Shan and the Chinese Tian Shan [64–66], but a decreasing trend in the interior range, the central Tian Shan [23]. Aizen et al. [20] argued that a strengthened westerly flow associated with the warm season precipitation (accounts for most of the annual total) could be the explanation, but the spatial distribution of precipitation decreasing from northwest to southeast reflects the effect of mountain blocking. The regions with increased precipitation undergo glacier retreating too, indicating the impact of current warming on glaciers is not compensated by more precipitation or the sensitivity of glaciers is higher to temperature change in central Asia [28, 67].

The variability and long-time change of the climate system in central Asia are closely related to the interconnections with the large-scale oceanic-atmospheric circulations, such as the El Nino/Southern Oscillation (ENSO), the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO). Several studies have reconstructed millennium-long records of these oscillations and found that the La Niña condition, warm phase AMO and positive NAO are correlated with the above average winter or annual precipitation in arid central Asia [6, 68, 69]. Although a lack of quantity and quality of direct observations hampers the confidence in the assessment of past changes, inferred long-term trends of the indices provided possible explanations of the climatic forcing/mechanisms during the LIA. Evidence derived from climate proxy data is another common approach to extend information on the past climate conditions. Through reconstructions using tree rings, e.g. [70–72], ice core, e.g. [18, 73], eolian sediment, e.g. [74] and lake sediment, e.g. [75], the regional climate during the LIA was depicted as cold and wet in arid central Asia. For example, the Dunde ice core record from the Qilian Mountain, ~500 km southeast of the Tian Shan, identified three long cold periods, around mid-fourteenth century, mid-sixteenth to seventeenth century and the nineteenth century during the LIA [73], which correspond well with the series of glacial advances dated in the moraine chronology [57–59]. IPCC AR5 [62] reported prevailed wetter conditions in central Asia during the LIA compared to the Medieval Climate Anomaly and the twentieth century. On a regional scale, the wet and cold conditions are the primary climatic driving for the LIA glacier expansions in the Tian Shan, but on a more local scale, the non-uniform response to similar climate changes implies other influential factors that need to be taken into account.

## **3.2. Local factors**

The chronology evidence of the LIA maximum extents at the selected study sites better allows us to use morphologic appearance to interpret potential LIA extent in less-studied areas in the Tian Shan. Indeed, more moraine chronological data across different mountain ranges are needed to examine the timing and the extent of the LIA glaciers and to depict the spatial

The retreat or advance of a glacier is attributed to the amount of snow accumulation and ablation and is a result of an integrated response to climate. Temperature, precipitation, or a composite of climate inputs acts as the major driving force on glacial fluctuations: increased snowfalls or decreased temperature could favour a positive mass balance, making a glacier grow; otherwise, glaciers may recede. Although it is well known that glaciers are a sensitive indicator of climate change, the complexity of the glacier-climate relationship is not an easy puzzle to solve because glaciers are a component linked with many other components in the natural systems and the forcings that influence glacier distribution and changes operate at different scales. It can take several decades for a glacier to respond to some change in climate, and this time lag varies non-linearly and due to many other non-climatic factors such as gla-

Like in many mountain ranges around the world, the Tian Shan glaciers are retreating or disappearing in response to the increasing atmospheric temperature in the past a few decades. Almost all meteorological stations have observed a warming trend since the 1970s in central Asia [23]. The IPCC Fifth Assessment Report AR5 [62] noted that the warming was particularly strong in winter (November to March), with a rate of 2.4°C per 50 years, in the semi-arid area of Asia. The estimate of the increase in mean annual temperature is about 0.1–0.2°C per decade [62]. Such changes in temperature cause less persistent snow accumulation and prolonged melting season for glaciers. This is likely associated with a weakening or spatial shift of the Siberian high pressure further to the east over the continental Asia in the past century [20, 23]. Precipitation changes driven by the zonal and meridional atmospheric circulation patterns do not show spatially coherent trends in central Asia [28, 63]. Instrumental data of recent decades revealed that the mean annual precipitation generally shows an increasing trend in both northern ranges of the Kyrgyz Tian Shan and the Chinese Tian Shan [64–66], but a decreasing trend in the interior range, the central Tian Shan [23]. Aizen et al. [20] argued that a strengthened westerly flow associated with the warm season precipitation (accounts for most of the annual total) could be the explanation, but the spatial distribution of precipitation decreasing from northwest to southeast reflects the effect of mountain blocking. The regions with increased precipitation undergo glacier retreating too, indicating the impact of current warming on glaciers is not compensated by more precipitation or the sensitivity of glaciers is

heterogeneity of LIA glacial events in the region.

**3. Reasons for variations**

44 Glacier Evolution in a Changing World

cier types and topography [60, 61].

higher to temperature change in central Asia [28, 67].

