soybean is one of the most important crops in the world , and brazil is its second largest producer . due to its use in animal feed , vegetable oil and biodiesel nevertheless , abiotic stresses , such as water deficit , cold , wind , heat or waterlogging , reduce productivity and present a major challenge in the quest for sustainable soybean production . in order to meet the ever - increasing demand , crop yield is highly affected by water deficit stress , particularly when it occurs during flowering and early pod expansion ( pedersen et al . , 2005 ) . however , soybean plants can acclimate to such conditions by triggering protective mechanisms that enable these plants to survive subsequent events of drought ( bray , 2004 ) . while studying soybean plants exposed to stress at different developmental stages , kron et al . ( 2008 ) observed that plant responses were more uniform in the v4 stage ( fehr et al . , 1971 ) . the genetic background of the cultivars br 16 ( drought sensitive ) and embrapa 48 ( drought tolerant ) under drought conditions was studied by oya et al . ( 2004 ) , and they found that at the vegetative stage , tolerant cultivars present higher growth rate and a larger leaf area compared to sensitive plants . however , to better understand plant physiology under stress , productivity analyses are hardly enough to distinguish significant tolerance differences among cultivars . the data indicate how cultivars behave under stress and , therefore , suggest which ones are suitable for further biochemical and molecular studies . a stress response is initiated when plants recognize the stress at the cellular level , it triggers a complex signal transduction network which is modulated by molecular events . gene products involved in water - deficit responses can be classified into two groups : functional or regulatory genes . functional genes include the following : proteins , osmolytes , chaperones , heat - shock proteins ( hsps ) , water - channel proteins ( multifunctional proteins involved in transport facilitation of solutes and water in leaves and roots ) , and other compounds probably conferring direct tolerance to abiotic stresses . under water stress conditions , a chemical imbalance in the cell leads to production of reactive oxygen species ( ros ) , which are damaging to lipids and proteins ( carvalho , 2008 ; molina et al . , enzymes involved in detoxification metabolism are found to protect against the stress in the tolerant common bean cultivar ( phaseolus acutifolius ) ( trkan et al . , 2005 ) . in drought - stressed tissues , the water movement within and between cells can be facilitated by aquaporins ( cocozza et al . , 2010 ) . the second group of genes involved in the response to water deficit includes molecules involved in further regulation of signal transduction and stress - responsive gene expression . these molecules are regulatory proteins , represented by various transcription factors such as dreb1 , aba - responsive element , nitrogen assimilation control protein , ethylene - response factors , kinases , phosphatases , enzymes involved in phospholipid metabolism , and other signaling molecules , such as calmodulin - binding protein ( shinozaki and yamaguchi - shinozaki , 2007 ) . in the peanut , a predicted drought tolerant legume , a set of functional and regulatory genes were detected in enriched subtractive libraries probably acting in a gradual process of drought acclimation ( govind et al . , 2009 ) . as discussed , the ability to tolerate water deficit is a complex trait controlled by many genes ( molina et al . , 2008 ; ergen and budak , 2009 ) . collections of cdnas expressed under stressed conditions have been a useful resource to study gene expression and regulation . the cdna libraries were associated to normalization steps and pcr amplification to obtain just the transcripts presented in a target situation ( diatchenko et al . , 1996 ) . a suppressive subtractive library approach makes it possible to search for genes expressed in treated samples but not in the control samples , if the forward subtraction is done . it can be used to assess changes in metabolism and in quantitative gene expression studies , such as those based on arrays . the method has been employed successfully in different research areas , such as the monitoring of citrus responses to fungus infection ( gonzlez - candelas et al . , 2010 ) and in fish infected by iridovirus ( xu et al . , 2010 ) . using the subtracted library of pigeonpea , priyanka et al . ( 2010 ) isolated a gene encoding a hybrid - rich - proline protein , which affords tolerance to water deficit and other abiotic stresses such as salt , heat , cold and abscisic acid treatment . in addition , cdna subtractive libraries have also allowed the identification of genes involved in the flower development of orange plants ( zhang et al . , 2008 ) and of genes involved in the varroa destructor mite tolerance to honey bees , drought has resulted in severe losses in soybean productivity worldwide . in order to expand previous knowledge about the water stress - sensitive br 16 and water stress - tolerant embrapa 48 soybean cultivars , the present work