The relationship between steady-state gas exchange of bean leaves and the levels of carbon-reduction-cycle intermediates

The relationship between the gas-exchange characteristics of attached leaves of Phaseolus vulgaris L. and the pool sizes of several carbon-reduction-cycle intermediates was examined, and very high levels of PGA and other phosphate-containing compounds were found with some conditions, especially under low oxygen.

Abstract

The relationship between the gas-exchange characteristics of attached leaves of Phaseolus vulgaris L. and the pool sizes of several carbon-reduction-cycle intermediates was examined. After determining the rate of CO2 assimilation at known intercellular CO2 pressure, O2 pressure and light, the leaf was rapidly killed (<0.1 s) and the levels of ribulose-1,5-bisphosphate (RuBP), 3-phosphoglyceric acid (PGA), fructose-1,6-bisphosphate, fructose-6-phosphate, glucose-6-phosphate, glyceraldehyde-3-phosphate, and dihydroxyacetone phosphate were measured. In 210 mbar O2, photosynthesis appeared RuBP-saturated at low CO2 pressure and RuBP-limited at high CO2 pressure. In 21 mbar (2%) O2, the level of RuBP always appeared saturating. Very high levels of PGA and other phosphate-containing compounds were found with some conditions, especially under low oxygen.