Stress Protective Effect of Rhododendron arboreum Leaves (MEL) on Chromium-Treated Vigna radiata Plants

Oxidative stress due to hexavalent chromium [Cr(VI)] in Vigna radiata seedlings, and stress amelioration with treatment of methanol extract of Rhododendron arboreum leaves was observed in the present study by analyzing growth parameters, stomatal morphology, malondialdehyde (MDA) content, histological analysis, pigment contents, Cr metal uptake, elemental analysis, and antioxidant analysis. Chromium treatment resulted in the decline of root length, shoot length, fresh weight, and dry weight. Scanning electron microscopic studies revealed that Cr treatment altered the stomatal structure. As compared to control plants, MDA content increased by 80.1% in Cr-treated plants. Histological analysis with confocal microscope confirmed the nuclear damage, membrane damage, enhanced H₂O₂ accumulation, and decline in pigment concentration. Atomic absorption spectrometry analysis revealed an accumulation of 43.3% Chromium in the plant tissues and decreased concentration of essential elements as consequences of Cr treatment. The methanol extract of R. arboreum leaves (MEL) alleviated Cr stress in Vigna radiata seedlings by restoring normal growth, stomatal structure, and pigment contents, as well as essential elements. Reduction in H₂O₂ accumulation, reduced MDA content by 29.2%, and decline in Cr accumulation to 32.8% was observed after MEL supplementation to Cr-stressed plants. Decreased nuclear and membrane damage along with increased lipid-soluble as well as water-soluble antioxidants after MEL application in Cr-stressed plants are further symptoms of stress amelioration properties of Rhododendron leaves.