aimed to study early responses in gene expression of leaves and roots under water stress . seeds of the soybean cultivars embrapa 48 and br 16 , classified as tolerant and sensitive to water deficit , respectively , were germinated on filter paper during four days in a growth chamber at 25  1 c of temperature and 100% relative humidity . seedlings were placed in 36 l boxes containing 50% hoagland s solution ( hoagland and arnon , 1950 ) , which was continuously aerated and replaced on a weekly basis . these boxes were then transferred to a greenhouse under a natural photoperiod of approximately 12/12 h light / dark cycle , temperature of 30  5 c and 60  10% relative humidity ( rh ) , where the plants were allowed to grow until the v4 stage ( fehr et al . , 1971 ) . the factors were two cultivars ( br 16 and embrapa 48 ) and seven times of water deficit ( 0 , 25 , 50 , 75 , 100 , 125 and 150 min ) . the stress was applied by removing the plants out of the hydroponic solution and leaving them in boxes without nutrient solution for up to 150 min under ambient - air exposure . for each time of water deficit , roots from 10 plants were collected , pooled and frozen in liquid nitrogen before storage at  80 c . photosynthetic rate ( a ) , stomatal conductance ( gs ) , intercellular co2 concentration ( ci ) , transpiration rate ( e ) and leaf temperature ( tl ) were evaluated using a li-6400 portable photosynthesis system ( licor , inc . ) . measurements were taken on the middle leaflet of the youngest soybean leaf , fully expanded , under photon flux density of 1.000 mol m s. the water use efficiency ( wue ) of plants was determined through the ratio between photosynthetic ( a ) and transpiration ( e ) rate . data was submitted to anova analysis through the programs sanest and sas ( statistical analysis system version 8.0 ) , and the treatment means were compared by the tukey test ( p < 0.05 ) . total rna was extracted from roots and leaves using trizol reagent ( invitrogen ) according to the manufacturer s instructions . samples from each biological replicate were extracted separately , and equimolar amounts of total rna were pooled before the mrna purification . the fasttrack mag mrna isolation ( invitrogen ) was applied to isolate the mrna poly a molecules by using oligo - dt conjugated magnetic beads . the mrna samples were pooled as illustrated in figure 1 to perform the cdna reverse transcription . libraries of roots and leaves from embrapa 48 and br 16 plants were constructed based on the method of diatchenko et al . first strand cdna was synthesized from 2 g of mrna poly a pooled samples ( tester and driver ) . after the second strand synthesis , cdnas ( tester and driver ) were digested with the restriction enzyme rsa i to produce blunt end fragments . once digested , the cdnas ( only tester samples ) were divided into two samples and each sample was ligated with two different adapters ( adaptor 1 and 2r , respectively ) . as our aim was to detect transcripts expressed only in water - deficit stressed plants , the sample t0 ( control plant ) was used as the driver in the hybridization step . the cdna driver ( with no adaptor ) was added to tester samples ( 1 and 2r ) and they were submitted to the first hybridization step to eliminate sequences common in both samples or present in the control ( driver ) . for the second hybridization , tester samples 1 and 2r from the first hybridization were mixed together , and the denatured cdna driver was added again to enrich the expressed sequences in the tester . the pcr amplification was performed using the double - strand cdnas with different adapters as template . the second pcr was carried out using the nested primers to enrich the differentially expressed sequences . the six libraries from br 16 cultivar ( three from roots and three from leaves ) were sequenced through 36 bp ( base pairs ) single reads in a genome analyzer lle machine . the embrapa 48 libraries were sequenced in a genome analyzer llz using single reads of 76 bp . after base - calling , reads were mapped on a reference genome ( schmutz et al . , 2010 ) using the soap ( li et al . , 2008 ) , and non - mapped reads were assembled into contigs through the edena program following the default parameters ( hernandez et al . , 2008 ) . contig sequences were submitted to the non - redundant protein database ncbi through blast x ( altschul et al . , 1997 ) , to search for similarity to known proteins . in addition , sequences were analyzed by the software autofact ( koski et al . , 2005 ) , which is an automated annotation tool that assigns biological information for a given sequence by comparing different databases . we used the uniref90 e uniref100 , kegg ( kanehisa and goto , 2000 ) , pfam ( finn et al . , 2010 ) , smart ( schultz et al . , 1998 ) databases . in order to establish the go ( gene ontology ) terms ( ashburner et al . , 2000 ) we employed the blast2go program to classify the sequences according to the molecular function and biological process described to the respective protein ( gtz et al . seeds of the soybean cultivars embrapa 48 and br 16 , classified as tolerant and sensitive to water deficit , respectively , were germinated on filter paper during four days in a growth chamber at 25  1 c of temperature and 100% relative humidity . seedlings were placed in 36 l boxes containing 50% hoagland s solution ( hoagland and arnon , 1950 ) , which was continuously aerated and replaced on a weekly basis . these boxes were then transferred to a greenhouse under a natural photoperiod of approximately 12/12 h light / dark cycle , temperature of 30  5 c and 60  10% relative humidity ( rh ) , where the plants were allowed to grow until the v4 stage ( fehr et al . , 1971 ) . the factors were two cultivars ( br 16 and embrapa 48 ) and seven times of water deficit ( 0 , 25 , 50 , 75 , 100 , 125 and 150 min ) . the stress was applied by removing the plants out of the hydroponic solution and leaving them in boxes without nutrient solution for up to 150 min under ambient - air exposure . for each time of water deficit , roots from 10 plants were collected , pooled and frozen in liquid nitrogen before storage at  80 c . photosynthetic rate ( a ) , stomatal conductance ( gs ) , intercellular co2 concentration ( ci ) , transpiration rate ( e ) and leaf temperature ( tl ) were evaluated using a li-6400 portable photosynthesis system ( licor , inc . ) . measurements were taken on the middle leaflet of the youngest soybean leaf , fully expanded , under photon flux density of 1.000 mol m s. the water use efficiency ( wue ) of plants was determined through the ratio between photosynthetic ( a ) and transpiration ( e ) rate . data was submitted to anova analysis through the programs sanest and sas ( statistical analysis system version 8.0 ) , and the treatment means were compared by the tukey test ( p < 0.05 ) . total rna was extracted from roots and leaves using trizol reagent ( invitrogen ) according to the manufacturer s instructions . samples from each biological replicate were extracted separately , and equimolar amounts of total rna were pooled before the mrna purification . the fasttrack mag mrna isolation ( invitrogen ) was applied to isolate the mrna poly a molecules by using oligo - dt conjugated magnetic beads . the mrna samples were pooled as illustrated in figure 1 to perform the cdna reverse transcription . libraries of roots and leaves from embrapa 48 and br 16 plants were constructed based on the method of diatchenko et al . first strand cdna was synthesized from 2 g of mrna poly a pooled samples ( tester and driver ) . after the second strand synthesis , cdnas ( tester and driver ) were digested with the restriction enzyme rsa i to produce blunt end fragments . once digested , the cdnas ( only tester samples ) were divided into two samples and each sample was ligated with two different adapters ( adaptor 1 and 2r , respectively ) . as our aim was to detect transcripts expressed only in water - deficit stressed plants , the sample t0 ( control plant ) was used as the driver in the hybridization step . the cdna driver ( with no adaptor ) was added to tester samples ( 1 and 2r ) and they were submitted to the first hybridization step to eliminate sequences common in both samples or present in the control ( driver ) . for the second hybridization , tester samples 1 and 2r from the first hybridization were mixed together , and the denatured cdna driver was added again to enrich the expressed sequences in the tester . the pcr amplification was performed using the double - strand cdnas with different adapters as template . the second pcr was carried out using the nested primers to enrich the differentially expressed sequences . the six libraries from br 16 cultivar ( three from roots and three from leaves ) were sequenced through 36 bp ( base pairs ) single reads in a genome analyzer lle machine . the embrapa 48 libraries were sequenced in a genome analyzer llz using single reads of 76 bp . after base - calling , reads were mapped on a reference genome ( schmutz et al . , 2010 ) using the soap ( li et al . , 2008 ) , and non - mapped reads were assembled into contigs through the edena program following the default parameters ( hernandez et al . , 2008 ) . contig sequences were submitted to the non - redundant protein database ncbi through blast x ( altschul et al . , 1997 ) , to search for similarity to known proteins . in addition , sequences were analyzed by the software autofact ( koski et al . , 2005 ) , which is an automated annotation tool that assigns biological information for a given sequence by comparing different databases . we used the uniref90 e uniref100 , kegg ( kanehisa and goto , 2000 ) , pfam ( finn et al . , 2010 ) , smart ( schultz et al . , 1998 ) databases . in order to establish the go ( gene ontology ) terms ( ashburner et al . , 2000 ) we employed the blast2go program to classify the sequences according to the molecular function and biological process described to the respective protein ( gtz et al . plants grown hydroponically were exposed to a short - term water deficit and the physiological parameters a , gs , ci , e , tl , troom and wue are presented in figure 2 . we employed the subtractive suppressive hybridization ( ssh ) technique to obtain an enriched collection of ests expressed early in response to water