Prochlorothrix Hollandica is more Sensitive to Photoinhibition than Chlamydomonas Reinhardtii

Abstract

Prochlorothrix hollandica belongs to Prochlorophyta (Lewin, 1976), a group of oxygenic photosynthetic prokaryotes assumed to be related to the progenote of the chloroplasts of higher plants and green algae (Barber, 1986). Unlike cyanobacteria, P. hollandica lacks phycobilisomes and possesses a chlorophyll a/b antenna complex which is however different from the light harvesting complex of photosystem (PS) II from chloroplasts of higher plants (Bullerjahn et al., 1987; Bullerjahn et al., 1990). In P. hollandica this membrane intrinsic pigment-protein complex appears to be associated with PS I (Bullerjahn et al., 1987; Bullerjahn et al., 1990). To date, no peripheral antenna was found to be bound to PS II of P. hollandica. Another important feature characterizing the P. hollandica thylakoids is the membrane morphology. In the chloroplast the photosynthetic membranes are structurally and functionally differentiated into appressed (grana) and nonappressed regions (stroma membranes) and their various membrane complexes are segregated in these two different membrane domains. PS II is mostly localized in the grana whereas PS I is restricted to the stroma membranes. In cynaobacteria the thylakoids do not display such spatial differentiation and segragation of the two photosystems is not observed. P. hollandica contains very limitted grana formations (Burger-Wiersma et al., 1986) and hence uneven distribution of PS I and PS II is very unlikely.