Ambily, P.K

Jacob, James

Krishnakumar, R.

English

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Stimulation and stress response in Hevea217Journal of Plantation Crops, 2009, 37 (3): 217-220Stimulation of latex production by externalapplication of ethephon (2-chloro-ethyl phosphonic acid)on the bark of the trees has been a common commercialpractice in rubber plantations for increasing theproductivity of the crop. Ethephon application prolongsthe latex flow and thereby increases the total latex volumeduring tapping (Ho and Paardekooper, 1965). It has beenreported that ethephon stimulation increased the internalpressure within the latex vessels by changing the waterrelations. Ethephon stimulation also caused change inthe physiological properties governing the flow of latex,the modifications occurring in the latex vessels, whichdo not plug up so easily (Hanower et al., 1979). Overstimulation with ethylene releasing compounds on theHevea bark reported to induce formation of metabolicdisorders like abnormal thickening of the bark, spongyappearance of necrotic areas, small local cracks andappearance of non-productive zones along the tappingcut etc. (Paranjothy et al., 1979).Ethephon application induces several compounds,which can make metabolic changes in the laticiferoustissue. It has been shown that ethephon stimulation oftrees increases the general latex metabolism, includingover-expression of some genes in the laticiferous tissue(Pujade-Renaud et al., 1997). Some of the effects ofstimulant application on the physiological response oflaticiferous tissue have been studied earlier (Coupe andChrestin, 1989; Yang and Fan, 1995; d’Auzac et al.,1997). Chrestin (1989) has suggested a possible oxidativestress in lutoid cells in the latex due to etheral application.Several studies were made on the physiological effect ofstimulation and exploitation intensities in relation totapping panel dryness (Vijayakumar et al., 1991; Xu etal., 1994; Nair et al., 2004). Apart from these, no studiesKeywords: Ethylene, Hevea, stress, stimulationEffect of stimulation in the stress responsesin Hevea brasiliensis(Manuscript Received: 30-03-07, Revised: 12-07-09, Accepted: 20-09-09)Short  scientific  reportwere made on ethephon-induced stress response inHevea. The present study was taken up to closely observeif a single dose of ethephon application can lead to stressresponses in the tissue.Twenty year old trees of Hevea brasiliensis (cloneRRII 105) which were never stimulated before wereselected for this experiment. The trees were in the sixthyear of tapping under the alternate daily (½S d/2 6d/7)tapping system in the B-panel. The trees were dividedinto two groups of ten trees each with uniform growth.One group was stimulated with ethephon and the otherkept as untreated control. The tapping panel of all thetrees were scraped well (2.5 cm below the tapping cut)to remove the dead tissues and rubber particles beforeethephon was applied. Commercially available ethephon(2-chloro-ethyl phosphonic acid) was diluted to 2.5 %with coconut oil and applied on the bark of theexperimental trees and the control trees were similarlytreated with coconut oil.Latex C-serum and bark tissues from both theexperimental and control trees were used for thefollowing analysis. Samples were collected two timesbefore stimulation at 10 days intervals (pre-treatment Aand B) and 3rd and 10th day after stimulation (post-treatment C and D). Total latex yield in each tree wasrecorded by measuring the latex volume after eachtapping. Determination of thiol levels in the latex wasmade using the method of Boyne and Ellman (1972).Proline content in the C-serum of the latex was analysedwith acid ninhydrin reagent using proline as standard(Bates et al., 1973). Ethanol (80 %) extract of the C-serum was used for determination of the phenol content(Swain and Hillis, 1959). Peroxidase enzyme activity inR. Krishnakumar, P.K. Ambily and James Jacob218the C-serum was determined after the method ofGuilbault (1976). Wound induced ethylene produced inHevea bark tissue was quantified through gaschromatography (Krishnakumar et al., 2006).The total latex volume was comparable betweenthe experiment and control groups of trees before theethephon application. As expected the latex volumeincreased in the experimental trees after the stimulantapplication (Fig.1). A significant increase in turgurpressure, initial flow rate and decrease in plugging indexare the factors leading to prolonged latex flow andincrease in the latex volume due to ethephon treatment(Abraham et al., 1971; Thomas et al., 1999).It was observed that the total phenol content inthe C-serum increased significantly after the stimulantapplication and the level was maintained high till theend of the experiment (Fig. 2). In untreated control trees,phenol level in the latex C-serum was small and remainedalmost steady. Phenols are generally formed andaccumulated in plant tissues when they are in a state ofstress (Archer, 1963), including when the plantsexperience biotic stresses caused by pests and diseases(Gupta et al., 1995). The accumulation of phenols in thelatex of experimental trees indicates that stimulation ledto internal stress in the laticiferous tissues, which is ageneral adaptation reaction noticed in Hevea trees dueto stimulation.The experimental trees had a high peroxidaseenzyme activity in the latex C-serum immediately afterthe stimulant application (Fig. 3). Peroxidases oftenincrease in plant tissues as a response to stresses andthis has vital role in the cells protecting them fromFig. 