Effect of Continous Light on CO2 Fixation and Chloroplast Structure of the Mosses Pleurozium schreberi and Ceratodon purpureus

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Abstract
When the mosses Pleurozium schreberi (Brid.) Mitt, and Ceratodon purpureus (Hedw) Brid. were exposed for 4 week to either continuous or rhythmie light of 75 or 150 μE m−2 s−1, the photosynthetic rate, calculated on the basis of chlorophyll and of dry weight, was lower in the moss plants exposed to continuous light. RUBP‐carboxylase activity was lower in these plants, too. On the other hand more starch was accumulated in the chloroplasts in continuous than in rhythmic light. Neither moss species showed any differences in the dark respiration rates. The chlorophyll content was lower in continuous light, especially at the higher intensity; but Chi a/Chl b ratio showed little change compared with that in rhythmic light. The reduction of chlorophyll did not affect the two chlorophyll protein complexes equally; the percentage of chlorophyll associated with CP I decreased, while that associated with CP II showed liltle change. The decrease in CP I chlorophyll appeared to be due to the partial destruction of stroma thylakoids: the size or the grana increased in continuous light. Many of the effects of continuous light in these mosses resembled those observed in higher plants in the early phases of senescence.