The effect of seed priming with melatonin on improving the tolerance of Zea mays L. var saccharata to paraquat-induced oxidative stress through photosynthetic systems and enzymatic antioxidant activities

Melatonin is essential in improving plant's biotic as well as abiotic stress tolerance, especially detoxification of herbicides. The purpose of the present research study was studying the probable positive impacts of melatonin on the enhancement of the growth as well as oxidative stress tolerance in sweet corn (Zea mays L. var saccharata). For this purpose, the effects of seven treatments of priming (hydro priming with water (H), melatonin (M) priming with 25, 50, 100, 150 and 200 mu M and non-priming (D)) and three doses of paraquat (PQ: 0, 5 and 7.5 L per hectare of recommended dose (5 L per hectare)) on physiological as well as biochemical responses belong to sweet corn were probed according to a completely randomized factorial design involving three replicates. The obtained results provided the indication that applying PQ, particularly at high levels (7.5 L ha -1), in the absence of priming, enhanced the rate of herbicide injury by 49.2%, as compared with 5 L ha -1, by increasing free radical production rate and membrane lipids' peroxidation, in addition to inhibiting the process of photosynthesis. Seed priming with melatonin positively impacted PQ exposed plants, even under the enhanced concentration of PQ (7.5 L ha -1). The maximum protection for the sweet corn plants could be observed at M150. Co-application of melatonin (M150) and PQ herbicide (7.5 L ha -1) reduced H2O2, MDA and herbicide injury by 3.0, 2.1 and 4.6 times, respectively, while it increased SOD, CAT, APX and POD by 2.9, 4.6, 2.4 and 2.0 times, respectively, as compared with D treatments. The obtained results provided the indication that melatonin priming could raise tolerance to oxidative stress which is triggered by PQ in sweet corn with the enhancement of antioxidant en-zymes' activity and reduction of herbicide injury.