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Plant and Cell Physiology, 1987, Vol. 28, No. 6 1141-1152
© 1987

Article

Control of Photosynthesis in Wheat by CO2, O2 and Light Intensity

John Kobza1 and Gerald E. Edwards2

Department of Botany, Washington State University Pullman, Washington 99164-4230, U.S.A.

2 To whom reprint requests should be sent.

The regulation of photosynthesis in wheat leaves under varying O2, CO2, and light was studied by analyzing certain metabolite pools and enzyme activities. Under high light when the rate of photosynthesis was limited by low intercellular levels of CO2 (C1) there was a high level of ribulose-1,5-bisphosphate (RuBP) (about 100 nmols per mg chlorophyll). As C, increased, there was a parallel decrease in the ratios of RuBP/3-phosphoglycerate (PGA) (from 0.18 to 0.08 under 21% O2) and triose-phosphate/PGA (from 0.16 to 0.07 under 21% O2). The results suggest carboxylation is limited at low Ci, and that there is high carboxylation and limited assimilatory power at high Ci. As photosynthesis increased with increasing Jight intensity under atmospheric levels of CO2 the ratios of RuBP/PGA and triosephosphate/PGA remained nearly constant (near 0.12 to 0.13) suggesting there may be a coordinate regulation by light of the different phases of the cycle. There was increasing activation of ribulose 1,5-bisphosphate carboxylase oxygenase (Rubisco) and fructose 1,6-bisphosphatase (FBPase) with increasing light intensity. The ways in which the light activation of the enzymes Rubisco and FBPase may regulate carbon metabolism in the cycle are discussed.

1 Current address: Biological Sciences Center, Desert Research Institute, PO Box 60220, Reno, Nevada 89506, U.S.A.

(Received March 24, 1987; Accepted June 23, 1987)
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