Physiological Responses of Five Almond Species to PEG-Induced Drought Stress

Effects of polyethylene glycol-induced drought stress on some physiological characteristics of young seedlings of five almond species (Prunus dulcis، P. eburnea، P. eleagnifolia، P. haussknechti and P. scoparia) were studied. Three different drought levels resulted from three osmotic potential of the nutrient solutions including Ψs =−0. 6، −1. 1 and −1. 6 MPa and a control treatment (Ψs =−0. 1 MPa) were applied over 2 weeks followed by 4 weeks of recovery. Leaf water potential (LWP) of treated plants was significantly decreased compared to the controls. Under severe stress، P. dulcis had the lowest LWP among examined species. Soluble sugars and free proline were significantly accumulated in leaves in response to drought stress. The greatest accumulation of soluble sugars was observed in P. eburnea and P. dulcis under severe stress as compared to the control. Also، proline was greatly accumulated in the leaves of P. dulcis and P. eburnea. Drought stress caused a significant decrease in chlorophyll a، chlorophyll b and total chlorophyll of the leaves، but total carotenoids content was not influenced by drought. P. haussknechti and P. dulcis showed lesser reduction in leaf chlorophyll content compared to the other species. The activities of antioxidant enzymes including superoxide dismutase، peroxidase، catalase، ascorbate peroxidase and glutathione reductase were significantly increased in leaves of the seedlings subjected to drought treatments. In conclusion، P. dulcis with the lowest LWP، the greatest proline accumulation، relatively higher accumulation of soluble sugars and relatively lesser reduction in leaf pigments under drought condition، showed the higher resistance to drought compared to the other almond species.