**3.1. Climatic driving**

Many non-climatic factors influence the development of each glacier and determine how each glacier responds to climate change individually and differently in future. For instance, glacier geometry and topography play an important role in the spatial pattern of glacier change variability. Such factors include glacier size, elevation range, hypsometry (areal distribution by elevation), surface orientation (aspect), slope, shape and surface characteristics (e.g. debriscover). They vary from region to region and from a glacier to another glacier. Understanding the role of the factors that lead to disparate glacier responses at a local scale will improve our knowledge of glacier-climate interaction and help predict future glacier changes.

Previous studies have explored the impact of a single topographic factor or a combination of factors on the glacier behaviour. For example, Pratt-Sitaula et al. [76] applied cosmogenic 10Be dating on moraines at ice extent maxima in five valleys at Annapurna, Nepal, and found that the glacial asynchrony at neighbouring valleys under no spatial differences in climate is attributed to the effect of hypsometric characteristic. They argued that mountain glaciers with source areas at higher altitude are more likely to lead to glacial advance, while glaciers with lower maximum altitudes tend to retreat when facing a uniform climate change from a coolerdrier late glacial to a warmer-wetter early Holocene [76]. Numerous studies utilized satellite remote sensing data to assess the sequential changes of glaciers during past decades and revealed that in all mountain regions where glaciers exist today, glaciers shrunk considerably over the past 150 years, after the end of the LIA, and many small glaciers have disappeared [32]. Glaciers of different sizes are proven to have strong correlations with the rate of glacier changes, and small glaciers are undergoing stronger retreat compared to large-sized glaciers, e.g. [77–80]. The presence of many small glaciers today are formed due to the rapid disintegration of medium-sized glaciers and are likely to disappear if the warming trend of climate continues [80]. Topographic conditions also matter to the sensitivity and the response time of glaciers to an instantaneous change in climate. Large glaciers that have multiple tributaries and low slope gradient take a longer time to adjust their extent, whereas smaller glaciers respond faster with a higher changing rate; thus, small glaciers are more sensitive to climate change. The influence of the aspect factor can be interpreted in terms of solar radiation receipt, as well as the wind effects to areas with moderate relief [77]. According to the analysis using large data sets from the World Glacier Inventory, Evans [81] measured slope aspect of a total of 66,084 glaciers in 51 regions over the world and found a broadly consistent poleward aspect in middle and high latitudes.

A limited number of studies have been conducted in the Tian Shan to examine the relationship between local factors and glacier changes. In northern Kyrgyz Tian Shan, Bolch [78] compared glacier retreats from 1955 to 1999 among several valleys. He mentioned that the heterogeneity of glacier changes is dependent on the size, as well as the climatic regime divided among northern slopes and southern slopes. Our previous study [82] in the central Chinese Tian Shan was the first to examine the importance of topographic factors to the spatial variability of changes in glacier area and equilibrium line altitude (ELA) since the LIA. The results showed that glacier size and mean elevation range are the two key factors and could explain up to 64% of the relative area change, but the ELA change cannot be well explained by the regression of the local factors [82]. Debris cover is another factor that can have either positive or negative impact on surface ablation because it modifies ice melt rates and the heat conduction in the ablation zone [83]. The thickness of the supraglacial debris was considered to be related to the ablation rate [84]. However, how debris cover influences glaciological processes is quite complex and varies case by case [85, 86]. Most glaciers in the central Tian Shan are the debriscovered type, and glaciers in the eastern Tian Shan are mostly clean-ice type.

A glacier advances or retreats as a result of both local conditions, i.e. topography and its geometry and climate conditions. Understanding these internal and external factors on glacier changes is helpful to discuss the sensitivity of glacier response and is important to interpret paleoclimatic conditions and future glacier evolution. With nearly uniform changes in climate at local scales, more research needs to be focusing on comprehensively investigating the role of local factors played in resulting non-uniform glacier responses.


*5.1.4 Exopolysaccharide production*

Exopolysaccharides are high molecular weight compounds that indirectly affect the solubilisation of P in soil [65]. Microorganisms secrete exopolysaccharides under stress conditions; exhibit the potential to promote phosphate solubilisation [3, 66]. Exopolysaccharides have a strong affinity with the metal ions in the soil, which have formed complexes with phosphates and release those phosphates. There is a positive correlation between the rate of phosphate solubilisation and the concentration of exopolysaccharides [3]. Different exopolysaccharides have different binding affinities with various metals, and there are also different binding strengths between the metals themselves. *Arthrobacter* sp. ArHy-505, *Azotobacter* sp. AzHy-510 and *Enterobacter* sp. EnHy-401 exhibits higher tricalcium phosphate solubilisation capacity by producing exopolysaccharides [65].


**Acknowledgements**

We are thankful to Mr. Zahir Rahman (B. Pharm, M. Phil) Plant Manager, Ferozsons Laboratories Ltd., Nowshera, for his technical input and moral support. **References**

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