the lipid benzoquinone sorgoleone ( 2-hydroxy-5-methoxy-3-[(8z , 11z)-8 , 11 , 14-pentadecatriene]-p - benzoquinone ) is a potent allelochemical that is produced as an oily exudate from the root hairs of sorghum ( sorghum bicolor ) ( czarnota et al.2001 ; dayan et al.2007 ) , along with a variety of structural analogues ( kagan et al.2003 ) responsible for inhibiting weeds and harmful algae ( einhellig and souza 1992 ; nimbal et al.1996 ; rimando et al.2003 ; uddin et al.2009 , 2012 ; weston and czarnota 2001 ) .
sorgoleone is released from the roots of sorghum continually during the growing season , which may prolong its presence in soil ( dayan 2006 ; dayan et al.2009 ; weidenhamer 2005 ) .
sorgoleone , its resorcinol analogue , and other related hydroquinones are produced solely by living root hairs and are exuded as golden - coloured droplets from the tips of root hairs ( czarnota et al.2003a ; dayan et al.2009 ) .
however , sorgoleone biosynthesis is linked intrinsically to the presence of living root hairs ( czarnota et al.2001 ; yang et al.2004 ) .
plants use a variety of sequestration and transport mechanisms to move and export bioactive products safely into the rhizosphere ( weston et al.2012 ) .
specific root exudates and rhizodeposits are important messengers for chemical communication systems that help regulate the interactions between roots and soil organisms , and mediate processes in response to environmental stressors ( uren 2000 ) .
roots , when they are under stress or encountering challenges in the rhizosphere , often react by releasing low - molecular - weight compounds , including amino acids , organic acids , and phenolics , as well as proteins .
these secretions can protect the plant , thus initiating a negative form of communication in the rhizosphere ( bertin et al.2003 ) .
alternatively , these exudates can elicit symbiotic responses that initiate legume rhizobium nitrogen fixation or attract common soil microbes , which are positive forms of communication ( mathesius and watt 2011 ; peters et al.1986 ; shi et al.2011 ) sorgoleone biosynthesis appears to occur exclusively in root hair cells , which in sorghum appear as cytoplasmically dense cells filled with numerous osmiophilic deposits ( czarnota et al .
these deposits presumably are associated with the rhizosecretion of sorgoleone , which can constitute as much as 85  % of the exudate dry weight in some cultivars ( bertin et al.2003 ; czarnota et al.2001 , 2003b ; duke 2003 ; rimando et al.2003 ) .
the cell - specific localization and prolific output of the sorgoleone biosynthetic pathway renders the use of expressed sequence tag ( est ) analysis an obvious method to isolate genes encoding sorgoleone biosynthetic enzymes ( baerson et al.2008 ) . labeling studies performed by fate and lynn ( 1996 ) first demonstrated that biosynthesis proceeds through the action of an alkylresorcinol synthase ( ars ) , a novel type iii polyketide synthase that acts on fatty acyl - coa starter units ( baerson et al.2008 ) .
subsequently , both the predicted 5-n - pentadecatrienyl resorcinol and a 3-methyl ether derivative of sorgoleone were identified in sorghum root extracts , indicating that dihydroxylation of the resorcinol ring is preceded by o - methylation at the 3-hydroxyl position ( baerson et al.2008 ; dayan et al.2003 ; fate and lynn 1996 ) .
once released into the rhizosphere , the resulting chemically unstable hydroquinone rapidly oxidizes to the bioactive sorgoleone benzoquinone , where it may persist in soil for extended periods ( czarnota et al.2001 ; einhellig and souza 1992 ; gimsing et al.2009 ; netzly et al.1988 ) .
synthesis of sorgoleone from the available palmitoleoyl - coa would , therefore , likely require , at minimum , the participation of a 12 and 15 fatty acid desaturase ( des ) , an ars , 3-o - methyltransferase ( omt ) , and cytochrome p450 ( baerson et al.2008 ) ( fig . 
