Increased CO2fixation byPisum sativumchloroplastsin vitroreflecting a change in coupling caused by illuminating the plants

摘要

Illumination of pea plants caused a doubling in the rate of CO2fixation by the subsequently isolated chloroplasts compared with the rate obtained for chloroplasts from plants in the dark. This enhancement in the CO2fixation rate was half-maximal for 800 lux incident on the plants and was 90%light saturated at 2000 lux. The half-time for the enhancement of the CO2fixation rate following illumination of the plants was about 4 min and the half-time for its reversal when the plants were placed back in the dark was 5 min. Illuminating the plants had relatively little effect on the O2evolution rate of the subsequently isolated chloroplasts. Moreover, the ferricyanide reduction rate by the isolated chloroplasts was also essentially unaffected by the illumination condition of the plants from which the chloroplasts were isolated. Consequently, light on the plant apparently causes a doubling in the CO2fixed per electron moving in the photosynthetic electron transport pathway. This enhanced coupling is discussed in terms of a concomitant increase in endogenous photophosphorylation and flattening of the chloroplastsin vivo, other changes caused by light incident on the plant.