BRINJAL UNDER SIEGE: MECHANISMS AND MANAGEMENT OF HEAVY METAL CONTAMINATION

Abstract

The pollution of agricultural soils with heavy metals has become an important problem for food security and human health, especially for vegetable crops grown in peri-urban and industrial regions. The solanaceous vegetable Brinjal (Solanum melongena L.) has a high tendency for root uptake and rapid translocational efficiency of toxic ions and thus is very sensitive to metal toxicity. The present review is an attempt to summarize the existing information regarding the sources, absorption of heavy metals, physiological disturbances and mitigation strategies under heavy metal stress in brinjal. The major toxic metals of concern are: Cadmium (Cd), Lead (Pb), Nickel (Ni), Copper (Cu), and Chromium (Cr) which are usually found in wastewater irrigation, industrial effluents and agrochemicals. Phytotoxic effects in the crop include inhibition of seed germination, stunted groweth, chlorosis, necrosis, and fruit yield and quality reduction, which are dose-dependent with regard to metal exposure. In the biochemical level, heavy metals induce overproduction of ROS which results in lipid peroxidation, loss of electrolytes and induction of antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Molecular responses include induction of phytochelatins (PCs) and metallothioneins (MTs); however, genetics understanding in brinjal is still in early stages as compared to model plants. Soil amendments such as biochar and chitosan, which bind metals and decrease bioavailability, and the use of biochar and foliar application of iron oxide nanoparticles (FeONPs), which boosts antioxidant defense, are some of the promising remediation strategies. Low-accumulating cultivars is a biological solution to the challenge of selection. There are still gaps in knowledge related to field scale testing of nano-remediation, interactions effects between multi-metal contamination, and the lack of molecular marker-assisted breeding programs. This review gives an in-depth account of the mechanism of heavy metal stress in brinjal and proposes future directions to grow brinjal safely.