Photosynthetic capacity (A
max) is a measure of the maximum rate at which leaves are able to
fix carbon during
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
. It is typically measured as the amount of carbon dioxide that is fixed per metre squared per second, for example as μmol m
−2 sec
−1.
Limitations
Photosynthetic capacity is limited by carboxylation capacity and electron transport capacity. For example, in high carbon dioxide concentrations or in low light, the plant is not able to regenerate
ribulose-1,5-bisphosphate
Ribulose 1,5-bisphosphate (RuBP) is an organic substance that is involved in photosynthesis, notably as the principal acceptor in plants. It is a colourless anion, a double phosphate ester of the ketopentose (ketone-containing sugar with five car ...
fast enough (also known RUBP, the acceptor molecule in photosynthetic carbon reduction). So in this case, photosynthetic capacity is limited by electron transport of the light reaction, which generates the NADPH and ATP required for the PCR (Calvin) Cycle, and regeneration of RUBP. On the other hand, in low carbon dioxide concentrations, the capacity of the plant to perform
carboxylation
Carboxylation is a chemical reaction in which a carboxylic acid is produced by treating a substrate with carbon dioxide. The opposite reaction is decarboxylation. In chemistry, the term carbonation is sometimes used synonymously with carboxylatio ...
(adding carbon dioxide to
Rubisco
Ribulose-1,5-bisphosphate carboxylase-oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is con ...
) is limited by the amount of available carbon dioxide, with plenty of Rubisco left over.¹ Light response, or photosynthesis-irradiance, curves display these relationships.
Current Research
Recent studies have shown that photosynthetic capacity in leaves can be increased with an increase in the number of
stomata per leaf. This could be important in further crop development engineering to increase the photosynthetic efficiency through increasing diffusion of carbon dioxide into the plant.²
References
* Hopkins, William G. and N. P. A. Hüner. 2009. Introduction to Plant Physiology, 4th ed. John Wiley & Sons, Inc.
* Tanaka, Y., S. S. Sugano, T. Shimada, and I. Hara-Nishimura. 2013. Enhancement of leaf photosynthetic capacity through increased stomatal density in ''Arabidopsis''. New Phytologist 198: 757–764.
Plant physiology
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