Study On Effects Of Dopamine On Cold Tolerance Of Watermelon Seedling And Its Mechanism

Chilling stress is one of the main abiotic stress factors that limit the normal growth and development of chilling-sensitive crops.Watermelon as a kind of chilling-sensitive vegetable,in the early spring planting process,chilling stress will seriously affect growth of watermelon seedling,disrupting the normal physiological metabolic activity,the accumulation of toxic substances,thereby causing the yield and quality of watermelon was declined.In this study,watermelon cultivars(Jing Xin NO.1)was conducted as the experimented materials,to study its effect on watermelon seedlings health index via application of dopamine through seed soaking;two different cultivars(chilling-tolerant cultivar Xi Nong NO.8 and chilling-sensitive cultivar Jin Xin NO.1)were used to explore the effects of dopamine treatment on the growth and physiological changes of watermelon seedlings under chilling stress.The results showed as followed:1.Application of dopamine soaking treatment improves the health index of watermelon seedling to some extent,and provides a new way to cultivate high-quality and strong seedlings of watermelon.2.Under chilling stress,the plant height,crown dry mass,root dry mass,total dry mass and root activity in watermelon seedling significantly increased,thereby increasing the health index of watermelon seedlings,improving the quality of watermelon seedlings and guaranteeing its strong growth of watermelon in the later period.3.During chilling stress,application of dopamine can increase the net photosynthetic rate and chlorophyll content of leaves of two watermelon cultivars,and improve the photosynthetic capacity of watermelon seedlings under chilling stress,which is helpful to alleviate chilling injury.4.Dopamine treatment significantly increased the content of proline and soluble protein in the leaves of two watermelon cultivars under low chilling stress,thereby increase the cold tolerance of seedlings,and improve the ability of seedlings to resist adversity.5.Under chilling stress,dopamine treatment reduces the level of malondialdehyde and superoxide anion in the leaves of two watermelon cultivars and increase the activity of antioxidant enzymes.This indicates that dopamine can activate the antioxidant system of watermelon seedlings under adverse conditions,and then improve the antioxidant properties of seedlings,reduce the accumulation of harmful substances in seedlings,and increase the ability of seedlings to resist adversity.6.Dopamine treatment can enhance the activities nitrate reductase(NR)and glutamine synthetase(GS),thus maintain the normal nitrogen metabolism in the seedlings of two watermelon cultivars under chilling stress.7.Under chilling stress,dopamine treatment can significantly improve the polyamine content in the leaves of the seedlings,strengthen the activity of polyamine synthase,and inhibit the activity of polyamine oxidase.This indicates that dopamine may regulate the polyamine content of the leaves of seedlings by participating in the metabolic process of seedling polyamines under stress conditions.By regulating the activity of polyamine metabolism enzymes,increasing the levels of polyamines in the leaves of seedlings,which contribute to remove excess reactive oxygen species of seedling and reduce the toxic effects,thereby increasing the cold tolerance of the seedlings,and improving the ability of the seedlings to resist chilling stress.