ETHYLENE,STRESS AND ENZYMATIC ACTIVITIES IN HEVEA LATEX: THE DIVERSITY OF RESPONSES

J.C. PREVOT, A. CLEMENT, V. PUJADE-RENAUD, SISWANTO and J.L. JACOB IRCAICIRAD B.P.5035 34032 MONTPELLIER Cedex 1 FRANCE

Latex is a fluid cytoplasm[1] which contains high quantity of rubber (30 to 50% of its fresh weight). It is expeled by tapping from articulated laticiferous cells located in Hevea phloem. Ethrel (Ethephon), an ethylene releaser is used on a large scale in Hevea brasiliensis as a latex production stimulant[2]. So, 25 mg of this product mixed with 750 mg of palm oil are applied on the tapping cut of rubber tree, 48 hours before tapping. The treatment causes the extension of latex flow time and the activation of latex regeneration in laticiferous cells between two tappings. The activation is able to cause considerable and transitory modifications in the laticifers metabolism[3]. Study of the mechanisms involved in the modifications has shown that although certain biologically important enzymatic reactions are not (or) little influenced, others may be activated or slowed. An exemple of each case is described and replaced in its physiological context.

Pyrophosphate : fructose-6-phosphate I-phosphotransferase (PP-PFK, EC 2.7.1.90) catalyses reversibly the following reactions:

F-6-P + PPi ++ F-l,6-dP + Pi Ethylene treatment causes significant decreases, in presence or not of activator: F2,6P,

of its potential activity and its specific activity as the cytosol protein content remains unchanged.

TABLE 1. Influence of ethylene on PP-PFK potential activity

Activities of PP-PFK nKat. ml-1 cytosol

Clones Before stimulation After stimulation

GT 1 PB 235

without F2,6P

4.2 ± 0.4 4.5 ± 0.9

with F2,6P

10.4 ± 0.5 7.9 ± 0.7

without F2,6P

2.2 ± 0.7 2.5 ± 0.8

with F2,6P

6.1 ± 0.7 6.0 ± 0.9

The activity of 6-phosphofructokinase (ATP-PFK, EC 2.7.1.11) a key enzyme in glycolysis[4] which catalyses irreversibly the phosphorylation of F-6-P into F-l,6-P in the presence of A TP, display no significant change before and after ethylene treatment. The values for the two clones GT 1 and PB 235 are between 2.4 ± 0.3 and 2.6 ± 0.4 nKat. ml-1 cytosol.

PP-PFK is essentially functionning to gluconeogenic pathway in latex[4] and acts as a glycolysis brake; so the ratio PP-PFKlATP-PFK activities after stimulation is decreased and can be one of the reasons of glucidic catabolism activation observed in situ[3].

The potential and specific activity of cytosolic glutamine synthetase (GS1, EC 6.3.1.2) 257

J. C. Pech et al. (eds.), Cellular and Molecular Aspects o/the Plant Honnone Ethylene, 257-258. © 1993 Kluwer Academic Publishers.

258

key enzyme for ammonium fixation and initial major step for N metabolism is significantly increased after ethylene treatment [Figure 1]. From the physiological point of view, this phenomenum, which may cause an acceleration in in situ N~ fixation and amino acids synthesis, is logically part of overall metabolic activation process already mentionned. In addition, it may be one of the causes of the decrease in glutathion (GSH) content observed[4] at the same time insofar as GS1 and the synthesis pathway of GSH possess glutamate and ATP as common substrates.

GT 1 CLONE 7 35

E 6-

trear~ - 30

:l L Gl

25 fI) 5---t{- Act. Tern. 0

1~ E

E ..... --\j- Act. Stirn.

..... 4- 20 1 -:;;

.:.! 0)

..5 c ---It}- Prot. Tern. fI) 3 ~V 15 ~

-!!! 0 .... L

-8- Prot. Stirn . . ~ ~-.~ a.

-0 2 &::::--e-e--~~~ 10 « (j)

1 5 C}

0 ..L- 0 0 1 2 3 4 5 6 7 8

TAPPINGS Figure 1. Influence of ethylene on GS1 activity.

References

[1] Dickenson, P.B. (1969) 'Electron microscopical studies of latex vessel system of Hevea brasiliensis', J. Rubb. Res. Inst Malaya 21,543-559.

[2] d'Auzac, J. and Ribaillier, D. (1969) 'L'ethyhlne nouvel agent stimulant la production de latex chez l'Hevea brasiliensis', C.R. Acad. Sci. Paris 268, 3046-3049.

[3] Coupe, M. and Chrestin, H. (1989) 'Physical-chemical and biochemical mechanisms of hormonal (ethylene) stimulation', in J. d'Auzac, J.L. Jacob and H. Chrestin (eds.) , Physiology of Rubber Tree Latex, CRC Press, Boca Raton, pp. 296-319.

[4] Jacob, J.L., Prev6t, J.C., Clement-Vidal, A., L'Huillier, L. and d'Auzac, J. (1990) 'Pyrophosphate fructose-6-phosphate phosphotransferase: an enzyme for regulation of laticiferous metabolism. In situ function and influence of stimulation', in Proc. IRRDB, Symposium Physiology and Exploitation of Hevea brasiliensis, Kunming, Chine, P.W. Allen and M.E. Crunin (eds.), IRRDB, Brickendonbury, pp. 1-10.