Photosynthetic changes that occur during aging of cypress (Cupressus sempervirens L.) needles

2-years-old cypress needles (A2) were physiologically most active with regard to net photosynthetic (P _N) and electron transport rates. Variable to maximum fluorescence (F_v/F_m) ratios of dark-adapted needles were higher in A2 needles than in current year (A1) or senescent (A4) needles. Lower F_v/F_m values in these stages seemed to be caused not by photoinhibition but by a low photochemical capacity as suggested from the chlorophyll (Chl) a/b ratios. In isolated thylakoids, lower rates of whole chain and photosystem 2 (PS2) activities were observed in A4 needles, while higher rates were observed in A2 needles. A similar trend was noticed for contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPC) and total soluble proteins. The artificial exogenous electron donor Mn²⁺ failed to restore the loss of PS2 activity in 3-year-old (A3) and A4 needles, while diphenylcarbazide and NH₂OH significantly restored the loss of PS2 activity. The marked loss of PS2 activity in A4 needles was primarily the result of the loss of 33, 28–25, 23, and 17 kDa polypeptides. A marked loss of RuBPC activity in A4 needles is mainly due to the loss of 15 (SSU) and 55 (LSU) kDa polypeptides.     

Photoinhibition of Photosynthesis in Sun and Shade Grown Leaves of Grapevine (Vitis vinifera L.)

The degree of photoinhibition of sun and shade grown leaves of grapevine was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence (F_v/F_m) and electron transport measurements. The potential efficiency of photosystem 2 (PS2), F_v/F_m, markedly declined under high irradiance (HI) in shade leaves with less than 10 % of F₀ level. In contrast, F_v/F_m ratio declined with about 20 % increase of F₀ level in sun leaves. In isolated thylakoids, the rate of whole chain and PS2 activity in HI shade and sun leaves was decreased by about 60 and 40 %, respectively. A smaller inhibition of photosystem 1 (PS1) activity was also observed in both leaf types. In the subsequent dark incubation, fast recovery was observed in both leaf types that reached maximum PS2 efficiencies similar to non-photoinhibited control leaves. The artificial exogenous electron donors DPC, NH₂OH, and Mn²⁺ failed to restore the HI-induced loss of PS2 activity in sun leaves, while DPC and NH₂OH were significantly restored in shade leaves. Hence HI in shade leaves inactivates on the donor side of PS2 whereas it does at the acceptor side in sun leaves, respectively. Quantification of the PS2 reaction centre protein D1 and the 33 kDa protein of water splitting complex following HI-treatment of leaves showed pronounced differences between shade and sun leaves. The marked loss of PS2 activity in HI leaves was due to the marked loss of D1 protein of the PS2 reaction centre protein and the 33 kDa protein of the water splitting complex in sun and shade leaves, respectively.     

Photoinhibition of photosynthesis in water deficit leaves of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L.) plants

Photoinhibition under irradiance of 2 000 μmol m⁻² s⁻¹ (HI) was studied in detached control (C) and water deficit (WD) leaves of grapevine (Vitis vinifera L.) plants. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence (F_v/F_m) and electron transport measurements. The potential efficiency of photosystem (PS) 2, F_v/F_m, marginally declined under HI in WD-leaves without significant increase of F₀. In contrast, F_v/F_m ratio declined markedly with significant increase of F₀ in C-leaves. In isolated thylakoids, the rate of whole chain and PS2 activity under HI were more decreased in C-than WD-leaves. The artificial exogenous electron donors diphenyl carbazide, NH₂OH, and Mn²⁺ failed to restore the HI-induced loss of PS2 activity in both C-and WD-leaves. Thus HI operates at the acceptor side of PS2 in both leaf types. Quantification of the PS2 reaction centre protein D1 following HI exposure of leaves showed pronounced differences between C-and WD-leaves. The marked loss of PS2 activity under HI of C-leaves was due to the marked loss of D1 protein of the PS2 reaction centre.     

