Investigation of physiological and biochemical effects of cysteine on arsenic and chromium toxicity in basil (Ocimum basilicum L.)

Heavy metal(oid)s emitted to the environment from natural and anthropogenic sources are increasing day by day and environmental pollution is reaching dangerous dimensions. These metal(oid)s, which spread to soil, water and air, have a toxic effect on plant metabolism and adversely affect animal and human health throught the food chain. In this study, the stress alleviating effect of exogenous cysteine (Cys) application on basil (Ocimum basilicum L. cv. midnight) seedlings grown under arsenic (As) and chromium (Cr) toxicity was investigated at morphological, physiological and biochemical levels. For this purpose, seedlings grown in hydroponic culture were determined root, shoot and leaf length, wet and dry weight, relative water content (RWC), chlorophyll fluorescence, chlorophyll a, b and total carotenoid content, electrolyte leakage, photosynthetic efficiency (transpiration rate, stomatal conductance, net photosynthesis rate, intercellular carbon dioxide concentration), Ca, Mg, Fe, K, Cr and As content, lipid peroxidation (TBARS), hydrogen peroxide (H2O2) content, enzymatic (catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), ascorbate peroxidase (APX), glutathione reductase (GR)) and non-enzymatic (phenolic acid) antioxidant defence system components were determined. The effects of As and Cr stress and exogenous Cys applications on these parameters varied according to metal(oid) type, application doses and different plant organs. Accordingly, exogenous Cys application increased growth parameters, RWC, chlorophyll fluorescence, chlorophyll a, b and total carotenoid contents, photosynthetic efficiency, and decreased electrolyte leakage, TBARS and H2O2 content of basil seedlings under As and Cr toxicity. On the other hand, depending on the increasing As and Cr concentrations, accumulation was detected in the root>stem>leaves, respectively, in basil seedlings and Cys significantly reduced As and Cr accumulation especially in the root. While As and Cr toxicity affected the antioxidant enzyme content differently according to the application dose and enzyme type, the highest effect of Cys was determined in POX activity. Furthermore, individual phenolic acid content generally increased with increasing As and Cr concentration and when co-applied with Cys. However, As and Cr exposure caused variability in the type and amount of volatile components, while 1,8-cineole in leaf, tetradecane in stem and nonadecane in root were determined as the main components of essential oil. According to these results, external application of Cys decreased the effect of As and Cr toxicity on basil seedlings. However, within the scope of this thesis study, it was revealed that basil could be a potential plant for phytoremediation in As and Cr contaminated soils.