Morphology and physiology of zinc-stressed mulberry plants

The aim of this study was to induce symptoms of zinc deficiency and Zn excess and to relate the generation of reactive oxygen species (ROS) and the altered cellular redox environment to the A effects of Zn stress in mulberry (Morus alba L.) cv. Kanva-2 plants. The antioxidative responses of Zn-stressed mulberry plants were studied by determining malondialdehyde content (MDA, a measure of lipid peroxidation) as indicator of oxidative damage and the ratio of dehydroascorbate (DHA) to ascorbic acid (AsA) as an index of the cellular redox state. The Zn-deficiency effects appeared as faint paling and upward cupping of the young emerging leaves. The paling intensified with time, and affected leaves finally developed necrotic spots. At advanced stage of Zn deficiency, newly emerged leaves were spindle-shaped, pale, and small in size. Apart from their stunted appearance, the plants supplied excess Zn did not show any specific visible symptom. Leaf water status of mulberry plant was affected in Zn-stressed plants. Deficient leaves had decreased water potential (T) and specific water content (SWC), contained less tissue Zn, less chloroplastic pigments, and high tissue Fe and Mn concentrations. However, excess supply of Zn was found to increase T and decrease tissue Fe. Both hydrogen peroxide and MDA accumulated in leaves of Zn-stressed plants. While the concentration of DHA did not vary in Zn-deficient leaves, it was increased in leaves of plants supplied excess Zn. The ratio of the redox couple (DHA to AsA) was increased both in Zn-deficient or Zn-excess plants. The activities of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), peroxidase (EC 1.11.1.7), and ascorbate peroxidase (EC 1.11.1.11) increased in Zn-stressed plants. The results suggest that deficiency or excess of Zn aggravates oxidative stress through enhanced generation of ROS and a disturbed redox homeostasis in mulberry plants.