1 Fig. 2Fig. 3 Fig. 4Fig.1. Total Latex volume, Fig.2. Phenol content in the C-serum, Fig.3. Peroxidase enzyme activity in the C-serum, Fig.4. Proline content in the C-serum duringpre-treatment (A& B) and post-treatment (C & D) periods in the experiment ( ) and control ( ) groups of Hevea brasiliensis (n = ± SE; ns = not significant;* P ≤ 0.01)Stimulation and stress response in Hevea219oxidative damage (Siegel, 1993). Peroxidases not onlyremove the toxic peroxide radical but also immobilizethe toxic phenolic-ligin precursors in plant tissues (Paulsand Thompson, 1984). In short, the high phenol levelsand peroxidase enzyme activity noticed in the stimulatedHevea trees are indications of intense stress response bythe laticiferous tissues due to ethephon application.Proline content also increased with the application ofethephon (Fig. 4). Proline has been known to accumulatein plant tissues as a common reaction to various formsof physiological stresses. It has been demonstrated earlierthat intensive tapping along with ethrel stimulationaggravated the localized water deficit in the tree, and thatthe corresponding rise in proline level was an indicationof the general adaptation reaction for all physiologicalresponse of the tree to stress (Yang and Fan, 1995).A significant decrease in the thiol content wasnoticed in the latex of the stimulated trees within threedays after the stimulant application. However, the thiollevel attained almost normal level by the 10th day afterthe treatment (Fig.5). The low thiol content in the latexof the ethephon treated trees indicates that they wereexperiencing internal stress as a result of ethephonapplication.Wound-induced ethylene produced by the barktissue of both stimulated experimental and unstimulatedcontrol trees was more or less in the same level beforestimulation. But after three days of stimulation this wasremarkably high in the ethephon treated trees than theuntreated controls (Fig. 6). Exogenous ethylene is knownto autocatalytically enhance the production ofendogenous ethylene (Kevin et al., 2002). This may beresponsible for the observed enhanced ethyleneproduction by the bark tissues even 10 days afterethephon application. There are reports that excess levelsof ethylene in plant tissue can cause oxidative stress andthereby damage the tissues and organelles by changingthe normal physiological and biochemical activitiesleading to irreversible damage and senescence (Siegel,1993). The high ethylene level generated in the barktissues of the ethephon treated trees may eventually resultin oxidative stress leading to oxidative damage of thelaticiferous tissues.Our earlier results indicated that wound inducedethylene production was related to oxidative stress andtapping panel dryness (TPD) (Krishnakumar and Jacob,2003). Several studies have shown that over-stimulationwith ethephon will lead to TPD (Vijayakumar et al.,1991). In the present study, even a single application ofethephon led to significant stress responses in the barkand latex, a general adaptation mechanism, which whenexceeds the metabolic capacity of the system can resultin adverse physiological processes including TPD.In the Hevea clone RRII 105, stimulation with2.5 % ethephon resulted in an abrupt stress response.Only a single dose of stimulant application was requiredto trigger stress responses in the tissue. Moreinvestigations are required to understand the stressresponse of the tree when the stimulation frequency isincreased. Assessing and characterizing these responsesare important in careful and judicious use of ethephonfor yield stimulation.Fig. 5 Fig. 6Fig.5. Thiol content in the latex, Fig.6. Wound induced ethylene levels in the bark tissues during pre-treatment (A & B) and post-treatment (C & D) periods inthe experiment ( ) and control ( ) groups of Hevea brasiliensis (n = ± SE; ns =  not significant;  * P ≤ 0.01)R. Krishnakumar, P.K. Ambily and James Jacob220ReferencesAbraham, P.D., Blencowe J.W., Chua, S.E., Gomez, J.B., Moir, G.F.J.,Pakianathan, S.W., Sekhar, B.C., Southorn, W.A. andWycherley, P.R. 1971. Novel stimulants and procedures inthe exploitation of Hevea: II Pilot trial using (2-chloroethyl)-phosphonic acid (Ethephon) and acetylene with varioustapping systems. J. Rubb. Res. Inst. Malaya. 23: 90-113.Archer, B.L., Barnad, D., Cockbain, E.G.C., Dickenson, P.B. andMc.Mullen, A.I. 1963. Structure, composition andbiochemistry of Hevea latex, in chemistry and physics ofrubber like substances, (Eds) Bateman, L., Mc Laren andsons, London.Bates, L.S., Waldren, P.R. and Teare, I.D. 1973. Rapid determinationof free proline for water stress studies. Plant and Soil 39:205-207.Boyne, A.F. and Ellman, G.L. 1972. A methodology for the analysisof tissue sulfhydral components. Anal. Biochem. 46:639-653.Coupe, M. and Chrestin, H. 1989. 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Effect of stimulation in the stress responses  in Hevea brasiliensis

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Effect of stimulation in the stress responses in Hevea brasiliensis

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