deficit stress . cdna libraries were constructed to detect genes up - regulated when compared to control plants . after sequencing and base calling , approximately 65% of the total reads produced for each library was mapped on the genome . contigs assembled were searched in the ncbi database in order to access the information about proteins . biochemical roles of the proteins were determined by using the biological process level 3 from gene ontology ( figure 3 ) . approximately 71% of the sequences in br 16 and 61% of embrapa 48 showed an associated putative biological or molecular function . consequently , the number of no match and unknown genes was larger in embrapa 48 than in br 16 plants . in br 16 , we observed 121 and 452 different roles for the genes expressed in the roots and leaves , respectively . in embrapa 48 categories employed in functional classification include the following : biological regulation ( gene expression regulation , protein modification regulation ) ; signaling ( kinases , phosphatases , secondary messengers ) ; response to stress ( water deficit , osmotic and salt stress , heat , cold ) ; response to stimulus ( chemical stimulus , endogenous stimulus ) ; response to biotic stimulus ( pathogen , fungus , insect ) ; cell organization ( cytoskeleton components , cell wall organization , cellular component assembly ) ; cell cycle ( actin filament - based process , cell division ) ; senescence ( aging , cell death ) ; other biological process ( cellular component organization , cell recognition , developmental process ) ; biosynthetic process ( carbohydrate , fatty acid , hormone , small and macromolecules , pigment , nucleotide ) ; catabolic process ( protein , fatty acid , cell wall , polysaccharide ) ; nitrogen compound metabolism ( glutamate and glutamine biosynthetic process , cellular nitrogen compound metabolic process ) ; oxidation reduction ( electron transport , lipid oxidation ) and secondary metabolism ( terpenoid , phytochelatin , phytoalexin and phenylpropanoid metabolic process ) . each category was normalized by the total number of sequences observed in the respective library , which enables comparison of the results during the time course of the water deficit ( figure 3 ) . applying the venn - master diagram , we also searched for genes expressed in more than one library as described in figure 4 . br 16 root tissue genes were categorized as involved in the electron transport process ( r1 and r2 libraries ) or as encoding proteins related to the stress response class ( r2-r3 library ) ( figure 4a ) . in br 16 leaves ( l1-l2 libraries ) , we also detected genes involved in signaling reactions or involved in the transport of metabolites and electrons ( oxidation reduction process ) ( figure 4b ) . in addition , the genes in the l2-l3 libraries were also related to stress response ( figure 4b ) . a general view of l1-l2-l3 libraries confirmed that genes functionally related to transport and stress responses were also expressed in leaves over the water deficit period ( figure 4b ) . it is important to emphasize that transcripts observed in r1-r2 , for example , were different from the transcripts found in r1-r2-r3 , although similar biological processes could be detected in both libraries . interestingly , in the embrapa 48 cultivar , transcription factors and genes involved in signal transduction were the most abundant transcripts in both r1 and r2 root tissues ( figure 4c ) . genes encoding transcription factors were also predominant in the r2-r3 libraries in addition to the ones related to transport process ( electrons and molecules ) . the same pattern was found in r1-r2-r3 libraries ( figure 4c ) . processes related to protein metabolism ( assembly , folding and modification ) were very active in l2-l3 libraries as well as genes involved in transport process , response to stress and signaling . stress response genes stand for 22% of the genes identified in l1-l2-l3 libraries ( figure 4d ) . we performed a comparison between genes expressed in roots and leaves in either cultivar using the venn - master diagram tool and looking for the biological processes observed in each group . when the same contig or glyma was detected in more than one library then , considering only the non - repeated genes from each group ( tissue or cultivar ) , we were able to observe genes expressed in root and leaves as well as genes expressed in embrapa 48 and br 16 plants ( figure 5a ) . to assess biological processes in roots and leaves of both cultivars , we highlighted the more abundant putative proteins and cellular components in each water - deficit stressed tissue ( figure 5b ) . according to our data , transcripts expressed by br 16 plants in roots and leaves showed that the most frequent biological processes were similar in both tissues ( figure 5b ) . however , in embrapa 48 , the process of response to stress was predominant among transcripts from leaves and less common in roots ( figure 5b ) . among genes expressed by plants in response to water deficit , we observed that transcripts classified in the response to stress category presented similarity to proteins with responsiveness to biotic as