Photoinhibition and Recovery of photosystem 2 in Grapevine (Vitis vinifera L.) Leaves Grown Under Field Conditions

Photoinhibition of photosynthesis was investigated in grapevine (Vitis vinifera L.) exposed to 2 or 4h of high irradiance (HI) (1 700–1 800 mol m^–2 s^–1) leaves under field conditions at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m) and photosynthetic electron transport measurements. When the photochemical efficiency of photosystem 2 (PS2), F_v/F_m, markedly declined, F₀ increased in both 2 (HI2) and 4 h (HI4) HI leaves sampled at midday. When various photosynthetic activities were followed on isolated thylakoids, HI4 leaves showed significantly higher inhibition of whole chain and PS2 activity than the HI2 leaves sampled at midday. Later, the leaves reached maximum PS2 efficiencies similar to those observed early in the morning during sampling at evening. The artificial exogenous electron donor Mn²⁺ failed to restore PS2 activity in both variants of leaves, while DPC and NH²OH significantly restored PS2 activity in HI4 midday leaf samples. Quantification of the PS2 reaction centre protein D1 and 33 kDa protein of water splitting complex following midday exposure of leaves showed pronounced differences between HI2 and HI4 leaves. The marked loss of PS2 activity noticed in midday samples was mainly due to the marked loss of D1 protein in HI2, while in HI4 it was mainly 33-kDa protein.     

Effect of Iron Deficiency Induced Changes on Photosynthetic Pigments,Ribulose-1,5-Bisphosphate Carboxylase,and Photosystem Activities in Field Grown Grapevine (Vitis Vinifera L. cv. Pinot Noir) Leaves

The effect of iron deficiency on photosynthetic pigments, ribulose-1,5-bisphosphate carboxylase (RuBPC), and photosystem activities were investigated in field grown grapevine (Vitis vinifera L. cv. Pinot noir) leaves. The contents of chlorophyll (Chl) (a+b) and carotenoids per unit fresh mass showed a progressive decrease upon increase in iron deficiency. Similar results were also observed in content of total soluble proteins and RuBPC activity. The marked loss of large (55 kDa) and small (15 kDa) subunits of RuBPC was also observed in severely chlorotic leaves. However, when various photosynthetic electron transport activities were analysed in isolated thylakoids, a major decrease in the rate of whole chain (H₂O methyl viologen) electron transport was observed in iron deficient leaves. Such reduction was mainly due to the loss of photosystem 2 (PS2) activity. The same results were obtained when F_v/F_m was evaluated by Chl fluorescence measurements in leaves. Smaller inhibition of photosystem 1 (PS1) activity was also observed in both mild and severely chlorotic leaves. The artificial electron donors, diphenyl carbazide and NH₂OH, markedly restored the loss of PS2 activity in severely chlorotic leaves. The marked loss of PS2 activity was evidently due to the loss of 33, 23, 28-25, and 17 kDa polypeptides in iron deficient leaves.     

Respiration and photosynthesis in cones of Norway spruce (Picea abies (L.) Karst.)

Summary Dark respiration and photosynthetic carbon dioxide refixation in purple and green Picea abies cones were investigated from budbreak to cone maturity. The rate of dark respiration per unit dry weight and CO₂ refixation capacity decreased during cone maturation. At the beginning of the growing season, photosynthetic CO₂ refixation could reduce the amount of CO₂ released by respiration in green and purple cones by 50% and 40%, respectively. The seasonal performance of the components of the cone carbon balance was calculated using information on the seasonal course of respiration, refixation capacity and the light response curves of cone photosynthesis, as well as the actual light and temperature regime in the field. The daily gain of CO₂ refixation reached 28%–34% of respiration in green and 22%–26% in purple cones during the first month of their growth, but decreased later in the season. Over the entire growth period refixation reduced carbon costs of cone production in both cone colour polymorphs by 16%–17%.     

