Physiological and biochemical responses of almond rootstocks to drought stress

Water availability is a very important factor for the growth and development of plants, which limits the plant production capacity. Rootstocks are widely utilized to improve plants tolerance to various biotic and abiotic stresses. In this study, physiological and biochemical responses of fifteen almond rootstock candidates to drought stress were investigated under in vitro conditions. The shoot tips from fifteen almond rootstock candidates were cultured in MS medium containing 1.0 mg/L BAP, 0.01 mg/L IBA, 30 g/L sucrose and 7 g/L agar. Plantlets were exposed to 0%, 1% and 2% polyethyleneglycol (PEG) as drought stress levels during four weeks. At the end of the stress period, the genotypes were evaluated in terms of total number of shoots per explant, the proline, chlorophyll, total phenolics, total flavonoids and total protein contents, and the superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) enzyme activities of the shoots were determined. The results showed that the drought stress increased total Ilavanoids, phenolic compounds and proline contents, while it reduced the number of shoots, chlorphyll a, b and total chlorophyll contents. Moreover, the drought stress increased the activities of APX, CAT and SOD enzymes in all genotypes. On the other hand, it decreased the protein content in six genotypes but increased the protein content in the nine genotypes. Based on the results, it was observed that the almond genotypes were generally tolerant to the drought. However, it was determined that the genotypes numbered 9, 29 and 185 showed more tolerant to the drought as compared to the other genotypes. These results suggest that improving the antioxidant system can enhance the drought tolerance of rootstocks.