1proposed biosynthestic pathway of the allelochemical , sorgoleone ( baerson et al.2008 ) proposed biosynthestic pathway of the allelochemical , sorgoleone ( baerson et al.2008 ) root hair development has been used as an important model to study the mechanisms of cell patterning and differentiation in higher plants ( schiefelbein 2000 ) .
mutational analysis has revealed that several genes in arabidopsis function in the specification of root epidermal cell types . among these , the ttg ( galway et al.1994 ) , gl2 ( masucci and schiefelbein 1996 ) , and wer ( wada et al.1997 ) genes are the best characterized .
studies on arabidopsis mutants , such as axr1 and ctr1 , indicate that auxin and ethylene function in root hair initiation . both methyl jasmonate ( meja ) and jasmonic acid ( ja ) have a pronounced effect on promoting root hair formation in arabidopsis .
the effect of meja and ja on root hair formation is blocked by ethylene inhibitors ag or aminoethoxyvinylglycine ( avg ) .
the stimulatory effects of meja and ja also are diminished in ethylene - insensitive mutants etr1 - 1 and etr1 - 3 ( zhu et al.2006 ) . to the best of our knowledge , the effects of jasmonates on gene expression in sorghum roots have not been reported .
the goal of this study was to correlate gene expression levels with the biosynthesis of sorgoleone after exposure to ja or meja for different time periods .
such knowledge may be useful for the future development of a bioherbicide by increasing levels of sorgoleone through molecular genetic manipulation .
sorghum seeds of the cultivar chalsusu , which has a high sorgoleone content ( uddin et al.2009 ) , were used .
seeds were treated with benomyl ( a powdery fungicide , 100  g dissolved in 20  l ) for 4  h , and then rinsed several times in distilled water .
seeds ( 25/petri dish ) were placed on the surface of sterile whatman # 1 filter paper ( diam , 90  mm ) saturated with different concentrations of ja or meja placed in sterile petri dishes ( 100    40  mm ) .
the dishes were then placed in a growth chamber at 25  c under standard cool white fluorescent tubes with a flux rate of 550  mol  s  m and a 16-h photoperiod for 1  week . to determine the concentrations of ja and meja that promote maximum sorgoleone biosynthesis ,
sorghum seeds were imbibed with solution containing different concentrations ( 0 , 0.5 , 1.0 , 5.0 , 10 , 50 , 100 , 250 , and 500  m ) of either ja or meja for 1  week . to examine how gene expression and sorgoleone accumulation in response to meja and ja changed over time
, 5-day - old sorghum seedlings were treated once with 5.0  m ja or meja , and then their roots were harvested for analysis at multiple time points ( 0 , 3 , 6 , 12 , 24 , 36 , 48 , 60 , and 72  h after treatment ) .
roots samples were stored in sealed clear polyethylene plastic bags at 80  c until use .
there were four replicates for each time point , and the entire experiment was repeated twice .
sorgoleone was extracted according to the procedures described previously ( czarnota et al.2003b ; netzly and butler 1986 ; netzly et al.1988 ) , except that methanol was used as a solvent instead of methylene chloride ( uddin et al.2010 ) .
seedling roots were excised and immersed in methanol ( 1:20  w / v ) for 30  s to extract .
the dried extract was dissolved in methanol ( 1  mg  ml ) , and the solution was filtered through a poly filter ( pore size , 0.45  m ) .
hplc quantification of sorgoleone was performed using the futecs ns-4000 hplc system ( futecs co. ltd . , daejeon , korea ) , with a c18 column ( 250    4.6  mm , particle size 5  m ; rstech , daejeon , korea ) .
sorgoleone was detected at 280  nm with a waters tunable absorbance detector after injection of 20  l of the methanol solubilized crude extract sample .
the column flow rate was 1  ml  min with a 40  min total run time for each sample .
the amount of sorgoleone was calculated on the basis of a standard curve obtained from a purified sample .
