EFFECT OF SUPPLEMENTARY PHOSPHORUS ON ACID PHOSPHATASE ENZYME ACTIVITY AND MEMBRANE PERMEABILITY OF ZINC-TOXIC TOMATO PLANTS

Abstract

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.

ACKNOWLEDGMENT

The author wishes to thank the University of Harran (Turkey) and the University of Hertfordshire (UK) for their supporting this project to be carried out. I also acknowledge my principal supervisor, David Higgs, for his advice, and technicians Bob Smith and Monica Kanwar for their technical support.