Control of carbohydrate metabolism by ethylene in latex vessels ofHevea brasiliensis MUEL. ARC in relation to rubber production

The treatment of the bark of regularly tapped trees with 2-ohloroethylphosphonio acid (CEPA) in the long run brings down sucrose level in the latex even when latex production is not increased. The sucrose deficit thus caused persists for a number of months after the treatment probably due to the depletion of carbohydrate reserves by the stimulation. The loss of carbohydrates not related to an increase of rubber produotion grows as the concentrations of applied CEPA are raised. The treatment increases the activity of phosphoenolpyruvate (PEP) carboxylase and decreases pyruvate deoarboxylation in mitochondria-free oytoplasmic latex serum. The pyruvate deoarboxylase has a sharp optimum at pH 6.5 and is almost inactive at pH 7.5 while PEP oarboxylase, like invertase, has the optimum at weakly alcaline pH and is only slightly active at pH 6.5. The CEPA-induced changes in the activity of these enzymes are related to an increase of latex pH after the treatment. Consistently with this the evolution of CO2 from sugars catabolised in the serum was found to decrease with increasing pH. It is concluded that the observed ethylene-induced changes in enzyme aotivities bring about in latex vessels a deviation of the glycolysis-fed metabolio flux from synthetic pathways to mitochondrial oxidations and consequently a decrease in the efficiency of sucrose conversion to rubber.