Ethrel (Ethylene Releaser)-Induced Increases in the Adenylate Pool and Transtonoplast ΔpH within Hevea Latex Cells

Abstract

The treatment of rubber tree (Hevea brasiliensis) bark with chloro-2-ethyl phosphonic acid (ethrel), an ethylene-releasing chemical, induced, after a lag period of 13 to 21 hours, a marked increase in the total adenine nucleotides (essentially ATP and ADP) of latex cells. This rise in the latex adenylate pool was concomitant with a marked decrease in the [ATP]/[ADP] ratio without significant changes in the adenylate energy charge. The apparent equilibrium constant for the adenylate kinase, which appeared to behave as a key enzyme in maintaining the adenylate energy charge in the latex, was considerably reduced, probably as a consequence of the alkalinization of the latex cytosol induced by the treatment with ethrel. To reduce the "sink effect" and activation of the metabolism induced in Hevea bark by regular tapping, the latex was collected by micropuncture (few drops) at increasing distance (5-50 centimeters) above and below an ethrel-treated area on the virgin bark of resting trees. The effect of ethrel was shown to spread progressively along the trunk. The increase in the adenylate pool (essentially ATP) was detectable as early as 24 hours after the bark treatment and was maximum after 6 or 8 days, 5 centimeters as well as 50 centimeters above and below the stimulated bark ring. The correlative vacuolar acidification and cytosolic alkalinization, i.e. the increase in the transtonoplast ApH, induced in the latex cells by ethrel were shown to be concomitant with the rise in ATP content of the latex. This suggests that the tonoplast H+-pumping ATPase, which catalyzes vacuolar acidification in the latex, is directly and essentially under the control of the availability of its substrate (i.e. ATP) in the latex. The results are discussed in relation to energydependent activation of metabolism, and increased rubber production, as induced by the stimulation of rubber trees with ethrel.

The rubber tree genome reveals new insights into rubber production and species adaptation

“…Ethylene treatment triggers a number of stimulated downstream biochemical cascades in relation to latex production: sugar loading and its catabolism 9,36,39,40 , water uptake 41 , energy availability 42 , cytosolic alkalinization 42 , nitrogen assimilation 43 and defence responses 44 . Many genes implicated in these events were among the DEGs identified in this study (Supplementary Tables 22 and 23), but not the rubber biosynthesis genes, which is consistent with the previous proposition that ethylene has little direct effect on genes in rubber biosynthesis 45 .…”

Purification and Characterization of Phosphoribosylpyrophosphate Synthetase from Rubber Tree Latex

“…ATP availability may therefore also play a role in regulating enzymatic activity. After ethylene stimulation, the cytosolic ATP content can reach 1.2 to 1.8 mM (Amalou et al, 1992). This would seem to induce increased PRPP synthesis, thereby enabling increased synthesis of the purine and pyrimidine nucleotides required for latex regeneration (d'Auzac et al, 1989).…”

Involvement of HbPIP2;1 and HbTIP1;1 Aquaporins in Ethylene Stimulation of Latex Yield through Regulation of Water Exchanges between Inner Liber and Latex Cells in Hevea brasiliensis

“…In particular, pH has been reported to finely tune aquaporin activity through the protonation of some of their His residues by cytosolic H + , inducing their gating (Chaumont et al, 2005;Fischer and Kaldenhoff, 2008;Verdoucq et al, 2008). Bark treatments with synthetic auxins (Tupy, 1973) as well as with Ethrel (Coupé et al, 1977;BzrozowskaHanower et al, 1979;Amalou et al, 1992) have been shown to induce marked alkalinization of the latex cell cytosol, which should help increase laticifer PIP2 activity.…”