Lead Induced Modulation in Growth, Chlorophyll Pigment, Nutrient Uptake, Antioxidant Enzyme Regulation, Gene Expression and Fruit Quality in two Tomato Cultivars

Abstract

Metal stress is one of the major restrictions for agricultural production. A pot experiment was set-up to appraise modulation in growth, oxidative defense, secondary metabolism and relative gene expression of two tomato cultivars viz., Roma (sensitive) and Nagina (tolerant) at flowering stage in response to different lead (Pb2+) regimes (160, 320, 640 and 1280 µM). The results showed that Pb2+ stress (1280 µM Pb) caused a considerable reduction in growth attributes, chlorophyll (Chl) pigments and ascorbic acid contents, and increase in malondialdehyde (MDA), hydrogen peroxide (H2O2), and total soluble protein (TSP) contents in both cultivars. A significant enhancement in ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT) activities and Cat2 gene expression was documented in Pb2+ stressed tomato plants. Fruit quality of Nagina was better than Roma cultivar. In this context, higher fruit ash contents, protein contents, fructose and glucose contents were observed in Nagina while Roma was inferior in this regard when under Pb2+ stress. Furthermore, Pb2+ reduced the fresh and dry biomass, moisture, fiber content and mineral (Na+, K+ and Ca2+) uptake in tomato fruits of both cultivars. The results indicated that significant amount of Pb2+ accumulates in the root compared with its concentration in shoot and leaves while only a small amount of Pb2+ reaches the fruit. The exposure to Pb2+ caused significant changes in Cat2 gene transcripts indicating the contribution of this gene in Pb2+ tolerance. The sensitive cultivar exhibited higher oxidative damage, decreases in the concentration of essential nutrients, poor oxidative defense system, and thus had low quality fruit.