Tall wheatgrass (Elymus elongatum Host) is a drought-tolerant, cool-season forage grass native to Iran. A proteomic approach has been applied to identify mechanisms of drought responsiveness and tolerance in plants undergoing vegetative stage drought stress and then recovery after rewatering. Uniformed clones were reproduced from a parent plant collected from Brojen (central region of Iran). Clones were grown in pots and drought was initiated by withholding water for 16 d. The leaf samples were taken in triplicate from both stressed/rewatered plants and continuously watered controls at five times: (i) 75% FC, (ii) 50% FC, (iii) 25% FC, (iv) 3 d after rewatering, and (v) 14 d after rewatering. Changes in the proteome pattern of shoots were studied using two-dimensional gel electrophoresis. Following the 16 d water stress, both shoot dry weight and leaf width decreased up to 67% compared with the well-watered plants, whereas proline content increased up to 20-fold. Leaf relative water contents (RWC) also declined from 85% to 24%. Out of about 600 protein spots detected on any given two-dimensional gel, 58 protein spots were reproducibly and significantly changed during drought stress and recovery. Only one protein (abscisic acid- and stress-inducible protein) showed significant changes in expression and position in response to severe drought. The fifty-eight responsive proteins were categorized in six clusters including two groups of proteins specifically up- and down-regulated in response to severe drought stress. Eighteen proteins belonging to these two groups were analysed by liquid chromatography tandem mass spectrometry leading to the identification of 11 of them, including the oxygen-evolving enhancer protein 2, abscisic acid- and stress-inducible protein, several oxidative stress tolerance enzymes, two small heat shock proteins, and Rubisco breakdown. The results suggest that E. elongatum may tolerate severe drought stress by accumulating proline and several proteins related to drought-stress tolerance. Recovery after rewatering might be another mechanism by which plants tolerate erratic rainfall in semi-arid regions.

Native cool‐season grasses are important for improvement of arid and semiarid rangelands in Iran. However, germination and seedling emergence of these species is a critical phase in these areas and are not well understood. The objective of this study was to evaluate the effect of low soil moisture on emergence of 36 populations of native cool‐season grasses from 15 species of seven genera including Elymus, Agropyron, Secale, Hordeum, Bromus, Festuca, and Dactylis that were collected from different locations of Iran. A pot experiment was conducted in a greenhouse using a completely randomized design with three replicates. The populations were evaluated under field capacity (FC, −0.33 MPa), 75, 50, and 25% FC. Decreasing soil water content from FC to 25% FC reduced overall mean emergence from 69.3% to zero. Significant differences occurred among species and soil moisture levels for all characters except root/shoot dry weight ratio. Seedling emergence rate and root and shoot growth were decreased by limiting soil water content, while root‐to‐shoot length ratio (43%) was increased. Minimum water requirement for seedling emergence of all species except Dactylis glomerata L. was 50% FC (−0.6 MPa). Cluster analysis and canonical discriminant analysis separated the populations into five clusters. Populations in Clusters I and III had intermediate, Cluster II the greatest, and Clusters IV and V the least tolerance to low soil moisture. Cluster I and III had greater root and shoot biomass and rapid emergence, whereas decreasing soil moisture caused a severe reduction of root growth of 60% compared with the control. In response to low soil moisture, Cluster II showed high final emergence and the greatest stability (low sensitivity index) of root growth. Clusters IV and V had delayed emergence, low growth potential, and high sensitivity index for shoot and root growth under low soil moisture. In response to low soil moisture, there were differences among species and accessions of the same species collected from different ecological regions. These results suggest that the genetic diversity of Cluster II could be used for plant breeding programs and renovation of pastures in arid and semiarid regions of Iran.

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