Stimulatory effects of 2,4-dichlorophenoxyacetic acid and of 1-naphthylacetic acid on sucrose level, invertase activity and sucrose utilization in the latex ofHevea brasiliensis

Abstract

Treatment of the bark ofHevea brasiliensis with 2,4-dichlorophenoxyacetic acid (2,4-D) or l-naphthylacetic acid (NAA) greatly increases sucrose level, invertase activity and sucrose utilization in the latex; the efficacy of 2,4-D is considerably greater than that of NAA. The greater sucrose utilization is the consequence of increased invertase activity. The changes occur as soon as the first tapping following bark treatment. It is suggested that the rise in both sucrose level and utilization in the latex serum mediate the effect of auxins on latex production. This is most likely related to a faciliation of latex outflow resulting from an increase in the osmotic and turgor pressure in the laticiferous tissue, as well as to enhanced regeneration of latex.The latex invertase has been found to be of a weakly alkaline type, with a sharp pH optimum at 7.15-7.20 in citrate-phosphate buffer. Its activity falls of rapidly on the acid side, being almost zero at pH 6.4. Since the natural pH of latex generally varies between pH 6.5 and 7.0, it is suggested that pH is an important factor in the regulation of invertase activity in the latex, and that the limiting nature of invertase-mediated sucrose hydrolysis in latex serum is caused by unfavourable conditions for invertase activity rather than by a scarcity of this enzyme.