Comprehensive Evaluation Of Cowpea Seedlings’ Tolerance To Coldness And The Effects Of Exogenous Regulating Substance On Chilling Tolerance Of Cowpea Seedlings

The growth and development of cowpea is very sensitive to low temperature.It grows very slowly under 15℃,and it’s growth is inhibited under 10℃.The temperature in the early spring of Chengdu Plain was not rised so obviously,sometimes the temperature will stay under 10℃ for some time that is negative to the early spring growth of cowpea.In recent years,using exogenous substance to enhance the plants ’ tolerance to stress including abiotic stress and biotic stress is a hot research subject.This research used two exogenous substances.One is Melatonin(N-acetyl-5-methoxytryptamine,MT),an indoleamine.it can removed reactive oxide species(ROS)intracellular,it plays a role of antioxidant and anti-aging.Another one is salicylic acid(SA),it is a kind of plant hormones,then it is also a non-enzymatic antioxidant.This research used 9 cowpea varieties to measure their cold-resistance physiological index under 8℃in a week,measured in 0d,1d,3d,5d,7d.Physiological indicators including relative conductivity,MDA content,the activity of antioxidant enzyme,proline content,chlorophyll content and so on.Principal component analysis and subordinate function value methods is applied to a ranking of their cold-resistance.Afterwards,used ‘Changfeng Green Dragon’(cold resistant variety)and ‘Black eyebrows’(cold sensitive variety)as materials for the second part of the study.Spraying exogenous MT and exogenous SA in different concentration to the two different cowpea seedlings under 8℃ for 8 days,measured physiological index every 2 days.The research results showed that:1.In the part one of the study,9 cowpea varieties’ variation trend of indexs is generally the same.Along with the extension of cold stress time,the relative conductivity and MDA content is significant increased.The activity of SOD and POD is rise in the first stage,and then decrease.Chlorophyll content was the same trend with activity of SOD.2.On the basis of the correlation analysis of the physiological index,the Principal component analysis and Subordinate function value method is applied to a ranking of their cold-resistance,the ranking is: ‘Extra King of Haiya’ > ‘Changfeng Green Dragon’ >‘Ningjiang No.3’>‘Green cowpea’>‘Spring and Autumn Red’>‘Qiuzi cowpea No.6’>‘Black eyebrows’ >‘Lvfeng 3000’.3.In the second part of study,along with the extension of cold stress time,the relative conductivity is increased.MDA content and chlorophyll content is rise in the first stage,and then decreased,MDA and chlorophyll level after cold stress is higher than the level before cold stress.The activity of SOD,POD,CAT was rising in the first stage,and then decreasing,rising in the end.The activity of antioxidant enzyme was increased after 8 days’ cold stress.Osmotic adjustment substances including proline content and soluble protein content were increased.4.Under the cold stress,applied melatonin in 150-200μmol/L or SA in 100mg/L decreased the relative conductivity.In the 0-6 days during cold stress,applied melatonin in50μmol/L or SA in 100-200mg/L could decrease MDA content of cowpea seedlings.Applied melatonin in 150μmol/L or SA in 50mg/L increased the soluble protein content.Applied melatonin in 50-150μmol/L or SA in 50mg/L increased the activity of antioxidant enzyme remarkable and decreased the decline of chlorophyll content.In the 0-4 days during cold stress,Application of melatonin in 50-100μmol/L or SA in 50-100mg/L could increase chlorophyll content.