Carbonic anhydrase in Tectona grandis: kinetics, stability, isozyme analysis and relationship with photosynthesis.
ABSTRACT Carbonic anhydrase (CA, EC: 220.127.116.11) activity in teak (Tectona grandis L.f.) was studied to determine its characteristics, kinetics and isozyme patterns. We also investigated effects of leaf age, plant age and genotype on CA activity and gas exchange parameters. Carbonic anhydrase extracted from leaves in 12 mM veronal buffer, pH 7.8, had a K(m) for CO(2) of 15.20 mM and a V(max) of 35,448 U mg(-1) chlorophyll min(-1), which values declined by 50 and 70%, respectively, after 1 week of storage at 4 degrees C. A 15% native polyacrylamide gel revealed the absence of CA isozymes in teak, with only a single CA band of 45 kD molecular mass observed across 10 segregating half-sib families and groups of trees ranging in age from 10 to 25 years. Activity remained stable during the first month in storage at 0 degrees C, but gradually declined to 25% of the initial value after 1 year in storage. During the period of active growth (February-May), maximal CA activity was observed in fully expanded and illuminated leaves. Significant variation was observed in CA activity across 10 1-year-old half-sib families and 21 5-year-old half-sib families. There was a positive correlation between CA activity and photosynthetic rate in a population of 10-year-old trees (P < 0.005). Positive correlations between CA activity and photosynthetic rate were found in 10 of 21 5-year-old half-sib families (P < 0.005 to P < 0.05), which showed greater diversity in CA activity than in photosynthetic characteristics. Thus, CA may serve as a biochemical marker for photosynthetic capacity in teak genotypes.
SourceAvailable from: Michal V Marek[Show abstract] [Hide abstract]
ABSTRACT: We tested the hypothesis that leaf age affects photosynthetic induction, because conductance to CO2 diffusion usually decreases with increasing leaf age. Photosynthetic inductions, primarily determined by the light modulation of Rubisco activity and stomatal opening, were investigated in both young and mature leaves, as defined by leaf plastochron index (LPI), from three poplar clones: Populus alba L., P. nigra L. and P. x euramericana (Dode) Guinier. In all clones, maximum assimilation rates (A max), maximum stomatal conductance (G Smax) and dark respiration rates (RD) were higher in young leaves (LPI = 3-5) than in mature leaves (LPI = 10-14), and A max decreased from P. alba via P. x euramericana to P. nigra. The clones with high photosynthetic capacity had low induction states 60 s after leaf illumination (IS60; indicating a slow initial induction phase), and required less time to reach 90% photosynthetic induction (T90). In contrast, the clone with the lowest photosynthetic capacity (P. nigra) exhibited high IS60 (high initial induction state) but a long induction time (high T90). A comparison of mature leaves with young leaves revealed significantly (P < 0.01) lower IS60 values in mature leaves of P. nigra only, and significantly higher T90 values in mature leaves of P. alba only. In all clones, young leaves exhibited a lower percentage of maximum transient stomatal limitation during photosynthetic induction (4-9%) compared with mature leaves (16-30%). Transient biochemical limitation, assessed on the basis of the time constants of Rubisco activation (tau), was significantly higher in mature leaves than in young leaves of P. alba; whereas there were no significant differences in tau between young and mature leaves of the other poplar clones. Thus, our hypothesis that leaf age affects photosynthetic induction was confirmed at the level of transient stomatal limitation, which was significantly higher in mature leaves than in young leaves in all clones. For the induction parameters IS60, T90 and tau, photosynthetic induction was more clone-specific and was dependent on leaf age only in some cases, an observation that may apply to other tree species.Tree Physiology 08/2008; 28(8):1189-97. DOI:10.1093/treephys/28.8.1189 · 3.41 Impact Factor
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ABSTRACT: Internal conductance to carbon dioxide is a key aspect of leaf photosynthesis although is still not well understood. It is thought that it comprises two components, namely, a gas phase component (diffusion from intercellular spaces to cell walls) and a liquid phase component (dissolution, diffusion in water, hydration equilibrium). Here we use heavy water ( D2O), which is known to slow down CO2 hydration by a factor of nearly three. Using C-12/C-13 stable isotope techniques and Xanthium strumarium L. leaves, we show that the on-line carbon isotope discrimination (Delta C-13, or Delta(obs)) associated with photosynthesis is not significantly decreased by heavy water, and that the internal conductance, estimated with relationships involving the deviation of Delta C-13, decreased by 8-40% in 21% O-2. It is concluded that in typical conditions, the CO2-hydration equilibrium does not exert an effect on CO2 assimilation larger than 9%. The carbon isotope discrimination associated with CO2 addition to ribulose-1,5, bisphosphate by Rubisco is slightly decreased by heavy water. This effect is proposed to originate from the use of solvent-derived proton/deuteron during the last step of the catalytic cycle of the enzyme (hydration/cleavage).Functional Plant Biology 01/2008; 35(3). DOI:10.1071/FP07282 · 2.57 Impact Factor
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ABSTRACT: During photosynthesis, CO2 moves from the atmosphere (C(a)) surrounding the leaf to the sub-stomatal internal cavities (C(i)) through stomata, and from there to the site of carboxylation inside the chloroplast stroma (C(c)) through the leaf mesophyll. The latter CO2 diffusion component is called mesophyll conductance (g(m)), and can be divided in at least three components, that is, conductance through intercellular air spaces (g(ias)), through cell wall (g(w)) and through the liquid phase inside cells (g(liq)). A large body of evidence has accumulated in the past two decades indicating that g(m) is sufficiently small as to significantly decrease C(c) relative to C(i), therefore limiting photosynthesis. Moreover, g(m) is not constant, and it changes among species and in response to environmental factors. In addition, there is now evidence that g(liq) and, in some cases, g(w), are the main determinants of g(m). Mesophyll conductance is very dynamic, changing in response to environmental variables as rapid or even faster than stomatal conductance (i.e. within seconds to minutes). A revision of current knowledge on g(m) is presented. Firstly, a historical perspective is given, highlighting the founding works and methods, followed by a re-examination of the range of variation of g(m) among plant species and functional groups, and a revision of the responses of g(m) to different external (biotic and abiotic) and internal (developmental, structural and metabolic) factors. The possible physiological bases for g(m), including aquaporins and carbonic anhydrases, are discussed. Possible ecological implications for variable g(m) are indicated, and the errors induced by neglecting g(m) when interpreting photosynthesis and carbon isotope discrimination models are highlighted. Finally, a series of research priorities for the near future are proposed.Plant Cell and Environment 06/2008; 31(5):602-21. DOI:10.1111/j.1365-3040.2007.01757.x · 5.91 Impact Factor