Modelling ¹⁸O₂ and ¹⁶O₂ unidirectional fluxes in plants. IV: Role of conductance and laws of its regulation in C₃ plants

详细信息    查看全文

• 作者：Marcel J. Andr¨¦
• 关键词：CO2 transfer ; Diffusion resistance ; Photorespiration rate ; Oxygenation capacity ; Atmosphere regulation ; Plant&ndash ; atmosphere coevolution
• 刊名：Biosystems
• 出版年：2013
• 出版时间：August, 2013
• 年：2013
• 卷：113
• 期：2
• 页码：115-126
• 全文大小：1359 K

文摘

Numerous studies focus on the measurement of conductances for CO₂ transfer in plants and especially on their regulatory effects on photosynthesis. Measurement accuracy is strongly dependent on the model used and on the knowledge of the flow of photochemical energy generated by light in chloroplasts. The only accurate and precise method to quantify the linear electron flux (responsible for the production of reductive energy) is the direct measurement of O₂ evolution, by ¹⁸O₂ labelling and mass spectrometry. The sharing of this energy between the carboxylation (P) and the oxygenation of photorespiration (PR) depends on the plant specificity factor (Sp) and on the corresponding atmospheric concentrations of CO₂ and O₂ (). The concept of plant specificity factor simplifies the equations of the model. It gives a new expression of the effect of the conductance (g) between atmosphere and chloroplasts. Its quantitative effect on photosynthesis is easy to understand because it intervenes in the ratio of the plant specificity factor (Sp) to the specificity of Rubisco (Sr). Using this ¡®simple¡¯ model with the data of ¹⁸O₂ experiments, the calculation of conductance variations in response to CO₂ and light was carried out.

The good fitting of experimental data of O₂ and CO₂ exchanges confirms the validity of the simple model. The calculation of conductance variation during the increase of external CO₂ concentration reveals a linear law of regulation between external and internal CO₂ concentrations. During CO₂ variations, the effects of g regulation tend to maintain a higher level of oxygenation (PR) in expense of a better carboxylation (P). Contrary to CO₂, the variation of O₂ creates a negative feedback effect compatible with a stabilization of atmospheric O₂. The regulation of g amplifies this result. The effect of light in combination with CO₂ is more complex. Below 800 ¦Ìmol quanta m^-2 s^-1 the ratio PR/P is maintained unchangeable in expense of carboxylation efficiency. Above that irradiance value, PR/P increases dramatically. It appears that the saturation curves of photosynthesis under high light could be simply due to the regulation by the conductance g and not by any biochemical or biophysical limitation. In conclusion, the regulatory effect of conductance operates in a way that it preserves the rate of photorespiration. This confirms a positive and protective role of photorespiration at the biochemical, whole plant and atmosphere levels. Since the effects of photorespiration are linked to the properties of Rubisco, they add new arguments for a co-evolution of plant and atmosphere, including the evolution of CO₂ conductance.