John Sunoj, V.S.

Kasturi Bai, K.V.

Muralikrishna, K.S.

Padmanabhan, Sughatha

English

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Maturity related changes in coconut leaf319Short  scientific  report Journal of Plantation Crops, 2011, 39 (2): 319-321Coconut (Cocos nucifera L.), a perennialplantation tree crop with a single apical growth point,puts forth leaves in succession which forms regularwhorls. In adult palms annually 12 to 14 leaves areproduced and the number of leaves on the crown in astanding crop varies from 20-40 depending upon thevariety, nutrition and environmental factors. However theleaves contributing to the production of spadices are only12-14 (Menon and Pandalai, 1958). Senescence is thefinal stage in the life span of a leaf and leads to death /abscission. In coconut, progressive senescence is seenby which the oldest leaf shed first which takes nearly 2to 2 ½ years from primordial initiation. Extensive reportsare available on physiological and biochemical changesduring leaf maturity /senescence of crop plants (Leopold,1980; Thompson et al., 1998). In coconut variations inleaf water potential (Voleti et al., 1993) as well asvariation in photosynthetic characteristics (Naresh Kumarand Kasturi Bai, 2009) among leaves of different maturitystages are reported. Ramadasan and Jacob Mathew (1987)reported that once the leaf is fully unfolded there is nochange in leaf area and dry weight. However no reportsare available on the biochemical changes especially inthe enzyme activities scavenging the reactive oxygenspecies produced during the leaf maturity/senescence.A study was conducted in CPCRI, Kasaragodduring 2009 to understand physiological and biochemicalchanges occurring in coconut leaf of differentphysiological maturity. Fifteen years old West Coast Tall(WCT) cultivar of growing under rainfed conditions wasthe material for the studies. Leaves of different maturitystages starting from spindle (non chlorophyllous youngestleaf), first (fully unfolded), 6th, 11th, 14th and 20th weredestructively sampled from five palms for the observationeach palm treated as single replication. The observationswere carried out during the month of September just afterthe cessation of monsoon i.e., non-stress condition wheresoil and atmospheric parameters are congenial for coconutPhysio-chemical changes in coconut leaf atdifferent maturity stages(Manuscript Received: 29-01-11, Revised: 14-02-11, Accepted: 09-05-11)Keywords: Coconut, leaf maturity, photosynthesis, scavenging enzymesgrowth (Kasturi Bai et al., 1988). Soil moisture contenton dry weight basis ranged between 7.2 and 10 %.Physiological parameters viz., net photosynthetic rate (PN)and stomatal conductance (gs) were recorded usingInfrared gas analyzer (ADC, LCA-4, UK.) as per methodstandardized by Rajagopal et al. (2000) and totalchlorophyll content was estimated by the method ofArnon (1949). Physiological parameters were recordedonly in the leaves with chlorophyll (i.e., 1st to 20th leaf).Bio chemical parameters viz., lipid peroxidation- LP(Heath and Packer, 1968) and related enzyme activitiesviz., super oxide dismutase-SOD (Beauchamp andFridovich, 1971) and peroxidase- POD (Kar and Mishra,1976),   were estimated as per the standard procedureswith slight modifications as suited to coconut(Chempakam et al., 1993). The data was statisticallyanalyzed using SPSS (Version10.0) 1999 package.The results (Table 1) revealed significant variationin net photosynthetic rate (PN) with leaf maturity. Justafter the leaf expansion, there is an increase in PN rate tothe tune of 38 % and remained relatively steady until adecline (50 %) by 20th leaf stage. Stomatal conductance(gs) on the other hand remained more or less steady up tothe 14th leaf stage and reduced significantly by 20th leafstage. Total chlorophyll content also showed an increasefrom 1st leaf to 14th leaf and decreased by 20th leaf.Attainment of maximum PN capacity at or prior to fullTable 1. Physio-chemical changes in coconut leaf at different maturity stages(Mean for 5 palms)Parameters Pn rate gs Total chlorophyll/leaf no. (µmol m-2.s-1) (mol m-2.s-1) content(mg.g-1f.wt)1st 4.62 0.20 0.746th 6.37 0.21 1.6111th 6.10 0.21 1.9914th 6.08 0.23 1.9120th 3.26 0.13 1.81CD (P=0.05) 0.41 0.01 0.31K.V. Kasturi Bai, Sughatha Padmanabhan, K.S. Muralikrishna and V.S. John Sunoj320activities and lipid peroxidation has been reported incoconut by Chempakam et al. (1993).  