Raising rice yield potential by manipulating photosynthesis: improvement of radiation conversion efficiency
2001
Murchie, E.H. | Hubbart, S. | Peng, S. and Horton, P.
Projected increases in rice grain yield are likely to require an increased rate of biomass production, which will demand a greater canopy phoyosynthetic assimilation rate (CAP). There is evidence that the radiation-conversion efficiency (RCF: the aboveground biomass produced per unit of radiation energy intercepted) for rice is lower than that of other C3 crops. One of the components of CAP is the leaf-level photosynthetic rate (P). We have investigated variation in light-saturated photosynthetic rates (Pmax) of rice plants in the field. We compared IR72 and the new plant type (NPT) and examined responses to (1) leaf age during grain filling and (2) position within the rice canopy. Photosynthesis during grain filling accounts for between 60% and 100% of the carbon in mature rice grain: following flowering, Pmax in the flag leaf either declined gradually (IR72) or was generally sustained for the greater part of the grain-filling period (NPT). In both cases, it was difficult to link changes in photosynthe is to the decline in Rubisco content. In fact, a rise in Rubisco content was noted after flowering, which did not correspond to a change in Pmax. Pmax declined according to leaf position within the canopy; this was linked to available light at each position and also occurred alongside a reduction in Rubusco content. However, Pmax of the NPT was considerably lower than that of IR72. An improved RCF could occur by raising leaf-level Pmax and by improving the photosynthesis responses of leaves lower in the canopy to high light. A coordination of biochemical and whole-plant studies will be needed.
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