Résumé
Rubber trees (Hevea brasiliensis Muell. Arg.) are a major crop of economic importance in Thailand. The main product harvested from the rubber trees is latex. Latex production depends on a biochemical process for synthesis, degradation, mobilization, and the storage of nonstructural carbohydrates (NSCs), such as starch and sucrose. The rubber trees demand carbohydrates and enzyme activities for growth, maintenance, and latex synthesis. Therefore, with the appropriate management of the taping system, the balance between growth and latex synthesis in the trees should be maintained since it is regarded as a balance between use and formation of NSCs, which is controlled by the involved enzymes. This research aimed at studying the effects of downward and upward tapping systems on NSCs content and on the activity of the enzymes in the wood and the bark of rubber tree trunks given that the two systems are related to latex yield. It was found that the latex yield was higher with the upward tapping system as compared to downward tapping. Furthermore, upward tapping had induced more sucrose synthase (SuSy) activity, which is involved with sucrose degradation, than downward tapping had. It was, therefore, concluded that the sucrose dynamic had depended on SuSy, which is the key enzyme located in bark with upward tapping. The sucrose had functioned as the local buffer in the bark, which is related to the balance system of high starch hydrolysis in the wood to produce higher rubber biosynthesis in latex cell metabolism with upward tapping.