summary
Genotypic variation in the temperature optimum for resource-saturated growth of microalgae has been used to provide envelopes of μm (maximum specific growth rate) as a function of temperature. The Q10 value for μm for batch-cultured algae with optimal growth temperatures in the range 5–40°C is 1.88; rather higher values (Q10= 2.08–2.19) are found, albeit with lower μ values at a given temperature, for continuous cultures. The envelope approach selects μ values for the smallest cells from the taxa (members of the Chlorophyta and Bacillariophyta) with the highest μ values at a given temperature. Larger cell size, or membership of the Dinophyta, gives a decreased μ at a given temperature. Phenotypic change in μ, within a given genotype grown at sub-optimal temperatures, has a Q10 in excess of 1.88. Analysis of constraints on the resource-saturated value of μ in the fastest-growing micro-algae suggest that, at their temperature optima, the cells are close (within a factor of 2) to their maximum potential growth rate, based on the known kinetic properties of their catalysts, the need for kinetic heterogenity in catalyses in metabolic pathways, and the need to allocate some cell resources to structural and storage components. Phenotypic and genotypic responses to lower temperatures for growth, in terms of reallocation of resources to increase the quantity per unit biomass of catalyst? as a means of offsetting lower catalytic capacity at lower temperatures, are limited. An exception is the light-harvesting and reaction centre apparatus which catalyses the temperature-insensitive processes of light absorption, excitation energy transfer and primary photochemistry, and which is present (as assayed by photosynthetic pigment per unit biomass) in smaller relative amounts during resource-saturated growth at lower temperatures. The involvement of other low-temperature ‘adaptations’ (e.g. homeoviscous behaviour of thylakoid membranes) in offsetting low temperature effects on catalytic rates is not clear. The scope for increasing the quantity of temperature-sensitive catalysts in the biomass as a means of offsetting the effects of low temperature on resource-saturated μ is potentially higher in the Dinophyta with their relatively low μ at their temperature optimum; however, this option does not appear to be taken up by the Dinophyta which have unexceptional Q10 values for μ.

For resource-limited growth, the phenotypic effect of suboptimal temperatures on growth, when light is the limiting resource, is often less marked than when growth is light saturated. When a chemical nutrient is limiting, the temperature effect on growth of a given genotype is often, but not invariably, decreased. Cases in which the effect of temperature on growth rate is decreased under light-limiting conditions can be interpreted in terms of the intrinsically low Q10 of growth when temperature-insensitive reactions (light absorption, excitation energy transfer, primary photochemistry) are limiting and the acclimatory effects of changed temperature and light regimes for growth on resource allocation between pigment-protein complexes and downstream catalysts of temperature-sensitive reactions. Cases in which light-limited growth rate is quite temperature sensitive may be accounted for by a decrease in absorptance as a result of a lower pigment content per cell at low growth temperatures. For growth limited by chemical nutrients, the variable responses make analysis difficult. It is tempting to assign a low Q10 for μ under these conditions to a limitation by some transport process (diffusion through unstirred layers, or, less plausibly, the cell membrane) with a low Q10, although the evidence favouring this interpretation is not abundant.

https://nph.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1469-8137.1988.tb00282.x

Temperature and algal growth

Water balance in land arthropods

There are many good treatments of water relations of plants, plant cells and plant tissues such as those by Dainty (1963 a), Slatyer (1967), Briggs (1967), Weatherley (1970) and, most recently, the excellent general book by House (1974) covering both plant and animal cells and tissues. There are also many articles in the old Encyclopedia of Plant Physiology, and there is the collection of articles in the three volumes edited by Kozlowski (1968 a, b; 1972).

Water Relations of Plant Cells

Extracellular ionic variations during spreading depression

Morphological and physiological studies indicate multiple routes for transport across capillary endothelium. However, the identification of the morphological counterparts of specific transport processes (or the assignment of specific transport roles to morphologically identifiable pathways) has been only partly achieved: the contribution of endothelial cell membranes to transport of water and small, lipid-insoluble molecules needs to be evaluated. The identification of the "small pore" pathway for water and lipid-insoluble molecules with the intercellular junctions still remains questionable. The contributions to total macromolecular transport of junctions, single vesicles (pinocytosis, cytopempsis), chains of vesicles, and fenestrae are not yet known.

Charles Randall. House

Papers

Water transport in cells and tissues