well as to abiotic stress . these transcripts represent proteins with antimicrobial activity or proteins involved in defense and immune responses . genes related to the response to virus , pathogenic bacterium , nematodes and fungi were also detected . under abiotic stress , we identified transcripts in response to osmotic and oxidative stress , desiccation , heat , cold , water deprivation , hyperosmotic salinity and high light intensity . to assess which transcripts are expressed in response to other adverse conditions , the genes placed in the response to stress category ( n = 458 ) were compared to transcripts from plants infected by phakopsora pachyrhizi , uromyces appendiculatus , virus and treated with bradirhyzobium japonicum ( figure 6 ) . plant water deficit responses and tolerance are complex biological processes that need to be analyzed at system - level using genomics and physiological approaches ( harb et al . , 2010 ) . studies aiming to detect differences among plants in response to stress using contrasting cultivars have been performed in some legumes ( trkan et al . , 2005 ) . empiric observations during growing seasons in the field are the first step to explore plant variability based on its yield under water deficit conditions . ( 2004 ) examined the physiological characteristics of the embrapa 48 and br 16 cultivars and determined that they were moderately tolerant and highly sensitive to drought , respectively . here , we studied these cultivars at the molecular level , and our data demonstrated that the water deficit applied was effective as it triggered changes in the plant physiological behavior ( figure 2 ) . as the stress increased in the plants , photosynthesis of both cultivars was affected and was strongly inhibited after 100 min . this inhibition was related to a drastic decrease in the stomatal conductance ( gs ) and transpiration rate ( e ) of both cultivars . we also observed an increase in the leaf temperature ( from 100 min ) and internal concentration of co2 ( from 125 min ) . the water deficit did not produce significant physiological differences between embrapa 48 and br 16 cultivars . this was expected as the short - term procedure to induce stress used here is usually not enough to produce effects on plant morphological and physiological characteristics needed to distinguish the two cultivars . the experimental treatment described here aimed to study the effects of the stress on the early plant responses at a molecular level . additionally , the hydroponic system allowed the obtainment of a clean root sample , as demonstrated by martins et al . as described in the literature , subtractive libraries have been employed in a wide range of studies such as gene expression studies ( kojima et al . , 2009 ; gonzlez - candelas et al . , 2010 ; jain and chattopadhyay , 2010 ; soria - guerra et al . , 2010 ) . most of these studies were based on the construction of a physical cdna collection by cloning fragments into a vector and on the traditional big dye sequencing technology . however , in vivo cloning can be considered a laborious and expensive procedure and also has technical limitations . in order to overcome these limitations , both cultivar cdnas were sequenced using two different chemistries based on sequencing by synthesis technology ( illumina ) . as shown in table 1 , we identified many genes being regulated under water deficit , more than is often detected through subtractive libraries . larger sets of genes were also detected in the characterization of stress - responsive genes to heat in wheat ( chauhan et al . , 2011 ) and by studying salt - induced genes of grapevine ( daldoul et al . , 2010 ) . both suppressive subtractive libraries were done through in vivo cloning and by the capillary sequencing method . ( 2010 ) found 12442 contigs in the transcriptome by combining subtractive libraries and massively parallel sequencing ( pyrosequencing ) . one of the advantages of the next generation sequencing ( ngs ) over the traditional sanger methodology is a more precise measurement of the transcript levels and isoforms , in addition to other revolutionary benefits ( marioni et al . , 2009 ; wang et al . , 2009 ) the advantages and limitations found in the ngs and capillary sequencing have led to comparative studies of both methods ( cheung et al . , 2008 ; hert et al . , 2008 ; tedersoo et al . , lower costs and quickness have made the ngs a powerful tool for functional genomics studies ( shendure and ji , 2008 ; harismendy et al . , 2009 ) . under water deficit different biochemical roles have been suggested for these responsive genes , and their expression patterns make an intricate network that can be related to either water deficit acclimation or the cellular damage response ( shinozaki and yamaguchi - shinozaki , 2007 ) . the expressed genes have been shown to belong to many classes of genes ( figure 3 ) . however , the largest class of genes expressed under stress remains unknown , partly because there is no similarity in databases available to date , and partly due to the gene functions are not understood yet ( reddy et al . many genes expressed under water deficit conditions