the sorgoleone standard was provided by franck dayan , united states department of agriculture - agricultural research service ( usda - ars ) , natural products utilization research unit . from the meja and ja treatment root samples
only the most optimal concentrations of meja and ja ( 5.0  m ) for maximum sorgoleone concentration were selected .
total rna was isolated from a root of s. bicolor using tri - reagent ( mrc , usa ) and rneasy plant mini kit ( qiagen , valencia , ca , usa ) . for quantitative real - time polymerase chain reaction ( qrt - pcr ) , 1  g of total rna was reverse - transcribed according to the manufacturer s protocol ( revertraace - a , toyobo , japan ) using an oligo ( dt)20 primer .
the cdna mixtures were used as templates for qrt - pcr . for transcript - level analysis by qrt - pcr , rnas from auxin treated sorghum roots were harvested , and single - stranded cdnas were synthesized from the isolated total rna by using the aforementioned protocols .
the gene - specific primer sets were designed for qrt - pcr ( table  1 ) .
specific primers for des2 ( ef206347 ) , des3 ( ef206348 ) ( pan et al.2007 ) , ars1 ( xm_002441794 ) , ars2 ( xm_002449699 ) ( cook et al.2010 ) , and omt3 ( ef189708 ) ( baerson et al.2008 ) were obtained from ncbi .
the pcrs were carried out in triplicates for 40  cycles on a miniopticon ( bio - rad laboratories , hercules , ca , usa ) using the qiagen quantitect sybr green pcr kit .
the pcrs were pre - denatured at 95  c for 5  min , then subjected to 40  cycles of amplifications with the following thermal cycles : denaturation for 30  s at 95  c , annealing for 30  s at 55  c ; extension for 30  s at 72  c .
identical pcr conditions were used for all targets.table 1primer set for quantitative rt - pcr - mediated amplification of five transcripts that encode enzymes involved in sorgoleone synthesis from sorghumprimer namesequences ( 5 to 3)des2-qfactaccagttcgaccccactccdes2-qrccgccttctcttcctgatttctdes3-qfctgaccatcacctcaacgacacdes3-qrcattgcaccaactgacttcaccars1-qfggagtaccacctctccagcaaars1-qrcagtttgtcgtcctccagaccars2-qfatcttcgtgctcgatgagttgars2-qratttccctccagttccaggttomt3-qfgtttgttgggggtgacatgtttomt3-qrcgtctccagaagcttggtgtct primer set for quantitative rt - pcr - mediated amplification of five transcripts that encode enzymes involved in sorgoleone synthesis from sorghum all data were analyzed using the sas 9.2 software ( sas 2010 ; sas institute inc . ,
analysis of variance was performed and means were separated by duncan multiple range test ( dmrt ) standard deviations were provided to indicate the variation associated with a particular mean value .
the root growth pattern , secondary root , root hair formation , and root growth of sorghum were influenced by jasmonates .
photographs of sorghum root revealed variation in rooting patterns among the treatments ( figs .  2 and 3 ) .
the number of secondary or branching roots was higher at lower concentrations of jasmonate treatment , and the highest number of secondary roots was observed at 5  m ( fig . 
ja treatment produced a slightly higher number of secondary roots compared with that induced by meja treatment .
greater numbers of healthy root hairs were formed in response to ja and meja treatments compared with those formed in the control .
root weight increased slowly with increases in the concentration of jasmonates ( ja and meja ) up to 5.0  m , and then declined slowly with further increasing concentrations of either compound ( fig . 
2photographs showing the root growth pattern of sorghum seedlings 7  days after methyl jasmonate ( meja ) treatment . a = control , b = meja ( 0.5  m ) , c = meja ( 1.0  m ) , d = meja ( 5.0  m ) , e = meja ( 10  m ) , f = meja ( 50  m ) , g = meja ( 100  m ) , h = meja ( 250  m ) , i = meja ( 500  m)fig .
