C₃ plants enhance rates of photosynthesis by reassimilating photorespired and respired CO₂

Abstract

Photosynthetic carbon gain in plants using the C3 photosynthetic pathway is substantially inhibited by photorespiration in warm environments, particularly in atmospheres with low CO2 concentrations. Unlike C4 plants, C3 plants are thought to lack any mechanism to compensate for the loss of photosynthetic productivity caused by photorespiration. Here, for the first time, we demonstrate that the C3 plants rice and wheat employ a specific mechanism to trap and reassimilate photorespired CO2. A continuous layer of chloroplasts covering the portion of the mesophyll cell periphery that is exposed to the intercellular air space creates a diffusion barrier for CO2 exiting the cell. This facilitates the capture and reassimilation of photorespired CO2 in the chloroplast stroma. In both species, 24-38% of photorespired and respired CO2 were reassimilated within the cell, thereby boosting photosynthesis by 8-11% at ambient atmospheric CO2 concentration and 17-33% at a CO2 concentration of 200 mmol mol -1 . Widespread use of this mechanism in tropical and subtropical C3 plants could explain why the diversity of the world's C3 flora, and dominance of terrestrial net primary productivity, was maintained during the Pleistocene, when atmospheric CO2 concentrations fell below 200 mmol mol -1 .

Coordination of Leaf Photosynthesis, Transpiration, and Structural Traits in Rice and Wild Relatives (Genus Oryza)

“…Also, the relative positions of mitochondria and peroxisomes compared with chloroplasts in lobed M cells ( Fig. 1; Sage and Sage, 2009) may enhance CO 2 refixation (Busch et al, 2013).…”

Initial Events during the Evolution of C4 Photosynthesis in C3 Species of Flaveria

“…As an indicator of photorespiratory CO 2 refixation, C* has advantages over the commonly used parameter G. Rubisco carboxylation capacity, R d , CO 2 refixation, and the oxygenationto-carboxylation ratio of Rubisco influence G (Tholen et al, 2012;Busch et al, 2013), whereas C* is largely a function of the refixation of (photo)respired CO 2 and the oxygenation-to-carboxylation ratio of Rubisco (von Caemmerer, 2000;Busch et al, 2013). All of the Flaveria species in this study have similar Rubisco specificity factors and, hence, similar oxygenation potentials (Kubien et al, 2008).…”

The Costs of Photorespiration to Food Production Now and in the Future

“…Although carbon dioxide transfer to the chloroplast has generally been considered to be a single diffusive path, as shown by Equation 4, evidence from photosynthetic isotope discrimination and subambient carbon dioxide concentrations has suggested that photorespiratory release from the mitochondria could justify a more complicated model (17,71,72,77) (Figure 2). This extended model partitions photorespired carbon loss between reentry into the chloroplast and release into the intercellular air space.…”