Mechanisms of the acido- and thermo-phily of Cyanidium caldarium Geitler I. Effects of temperature, pH and light intensity on the photosynthetic oxygen evolution of intact and treated cells

Photosynthetic oxygen evolution in an acido- and thermo-philicunicellular alga, Cyanidium caldarium, was measured under variousconditions, using a Clark-type oxygen electrode. 1). Maximum Hill reaction activity with p-benzoquinone as theHill oxidant was obtained at 45°C in a wide pH range from1.0 to 7.0. 2) The pH activity curve showed two peaks at pH3.0 and 7.0. The Hill activity had an optimum at pH 3.0 in cellspreilluminated under strong light (300,000 lux, 30 min, 40°C).Sonication of algal cells abolished the pH 3.0 component ofthe Hill reaction producing an activity maximum at pH 7.0. 3)Endogenous O₂ evolution in the absence of the Hill oxidant,which lasted for several minutes after illumination, had a maximumat pH 7.0. 4) This endogenous O₂ evolution was abolished bysonication. 5) KCN inhibited endogenous O₂ evolution, but notthe Hill reaction in the presence of p-benzoquinone. (Received August 19, 1974; )     

Chloroplast Nucleoids during Greening of Cyanidium caldarium M-8 Type

Cyanidium caldarium M-8 type grown in the dark was illuminatedfor 3 days, and changes of its cell and cell organelle structuresand of photosynthetic activity were observed quantitatively.Dark grown (DG) cells showed no photosynthetic activity andno phycocyanin. During 3 day illumination they fully recoveredtheir photosynthetic activities as measured by Hill reaction,and also synthesized chlorophyll a and phycocyanins. Sizes ofcell, cell nucleus, chloroplast and its nucleoid observed byfluorescence microscopy after staining with DAPI increased simultaneouslyupon illumination. The chloroplast and its ring shaped nucleoidsizes increased especially rapidly, concomitant with the recoveryof Hill activity. In fully recovered cells after 3 days, a goodcorrelation was found among the sizes of cells, chloroplastsand chloroplast nucleoids. ( Revision received June 28, 1986. Accepted December 23, 1986)     

Mechanisms of the acido- and thermo-phily of Cyanidium caldarium Geitler II. Physiological role of the cell wall

1) A partially disintegrated cell preparation of Cyanidium caldarium(i.e. the 100G fraction; cells from which the outer parts ofthe cell wall had been removed) was obtained by differentialcentrifugation of a cell suspension treated with a French press.2) The 100G fraction cells had completely lost the outer partsof their cell walls, but retained their subcellular structureunchanged and had Hill activity that was equally as high asthat of the intact cells. 3) The Hill activity of the 100G fractionshowed an optimum at pH 7.0 and at 35°C. This activity waslost under acid and high temperature conditions (e.g. pH 3,50°C) under which intact cells showed high activity. 4)The Hill activity of the 100G fraction was lost by heat treatment(55°C, 10min), acid-treatment (pH 3.0, 10 min) or pre-illumination(3xl0⁵lux, 30 min) though intact cells were not inactivatedby these treatments. However, no remarkable difference in sensitivitytowards inhibitors was found between the 100G fraction and intactcells. 5) We thus concluded that the cell wall plays an importantrole in the acido- and thermo-phily of Cyanidium cells. (Received August 19, 1974; )