3photographs showing the root growth pattern of sorghum seedlings 7  days after jasmonic acid ( ja ) treatment . a = control , b = ja ( 0.5  m ) , c = ja ( 1.0  m ) , d = ja ( 5.0  m ) , e = ja ( 10  m ) , f = ja ( 50  m ) , g = ja ( 100  m ) , h = ja ( 250  m ) , i = ja ( 500  m)fig . 4photomicrograph of sorghum roots showing root hairs 7  day after jasmonate treatment ( bar=90  m ) . a = control , b = methyl jasmonate ( meja ) ( 5  m ) , c = jasmonic acid ( ja ) ( 5  m)fig .
each point is the mean of four replicates with an average of 10 seedlings for each replicate .
ja , jasmonic acid , meja , methyl jasmonate . means with the same letter adjacent to the symbols are not different at p<0.05 according to a duncan multiple range testfig .
each point is the mean of four replicates with an average of 10 seedlings for each replicate .
ja , jasmonic acid , meja , methyl jasmonate . means with the same letter adjacent to the symbols are not different at p  <  0.05 according to a duncan multiple range test photographs showing the root growth pattern of sorghum seedlings 7  days after methyl jasmonate ( meja ) treatment . a = control , b = meja ( 0.5  m ) , c = meja ( 1.0  m ) , d = meja ( 5.0  m ) , e = meja ( 10  m ) , f = meja ( 50  m ) , g = meja ( 100  m ) , h = meja ( 250  m ) , i = meja ( 500  m ) photographs showing the root growth pattern of sorghum seedlings 7  days after jasmonic acid ( ja ) treatment . a = control , b = ja ( 0.5  m ) , c = ja ( 1.0  m ) , d = ja ( 5.0  m ) , e = ja ( 10  m ) , f = ja ( 50  m ) , g = ja ( 100  m ) , h = ja ( 250  m ) , i = ja ( 500  m ) photomicrograph of sorghum roots showing root hairs 7  day after jasmonate treatment ( bar=90  m ) . a = control , b = methyl jasmonate ( meja ) ( 5  m ) , c = jasmonic acid ( ja ) ( 5  m ) effects of jasmonates for the production of secondary roots in sorghum roots . each point is the mean of four replicates with an average of 10 seedlings for each replicate .
means with the same letter adjacent to the symbols are not different at p<0.05 according to a duncan multiple range test dose - response curves showing the effects of jasmonates on root growth . each point is the mean of four replicates with an average of 10 seedlings for each replicate .
means with the same letter adjacent to the symbols are not different at p  <  0.05 according to a duncan multiple range test the dose response experiment indicated that sorgoleone content varied widely depending on the concentrations of exogenous jasmonates ( fig .  7 ) .
root dry weight and levels of sorgoleone increased with increases in both ja and meja concentrations up to 5.0  m , and then declined with increasing concentrations of either of the jasmonates . compared with untreated controls ,
sorgoleone levels were 4.1 , 2.3 , and 1.7-fold higher after treatment with 5 , 1.0 , and 0.5  m of ja , respectively ( fig . 
the level of sorgoleone was highest at a concentration of 5.0  m ja , with a level approximately 10 times lower ( 2.8  mg / g root fresh weight ) in roots exposed to 500  m ja.fig .
each point is the mean of four replicates with an average of 10 seedlings for each replicate .
ja , jasmonic acid , meja , methyl jasmonate . means with the same letter adjacent to the symbols are not different at p  <  0.05 according to a duncan multiple range test dose - response curves showing the effects of jasmonates on sorgoleone production .
each point is the mean of four replicates with an average of 10 seedlings for each replicate .
ja , jasmonic acid , meja , methyl jasmonate . means with the same letter adjacent to the symbols are not different at p  <  0.05 according to a duncan multiple range test the concentration - dependent effects of meja on sorgoleone accumulation were almost identical for meja , with 5.0  m meja producing more sorgoleone than any other concentration . compared with an untreated control , sorgoleone levels were 3.4 , 2.1 , and 1.8-fold higher after exposure to 5 , 1.0 , and 0.5  m of exogenous meja , respectively ( fig . 
