Effect Of Exogenous Melatonin On Alleviating Calcium Deficiency Stress In Tomato

Tomato?Solanum lycopersicum L.?is a widely cultivated vegetable crop in the world,and it needs abundant calcium,whose deficiency will cause disease appearance,resulting in lower yield and quality as well as serious economic losses.In this study,‘Ailsa Craig'and‘Microtom'were used as experimental materials to simulate calcium deficiency environment by hydroponic culture method.The effects of different concentrations of exogenous melatonin?MT?on growth index,photosynthesis,reactive oxygen species metabolism and quality of tomato under calcium deficiency stress were studied.The study could provide a foundation for the application of melatonin in regulating plant calcium utilization in tomato plant.The main results as follows:1.After 10 days of 1%Ca²⁺Hogland treatment?T1?,the growth of tomato seedlings were significantly inhibited and the plant was short and thin.The leaves of tomato were yellowing,the edges of the leaves were scorched,the surface of the leaves had necrotic spots,and the apical meristem was atrophied or even black and necrotic.(0.25?mol L^-1,0.5?mol L^-1,1.0?mol L^-1 and 2.0?mol L^-1)all showed effects on alleviating the symptom caused by calcium deficiency and the 0.5?mol L^-1 melatonin treatment?T3?showed the best effect.2.Calcium deficiency significiantly inhibited the growth of tomato plant.Under the calcium deficiency stress?T1?,the plant height,stem diameter,dry and fresh weight of root and shoot were significantly lower than CK.After applying different concentrations of melatonin,the plant height,stem diameter,dry and fresh weight of root and shoot increased with increasing concentration between 0⁰.5?mol L^-1 melatonin treatment,and then decreased with the increasing melatonin concentration.Therefore,the best effect of melatonin treatment was 0.5?mol L^-1,in which the plant height,stem diameter,fresh weight of shoot and underground,dry weight of shoot and root were increased by 105.00%,79.00%,211.00%,348.00%,240.00%and 614.00%respectively compared with T1.The calcium deficiency stress also significantly inhibited the growth of tomato root system,and the root surface area,total root length and root activity were significantly lower than CK.Exogenous application of 0.5?mol L^-1melatonin significantly increased root surface area,total root length and root activity of seedlings.The chlorophyll content and photosynthetic parameters of tomato also decreased significantly under calcium deficiency stress,while 0.5?mol L^-1 melatonin treatment increased the overall chlorophyll content and photosynthetic parameters.The antioxidant enzyme activity of root and leaf decreased under calcium deficiency stress.As results,the ROS accumulation,lipid peroxidation and membrane damage of tomato were caused.Exogenous application of 0.5?mol L^-1 increased the activities of SOD,POD,CAT and APX,decreased the ROS and MDA accumulation,alleviating the oxidative damage of tomato plants under calcium deficiency stress.This study also showed that exogenous application of melatonin at 0.5?mol L^-1 could promote the accumulation of calcium in tomato.3.Under the stress of calcium deficiency,the appearance quality of the fruit was affected.The fruit weight,fruit firmness,fruit diameter and longitudinal diameter of tomato were lower than CK,but the fruit shape index did not change significantly.Exogenous application of 0.5?mol L^-1 melatonin has certain improvement on the appearance quality of fruit.