Effect of Supplementary Phosphorus on Acid Phosphatase Enzyme Activity and Membrane Permeability of Zinc-Toxic Tomato Plants

A short term experiment with tomato (Lycopersicon esculentum) cultivar Blizzard was conducted in a controlled temperature (CT) room to investigate the effect of phosphorus (P) supplemented in nutrient solution on acid phosphatase enzyme [EC.3.1.3.2.] (APE) activity and membrane permeability in tomato cultivars grown at high zinc (Zn) (77.0 μmol L−1). Zinc concentrations in complete nutrient solution were either 7.7 or 77.0 μmol L−1. One week after application of high Zn (77.0 μmol L−1), supplementary P at 1 mmol L−1 was added into the nutrient solution for three weeks. There were significant reductions in both dry weights and chlorophyll contents in the plants grown at high Zn (77.0 μmol L−1) compared with those in the control (7.7 μmol L−1) treatment. Application of supplementary P led to marked increases in both dry weight and chloro-phyll concentrations, achieving values not significantly different compared to the control. Zinc concentration in plant tissues increased to a toxic level in the high Zn treatment. Application of supplementary P decreased Zn concentration in the leaves and roots of plants grown at high Zn, but Zn concentrations were still at critical toxic levels. Leaf P declined to a deficient level in the high Zn (77.0 μmol L−1) treatment, but was markedly increased in the roots. Supplementary P corrected P deficiency in leaves of plants grown at high (77.0 μmol L−1) Zn. APE activity increased in the leaves and roots of plants grown at high zinc. Supplementary P decreased APE activity in zinc-toxic tomato plants. Membrane permeability was impaired in plants grown at high Zn. Supplementary P maintained membrane permeability by decreasing electrolyte leakage from leaves of Zn-toxic plants.