The marine diatom Skeletonema costatum was grown at different pH values in a semicontinuous cultivation system which kept the pH at a pre-set value. Growth rate was nearly constant at pH 6·5–8·5 (average 2·4 divisions day−1) and declined at pH > 9. Organic carbon (C) production decreased from an average of 5·3 mg l−1 at pH 6·5–8·5 to 2 and 1 mg l−1 at pH 9·0 and 9·4, respectively. Storage β-1,3-linked glucan decreased from a high of 7·1 mg l−1 at pH 6·5 to 0·2 mg l−1 at pH 9·4, and, concomitantly, the percentage of total organic C as glucan C decreased from 60% to 10%. Cellular concentration of amino acids varied from about 62 to 8 mM over the pH range 8·0–9·4. At pH 9·4 the concentration of glutamine was below the detection limit. The extracellular production of carbohydrates in the pH range 6·5–8·5 was only 3·7% (average) of total C production and increased at pH 9·0 and 9·4. The decrease in growth rate at pH > 9·0 might be caused by a decrease in the rate of some important biochemical reactions, as well as by a change in cell membrane properties in this pH range.

Sexually reproducing populations of the marine red alga Peyssonnelia rosenvingii Schmitz (Peyssonneliaceae, Gigartinales), for which only spermatangia and monosporangia, borne on the same thalli, have previously been known, are reported from the cold-temperate region of Japan. Plants are reproductive in late autumn and early winter. Each carpogonial branch consists of four or five cells, and the suprabasal cell of three- to five-celled auxiliary cell branches functions as an auxiliary cell. The absence of spermatangia and the presence of large, non-reproductive plants during the fertile season suggest that the spermatangial sori are ephemeral. After presumed fertilization a connecting filament develops from the hypogynous cell and runs in the horizontal plane. It branches irregularly and fuses with several auxiliary cells, forming several gonimoblasts along its length. Each gonimoblast produces five to eight carposporangial chains in conspicuously elevated nemathecia up to 350 μm high. Tetrasporangia are also formed in similar nemathecia up to 300 μm high and have three- to eight-celled pedicels.

The polarized apical cells of Sphacelaria rigidula display a well-organized cortical F-actin cytoskeleton. This consists of bundles of actin filaments (AFs), assuming definite patterns of organization in different regions of the cell cortex. At the tip region of the apical dome the AFs appear randomly oriented, showing a diffuse fluorescence. Immediately below, at the base of the apical hemisphere, the AFs form a ring-like band around the plasmalemma transverse to the polar cell axis. The rest of the cell cortex is traversed by AFs showing an axial or slightly inclined or helical orientation. Examination of the apical cells of S. rigidula in appropriate thin sections revealed that the wall has a multi-layered structure. In the tip region of the apical dome the cell wall bears randomly oriented cellulose microfibrils (MFs), while in the basal part of the apical dome it is reinforced by a layer of densely arranged transverse MFs. As the cell grows at the apex, the transverse MFs are continuously displaced towards the cell base. Below the transverse MF layer, an additional layer with axial or slightly oblique MFs starts being depositing internally, on the tubular part of the cell. Externally to them, the layer of transversely oriented MFs remains visible. The above observations were confirmed in apical cells of S. tribuloides. MF orientation in the innermost wall layer of the apical cells coincides with that of the cortical AFs observed by fluorescence. This mutual alignment between AFs and MFs in a cell that lacks cortical microtubules (MTs) suggests that the AFs are involved in the oriented deposition of MFs. Experimental disruption of AFs with cytochalasin B caused abnormal MF deposition, a fact strongly supporting the above hypothesis. The transverse MFs forming at the base of the apical dome define the diameter and consequently the cylindrical shape of the apical cells. It is suggested that in the brown algal cells examined the AFs play a morphogenetic role similar to that of cortical microtubules in higher plant cells.