The Role Of Sucrose Metabolism On Latex Biosynthesis After Trunk Ethylene Stimulation

Natural rubber produced by Hevea brasiliensis is one of most important strategic resources in modern industry.Ethephon was widely used in rubber tree to stimulate latex production.Numerous studies using latex as research object demonstrated that ethephon treatment prolong the time of latex flow,promote expression of aquaporins and increase the sucrose transportation into laticifer to increase latex production.Rubber biosynthesis is the coordinated multiplex biochemical reactions in latificers.During the process,sucrose acts as the input raw material and finally irreversibly turns into rubber biosynthesis.Previous analysis indicated that sucrose metabolism and its translocation to the laticifers is closely related to rubber biosynthesis and thus to the yield of latex when using laticifers or latex as the research object.But how rubber tree leaves were affected physiologically after ethephon treatment on the trunk is still not known.Grafted seedlings were used to detect the physiological changes of leaves after the trunk treatment with 0%,0.6%and 1.1%ethephon.The physiological changes include the content of sucrose,fructose,glucose,Chlorophyll,amylose and amylopectin,as well as the key enzymes(sucrose synthase,sucrose phosphate synthase and invertase)related to sucrose metabolism were systematically detected.The leaves were cultured in vitro with different concentration of sucrose to study the relationship between the change of leaf secreting sugar,the change of petioles latex production and sucrose metabolism.At the same time,eight months old rubber tree(Reyan 7-33-97)seedlings were used to detect the photosynthetic rate after 0,12,24,36 and 48h’s 0.6%ethephon treatment.The main results are as follows:1.rubber tree leaf can secrete sugar in vitro culture condition.The higher the concentration of sucrose in liquid culture,more sugar was secreted and more latex produced in the petiole.The petiole latex yield was related to sucrose metabolism in leaves.2.A system using ethephon stimulation to increase latex production in rubber tree seedlings was established.3.Ethephon stimulation affects the leave photosynthesis of rubber tree:the net photosynthetic rate,transpiration rate and stomatal conductance decreased significantly,but the intercellular carbon dioxide concentration increased.Ethephon treatment do not increase the sucrose content of leaves via photosynthetic rate enhancement.4.Trunk ethephon treatment affects the leaves sucrose content.HPLC-ELSD was used to detect sugar content and it showed that sucrose content decreased significantly with concomitant of glucose and fructose increase.And trunk ethephon treatment decreased the starch content in leaves.5.The activity in sucrose synthesis were effected after trunk ethephon treatment:ethephon treatment on Reyan 72059 increased sucrose synthase(SS),sucrose phosphate synthase(SPS)and ethephon treatment on Reyan 72059 increased sucrose synthase.It showed that the sucrose synthesis increased after ethephon treatment.7.The key enzymes activity of sucrose cleavaging were effected by trunk ethephon treatment:ethephon treatment on Reyan 8-79 and Reyan 72059 increased cell wall invertase(CWI),vacuolar invertase(VIN)and sucrose cleavage synthase,and the activities of neutral/alkaline invertase(NIN)did not change.These results suggested that ethylene stimulation can induced leave physiological change and leaf sucrose metabolism,which may plays an important role on ethylene stimulate latex production of rubber tree.This paper might give a clue on the latex biosynthesis from the "source(leaf)-library(laticifer)" relationship.