Preliminary Study On Physiological And Biochemical Responses,heat-tolerance Mechanism Of Sargassum Hemiphyllum Var.chinense Under High Temperature Stress

During the growth and development of Sargassum hemiphyllum var.chinense,the temperature is the key factor that influences and restricts its growth.In the early summer period,S.hemiphyllum var.chinense are facing high temperatures,which growth become much more slow,and came into the dormancy,by November,the temperature was reduced and the seedlings were regenerated again.The short growth period and long term of dormancy serious restricted the cultivation development and market support of raw material.The fundamental solution is that alleviate the harm caused by high temperature stress on S.hemiphyllum var.chinense,improve its heat resistance,and ultimately cultivate new varieties with high resistance.In his study,taking seedlings of two species of Sargassum from Leizhou Peninsula as objects,assessment on their heat tolerance were measured by electricity conducting method and Logistic equation,Heat tolerance of plants was compared by calculating their half-lethal temperature.Meanwhile,the responses of the variants,membrane lipid peroxides,antioxidant enzymes,photosynthetic pigments and osmotic adjustment substances were studied under different high temperature stress,and also studied the effects of exogenous SA and Ca²⁺ on the physiological and biochemical characteristics of Sargassum fusiforme seedlings under high temperature,analyzed the feasibility of exogenous substances regulate the damage on Sargassum under high temperature stress,so as to screen out suitable for foreign substances and their concentration.The results are as follows:?1?The results showed that the relationship between treatment temperature of 2species of Sargassum and rate of injured cells varied in the “S”curve model,which accorded with Logistic equation by significance test.By calculating with formulas,half-lethal temperatures of two species of Sargassum,S.hemiphyllum var.chinense is46.2? and S.henslowianum is 51.4?.Heat tolerance of two Sargassum varieties in the decreased order as follow: S.hemiphyllum var.chinense lower than S.henslowianum.?2?The changes of membrane growth,membrane lipid peroxides,antioxidant enzymes,photosynthetic pigments and osmotic adjustment substances were studied under different high temperature stress.The results as follows: 1)during the experiment,the RGR of thetreatment group showed a decreasing trend at different degrees,except that the CK group continued to increase slowly;2)compared with CK group,the photosynthetic pigment content of the treated group decreased;3)MDA content showed an upward trend,and increased with the increase of stress temperature and prolonged stress time;4)within 36 hours,the SOD activity of each group showed a slow upward trend,to 36 h,all teams have reached the maximum,POD activity showed a tendency to rise first and then decrease,within 24 h,the change of CAT activity was not significant?P>0.05?,the average remained at 1.946 U/mgprot or so,from the beginning of 24 h,the treatment group?26?,29?,32??began to grow rapidly,at 36 h treatment,the group reached the peak,to 72 h,there was no significant difference between the CK;5)Since 24 h,the content of soluble protein in the treated group?26?,29?,32??decreased significantly with time,compared with its 24 h,respectively,decreased by 161.54%,213.46%,250%,the content of free proline in CK group was relatively stable and remained at a low level,with an average of 2.99mg·g-1,high temperature treatment group,such as 26,29,32?,after 24 hours,showed a substantial increase,and the higher the temperature,the more free proline content.?3?In order to study the feasibility of exogenous substances?SA?regulate the damage on Sargassum under high temperature stress,screening out the appropriate concentration,this study analyzed the effects of different concentrations of salicylic acid on physiological metabolism of algae seedlings under high temperature.The results as follows: 1)with the increase of concentration,RGR showed a trend of increasing first and then decreasing,and the concentration reached the highest value of 10.0 ?g·mL-1;2)When dealing with 12 h,the dosage of Chl-a in the treatment group such as 5.0,10.0 ?g·mL-1,increased rapidly,and the maximum value was 10.0 ?g·mL-1in the same period,at 12 h,the Car content of treatment groups which included 5.0,10.0 and 20.0 ?g·m L-1increased rapidly,at 24 hours,the rats in each group reached the maximum in the same group;3)the MDA content in the treatment group was lower than that in the CK group,within 72 h,the content of MDA in 10.0?g·mL-1treatment group was lower than that in other groups,5.0 ?g·mL-1treatment group was slightly higher,the highest group was 50 ?g·mL-1 treatment;4)the activity of antioxidant enzymes in the experimental period showed a trend of increasing first and then decreasing,at the time of 24 h,the three antioxidant enzymes in each group reached the highest value in the same experimental group.the contents of SOD and POD in the treatment group were significantly higher than those in the control group?P<0.05?And there was significant difference between CK group and CK group?P<0.05?;5)the contents of soluble protein were increased in all treatments,and reached the maximum at 24 h,and the contents of free proline increased first and then decreased,all group reached themaximum at 12 h,and the upward trend was the most obvious at 10.0 ?g·mL-1.?4?In order to study the feasibility of exogenous substances(Ca²⁺)regulate the damage on Sargassum under high temperature stress,screening out the appropriate concentration,this study analyzed the effects of different concentrations of CaCl2 on physiological metabolism of algae seedlings under high temperature.The results as follows: 1)with the increase of concentration,RGR showed a trend of increasing first and then decreasing,and the concentration reached the highest value of 10.0 mg·mL-1;2)after treatment for 12 hours,the content of chlorophyll a in each treatment group is increased,at 24 h,20.0mg·mL-1 treatment group increased to the maximum,and the trend of Car was similar to that of Chl-a;3)the content of MDA wihch increased with the increase of treatment time in the experimental period,and its content in the treatment group was lower than that in CK group;4)during the treatment of 36 h,the SOD activity of each group increased slowly,and the treatment group decreased significantly during the 36h-48 h period?P<0.01?,POD showed a tendency to rise first and then decrease,at 24 h,the groups reached the maximum of their test cycles,at the beginning of treatment,CAT,SOD and POD had similar vary characteristics,At 0 hours,there was no significant difference between the groups,at the end of 24 h,all treatment groups is increased,with 5.0 mg·mL-1treatment group the fastest growth;5)during the 24 hours,the SP content of each group showed a rising trend with the prolongation of treatment time.At 24 hours,the rats in each group reached the maximum value in the cycle.