Simple oscillations in photosynthesis of higher plants

Abstract

Illumination of leaves of Vicia faba L. provoked oscillations in the rates of CO 2 uptake and O 2 evolution. The oscillations were marked under anaerobic conditions, but were absent at 20% O 2. The minimum CO 2 concentration required for the appearance of oscillations was 600 μl · l −1. The higher the CO 2 concentration, the stronger the oscillations. The effect of CO 2 concentration was saturated at 1000 μl CO 2 · l −1. The period of the oscillations was 5–6 min at a light intensity of 80 nE · cm −2 · s −1 and became longer on lowering of the intensity. No oscillations appeared at intensities below 12 nE · cm −2 · s −1. Oscillations could also be generated by increasing the CO 2 concentration in the atmosphere during strong illumination under anaerobic conditions. The chlorophyl a fluorescence yield showed oscillations, similar in shape and frequency to those of photosynthesis, after such an environmental change. Oscillations were also observed in photosynthesis of other C 3 plants, Lycopersicon esulentum Mill and Glycine max Merrill, under the same conditions as those required for V. faba, but were absent for the C 4 plants, Zea mays and Amaranthus retroflexus L.