Decline of Photosynthetic Pigments,Ribulose-1,5-Bisphosphate Carboxylase and Soluble Protein Contents,Nitrate Reductase and Photosynthetic Activities,and Changes in Thylakoid Membrane Protein Pattern in Canopy Shade Grapevine (Vitis Vinifera L. cv. Moscato Giallo) Leaves

In canopy shade leaves of grapevine (Vitis vinifera L. cv. Moscato giallo) grown in the field the contents of chlorophyll (Chl), carotenoids (Car), and soluble protein per fresh mass were lower than in sun leaves. RuBPC activity, in vivo nitrate reductase activity (indicator of nitrate utilisation), apparent electron transport rate, and photochemical fluorescence quenching were also significantly reduced in canopy shade leaves. When various photosynthetic activities were followed in isolated thylakoids, canopy shade leaves exerted a marked inhibition of whole chain and photosystem (PS) 2 activity. Smaller inhibition of PS1 activity was observed even in high-level canopy shade (HS) leaves. The artificial exogenous electron donors, DPC and NH₂OH, significantly restored the loss of PS2 activity in HS leaves. Similar results were obtained when F_v/F_m was evaluated by Chl fluorescence measurements. The marked loss of PS2 activity in canopy shade leaves was due to the loss of 47, 43, 33, 28–25, 23, 17, and 10 kDa polypeptides.     

Chloroplastic Carbon Dioxide Concentration in Norway Spruce (Picea Abies [L.] Karst.) needles relates to the position within the crown

Differences between sun (E) and shaded (S) foliage were studied in a Norway spruce (Picea abies [L.] Karst.) stand. Response curves describing the dependence of the CO2 assimilation rate (PN) on the CO2 concentration at the catalytic site of ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBPCO (PN-Cc) were estimated using the simultaneous measurements of chlorophyll fluorescence and leaf gas exchange. Higher PN, higher electron transport (Ja), higher carboxylation capacity (Vc), and higher RuBPCO activity () for sun acclimated needles was found. The S-needles had higher portion of internal limitation and higher CO2 compensation concentration () than the E-needles. Because higher degree of limitation of photosynthesis by carboxylation was ascertained, it can be assumed that photosynthesis in shade foliage is limited mainly by lower carboxylation capacity and by low chloroplastic CO2 concentration     

Cultivar Differences in Photosynthetic Tolerance to Photooxidation and Shading in Rice (Oryza Sativa L.)

Forty-four genotypes from the rice germplasm were identified under photoinhibition/photooxidation and shade conditions and divided into four basic types: (1) cultivars tolerant to both photooxidation and shading, (2) cultivars tolerant to photooxidation but sensitive to shading, (3) cultivars tolerant to shading but sensitive to photooxidation, and (4) cultivars sensitive to both photooxidation and shading. Photosynthetic characteristics of a cultivar tolerant (cv. Wuyugeng 3) and a cultivar sensitive (cv. Xiangxian) to photooxidation and shading were compared. The photochemical efficiency (F_v/F_m) of photosystem 2 (PS2) and the content of PS2-D1 protein in the tolerant cultivar Wuyugeng 3 decreased less under photooxidative conditions as compared with Xiangxian. Under similar conditions, superoxide dismutase was induced rapidly to a higher activity and the active oxygen (O^–) built up to a lower level in Wuyugeng 3 than in Xiangxian. Net photosynthetic rate (P _N) decreased by 23 % in Wuyugeng 3 vs. 64 % in Xiangxian. Shading (80 %) during the booting stage caused only small decreases (7–13 %) in ribulose-1,5-bisphosphate carboxylase activity and P _N in Wuyugeng 3 but severe decreases (57–64 %) were observed in Xiangxian which corresponded to the decreases in grain yield of the two cultivars (38 and 73 %, respectively). We described a simple and effective screening method and physiological basis for breeding crops for enhanced tolerance to both high and low irradiance.     

Photoinhibition of photosynthesis in leaves of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L. cv. Riesling). Effect of chilling nights

Photoinhibition of photosynthesis was investigated in control (C) and chilling night (CN) leaves of grapevine under natural photoperiod at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m) and photosynthetic electron transport measurements. When the potential efficiency of photosystem (PS) 2, F_v/F_m was measured at midday, it markedly declined with significant increase of F₀ in CN leaves. In isolated thylakoids, the rate of whole chain and PS2 activity were markedly decreased in CN leaves than control leaves at midday. A smaller inhibition of PS1 activity was also observed in both leaf types. Later, the leaves reached maximum PS2 efficiencies similar to those observed in the morning during sampling at evening. The artificial exogenous electron donors diphenyl carbazide, NH₂OH, and Mn²⁺ failed to restore the PS2 activity in both leaf types at midday. Thus CN enhanced inactivation on the acceptor side of PS2 in grapevine leaves. Quantification of the PS2 reaction centre protein D1 following midday exposure of leaves showed pronounced differences between C and CN leaves. The marked loss of PS2 activity in CN leaves noticed in midday samples was mainly due to the marked loss of D1 protein of the PS2 reaction centre.     

