The Effect Of Low Light On The Secondary Matter And Related Enzyme Activities Of Cucumber Seedlings

Cucumber(Cucumis sativus L.)Known as cantaloupe,originated in the southern foothills of the Himalayas,it is one of the warm and bright vegetable crops.Cucumber production in winter and spring protected areas in northern China is often accompanied by low temperature and low light stress,which seriously affects the yield and quality of cucumber,so it is very important to cultivate cucumber varieties tolerant to weak light.In this study,cucumber lines with different tolerance to weak light were used to study the effects of different low light treatments on secondary metabolic enzymes and metabolites of cucumber seedling plants.To elucidate the physiological response characteristics of cucumber plants to weak light stress through secondary metabolism,in order to provide theoretical basis for the cultivation and improvement of cucumber varieties tolerant to weak light.The results of the experiment are as follows:1.At the beginning of low light treatment,the enzyme activities of phenylalanine ammonia-lyase(PAL),Peroxidase(POD)and polyphenoloxidase(PPO)in the leaves and Hypocotyl of cucumber seedlings increased rapidly at the beginning of low light treatment.With the prolongation of low light treatment time,the activities of the three enzymes decreased obviously after 15 days of low light treatment.The activities of three enzymes in leaves and Hypocotyl of cucumber lines with different tolerance increased at first and then decreased with the prolongation of low light treatment time,but there was no significant difference in the activities of three enzymes between the leaves and Hypocotyl of the two lines at the beginning of low light treatment.There were significant differences in the later stage of treatment.The activity of three enzymes in leaves and Hypocotyl of weak light tolerant strain M14 began to decrease earlier than that of weak light tolerant strain M67.2.The contents of total phenols,tannins,flavonoids and lignin in leaves and Hypocotyl of cucumber seedlings in one leaf and one heart stage increased at first and then decreased,but there was no significant difference in flavonoids contents in leaves and Hypocotyl of different tolerant lines in the early stage of low light treatment.The contents of the four secondary substances decreased with the prolongation of stress time,and were lower than those of the control after 15 days of low light treatment.The content of secondary biomass in leaves and Hypocotyl of weak light resistant line began to decrease earlier than that of weak light tolerant strain.3.After 15 days of low light treatment,the activities of PAL,POD and PPO in leaves and Hypocotyl of cucumber seedlings decreased to varying degrees.The activities of three enzymes in leaves and Hypocotyl of cucumber seedlings at one leaf stage were significantly lower than those of the control,and the enzyme activities of strain M14 without weak light were significantly lower than those in line M67.4.After 15 days of low light treatment,the total phenols,tannins and flavonoids of three secondary metabolites in the leaves and Hypocotyl of cucumber seedlings decreased in different degrees,among which,the total phenols,tannins and flavonoids in the leaves and Hypocotyl of cucumber seedlings decreased in different degrees.The contents of these three metabolites in leaves and Hypocotyl of cucumber seedlings in one leaf stage were significantly lower than those in the control,and the contents of total phenols,tannins and flavonoids in the light tolerant strain M14 were significantly lower than those in the weak light tolerant strain M67.the contents of these three metabolites in the leaves and Hypocotyl of cucumber seedlings were significantly lower than those in the control.After 15 days of treatment,the four secondary metabolites in the leaves and Hypocotyl of the weak light tolerant strain M67 seedlings increased,while the weak light tolerant strain M14 decreased.The first spreading of cotyledon and the same performance of the two leaves were also similar.