Correlated influence of cation concentration and excitation intensity on PS II activity-II. Comparative study between green plant and brown-alga chloroplasts

Abstract

A preparation of photochemically active chloroplasts of Fucus was added to a low-salt medium with high osmolarity (HEPES AMPD buffer, 1M sorbitol). The rate of DCIP reduction (DCIPr) and the variable fluorescence (Fv) of these phaeoplasts were measured and compared with the same activities in spinach chloroplasts. A study of the influence of mono- and divalent-cations showed that salt effects on PS II activity also exist in Fucus. (i) Mg(++) action on Fv is similar, although noticeably weaker in Fucus than in spinach chloroplasts. (ii) Na(+) has no effect on Fv of Fucus chloroplasts, but its influence on DCIPr is more pronounced than in spinach. (iii) Mg(++) influence on DCIPr is largely dependent upon excitation energy. In subsaturating light (100\2-1000 W m(\t-2)), Mg(++) stimulation increases up to 100 mM, almost doubling the level. In very low wight conditions (3Wm(\t02)), however, this stimulation saturates at about 10 mM; higher concentrations are no longer effective but do not quench DCIPr noticeably, unlike the case in spinach. Therefore, cations act through similar pathways on Fucus as on spinach isolated chloroplasts but the effects on PS II centers are preponderant in Fucus whereas the modifications in non-radiative decay or pigment array size are weaker.

Subunit organization of PSI particles from brown algae and diatoms: polypeptide and pigment analysis

“…Chloroplasts were prepared according to Berkaloff and Duval (1980): the thalli were ground 2 x 30s in a Turmix blendor in a 50 mM Hepes-Na buffer (pH 7.4), 2 mM MgC12, 2 mM MnC12, 10 mM KC1, 1 M sorbitol; the cell homogenate was filtered through Blutex and centrifuged at 35 x g for 5rain; the supernatant was centrifuged twice at 1300 x g for 10min and resuspended in a 10raM Hepes-Na buffer (pH 7.4), with the same additives as above at a chlorophyll concentration of 100/~g Chl a/ml. Digitonin was added at a detergent/Chl ratio of 100 just before the homogenate was passed through a French pressure cell (2 x 136 MPa), incubated for one hour at room temperature, then loaded on the top of a sucrose gradient and centrifuged at 140000 x g during 15h (Caron et al 1985).…”

In vivo ANALYSIS OF SLOW CHLOROPHYLL FLUORESCENCE INDUCTION KINETICS IN ALGAE: PROGRESS, PROBLEMS AND PERSPECTIVES

“…In higher plants, a correlation exists between the cation-induced changes in the degree of stacking and variable fluorescence yield. Cationdcpendent changes of fluorescence are measurable in Fucus,73…”

Fucoxanthin-Chlorophyll a/c Light-Harvesting Complexes of Laminaria saccharina: Partial Amino Acid Sequences and Arrangement in Thylakoid Membranes

“…Thylakoid and LHC Preparations. Procedures followed for the preparation of chloroplasts from brown algae have been published by our laboratory (Berkaloff & Duval, 1980). All the buffers used contained protease inhibitors (1 mM benzamidine and 1 mM PMSF).…”