exposure to concentrations of meja greater than 5.0  m caused a less dramatic decrease in sorgoleone content than observed for ja ( fig .  7 ) .
after exposure to 500  m of meja , the level of sorgoleone was 5.0  mg / g root fresh weight , which is 4.6 times lower than the highest content of sorgoleone observed in roots incubated with 5  m of meja .
sorgoleone accumulation was maximal after treatment with 5.0  m of either ja or meja , with the next highest levels of accumulation observed following treatments with jasmonates at 1.0  m and 0.5  m , respectively ( fig . 
7 ) . in the case of exposure to 5.0  m meja , increasing exposure time caused sorgoleone levels to increase for up to 72  h after the beginning of the treatment ( fig .  8) . compared with the control at 0  h
, 5.0  m meja produced 2.3 times more sorgoleone 72  h after the beginning of the treatment . in the case of exposure to 5.0  m ja , increasing exposure time caused sorgoleone levels to increase for up to 60  h after the beginning of the treatment ( fig . 
5.0  m ja produced almost twice as much sorgoleone at 60  h after treatment .
sorgoleone levels were highest at 24  h , when they were 1.2 times higher than levels in control plants at 0  h.fig .
8time - courses of sorgoleone production induced by application of jasmonates ( 5.0 m ) to sorghum roots .
each point is the mean of four replicates with an average of 10 seedlings for each replicate .
ja , jasmonic acid , meja , methyl jasmonate . means with the same letter adjacent to the symbols are not different at p  <  0.05 according to a duncan multiple range test time - courses of sorgoleone production induced by application of jasmonates ( 5.0 m ) to sorghum roots . each point is the mean of four replicates with an average of 10 seedlings for each replicate .
ja , jasmonic acid , meja , methyl jasmonate . means with the same letter adjacent to the symbols are not different at p  <  0.05 according to a duncan multiple range test the effects of ja and meja on the levels of transcript of five genes involved in sorgoleone biosynthesis were monitored .
levels of transcript of the sorgoleone biosynthetic genes , des2 , des3 , ars1 , ars2 , and omt3 increased after exposure to either ja or meja at 5.0  m . the extent to which the levels of transcript were affected by either ja or meja was dependent on the length of time the plants were exposed to jasmonates .
shortly after the application of ja , levels of transcripts were comparable to those in control seedlings , although higher transcript levels were noted than in control seedlings at some subsequent time points ( fig . 
the time after initial exposure when transcript levels were highest differed among the genes . in the case of ars1 , the highest levels of transcript accumulation occurred 48  h after initial exposure . at 48  h levels of ars1 transcript were 1.8-fold higher than in untreated seedlings at 0  h ( fig .  9 ) .
levels of ars2 and des2 transcript were highest 36  h after treatment , with increases of 5.2 and 3.3-fold , respectively when compared with untreated seedlings at 0  h ( fig . 
the largest increase in transcript accumulation was apparent for the des3 gene , 12  h after ja treatment , when des3 transcripts were 3.2-fold more abundant than in untreated seedlings at 0  h ( fig . 
9time course of induction of sorgoleone biosynthetic genes in response to jasmonic acid at 5.0 m in the sorghum root .
con , control ; ja , jasmonic acid . means with the same letter in both column bars are not different at p  <  0.05 according to a duncan multiple range test time course of induction of sorgoleone biosynthetic genes in response to jasmonic acid at 5.0 m in the sorghum root .
con , control ; ja , jasmonic acid . means with the same letter in both column bars are not different at p  <  0.05 according to a duncan multiple range test transcripts of different sorgoleone biosynthetic genes responded differently to exposure to meja . the times when the largest increase in transcript abundance was apparent after treatment with ja differed among the genes .
gene expression was lower than in the untreated control shortly after initial exposure of sorghum seeds to meja . compared with transcript levels in seedlings
not treated with meja , transcript accumulation was highest for most of the genes 36  h after meja treatment ( fig . 
