Phytochrome-Dependent Regulation of CO2 Gas Exchange and Switching Between Respiratory and Photosynthetic Carbon Metabolism in Wheat Leaves.

The spectral composition of light in the red and far-red bands is an essential environmental factor regulating plant growth. The rate of PAR-saturated CO2 assimilation of the dark-adapted plants increased 2.7-fold after short-term red-light irradiation. Dark respiration decreased and the ratio photosynthesis/respiration increased from 2.7 to 12.4. The activity of the NAD-glyceraldehyde phosphate dehydrogenase decreased by 40%-50%, while the activity of the NADP-enzyme increased by 1.8-2.0-fold, and the carboxylase activity of Rubisco increased by 2.5-3.0-fold. The activities of both dehydrogenases were returned to control levels by plants being exposed to far red light. Rubisco activity was also returned to near control levels. The dose dependence of NADP-glyceraldehyde phosphate dehydrogenase activity increased linearly up to 17-20 kJ m-2 red light, and the NAD-dependent one decreased linearly up to 8-10 kJ m-2 red light. The fresh and dry weight of whole plants increased by 40%-45% when they were exposed to short-duration red light for 15 days. The results suggest that phytochrome is involved in switching from dark respiratory metabolism to photosynthetic metabolism and leads to the accumulation of additional plant biomass during ontogeny.