Inter-relationships between zinc nutrition, growth parameters, and nutrient physiology in a hydroponically grown tomato cultivar

An experiment was carried out to investigate the role of zinc (Zn) in physiological and nutritional development of the tomato (Lycopersicon esculentum Mill.) cultivar Moneymaker grown hydroponically in a controlled temperature room. The experiment was a 2 x 3 factorial arrangement with two levels of nutrient solution Zn concentrations, 0.01 or 0.10 mg L(-1), and three levels of foliar applied Zn, 0, 23, or 230 mg L(-1). Low (0.01 mg L(-1)) nutrient solution Zn seems to be inadequate for optimum plant growth; in this treatment plants showed Zn deficiency symptoms. Foliar application of Zn at 23 mg L(-1) alleviated Zn deficiency by enhancing Zn concentration in the leaves, dry weight, and chlorophyll content. However, foliar application of Zn at 230 mg L(-1) Zn caused adverse effects on both dry weight and chlorophyll content. Phosphorus (P) reached a detrimental level in the leaves of plants grown at 0.01 mg L(-1) Zn in nutrient solution, but 23 mg L(-1) Zn applied via the leaves reduced P concentrations from toxic to adequate levels. Concentration of iron (Fe) was also higher but not detrimental in the leaves of plants grown at 0.01 mg L(-1) Zn. Foliar application of both concentrations of Zn slightly reduced Fe concentration in the leaves. Membrane permeability was impaired both in the plants grown at low Zn and in those receiving the high (230 mg L(-1)) foliar application. Foliar Zn at 23 mg L(-1) maintained membrane permeability by decreasing electrolyte leakage from leaves of Zn-deficient plants. Low (0.01 mg L(-1)) Zn in the nutrient solution resulted in plants with very leaky root systems as measured by high potassium (K) efflux; this leakiness was ameliorated by foliar application of Zn at 23 mg L(-1). Cumulative potassium release from intact roots was higher in both the Zn-deficient plants (0.01 mg L(-1)) and those receiving high (230 mg L(-1)) foliar Zn. These data show that Zn nutritional status affects root membrane integrity.