Antioxidative responses to short-term salinity stress induce drought tolerance in walnut

This experiment was to evaluate the possibility of rapid induction of drought tolerance in greenhouse grown Juglans regia 'Chandler' by imposing a controlled salt stress. The plants were preconditioned by controlled salt stress (100 mM of Na2SO4, CaCl2 or KNO3, 50mM of Na2SO4 + CaCl2, 50mM of Na2SO4 + KNO3, 50mM of CaCl2 + KNO3, and 30 mM of each salt in half strength Hoagland's nutrient solution). After 9 days, investigation of physiological and biochemical responses of the plants indicated that the halopriming treatments increased hydrogen peroxide concentration in the leaves which resulted in accumulation of phenolics and anthocyanins, and enhanced activity of ascorbate peroxidase in the leaves. Increase in catalase activity was observed which was associated to protein accumulation in the leaves. Investigating leaf greenness, concentrations of chlorophylls, and CO2 assimilation rate indicated that the halopriming treatments had no adverse effects on the plants' health and performance. The plants' drought tolerance was evaluated by withholding irrigation for 30 days. After the drought period, concentrations of hydrogen peroxide and malondialdehyde, and plasma membrane injury index in leaves of the preconditioned plants were lower than those in the non-preconditioned plants. Lower oxidative damage and higher chlorophylls' concentration and CO2 assimilation rate in the preconditioned plants were observed, which were related to enhancement in catalase and ascorbate peroxidase activity and higher concentrations of phenolics and anthocyanins in their leaves. The best results in inducing drought was obtained by halopriming with Na2SO4 or Na2SO4 + KNO3. Controlled salt stress as a rapid, environmentally friendly and inexpensive approach for inducing drought tolerance in greenhouse grown walnut 'Chandler' was suggested.