Anthropogenic activities are a major source for contaminating the agricultural soil with heavy metals, which can affect physiological and metabolic processes in plants. Among the heavy metals, chromium (Cr) is the most toxic pollutant that negatively affects plants' metabolic activities, growth, and yield. Chromium reduces the plant growth and development by influencing the photosynthetic performance and antioxidant enzyme activities. This study was designed to examine the promotive role of exogenously applied glycinebetaine (GB) on plant morphophysiological and biochemical attributes in cauliflower (Brassica oleracea botrytis L.) under Cr toxicity. Four levels (0, 10, 100, and 200 μM) of Cr were tested under the application of GB (1 mM). The results delineated that Cr stress caused a considerable reduction in plant growth, photosynthetic pigment, gas exchange parameters, and biomass production. At high concentration (200 μM), chromium stress decreased the plant height (57%), root length (32%), number of leaves (45%), and leaf area (29%) as compared with controls. Due to Cr stress, the electrolyte leakage and accumulation of malondialdehyde and hydrogen peroxide increased both in the roots and leaves of cauliflower, whereas antioxidative enzyme activities (SOD, CAT, and POD) decreased both in the roots and leaves of cauliflower due to Cr stress. At 200 μM of chromium treatment, root dry weight, stem dry weight, leaf dry weight, and flower dry weight declined up to 43%, 40%, 53%, and 72%, respectively. With the application of GB, dry biomass of plant increased significantly as compared with no GB treatment under chromium stress. As Cr level increased in growth media, its concentration also increased in all plant parts including roots, stem, leaves, and flowers. However, GB application efficiently alleviated the Cr toxic effects on cauliflower and maintained higher plant growth, biomass production, photosynthetic attributes, and gas exchange traits as compared with their respective controls. Exogenously applied GB decreased oxidative stress and improved antioxidative enzyme activities as compared with treatments without GB application. Furthermore, Cr concentrations taken by plants were decreased due to GB application. These findings suggest that GB can play a positive role to maintain plant morphology and photosynthetic attributes under Cr toxic conditions in cauliflower.
Keywords: Antioxidant enzymes; Chromium stress; Glycinebetaine; Oxidative damage; Photosynthetic attributes; Plant growth.