Zinc Stress–Induced Changes in Biochemical Parameters and Oil Content of Mustard

Abstract

An experiment with mustard (Brassica campestris L.) cv T 59 was conducted in a glasshouse under controlled culture conditions to determine the effect of variable zinc (Zn) on biomass, reproductive yield, seed oil, and some aspects of metabolism. Plants were raised in refined sand, and Zn was administered at variable levels ranging from acute deficiency to excess (0.00065 to 65 mg Zn L−1). At 0.00065 mg Zn L−1, symptoms of Zn deficiency were depression in growth, short internodes, chlorosis and necrosis of mature leaves, along with development of purple pigmentation at leaf margins, which later covered the entire lamina. Biomass, economic yield, and seed oil content were highest at 0.065 mg Zn L−1. Zinc at less and more than 0.065 mg Zn L−1 reduced vegetative yield, pod and seed weight, concentration of chlorophyll (a and b), sugars, starch, and protein and elevated the concentration of phenols and activity of acid phosphatase and peroxidase in mustard leaves. The activity of carbonic anhydrase (except at 65 mg Zn L−1), aldolase, and leaf Zn increased with an increase in Zn from deficiency to excess whereas ribonuclease activity was related inversely to Zn supply. In addition to various changes in metabolism of mustard, Zn at higher levels (6.5 and 65 mg Zn L−1) induced symptoms of toxicity on old leaves as interveinal chlorosis, necrosis, and reduction in growth and leaf size. Phosphorus (P) content in leaves decreased concomitantly with an increase in Zn supply from 0.00065 to 65 mg Zn L−1. The values of deficiency, threshold of deficiency, threshold of toxicity, and toxicity in leaves were respectively 18, 25, 200, and 380 µg Zn g−1 dry matter. The activity of aldolase and carbonic anhydrase appear to be reliable biological indicators for evaluating the Zn status of mustard.