Caractérisation des gènes de tolérance à la sécheresse chez le blé dur

Abstract

The knowledge of molecular tolerance mechanisms to drought in cereals and particularly in wheat remain essential in order to cope with the stress negative effects. Plant response rely on the expression of several genes, the outcome is a modification in their transcriptional programs. The main objective of the present study was to perform a comparative analysis of durum wheat genotype response to drought at physiological, biochemical and molecular level by focusing on two stress responsive genes. Tree experimentations have been done on Algerian durum wheat genotypes, two of them under controlled conditions in growth chamber and the third one under semi controlled conditions in a green house. Under controlled conditions, the water stress was applied by adding polyethylene glycol to the media and under semi controlled conditions, it was applied by withholding water. At physiological and the biochemical level, the characterization of the genotypes response to water stress was analyzed through several indices such as: germination rate, leaf and root length, root number, LR/LF ratio, dry matter, relative water content, leaf temperature, chlorophyll content (SPAD index), stomatal conductance, electrolyte leakage, sugar accumulation. Also a 1D SDS-PAGE electrophoresis of heat stable proteins was performed. The conducted studies highlighted significant differences between varieties and drought treatments for most of the studied traits, except for: leaf and root length and leaf temperature (under polyethylene glycol induced drought stress). Water stress induced a decrease in germination rate, root number, chlorophyll content and stomatal conductance that result in a decrease in dry matter production. Also a decrease in relative water content, combined with an increase in electrolyte leakage and sugar content. The observed differences regarding protein bands revealed by 1D SDS-PAGE electrophoresis affected as well their intensity and their molecular weight. Expression level of an aquaporin gene (TdPIP2,1) and a dehydrin gene (DHN-5) were also investigated in different plant tissues and under different drought stress conditions for two varieties (Waha and Beliouni). The dehydrin gene (DHN-5) was not expressed in well watered plants but only in the stressed ones in roots, leaves and blades. While the aquaporin gene (TdPIP2,1) was expressed in both, with a higher amount in stressed plants in roots, leaves and blades. Moreover, the transcript level of the two genes was more accumulated in Beliouni. The upper expression of these genes may improve water deficit tolerance and lead to suitable cellular response in order to cope with drought stress damages through several mechanisms. There is a strong connection between the modifications that occurs on the molecular, cellular level and those that occurs on physiological level. The identification of a possible connection between activated stress responsive genes can be useful by providing a starting point to further elaborate biotechnological approaches.