The negativecorrelation observed between SOD and LP in the presentstudy (Fig.2) corroborate with the above finding. In thepresent observation high SOD activity was observed inthe spindle leaf and showed decrease with the maturityof the leaf. On the other hand, POD activity decreasedfrom spindle to 11th leaf and increased with leaf maturity.POD has been implicated in plant senescence by virtueof its ability to oxidize 3-indole acetic acid (Parish, 1968).Higher increase in the activity of this enzyme duringdevelopment and senescence has been reported inCajanus (Mukherjee, 2003) thus corroborating with ourobservation in coconut. Variations in individual antioxidative enzyme activities have been reported by variousworkers (Kanawaza et al., 2000; Shrivalli and Khanna-Chopra, 2001). Chlorophyll degradation due to lipidperoxidation is known to occur (Heath and Packer, 1968)and the decline in chlorophyll content in coconut withleaf maturity can be attributed to the lipid peroxidationin the chloroplast membranes.Fig.1. Changes in SOD, POD and LP during leaf maturity stagesleaf expansion has been observed in cashew (Balasimha,1991). Flore and Lakso (1989) related the ontogenicdecline in leaf PN to the declining sink demand forassimilates. However, in coconut since each leaf axilsubtends a bunch of different maturity stage, the sinkdemand is always higher. Recently Naresh Kumar andKasturi Bai (2009) observed significant variation inphotosynthetic characteristics in different shapes ofcoconut canopy as well as between leaves of differentmaturity stages under irrigated and rainfed conditions.In silverbrich, Oleksyn et al. (2000) observed decreasein photosynthetic rate after the leaves are fully developedbut the rate of decline was found to vary due to growthhabit or growth environment.It has been suggested that with the decrease inphotosynthetic rate the photosynthetic electron flux toO2 will increase, resulting in the increased production ofreactive oxygen species which include superoxideradicals, hydrogen peroxide, hydroxyl radicals etc. andare extremely damaging to cell wall lipids, proteins andpigments unless they are rapidly scavenged within thechloroplasts by the activities of antioxidative enzymes(Asada, 2006).  In aerobic cells, the enzyme SOD protectscells by converting the superoxide radicals to hydrogenperoxide while catalase and peroxidase convert hydrogenperoxide to water and molecular oxygen. But duringmaturity/senescence, the balance between production andelimination will get disturbed. The observations incoconut revealed a rapid increase in the lipid peroxidationfrom spindle leaf to the first leaf and thereafter steadyincrease (Fig.1). Simultaneously with the increase in lipidperoxidation, there was decrease in the enzyme activitiesviz., SOD and POD. Increased lipid peroxidation anddecline in anti oxidant enzyme activities have beenreported as the possible cause of leaf senescence indifferent plants by various workers (Dhindsa et al., 1981;Hurng and Kao, 1994; Prochazkova et al., 2001).Negative correlation between anti oxidant enzymeFig.2. Correlation between SOD and lipid peroxidation (LP) in coconut (Eachpoint represents mean of five observations)From the foregoing it can be concluded that incoconut physio- chemical changes take place with leafmaturity. Naresh Kumar and Kasturi Bai (2009) reporteddecrease in photosynthetic rates beyond 10th month leafmaturity even after providing radiation at saturatinglevels. In a source limited crop like coconut (NareshKumar and Kasturi Bai, 2009) during adverse climaticconditions, vegetative growth gets priority overreproductive growth which will affect dry matterproduction and yield. This is mainly because increase inLAI will shade the lower leaves making them parasiticto other leaves. Actually the main purpose of leafsenescence is to enable nutrient recycling from the agingleaves to the developing tissues. This catabolic processMaturity related changes in coconut leaf321requires energy and as suggested by Oleksyn et al. (2000)this may be provided by the ATP generated by thesenescent leaves via respiration. It is estimated that inperennial plantation crop, 75 % of the photosynthate arelost through respiration which otherwise would have beendiverted for economic produce (Corley, 1983). Thisimplies that proper management of leaves in the crownis highly crucial for optimizing the productivity ofcoconut palm.AcknowledgmentAuthors acknowledge Mr. Amaranth for statisticalsupport and Mr. K. Keeran for the technical help.ReferencesArnon, D.I. 1949. Copper enzymes in isolated chloroplasts,polyphenol oxidase in Beta vulgaris. Plant Physiol. 