The combined effects of light intensity and continuous light on the CO2 fixation, chlorophyll content and chloroplast structure of the protonema of Ceratodon purpureas

Abstract

Summary The effects of two light intensities, 200μW/cm 2 and 1400 μW/cm 2 , were studied in combination with the effects of continuous and rhythmic light. Estimated on the basis of dry weight, the rate of CO 2 fixation was lower in continuous than in rhythmic light at both intensities. Estimated on the basis of the chlorophyll content, the rate of CO 2 fixation at a certain stage of differentiation was higher in continuous light of high intensity than in rhythmic light. The chlorophyll content was greater at the low than at the high light level in both rhythmic and continuous light, but the difference was more pronounced in continuous light. Irrespective of the light intensity the chloroplasts were more rounded in continuous light, being longer and narrower in rhythmic light. The size of the grana was greater in continuous light and this effect was also independent of light intensity. The chlorophyll a/b ratio was lower at the low light intensity and in continuous light, being inversely proportional to the number of lamellae per granum.