Starch Synthesis and Mobilization in Wood and Bark of Rubber Tree, in Relation with Latex production, (1) Methodological approach

摘要

In robber tree, starch reserves are necessary for growth and latex regeneration when the demand exceeds supply from photosynthesis. It tends to accumulate in the wood near the tapping cut [1,2] whereas sucrose remains rather stable in the wood and decreases in the latex vessels where it is used to regenerate the exported latex [3].Thus higher starch storage and mobilization ability could sustain higher latex yield. However the enzymatic processes driving the dynamics of starch synthesis and hydrolysis as related to tapping are not known. The objective of the study is to analyze the effects of tapping on the enzymes involved in starch and sucrose metabolism in the wood of rubber trees. The first approach of this study was to set up the most adapted methodology on measurement of total nonstructural carbohydrates (NSC) and related enzymes activities. The experiment was conducted in Hevea brasiliensis (robber tree), clone RRIM600. Treatments include untapped trees (Control) and yielding trees tapped with Ethephon stimulation (ET). Each treatment includes 6 trees. Samples have been collected along the trunk and separated into 2 parts, wood and bark, from both sides of the trees tapped and untapped panel. The activity of acid invertase (AI), amylase (AMY), sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) were assessed in the soft bark with a method of sample preparation improved for protein recovery and concentration by acetone precipitation. The method yielded higher enzyme activities of SuSy and SPS. In addition, the substrates and product of starch metabolism, i.e. starch, sucrose, fructose and glucose concentrations have been enzymatically measured. The results showed that starch was the major component in wood and sucrose was mostly found in bark. There was no difference between the former drainage area and resting area after 2 untapped years before restarting tapping.