Changes in Photosynthetic Capacity and Activity of RuBPC-ase and Glycolate Oxidase during the Early Growth of Moss Protonemata in Continuous and Rhythmic Light

Abstract

Summary Photosynthetic activities in the protonema of Ceratodon were followed during two weeks in rhythmic and continuous light. In continuous light, the rates of CO2 fixation were high two days after sowing. In rhythmic light, the period of high fixation continued until the fifth day after sowing. The CO2 fixation rates calculated on the basis of the dry weight and the chlorophyll content decreased in both light conditions, but ageing was much faster in continuous light. Photosystem II activity (oxygen evolution) was decreased by continuous light as well as age, whereas photosystem I activity (oxygen consumption) was mostly affected only by ageing. RuBPC-ase activity first increased and then decreased in continuous light, but did not reach its peak in rhythmic light. Glycolate oxidase activities were very low in both light conditions. The declining CO2 fixation seemed to correlate more closely with the decreasing photosystem II activity and increasing thickness of the cell wall, than with the activities of the assayed enzymes.