Photosystem 2 Efficiency and Thylakoid Protein Pattern in DCMU-Treated Wheat Seedlings during Senescence

Changes in various components of photosynthetic apparatus during the 6-d dark incubation at 25 °C of detached control and DCMU-treated Triticum aestivum L. leaves were examined. The rate of photosystem 2 (PS2) activity was decreased with increase of the time of dark incubation in control leaves. In contrast to this, DCMU-treated leaves demonstrated high stability by slowing down the inactivation processes. Diphenyl carbazide and NH₂OH restored the PS2 activity more in control leaves than in DCMU-treated leaves. Mn²⁺ failed to restore the PS2 activity in both control and DCMU-treated samples. Similar results were obtained when F_v/F_m was evaluated by chlorophyll fluorescence measurements. The marked loss of PS2 activity in dark incubated control leaves was primarily due to the loss of D1, 33, and 23 kDa extrinsic polypeptides and 28-25 kDa LHCP2 polypeptides.     

Seasonal development of the photosynthetic performance of Norway spruce (Picea abies [L.] Karst.) under magnesium deficiency

In order to investigate the influence of different magnesium nutrition on photosynthesis, one hundred 6-year-old spruce trees derived from one clone were planted in October 1990 into a special out-door experimental construction, where they were cultivated in sand culture with an optimal supply of nutrients, except magnesium, via circulating nutrient solutions. Magnesium was added to the nutrient solutions in three different concentrations, varying from optimal to severe deficient supplies. During the first vegetative period in 1991, photosynthetic performance and carboxylation efficiency were measured under saturating light, controlled CO₂ conditions, optimal temperature and humidity, using a minicuvette system.During summer, the trees under moderate magnesium deficiency developed tip yellowing symptoms on older needles, while the youngest needles remained green with unchanged chlorophyll contents. Trees under severe magnesium deficiency showed yellowing symptoms on all needle age classes combined with decreased chlorophyll contents in the youngest needles as well. In comparison with the controls, the photosynthetic performance of the 1-year-old needles was significantly lower in both deficiency treatments. The same was observed in the youngest needles of the trees under severe deficiency. Trees under moderate deficiency treatment decreased in photosynthetic performance during the summer without reduction of chlorophyll contents. The reduction of photosynthetic rates corresponded to a decrease in carboxylation efficiency, which is taken as a measure of the activity of the enzyme ribulose-1,5-bisphosphate carboxylase. This reduction, together with the observed increase of carbohydrate contents in needles of trees growing under magnesium deficiency, led to the assumption that the photosynthetic carbonfixation is reduced as a consequence of the accumulation of carbohydrates.     

Partial decline of Arachis hypogaea L. photosynthesis triggered by drought stress

Photosynthetic capacity (PC) of three peanut cultivars (Arachis hypogaea L. cvs. 57-422, 73-30, and GC 8-35) decreased during drought stress (decline in relative water content from ca. 95 to 70 %) and recovered two days after rewatering. Mild water stress was not limiting for the total ribulose-1,5-bisphosphate carboxylase/oxygenase activity, since this enzyme activity increased under drought. Photosystem (PS) 2 and PS1 (the latter only in cv. GC 8-35) electron transport activities decreased under drought. The ratio of the variable to maximal chlorophyll fluorescence (Fv/Fm) decreased mainly in the cv. GC 8-35. All cultivars showed decreases in photochemical quenching (qP) and quantum yield of PS2 electron transport (Φe). Increase of basal fluorescence (F0) was observed in the cvs. 73-30 and GC 8-35, while the cv 57-422 showed a decrease. After rewatering a sharp increase was observed in the majority of the parameters. Thus under the present stress conditions, the cv GC 8-35 was the most affected for all the parameters under study. The cv. 57-422 showed a higher degree of tolerance being gradually affected in photosynthetic capacity (PC) in contrast to the two other cvs. which showed a sharp decrease in PC at the beginning of the drought cycle. This revised version was published online in September 2006 with corrections to the Cover Date.     

