Seed Treatment with α-Tocopherol Regulates Growth and Key Physio-Biochemical Attributes in Carrot (Daucus carota L.) Plants under Water Limited Regimes

The influence of seed priming with varying levels (50 and 100 mg L−1) of alpha-tocopherol (Toc) was investigated in carrot plants under water-deficit conditions. For this purpose, two cultivars of carrot, DC4 and DC90, were selected and subjected to well-watered (100% field capacity (FC)) and water-deficit stress (50% FC). After 21 days of water-deficit conditions, a significant suppression was observed in shoot and root fresh and dry weights, their lengths, chlorophyll a, b and total contents, and total soluble proteins (TSP). However, an up-regulatory effect of water stress was observed on the concentrations of glycinebetaine (GB), hydrogen peroxide (H2O2), malondialdehyde (MDA), ascorbic acid (AsA), total phenolics as well as the activities of catalase (CAT) and peroxidase (POD) enzymes. Exogenous application of alpha-tocopherol was effective in reducing the accumulation of H2O2 and MDA contents and improving all growth attributes, contents of chlorophyll, proline, GB, AsA, total phenolics, TSP, and the activities of CAT and POD enzymes. Of both carrot cultivars, cv. DC4 had better performance in terms of growth attributes, whereas the response of the two cultivars was similar in all other attributes varying water regimes. Overall, it is suggested that seed priming with 100 mg L−1 Toc was effective in improving plant growth attributes, osmoprotectants and the oxidative defense system of carrot plants under water-deficit conditions.