10 ) , in particular for omt3 ( increased up to 8.1-fold ) , des2 ( increased up to 5.2-fold ) , ars2 ( increased up to 2.8-fold ) , and des3 ( increased up to 2.4-fold ) . levels of des2 transcript were 4.1-fold higher 3  h after treatment with meja than in seedlings that received no meja ( control ) . the highest level of ars1 transcript was observed 24  h after treatment with meja , and was 3.7-fold higher than the level of ars1 transcript in seedlings not treated with meja ( 0  h ) ( fig .  10).fig .
10time course of induction of sorgoleone biosynthetic genes by application of methyl jasmonate at 5.0 m treatment in the sorghum root .
con , control ; meja , methyl jasmonate . means with the same letter in both column bars are not different at p<0.05 according to a duncan multiple range test time course of induction of sorgoleone biosynthetic genes by application of methyl jasmonate at 5.0 m treatment in the sorghum root . each value is the mean of 3 replicates .
con , control ; meja , methyl jasmonate . means with the same letter in both column bars are not different at p<0.05 according to a duncan multiple range test
several possible mechanisms might account for the increase in root hair density ( ma et al.2001 ) .
second , increased abundance of trichoblasts with branched root hairs may contribute to an increase in root hair density .
third , atrichoblasts may be recruited into trichoblasts during root hair development under certain conditions .
our results suggest that the initiation of recruitment of more trichoblast cells into root hairs may be an important cause of meja - induced root hair development .
the induction of branched hair formation may be a novel effect of meja on root hair development .
investigation of whether jas activate root hair formation via ethylene in arabidopsis revealed that the effects of jas were abolished in the ethylene - insensitive mutants etr1 - 1 and etr1 - 3 , or by inhibitors of ethylene action ( ag ) or biosynthesis inhibitors ( avg ) .
furthermore , ibuprofen and sham , which inhibit ja biosynthesis , repressed acc - driven or eto1 - 1-induced root hair formation .
collectively , these reports support a role for the interaction between jas and ethylene in the regulation of root hair development in arabidopsis .
( 2003a ) confirmed that sorghum root hairs are physiologically active , and that they contain a complex network of smooth endoplasmic reticulum and possibly golgi bodies .
small globules of cytoplasmic exudates also were observed to deposit an oily material between the cell wall and the plasma membrane near the root hair tips .
( 1992 ) indicated that sorgoleone production is quite sensitive to environmental conditions , and it is well documented that sorgoleone production depends mainly on root hair formation ( czarnota et al.2003b ; dayan 2006 ; dolan 2001 ; yang et al.2004 ) . herein we report that root growth pattern , secondary root , root hair formation , and root growth of sorghum are influenced by the use of jasmonates .
our study shows that sorghum roots develop many branches ( fig .  4 ) , as well as more root hairs ( fig .  5
) , when the proper concentrations of jasmonates ( up to 5  m ) are applied . clearly
, healthy root hairs in higher numbers than those in the control were formed in response to ja and meja treatment .
root weight increased slowly with increased concentrations of jasmonates ( ja and meja ) up to 5.0  m and then declined slowly with further increasing concentrations of these compounds ( fig . 
zhu et al . ( 2006 ) have reported that jasmonates promote root hair formation in arabidopsis , which agrees with our findings .
jasmonates are a class of plant hormones that mediate various aspects of gene and metabolic regulation , defense , stress responses , reproduction , and possibly communication .
the role of ja in plants has received considerable attention , and various modes of action for ja and its methyl ester ( meja ) have been proposed ( farmer 2007 ; farmer and ryan 1990 ) .
farmer ( 2007 ) , working largely with the model plant arabidopsis thaliana , concluded that the two groups take different routes to the genes involved .
