When mannose is provided in the transpiration stream to spinach (Spinacia oleracea) leaf discs, a series of specific and nonspecific changes occur in CO(2) and H(2)O vapor exchange as a function of feeding time. The initial increases in apparent photosynthesis and transpiration are nonspecific effects due to osmotic changes leading to passive stomatal opening. The mannose-specific effects are: (a) time-dependent changes in the CO(2) concentration required for saturation; (b) complex kinetics of the inhibition of CO(2) assimilation dependent on CO(2) and O(2) concentrations and the duration of feeding (high CO(2) and low O(2) lead to rapid inhibitions of photosynthesis); (c) elimination of the capacity of 2% O(2) to stimulate photosynthesis; and (d) oscillations in the CO(2) exchange rate following transitions from 20% to 2% O(2). The mannose-specific effects are reversible by orthophosphate. The mannose-dependent changes in gas exchange are attributed to altered [ATP]/[ADP] ratios.