Non-osmotic effects of external sugars on the cell water content and transport of cations across the plasmalemma inHydrodictyon reticulatum.

Saccharides added to the cultivation medium influence the properties of the cell wall of the strictly autotrophic green algaHydrodictyon reticulatum, most probably in such a way that they interfere with the processes of growth and repair of microfibrils. Natural monosaccharides (glucose, fructose, galactose, mannose, sucrose, cellobiose, raffinose) reduce the cell water content, increase the intracellular concentration mostly of both potassium and sodium cations and reduce the ohmic resistance of the cell membrane.

Effects of external saccharides on cell wall properties and ion transport inHydrodictyon reticulatum.

Various saccharides, when present at osmotically insignificant concentrations in growth media, were tested as to their effects on the cell walls of the green algaHydrodictyon reticulatum, manifesting themselves in differences in cell water and ion contents. BothD: -xylose andD: -mannose reduce the cell water content andD: -galactose does occasionally the same but onlyD: -xylose reduces significantly the intracellular sodium concentration, presumably by forming steric hindrances at the outlets of the sodium pumps at the outer surface of the cell membrane. No significant effects of eitherL: -arabinose orD: -arabinose on the cell water and ion contents were found.

Cell volume regulation in Claviceps fusiformis. An animal-type Na,K-ATPase operating in a fungus?

Claviceps fusiformis, an ergot pathogen of pearl millet, was equilibrated in media without and with 0.1 mM ouabain (g-strophantin). Highly significant effects of ouabain on the contents of sodium ions and water were found, suggesting that an active transport of sodium ions, similar to that in animal cells, regulates the cell volume of the fungus. The basic role of the sodium pump appears to be to decrease larger cell volumes and to increase the small ones; for this purpose it can even reverse its direction.

Ba2+ ions hyperpolarize algal cell membrane and enhance plasmalemma resistance without affecting ion and water contents.

Culturing the fresh-water alga Hydrodictyon reticulatum for 9 days in the presence of 0.2 and 0.4 mmol/l Ba2+ increases the membrane potential about twice and the plasmalemma resistance 5-10 times without having any significant effect on the cell contents of water and Na+, K+ and Cl- ions. While in control cells the membrane potential is determined by the diffusion potential of K+, in Ba(2+)-treated cells the factor determining membrane potential and resistance is the unequal distribution of protons across the membrane.

The plasmalemma redox system of a fresh-water alga and membrane electrical parameters.

In order to learn more details about the plasmalemma redox system in the alga Hydrodictyon reticulatum the electrophysiological characteristics of the plasma membrane as influenced by artificial electron acceptors were estimated. Ferricyanide anion as well as TTF+ depolarized the membrane potential, the effect being more marked in the dark than in the light. In the presence of ferricyanide the membrane resistance in the light was decreased by about 29% on the average, in the dark it remained unchanged. On the other hand, TTF+ brought about a large increase in membrane resistance, notwithstanding the light conditions. The results are discussed in view of the impairing influence of both electron acceptors on the active inflow of chloride ions (Rybová, R. et al. (1990) Bot. Acta 103, 404-407). The electrogenic outflow of electrons appears to make the largest contribution to the membrane depolarization. The inhibition of a pumping mechanism coupling the active uptake of Cl- in some way to the transmembrane electron flow is envisaged as a plausible explanation for membrane resistance increase by TTF+.

Effects of amiloride on the transport of sodium and other ions in the alga Hydrodictyon reticulatum.

The diuretic amiloride, an almost specific inhibitor of sodium transport in animal cells and tissues, appears to produce a number of effects in the alga Hydrodictyon reticulatum. At 1 mmol/l concentration it markedly reduces the influx of sodium ions (but not their active outflux), the influxes of potassium, chloride as well as of bicarbonate ions, and causes a profound decrease in the plasmalemma membrane potential. This plurality of inhibitory effects suggests that individual transport processes in the alga are mutually coupled.