Differential responses of exogenous melatonin on growth, photosynthesis and antioxidant defence system in two Brassica napus L.cultivars under chromium stress

Rapid industrialization throughout the world during last few decades causing high chromium resulted widespread of agricultural soil contamination. The increased chromium contents beyond permissible level in some agricultural land areas increasing widespread concern about food safety.This study was carried out for evaluation of metal toxicity damage and its possible mitigation and improved photosynthetic efficiency by melatonin treatment in canola plants exposed to four melatonin levels (0,1,5,10µM) treated with chromium stress (0,50,100µM) for two days.Chlorophyll fluorescence a transients considered one of the best tool for photosynthetic (photosystem II) efficiency analysis of two canola cultivars Ac-Excel and DGL with or without melatonin treatment against chromium stress analyzed by using OJIP test (at different time scale) chromium treated and non-treated plants. Enhanced ROS scavenging antioxidants enzymes (SOD, POD, APX,CAT) and H2O2, MD Aactivity photo synthetic efficiency was observed against chromium stress. DGL cultivar showed greatly affected and showed maximum reduction in performing index of photosystem II and yield for primary photochemistry as compared to chromium treated and non-treated plants as compared to Ac-Excel. Performing index primarily comprises of active number of reaction centers as per absorption, primary photochemistry yield and efficiency of electron transfer in electron transport chain activities were observed high in Ac-Excel cultivar. However exogenous application of melatonin protected the oxygen evolving complex of PSII and helped out in maintaining PSII activity. Thus OJIP fluorescence transients are quite helpful for understanding the intersystem electron transport beyond photosystem II response of canola cultivars in chromium stress. Findings: Exogenous application of Melatonin can improve plant growth and development in heavy metal stress by modulation of photosynthesis in terms of enhanced photosystem II efficiency and redox potential in certain environmental stress conditions.