Morphology and oxidative physiology of sulphur-deficient mulberry plants

The aim of the study was to induce S deficiency symptoms and to relate the generation of reactive oxygen species (ROS) and altered cellular redox environment with the effects of S deficiency in mulberry (Morus alba L.) cv. Kanva-2 plants. A study of antioxidant responses, malondialdehyde (MDA) content as an indicator of oxidative damage and ratio of dehydroascorbate (DHA) to ascorbic acid (AsA) as an index of cellular redox environment in S-deficient mulberry plants was undertaken. The S deficiency effects appeared as paling of the youngest emerging leaves. Soon, the leaves, as they expanded, became devoid of the green pigment and turned completely yellow. These leaves showed upward curling of the leaf margins and prominent wrinkles in the lamina tissues. Sulphur-deficient plants showed improved leaf water status, as indicated by increases in the degree of succulence (DS), specific water content (SWC), relative water content (RWC) and water potential (Ψ) of leaves, contained less tissue S concentration, less chloroplastic pigments, decreased tissue Fe and Cu and had improved tissue Mn concentrations. Increased hydrogen peroxide concentration under deficiency of S did not induce oxidative damage as indicated by decreased MDA concentration. The S-deficient plants exhibited significant decreases in the concentrations of DHA and total ascorbate. The ratio DHA/AsA decreased in these plants. While the activity of catalase (EC 1.11.1.6) decreased in S-deficient plants, activities of peroxidase (EC 1.11.1.7), superoxide dismutase (EC 1.15.1.1), and ascorbate peroxidase (EC 1.11.1.11) were increased. The results suggest that deficiency of S induced oxidative stress, however, because of low tissue Fe and Cu and enhanced antioxidant enzymes activities other than catalase, provided ample protection against oxidative challenge to the S-deficient mulberry plants.