Genome-wide expression profiling of barley in response to drought stress under different potassium application levels

Climate models predict a gradual increase of temperature and CO2 concentration leading to the escalation of drought incidence and duration in many regions around the world. Potassium is one of the most abundant elements in plants and performs vital functions in drought stress adaptation, growth and metabolism.

In this study the physiological responses of two candidate cultivars (cv. Sahin-91 and cv. Milford) were monitored over a time period where plants were subjected to different potassium application levels and two drought stress conditions. Massive analysis of cDNA ends was performed on selected cultivar (Milford) to study the genome wide expression responses under selected treatments.

The results showed that H₂O₂ concentration raised about three folds when K supply decreased from 0.8 mM (adequate K) to 0.04 mM (low K) in both cultivars. In line with H₂O₂ concentration, the activities of antioxidant enzymes such as APX, CAT and GR increased significantly with distinct response patterns. On an averaged normalized basis, of the total 113.601.960 reads, almost 23000 genes were transcribed more than 5 times. In drought induced treatments, 2784 genes were significantly up/down regulated under low and adequate potassium levels. Among these, 81 genes related to processes of photosynthesis were expressed differently which the function of few up-regulated (psbD,pasbZ) is to repair the photosystem (ll) and thereby maintaining its activity under ROS damaging conditions. Highest rate of differentially expressed photosynthetic genes which were down regulated belong to (CAB and PORC) being responsible for production of chlorophyll a/b binding proteins and chlorophyll biosynthesis, respectively.