Effects Of High Temperature On Protective Enzyme In Resistant And Susceptible Plutella Xylostella

Pesticides and thermal stimulation were lead to changes of the protective enzyme activity. It was not clear that whether Plutella xylostella (Diamondback moth, DBM) resistance to beta-cypermethrin was also associated with the change of protective enzymes or not. A systematic study was conducted to determine the effects of high temperature (HT) on the activities of protective enzyme and the quantitative relationship between protective enzymes and free radicals. Anti-beta-cypermethrin-susceptible (S) and-resistant (R) DBM were used.In this study, the relationship between high temperature stress and insects resistance was detected based on comparing the difference of protective enzymes activities between S and R DBM. Impacts of the high temperature on superoxide dismutase, peroxidase and catalase were detected by comparing the differences of protective enzyme activity among different temperature.Following conclusions were drew from the experiment:(1) SOD activity increased sharply under33.5℃for8short-term stress. After that the increase slowed down with steady upward trend. As the temperature increased, the increase extent of SOD activity became smaller. The promotion rate reached its highest point at24h control under33.5℃.while at48h and72h, the control respectively were under42℃and47℃.which indicated that the time of the highest peak reached delayed under higher temperature, but the amplitude of the promotion rate decreased with increasing temperature.(2) CAT activity firstly steady increased,then the increase was smaller as the control temperature got higher in72h.Then decline when close to death. Under the control temperature, the difference was not obvious between R and S DBM. After24hours it became significant, which was2times and1.89times than that of the control group.33.5℃had peaks at1h and48h which indicated that CAT took part in short-term and long-term high reaction mechanism.(3) POD activity was increased largely when the temperature was lower than 37℃. while it was higher than37℃, it began to decline. During short-term high-temperature processing, R DBM reached its highest point earlier than S DBM.while S DBM was31%than that of R DBM at1h. Prolong to8h. its rised to57%. Extension the processing time, the differentiation between them was reduced. When there was high-temperature long-term treatment, CAT promote rate of R DBM gradient declined. S DBM did not change significantly.(4) The content of free radicals did not change significantly both R and S DBM in the short-term treatment (Slight increased from1hour to8hours). When the processing time was extended to24and72hours, it was increased markedly. Under high temperature, content of free radicals in R DBM accumulated faster and more, than that in S DBM. But the promotion rate of free radicals in S DBM was higher.This study showed that superoxide dismutase was rising rapidly and reached its maximum in a short time which was more sensitive to high temperature stress. Followed by catalase and peroxidase. Three of them coordinated with each other to kept the content of free radicals at a low level.