24:1-15.Asada, K. 2006. Production and scavenging of reactive oxygen speciesin chloroplasts and their functions. Plant Physiol. 141:391-396.Balasimha, D. 1991. Photosynthetic characteristics of cashew trees.Photosynthetica 25(3): 419-423.Beauchamp, C. O. and I. Fridovich.1971. Superoxide dismutase:Improved assay and an assay applicable to acrylamide gels.Anal. Biochem. 44: 276-287.Chempakam, B., Kasturi Bai, K.V. and Rajagopal, V. 1993. Lipidperoxidation and associated enzyme activities in relation toscreening for drought tolerance in coconut (Cocos nuciferaL.). Plant Physiol and Biochem. 20: 5-10.Corley, R.H.V. 1983. Potential productivity of tropical perennial crops.Expl. Agric. 19: 217-237.Dhindsa, R.A., Plumb-Dhindsa, P. and Thorpe, T.A. 1981. Leafsenescence:  correlated with increased permeability and lipidperoxidation, and decreased levels of superoxide dismutaseand catalase, J. Exp. Bot. 126: 93-101.Flore, J. A. and Lakso, A. N. 1989. Environmental and physiologicalregulation of photosynthesis in fruit crops. Hort. Rev. 11: 111-157.Heath, R.L. and Packer, L. 1968. Photoperoxidation in isolatedchloroplasts. I. Kinetics and stoichiometry of fatty acidperoxidation. Arch. Biochem. Biophys. 125: 189–198.Hurng, W.P. and Kao, C.H. 1994. Lipid peroxidation and antioxidativeenzymes in senescing tobacco leaves during post flooding.Plant Sci. 96: 41-44.Kanawaza, S. Sano, S., Koshiba, T. and Ushimaru, T. 2000. Changesin antioxidative enzymes in cucumber cotyledons duringnatural senescence: comparison with those during dark-induced senescence. Physiol. Plant. 109: 211-216.Kar, M. and Mishra, D.1976. Catalase, peroxidase and poly phenoloxidase activities during rice leaf senescence. Plant Physiol.57:315-319.Kasturi Bai, K.V., Voleti, S.R. and Rajagopal, V.1988. Water relationsof coconut palms as influenced by environmental variables.Agri..Forest.Meteorol. 43: 193-199.Leopold, A.C. 1980. Aging and senescence in plant development.pp.1-12. In: Senescence in plants. (Ed) Thimann, K.V., CRCPress, Boca Raton.Menon, K.P.V. and Pandalai, K.M. 1958. The  Coconut  Palm. Amonograph. pp. 293-303. The times of India Press, Bombay.Mukherjee, D. 2003. Physiological changes I leaves, flowers and podsduring development and senescence in Cajanus cajan L. J.Indian Bot. Soc. 82: 78-84.Naresh Kumar, S. and Kasturi Bai, K.V. 2009. Photosyntheticcharacters in different shapes of coconut canopy underirrigated and rainfed conditions. Indian J. Plant Physiol.14(3):215-223.Oleksyn, J., Zytkowiak, R., Reich, P.B, Tjoelker, M.G and Karolewski,P. 2000. Ontogenetic patterns of leaf CO2 exchange,morphology and chemistry in Betula pendula trees. Trees14:271-281.Parish, R. W. 1968. Studies on senescing tobacco leaf disks withspecial reference to peroxidase. 1. The effects of cutting andof inhibition of nucleic acid and protein synthesis. Planta82: 1-13.Prochazkova, D., Sairam, R.K., Srivastava, G.C. and Singh, D.V.2001.Oxidative stress and antioxidant activity as the basis ofsenescence in maize leaves.  Plant Science 161: 765-771.Rajagopal, V., Naresh Kumar, S., Kasturi Bai, K. V. and Laxman,R.H. 2000. Day time fluctuations in juvenile coconut palmsgrown under rainfed and irrigated conditions. J. Plant. Biol.27(1): 27-32.Ramadasan, A. and Jacob Mathew. 1987. Leaf area and dry matterproduction in adult coconut palms. J. Plantn. Crops 15: 59-63.Shrivalli, B. and Khanna-Chopra, R. 2001. Induction of new isoformsof superoxide dismutase and catalase enzymes in the flagleaves of wheat during monocarpic senescence. Biochem.Biophys. Res. Commun. 288:1037-1042.Thompson, J.E., Froese, C.D., Madey, E., Smith, M.D. and Hong, Y.1998. Lipid metabolism during plant senescence. Prog LipidRes. 37:119-141Voleti, S.R., Kasturi Bai, K.V. and Rajagopal, V. 1993. Water potentialin the leaves of coconut (Cocos nucifera,L.) under rainfedand irrigated conditions. pp: .243-245. In: Advances  inCoconut   Research   and   Development.  (Eds) Nair, M. K.,H. H. Khan, P. Gopalasundaram, E.V. V. Bhaskara  Rao.,Oxford & IBH publishing Co Pvt. Ltd. New Delhi.Central Plantation Crops Research Institute,(Indian Council for Agricultural Research)Kudlu, PO, Kasaragod 671 124,Kerala, IndiaK.V. Kasturi Bai*,Sughatha Padmanabhan,K.S. Muralikrishna,V.S. John Sunoj*e mail: kasturikv@yahoo.com

Physio-chemical changes in coconut leaf at  different maturity stages

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Physio-chemical changes in coconut leaf at different maturity stages

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