THE ROLE OF SELENIUM IN MITIGATING THE HARMFUL EFFECTS OF ALKALINITY STRESS IN TOMATO SEEDLINGS

Tomato is considered one of the most popular vegetables worldwide playing a vital role in human nutrition.Alkalinity is common environmental stresses which limits agricultural crop production.In order to investigate the impact of trace elements of selenium on agro-physiological features of tomato under alkaline stress conditions, two experiments were organized as a randomized complete block design and each treatment four replications were conducted in the greenhouse of Horticultural Department, Faculty of Agriculture, Ain-shams University, Egypt.The experimental groups were the followings: (1) untreated plants (control), (2) plant treated with of 75 mM sodium carbonate (Na2CO3), (3) plants treated with selenium (Se, at rate of 5 M and (4) plants treated with selenium and sodium carbonate.the obtained results showed that the exogenous application of Se caused a significant improvement in shoot biomasses, leaf photosynthetic pigments (Chlorophyll a, b, total and carotenoids), and leaf relative water and leaf proline content compared to untreated plants, under normal and alkaline stress conditions.Under alkaline stress conditions, application of Se significantly increased the activity levels of leaf antioxidant enzymes (SOD, CAT, POX and APX) when compared with control treatment.On the contrary, higher reduction in the sodium content (Na), Na/K ratio, hydrogen peroxide (H2O2), malondialdehyde (MDA) and membrane stability index (MSI) was observed in the leaves of tomato plants sprayed with Se more than untreated ones.In both conditions, application of selenium increased the potassium content (K) in the plant leaves more than that in untreated plants.Based on the results, selenium applications could be suggested as promising treatment to alleviate adverse effects of alkalinity stress on agro-physiological and biochemical characteristics.