are present in the contrasting cultivars embrapa 48 and br 16 ( figure 5a ) . among others , common processes affected by the stress are those related to transport , protein folding and assembling as well as protein degradation and ubiquitination . some proteins are synthesized in requirement of defense pathways triggered by the stress whereas other proteins are degraded because its aggregation or denaturation events are predominant in water stress conditions . the transport category involves the translocation of ions , lipids , sugar and others molecules . also included in this category are the genes for aquaporins , which are proteins that might be directly involved in water deficit acclimation by facilitating water movement across the membranes ( zhao et al . , 2008 ) . we have identified several transcripts encoding the tonoplast and plasma membrane intrinsic proteins that were more frequently found in roots rather than in leaves , especially in the br 16 plants ( figure 5b ) . roles played by aquaporins in plants can be regulated in different complex ways , but the expression of aquaporins throughout the plant would most likely be regulated by water potential gradient ( zhao et al . , 2008 ) . however , there are differences between the mrna changes and its respective protein level . the changes expressed here by soybean plants in response to water stress are only at the transcriptional level . br 16 plants did not show an expressive quantitative difference in the biological processes affected by water deficit between roots and leaves ( figure 5b ) . nonetheless , embrapa 48 did show a significant contrast between both tissues ( figure 5b ) regarding the genes included in the response to stress class ( water deficit , osmotic and salt stress , heat and cold ) . in abiotic stress responses , genes are induced to protect the plants against a disturbance in cell homeostasis . under water stress , plants can become susceptible to other abiotic or biotic stresses because their normal metabolism is directed towards the acclimation to the first stress . several studies have tried to make a connection between plant responses to water deficit and heat ( sakuma et al . , 2006 ; montero - barrientos et al . , 2010 ) , cold ( li et al . , 2010 ) , or reactive oxygen species enhanced due to drought ( kocsy et al . , 2005 ; khanna - chopra and selote , 2007 ) . in the response to stress category , we observed that various transcripts were similarly involved in several abiotic stresses such as osmotic stress , cold , heat and salinity as well as those involved in response to biotic stimulus ( bacterium , fungus , nematode , virus ) ( figure 6 ) . from subtracted libraries of pigeonpea , 2010 ) identified a hybrid - proline - rich encoding gene whose multiple stress - responsive characteristics have been demonstrated under peg , mannitol , salt and heat stress , cold and aba - treatment . another gene from pigeonpea , a cyclophilin gene , presented a stress - responsive nature in arabidopsis thaliana ( sekhar et al . , 2010 ) . a bzip transcription factor gene found in soybean plants was also associated with multiple stress responses , being its expression induced by aba - treatment , drought , high salt and low temperature ( gao et al . a hydroponic system was applied successfully to grow soybean plants and to produce clean roots in a short - term water deficit experiment . we described a large collection of cdnas expressed by soybean plants under water deficit and their respective biochemical processes . although the analyses presented here represent a first step in gene expression investigation , the results indicate changes which are triggered in roots and leaves of tolerant and sensitive soybean plants .
soybean has a wide range of applications in the industry and , due to its crop potential , its improvement is widely desirable . during drought conditions , 
 soybean crops suffer significant losses in productivity . 
 therefore , understanding the responses of the soybean under this stress is an effective way of targeting crop improvement techniques . in this study 
 , we employed the suppressive subtractive hybridization ( ssh ) technique to investigate differentially expressed genes under water deficit conditions . 
 embrapa 48 and br 16 soybean lines , known as drought - tolerant and -sensitive , respectively , were grown hydroponically and subjected to different short - term periods of stress by withholding the nutrient solution . using this approach , 
 we have identified genes expressed during the early response to water deficit in roots and leaves . 
 these genes were compared among the lines to assess probable differences in the plant transcriptomes . in general , 
 similar biochemical processes were predominant in both cultivars ; however , there were more considerable differences between roots and leaves of embrapa 48 . 
 moreover , we present here a fast , clean and straightforward method to obtain drought - stressed root tissues and a large enriched collection of transcripts expressed by soybean plants under water deficit that can be useful for further studies towards the understanding of plant responses to stress .