Photosynthesis and oxidative stress responses to water deficit in five different mulberry (Morus alba L.) cultivars

Abstract

Photosynthetic rates, antioxidant enzyme activities, glycine betaine and abscisic acid (ABA) contents, lipid peroxidation rates and electrolytic leakage were determined in five mulberry (Morus alba L.) cultivars (BC2-59, K-2, MR-2, S-13 and TR-10) by imposing progressive water deficit until the predawn leaf water potential (ψ) reached -1.5 or -2.50 MPa. Photosynthetic rates and the activities of ribulose-1,5-bisphosphate carboxylase, sucrose phosphate synthase, fructose-1,6-bisphosphatase were decreased with decreasing leaf water potentials. However, cultivars (cvs) S-13 and BC2-59 showed high rates of photosynthesis even under drought stress conditions when compared with other three cultivars (K-2, MR-2 and TR-10). Antioxidant enzymes including superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC1.11.1.11), peroxidase (POD, EC 1.11.1.7), glutathione reductase (GR, EC 1.6.4.2) and monodehydroascorbate reductase (MDAR, EC 1.6.5.4) were significantly high in the water stressed leaves. Significantly, higher antioxidant enzyme activities were observed in the leaf extracts of S-13 while the lowest activities were recorded with cv TR-10. Lower rates of membrane lipid peroxidation and electrolytic leakage were noticed in the leaves of BC2-59 and S-13 under water deficit. Quantitative differences were noticed in foliar glycine betaine and abscisic acid contents among five cultivars in response to drought. The leaves of BC2-59 and S-13 accumulated more glycine betaine and abscisic acid under water stress compared to K-2, TR-10 and MR-2. The results of the present investigation demonstrate that among five mulberry cvs S-13 and BC2-59 have high photosynthetic activity and efficient antioxidative characteristics which could provide better protection against oxidative stress in leaves under water deficit conditions.