EFFECTS OF SOLAR-RADIATION ON THE PHOTOSYNTHETIC ACTIVITY OF THE RED ALGA CORALLINA-ELONGATA ELLIS ET SOLAND

The photoinhibition of photosynthesis was investigated in two morphoty pes of the red alga Corallina elongata, i.e. sun and shade types, usin g pulse amplitude modulated (PAM) chlorophyll fluorescence and oxygen evolution. The contents of chlorophyll, phycoerythrin, phycocyanin and soluble protein were analysed. Exposure to solar radiation caused a s trong decrease in the effective photosynthetic quantum yield. This dec line was more pronounced in the shade than in the sun morphotype. The plants partially recovered from this effect, indicating that it was ma inly due to reversible photoinhibition and, to a smaller extent, non-r eversible photodamage. Photoinhibition occurred in this alga even in i ts natural habitat when the sun was at high angles. Recovery from phot oinhibition was higher in algae grown in the sun than in the shade. Th e net photosynthetic oxygen production was higher in the shade than in the sun morphotype, A decrease in oxygen evolution was observed at ab out noon, recovering at dusk. The concentrations of chlorophyll a (Chl a) and phycoerythrin were higher in the shade than in the sun morphot ype. The Chl a and phycocyanin contents did not change significantly t hroughout the day, However, a clear daily variation in phycoerythrin c ontent was observed with a strong decrease around noon, The soluble pr otein concentration decreased around noon, but only in the sun morphot ype. The relationship between the photosynthetic quantum yield, oxygen evolution and pigment concentration is discussed, together with photo inhibition. (C) 1997 Elsevier Science S.A.