Photosynthetic Assimilation of Sun versus Shade Norway Spruce [Picea abies (L.) Karst] Needles Under the Long-Term Impact of Elevated CO2 Concentration

The long-term impact of elevated concentration of CO₂ on assimilation activity of sun-exposed (E) versus shaded (S) foliage was investigated in a Norway spruce stand [Picea abies (L.) Karst, age 14 years] after three years of cultivation in two domes with adjustable windows (DAW). One DAW was supplied with ambient air [AC, ca. 350 µmol(CO₂) mol^–1) and the second with elevated CO₂ concentration [EC = AC plus 350 µmol(CO₂) mol^–1]. The pronounced vertical profile of the photosynthetic photon flux density (PPFD) led to the typical differentiation of the photosynthetic apparatus between the shaded and sun needles. Namely, photon-saturated values of maximal net photosynthetic rate (P _Nmax) and apparent quantum yield () were significantly higher/lower for E-needles as compared with the S-ones. The prolonged exposure to EC was responsible for the apparent assimilatory activity stimulation observed mainly in deeply shaded needles. The degree of this stimulation decreases in the order: S-needles dense part > S-needles sparse part > E-needles dense part > E-needles sparse part. In exposed needles some signals on a manifestation of the acclimation depression of the photosynthetic activity were found. The long-term effect of EC was responsible for the decrease of nitrogen content of needles and for its smoother gradient between E- and S-needles. The obtained results indicate that the E- and S-foliage respond differently to the long-term impact of EC.     

Inhibition of photosynthesis by high temperature in oak (Quercus pubescens L.) leaves grown under natural conditions closely correlates with a reversible heat-dependent reduction of the activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase

Inhibition of the net photosynthetic CO₂ assimilation rate (P_n) by high temperature was examined in oak (Quercus pubescens L.) leaves grown under natural conditions. Combined measurements of gas exchange and chlorophyll (Chl) a fluorescence were employed to differentiate between inhibition originating from heat effects on components of the thylakoid membranes and that resulting from effects on photosynthetic carbon metabolism. Regardless of whether temperature was increased rapidly or gradually, P_n decreased with increasing leaf temperature and was more than 90% reduced at 45 °C as compared to 25 °C. Inhibition of P_n by heat stress did not result from reduced stomatal conductance (g_s), as heat‐induced reduction of g_s was accompanied by an increase of the intercellular CO₂ concentration (C_i). Chl a fluorescence measurements revealed that between 25 and 45 °C heat‐dependent alterations of thylakoid‐associated processes contributed only marginally, if at all, to the inhibition of P_n by heat stress, with photosystem II being remarkably well protected against thermal inactivation. The activation state of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) decreased from about 90% at 25 °C to less than 30% at 45 °C. Heat stress did not affect Rubisco per se, since full activity could be restored by incubation with CO₂ and Mg²⁺. Western‐blot analysis of leaf extracts disclosed the presence of two Rubisco activase polypeptides, but heat stress did not alter the profile of the activase bands. Inhibition of P_n at high leaf temperature could be markedly reduced by artificially increasing C_i. A high C_i also stimulated photosynthetic electron transport and resulted in reduced non‐photochemical fluorescence quenching. Recovery experiments showed that heat‐dependent inhibition of P_n was largely, if not fully, reversible. The present results demonstrate that in Q. pubescens leaves the thylakoid membranes in general and photosynthetic electron transport in particular were well protected against heat‐induced perturbations and that inhibition of P_n by high temperature closely correlated with a reversible heat‐dependent reduction of the Rubisco activation state.     

Effect of water deficit on photosynthetic and other physiological responses in grapevine (Vitis vinifera L. cv. Riesling) plants

The grapevine (Vitis vinifera L. cv. Riesling) plants subjected to water deficit were studied for changes in relative water content (RWC), leaf dry mass, contents of chlorophyll (Chl), total leaf proteins, free amino acids, and proline, and activities of ribulose-1,5-bisphosphate carboxylase (RuBPC), nitrate reductase (NR), and protease. In water-stressed plants RWC, leaf dry matter, Chl content, net photosynthetic rate (P _N), and RuBPC and NR activities were significantly decreased. The total leaf protein content also declined with increase in the accumulation of free amino acids. Concurrently, the protease activity in the tissues was also increased. A significant two-fold increase in proline content was recorded.     

