The Regulation of Invertase Activity in the Latex of Hevea brasiliensis Muell. Arg

Abstract

Treatments which increase latex yield, e. g. bark scraping, latex tapping, and bark application of 2, 4-D or 2-chloroethylphosphonic acid (CEPA) were found to enhance the activity of latex invertase. In previously untapped trees, both the introduction of tapping and the application of 2, 4-D brought about an increase in the level of invertase. In regularly tapped trees, the amount of latex invertase is several times higher than in untapped trees and evidence was obtained that its activity is regulated by the variation of latex pH. The pH of latex of the clone investigated (PR 107) was shown to vary between 6.3 and 7.1 whereas the activity of invertase, as assayed directly in the latex, has a sharp optimum at pH 7.5 and falls rapidly with the shift of pH to the acid side. There was no increase in the content of latex invertase when trees adapted to regular tapping were treated with 2, 4-D. The effect of auxin on actual invertase activity was essentially mediated through related increase of latex pH. The CEPA and bark scraping were also shown to increase latex pH in tapped trees. The treatment of the bark of tapped trees with CEPA increased the level of latex sucrose, as did auxins. Bark scraping also had a slight stimulatory effect. The Km of latex invertase as a function of pH was found to change in the same way as Vmax, being highest at pH optimum.