Effects of drought stress on seed sink strength and leaf protein patterns of common bean genotypes

Assimilate availability and the capacity to utilise them in the reproductive structures to a large extent determine reproductive sink establishment and yield of crops under drought stress. This study was carried out to investigate the effect of drought stress imposed at early pod-fill stage on seed sink strength of common bean ( Phaseolus vulgaris L.) genotypes differing in drought resistance. Quantitative and qualitative changes in leaf protein patterns was assessed using 2D-gel electrophoresis. A drought-resistant inbred line (SEA 15) and a droughtsusceptible cultivar (BrSp) were grown under non-stress and drought stress conditions in a vegetation hall during the summer of 2004. Drought stress commenced at early pod-filling stage caused 53 and 30% seed yield reductions in BrSp and SEA 15, respectively. The effect of drought on seed yield was primarily due to the significant reduction in number of seeds per plant (48% for BrSp vs. 35% for SEA 15). Whereas seed sucrose concentrations of BrSp decreased by 29 to 47% under drought conditions, the stress resulted in an increase (up to 43%) in concentration of the carbohydrate in SEA 15 seeds. Despite the genotypic difference found for seed sucrose import, seed starch accumulations of the two genotypes decreased under drought stress. For both genotypes, none of the seed sink capacity parameters (numbers and volumes of cotyledonary cells and starch granules per seed) were significantly affected by the stress imposed implying that the drought-induced decrease in seed starch accumulation could be due to limitations in assimilate availability and/or other sink activity factors within the seed. A total of 230 leaf proteins were differentially expressed due to drought out of which 23.5, 15.1, 4.3 and 3.5% were down-regulated, up-regulated, newly appeared and disappeared, respectively. Identification and assigning possible functions in the crop\u2019s response to drought of the stress-induced proteins warrant further study.La disponibilit\ue9 des assimilats et la capacit\ue9 de les utiliser dans des structures reproductrices, d\ue9terminent en grande partie l\u2019\ue9tablissement du \u201csink\u201d reproducteur et les rendements des cultures en conditions de secheresse. Cette \ue9tude avait pour objectif l\u2019\ue9tude de l\u2019effet du stress hydrique impos\ue9 au stade du remplissage des gousses, sur la consistence du \u201csink\u201d de graines de g\ue9notypes du haricot commun ( Phaseolus vulgaris L.) de diff\ue9rente r\ue9sistance \ue0 la secheresse. Des changements quantitatfs et qualitatifs dans les structures de prot\ue9ine des feuilles \ue9taient \ue9valu\ue9s par l\u2019\ue9lectrophor\ue8se 2D-gel.Une souche pure r\ue9sistante \ue0 la s\ue9cheresse (MER 15) et un cultivar non r\ue9sistant \ue0 la s\ue9cheresse (BrSp) \ue9taient cultiv\ue9s \ue0 la fois en conditions de stess et sans stress hydrique dans un hall de vegetation au cours de l\u2019\ue9t\ue9 2004. Le stress hydrique impos\ue9 t\uf4t au stade de remplissage de gousses a entrain\ue9 une r\ue9duction de rendement en grains de 53 \ue0 30% dans BrSp et SEA 15, respectivement. L\u2019effet du stress hydrique sur le rendement en grains \ue9tait principalement d\ufb \ue0 la r\ue9duction significative du nombre de grains par plant (48% pour BrSp contre 35% pour SEA 15). Alors que les concentrations en sucrose dans les grains de BrSp avaient d\ue9cru de 29 \ue0 47% en conditions de s\ue9cheresse, la concentration en hydrates de carbone a augment\ue9 jusqu\u2019\ue0 43% dans les grains de SEA 15. Malgr\ue9 la diff\ue9rence g\ue9notypique trouv\ue9e pour l\u2019importation du sucrose dans la graine, l\u2019accumulation de l\u2019amidon dans la graine de deux genotypes a d\ue9cru en conditions de s\ue9cheresse. Pour les deux genotypes,aucun des param\ue8tres de la capacit\ue9 du sink du grain (nombres et volumes de cellules de cotyledons et granules d\u2019amidon par grain) \ue9taient significativement affect\ue9s par le stess impos\ue9, induisant une r\ue9duction dans l\u2019accumulation de l\u2019amidon dans le grain qui serait due \ue0 la disponibilit\ue9 des assimilats et/ou d\u2019autres facteurs de l\u2019activit\ue9 du sink dans la graine. Au total 230 prot\ue9ines dans les feuilles \ue9taient exprim\ue9es de fa\ue7on diff\ue9rentielle suite \ue0 la s\ue9cheresse en dehors de laquelle 23.5, 15.1, 4.3 et 3.5% \ue9taient respectivement sous r\ue9gul\ue9s, sur-r\ue9gul\ue9s, nouvellement apparus et disparus. L\u2019identification et l\u2019attribution des fonctions possibles des prot\ue9ines sous tress induit en r\ue9ponse de la plante \ue0 la s\ue9cheresse n\ue9cessitent une \ue9tude suppl\ue9mentaire