The influence of acid irrigation and liming on the soil microbial biomass in a Norway spruce (Picea abies [L.] K.) stand

Over a period of three years (1990–1992) microbial biomass-C (C_mic), CO₂ evolution, the C_mic:C_org ratio and the metabolic quotient for CO₂ (qCO₂) were determined in a Norway spruce stand (Höglwald) with experimentally acid-irrigated and limed plots since 1984. A clear relationship between soil pH and the level of microbial biomass-(C_mic) was noted, C_mic increasing with increasing soil pH in O_h or A_h horizons. More microbial biomass-C per unit C_{org} (C_mic:C_org ratio) was detected in limed plots with elevated pH of O_h or A_h horizons as compared to unlimed plots with almost 3 times more C_mic per unit C_org in the limed O_h horizon. Differences here are significant at least at the p=0.05 level. The positive effects of liming (higher pH) on the C_mic:C_org ratio was more pronounced in the upper horizon (O_h)). The total CO₂ evolution rate of unlimed plots was only half of that noted for limed plots which corresponded to the low microbial biomass levels of unlimed plots. The specific respiratory activity, qCO₂, was similar and not significantly different between the unlimed control plot and the limed plot.Acid irrigation of plots with already low pH did not significantly affect the level of microbial biomass, the C_mic:C_org ratio or qCO₂. An elevated qCO₂ could be seen, however, for the limed + acid irrigated plot. The biomass seemed extremely stressed, showing with 3.8 g CO₂-C mg_-1 C_mic h_-1 (O_h) the highest qCO₂ value of all treatments. This was interpreted as a reflection of the continuous adaptation processes to the H⁺ ions by the microflora. The negative effect of acid irrigation of limed plots was also manifested in a decreased C_mic:C_org ratio.     

Photosynthesis in rice under a salt stress

In four cultivars of Oryza sativa L., a gradual decrease in the activity of photosystems 1 and 2 as well as in chlorophyll (Chl) fluorescence transients and emission at 688 nm was observed with an increase in NaCl concentration. This decrease was more pronounced in salt-sensitive cultivars as compared to the tolerant ones. A drastic decrease in net photosynthetic rate was found in both cultivar types. This revised version was published online in June 2006 with corrections to the Cover Date.     

Changes in photosynthetic apparatus during dark incubation of detached leaves from control and ultraviolet-B treatedVigna seedlings

Changes in various components of photosynthetic apparatus during the 4 d dark incubation at 25°C of detached control and ultraviolet-B (UV-B) treatedVigna unguiculata L. leaves were examined. The photosynthetic apparatus was more degraded in younger control seedlings and for a longer time UV-B treated seedlings than in the older or for a shorter time UV-B treated seedlings. This was shown by determining the losses in chlorophyll (Chl) and protein contents, variable fluorescence yield, photosystem (PS) 2, PS1 and ribulose-1,5-bisphosphate carboxylase (RuBPC) activities, and photosynthetic¹⁴CO₂ fixation. In contrast, the Car/Chl ratio increased during the dark incubation due to less expressed degradation of Car.     

Ameliorating effect of triacontanol on salt stressedErythrina variegata seedlings. Changes in composition and activities of chloroplasts

The detrimental effect of NaCl was found at the oxidation site of photosystem 2 (PS2). An impairment of PS2 was caused by damage of the oxygen evolving polypeptides (33, 23 and 20 kDa) of thylakoid membranes as well as by changes in the unsaturated and saturated fatty acids. Application of triacontanol, TRIA (1 mg kg^-1) ameliorated the effect of NaCl and promoted the ratio of unsaturated to saturated fatty acids, the rate of¹4CO₂ fixation and the activity of ribulose 1,5-bis-phosphate carboxylase. We thank Prof. T.M. Haridasan for providing laboratory fucilities. Financial support from the Society for Social Forestry Research and Development, Tamilnadu is gratefully acknowledged.