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Growth at elevated CO 2 : photosynthetic responses mediated through Rubisco
Author(s) -
BOWES G.
Publication year - 1991
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1991.tb01443.x
Subject(s) - rubisco , photorespiration , photosynthesis , carbon fixation , chloroplast , biology , ribulose , acclimatization , biochemistry , pyruvate carboxylase , botany , chemistry , enzyme , gene
. The global uptake of CO 2 in photosynthesis is about 120 gigatons (Gt) of carbon per year. Virtually all passes through one enzyme, ribulose bisphosphate carboxylase/oxygenase (rubisco), which initiates both the photosynthetic carbon reduction, and photorespiratory carbon oxidation, cycles. Both CO 2 and O 2 are substrates; CO 2 also activates the enzyme. In C 3 plants, rubisco has a low catalytic activity, operates below its K m (CO 2 ), and is inhibited by O 2 . Consequently, increases in the CO 2 /O 2 ratio stimulate C 3 photosynthesis and inhibit photorespiration. CO 2 enrichment usually enhances the productivity of C 3 plants, but the effect is marginal in C 4 species. It also causes acclimation in various ways: anatomically, morphologically, physiologically or biochemically. So, CO 2 exerts secondary effects in growth regulation, probably at the molecular level, that are not predictable from its primary biochemical role in carboxylation. After an initial increase with CO 2 enrichment, net photosynthesis often declines. This is a common acclimation phenomenon, less so in field studies, that is ultimately mediated by a decline in rubisco activity, though the RuBP/P i ‐regeneration capacities of the plant may play a role. The decline is due to decreased rubisco protein, activation state, and/or specific activity, and it maintains the rubisco fixation and RuBP/P i regeneration capacities in balance. Carbohydrate accumulation is sometimes associated with reduced net photosynthesis, possibly causing feedback inhibition of the RuBP/P i regeneration capacities, or chloroplast disruption. As exemplified by field‐grown soybeans and salt marsh species, a reduction in net photosynthesis and rubisco activity is not inevitable under CO 2 enrichment. Strong sinks or rapid translocation may avoid such acclimation responses. Over geological time, aquatic autotrophs and terrestrial C 4 and CAM plants have genetically adapted to a decline in the external CO 2 /O 2 ratio, by the development of mechanisms to concentrate CO 2 internally; thus circumventing O 2 inhibition of rubisco. Here rubisco affinity for CO 2 is less, but its catalytic activity is greater, a situation compatible with a high‐CO 2 internal environment. In aquatic autotrophs, the CO 2 concentrating mechanisms acclimate to the external CO 2 , being suppressed at high‐CO 2 . It is unclear, whether a doubling in atmospheric CO 2 will be sufficient to cause a de‐adaptive trend in the rubisco kinetics of future C 3 plants, producing higher catalytic activities.