[Alleviation Effects of Exogenous Melatonin on Ni Toxicity in Rice Seedings]

The alleviation effect of exogenous melatonin (MT) on Ni toxicity in rice seedings was investigated. The results showed that low concentration of Ni stress (10, 50 μmol·L^-1) had little effect on the growth of root of rice seedings, while higher concentration of Ni stress (100-1000 μmol·L^-1) significantly inhibited the growth of rice root. Compared with the control treatment, the addition of 100 and 1000 μmol·L^-1 Ni would decrease the total length and surface area of root by 63.3%-98.0% and 56.9%-96.3%, respectively. The results showed that addition of exogenous melatonin had a positive effect on the growth of rice seedings under Ni stress. This kind of positive effect was even more obvious in the root of rice seedings. The total length of rice root decreased by 58.4%-83.8% at Ni concentration of 100 μmol·L^-1, whereas it decreased by only 8.7%-29.1% when 100 μmol·L^-1 Ni and 10 μmol·L^-1 MT were added, compared with the control treatment. The addition of exogenous melatonin had significant alleviation effects on oxidative stress in rice seedings caused by Ni. Compared with the 100 μmol·L^-1Ni treatment, addition of 10 μmol·L^-1 exogenous MT could significantly decrease the production rate of O₂^-· by 43.2%-50.2% and the relative electrolytic leakage by 25.7%-31.6%, whereas increase the activities of CAT by 21.9%-33.7% and the soluble protein content by 82.6%-84.6%. The results suggested that application of exogenous melatonin could effectively alleviate the toxic effects of Ni on rice seedings.