MORPHOLOGICAL AND BIOCHEMICAL ADAPTATIONS OF LOCAL CULTIVARS OF BARLEY (Hordeum vulgare L.) UNDER DROUGHT

Abstract

Barley (Hordeum vulgare L.) ranks fifth among important crops worldwide having the annual production of 136 million metric tonnes. In comparison with other cereal crops, it is more tolerant to water shortage, cold environments and salinity and hence is a crop of marginal lands. Drought is an important factor limiting barley yield because about two third of the area of barley production in Pakistan is rainfed. The present study was focused to unravel the morphological and biochemical dynamics and processes underlying adaptation to drought in local genotypes of barley. After initial screening in hydroponics at early growth stage, the barley genotypes were grouped into drought sensitive and tolerant categories using Ward’s hierarchical clustering procedure. The drought sensitive group comprised of nine genotypes (004186, Jau-83, Sanober-96, 004222, Haider-93, 004325, 005130, Soorab-96 and Jau-87) while the tolerant group consisted of six genotypes (004223, 004360, Frontier -87, 004201, 017655 and 005137). Drought linked simple sequence repeat (SSR) primers also separated sensitive and tolerant genotypes into different groups in UPGMA clustering. Among the drought sensitive group, 004186 was found to be the most sensitive genotype and 004223 as the most tolerant one in the tolerant group. Dehydrins are the proteins who play an important role in plant adaptation to drought. Immunoblots were used to characterize dehydrins in local barley genotypes. The maximum dehydrin expression was found in the most drought tolerant genotype 004223 while the most sensitive genotype 004186 lack this expression. Further characterizations of barley genotypes were done in a pot experiment at tillering, booting and milking stages of development. The data recorded was analysed using CRD. The milking stage came out 18 to be the most responsive towards drought. Genetic diversity analysis was done using Inter simple sequence repeat (ISSR) primers. The resultant dendrogram clustered barley cultivars and landraces into two separate groups. Global changes in protein profiles of the most sensitive (004186) and the most tolerant genotype (004223) were further investigated using proteomics technique. After the extraction of proteins from shoots, their separation was carried out by 2D-PAGE and staining was done with coomassie brilliant blue. Among the commom proteins between sensitive and tolerant genotypes in response to drought, the expression of Vacuolar Proton ATPase subunit E was increased while Photosystem I reaction centre II was decreased. Many of the proteins involved in photosynthesis and metabolism were decreased in the sensitive genotype under drought, however, they were increased in the tolerant genotype. Similarly, proteins related to energy, defense and transportation were also increased in the tolerant genotype only. To further investigate the response of three most drought tolerant genotypes (004223, 004360 and Frontier-87), a confirmatory experiment was conducted using proteomics approach. Among these genotypes, the twofold increase in the expression of Alpha SNAP and Methionine synthase alongwith Glycine decarboxylase indicated their crucial role in water stress tolerance. In conclusion, these target proteins involved in maintaining ion balance, chromatin protection and suppression of ROS came out to be the candidates for drought stress acclimation in barley genotypes.