( 2007 ) analyzed eight related gene transcripts of unknown function that are rapidly upregulated in developing arabidopsis stamens treated with jasmonates .
by contrast , chini et al . ( 2007 ) characterized a mutant called jasmonate - insensitive3 - 1 ( jai3 - 1 ) . working with different genes
, both groups found that over - expression of the full - length transcripts had little or no effect on jasmonate perception .
however , over - expression of shortened forms that encode proteins truncated at the carboxyl terminus reduced sensitivity to jasmonates . additionally , although full - length proteins were unstable in vivo when treated with jasmonates , proteins with a truncated carboxyl terminus resisted degradation in response to such treatment .
( 2011 ) reported that induced systemic resistance ( isr ) occurs in response to the application of meja , and systemic acquired resistance ( sar ) occurs after treatment with salicylic acid or benzothiadiazole , whereas some of the arabidopsis genotypes affected in defense signaling show altered numbers of culturable bacteria in their rhizospheres ; however , the effects depend on soil type .
genes involved in jasmonate biosynthesis , secondary metabolism , and cell - wall formation , and those encoding stress - protective and defense proteins are up - regulated by meja treatment ( cheong and choi 2003 ) . in this study ,
five transcripts - des2 , des3 , ars1 , ars2 , and omt3-that encode enzymes involved in sorgoleone biosynthesis were shown to accumulate in response to treatment with ja and meja .
levels of omt3 transcript accumulated to levels 8.1-fold higher than in seedlings not treated with meja .
this observation is supported by other reported documents ( bonfill et al.2011 ; kim et al.2009 ; korsangruang et al.2010 ; lystvan et al.2010 ; rhee et al.2010 ) , where they investigated the capability of ja and its methyl ester , meja , to induce the accumulation of various secondary metabolites , and showed higher levels of expression for their respective genes and also from previous work ( uddin et al.2011 ) , where they observed that sorgoleone biosynthetic genes are up or down - regulated by auxins .
the application of phytohormones to excised sections or organs ( e.g. , root , elongating region of hypocotyl , basal region of hypocotyl , and plumule ) of intact soybean seedlings resulted in the accumulation of mrnas for pghl-4 to levels that are many - fold greater than those found in untreated organs of seedlings ( hagen and guilfoyle 2002 ) .
the results obtained using jasmonates to enhance sorgoleone production suggest that sorghum roots benefit from exposure to jasmonates by developing more sorgoleone - rich root hairs , showing different rooting pattern and root weight variation among the jasmonate treatments .
transcript accumulation was apparent for all of the seven genes tested , particularly omt3 , for which transcript levels increased up to 8.1-fold after a 36  h exposure to meja compared with omt3 transcript levels in untreated seedlings .
in summary , these findings suggested that jasmonates ( ja and meja ) are potent substances for promoting root hair formation and sorgoleone accumulation and up - regulating gene expression in sorghum .
further research should focus on the involvement of these products in the regulation of root responses to stress .
 this study investigated the roles of jasmonates in the regulation of sorgoleone accumulation and the expression of genes involved in sorgoleone biosynthesis in sorghum roots . both methyl jasmonate ( meja ) and jasmonic acid ( ja ) substantially promoted root hair formation , secondary root development , root weight , and sorgoleone accumulation in sorghum roots . 
 sorgoleone content varied widely depending on the concentration of ja or meja and the duration of their application . 
 root weight and sorgoleone accumulation were highest after the application of ja or meja at a concentration of 5.0  m , and then declined with increasing concentrations of jasmonates . at 5.0  m , ja and meja increased sorgoleone content by 4.1 and 3.4-fold , respectively . 
 transcript accumulation was apparent for all genes , particularly for the o - methyltransferase 3 gene , which increased in expression levels up to 8.1-fold after a 36-h exposure to meja and 3.5-fold after a 48-h exposure to ja . 
 the results of this study pave the way for more effective biosynthesis of sorgoleone , an important and useful allelochemical obtained from a variety of plant species . 
Introduction
Materials and Methods
Results
Discussion