Supplementation of amino acids (L-Methionine and Proline) mitigates drought stress in canola ( <i>Brassica napus</i> L.) plants through the modulation of physio-biochemical attributes and key antioxidant enzymes, and oxidative stress management

Abiotic stress, as caused by a lack of water that inhibits a plant’s ability to meet its water requirements, results in stunted growth, wilting, early leaf drop, and compromised photosynthesis. A study was conducted to understand the role of amino acid-induced (L-methionine and proline) regulation in the growth and defense system of canola ( Brassica napus L.) plants subjected to drought conditions. Drought stress [60% field capacity (F.C.)] considerably affected all physio-biochemical parameters. In both canola cultivars (cv. Punjab and cv. Rachna), drought stress enhanced the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD) enzymes, proline, glycine betaine, H 2 O 2 , MDA, and relative membrane permeability (RMP). Foliar-applied different treatments, i.e., control (no spray), Met, Pro, and Met + Pro of amino acids were given to canola cultivars. Of all treatments, Met increased the SOD enzyme activity, dry and fresh weights of roots, shoots, and root lengths, H 2 O 2 , siliquae dry weight, and the no. of siliquae. While exogenously applied, Pro enhanced the RMP, chlorophyll, total soluble proteins (TSP), and number of seeds per siliqua in cv. Punjab and MDA, ascorbic acid, activity of APX enzyme, siliqua fresh weight, and seed yield per plant in cv. Rachna. Met + Pro improved the dry and fresh weights, chlorophyll contents ( a and b ) , leaf area, and POD enzyme activity in cv. Punjab and relative water content, proline, total phenolic, and activity of CAT enzyme in cv. Rachna. Overall, foliar applied Met + Pro showed more positive effects in improving the drought tolerance of canola plants in terms of growth, seed yield, and oxidative defense system of both canola cultivars, more promisingly in cv. Rachna.