The efflux of inorganic sulphur from spinach chloroplasts

The Effect of pH on the Uptake of 35S(-II) by Wine Yeasts

The rates of uptake of 35S from S(-II) solutions by wine yeasts, Saccharomyces cerevisiae strains R92 and R104 and Saccharomyces chevalieri strain R93, were measured at a variety of solution pH values between pH 3.1 and pH 7.8. A pH effect was observed, the rates of uptake being higher at the lower pH values, but this effect was not related entirely to changes in the H2S or HS- concentration. The transport process of S(-II) appeared to be due to simple diffusion of H2S(aq) and carrier mediated transport of HS-(aq). The kinetic constants Km and V max were calculated for the carrier component of the mechanism at pH 7.2 and the permeability coefficient P was calculated for the diffusion of H2S(aq) at pH 3.1 and 7.2. By using these parameters, it was possible to calculate a theoretical ini tial rate of uptake over a range of extracellular S(-II) concentrations (0 to 50 mmoll-1) at pH 3.1 and pH 7.2. The experimentally determined initial rates were found to agree, within the experimental error, with the theoretical values. The initial rate of uptake of S(-II) and the values of Km for yeast strain R104 (a low sulfide producer) were found to be less than those for both strain R92 (a normal sulfide producer) and for strain R93 (a high sulfide producer).

Effect of sulfur dioxide and sulfite on photochemical energy storage of isolated chloroplasts--a photoacoustic study

Photoacoustic spectroscopy was used to study the effect of sulfite and SO(2) on isolated corn mesophyll chloroplasts by monitoring the photochemical energy storage. Sulfite incubation of isolated chloroplasts, either in light or in darkness, caused a decrease in photochemical energy storage. The more pronounced decrease in light indicates a light-dependent sulfite inhibitory site(s) in chloroplasts. Also diphenylcarbazide caused a partial recovery of energy storage in sulfite treated chloroplasts indicating a possible site of damage at the water oxidizing system. Although the chloroplast membranes were found to be insensitive to high concentrations of SO(2) for relatively short exposure periods (10 min) in light, exposure of chloroplasts to 28.5 ng cm(-3) SO(2) for 10 min caused a decrease in energy storage. An attempt was made to explain the mechanism of action of sulfite and SO(2) in chloroplasts.

Sulfur-dioxide fluxes into different cellular compartments of leaves photosynthesizing in a polluted atmosphere : II. Consequences of SO2 uptake as revealed by computer analysis

A computer model is used to analyze fluxes of SO2 from polluted air into leaves and the intracellular distribution of sulfur species derived from SO2. The analysis considers only effects of acidification and of anion accumulation. (i) The SO2 flux into leaves is practically exclusively controlled by the boundary-layer resistance of leaves to gas diffusion and by stomatal opening. At constant stomatal opening, flux is proportional to the concentration of SO2 in air. (ii) The sink capacity of cellular compartments for SO2 depends on intracellular pH and the intracellular localization of reactions capable of oxidizing or reducing SO2. In the mesophyll of illuminated leaves, the chloroplasts possess the highest trapping potential for SO2. (iii) If intracellular ion transport were insignificant, and if bisulfite and sulfite could not be oxidized or reduced, leaves with opened stomata would rapidly be killed both by the accumulation of sulfites and by acidification of chloroplasts and cytosol even if SO2 levels in air did not exceed concentrations thought to be permissible. Acidification and sulfite accumulation would remain confined largely to the chloroplasts and to the cytosol under these conditions. (iv) Transport of bisulfite and protons produced by hydration of SO2 into the vacuole cannot solve the problem of cytoplasmic accumulation of bisulfite and sulfite and of cytoplasmic acidification, because SO2 generated in the acidic vacuole from the bisulfite anion would diffuse back into the cytoplasm. (v) Oxidation to sulfate which is known to occur mainly in the chloroplasts can solve the problem of cytoplasmic sulfite and bisulfite accumulation, but aggravates the problem of chloroplastic and cytosolic acidification. (vi) A temporary solution to the problem of acidification requires the transfer of H(+) and sulfate into the vacuole. This transport needs to be energized. The storage capacity of the vacuole for protons and sulfate defines the extent to which SO2 can be detoxified by oxidation and removal of the resulting protons and sulfate anions from the cytoplasm. Calculations show that even at atmospheric levels of SO2 thought to be tolerable, known vacuolar buffer capacities are insufficient to cope with proton production during oxidation of SO2 to sulfate within a vegetation period. (vii) A permanent solution to the problem of acidification is the removal of protons. Protons are consumed during the reduction of sulfate to sulfide. Proteins and peptides contain sulfur at the level of sulfide. During photosynthesis in the presence of the permissible concentration of 0.05μl·l(-1) SO2, sulfur may be deposited in plants at a ratio not far from 1/500 in relation to carbon. The content of reduced sulfur to carbon is similar to that ratio only in fast-growing, protein-rich plants. Such plants may experience little difficulty in detoxifying SO2. In contrast, many trees may contain reduced sulfur at a ratio as low as 1/10 000 in relation to carbon. Excess sulfur deposited in such trees during photosynthesis in polluted air gives rise to sulfate and protons. If detoxification of SO2 by reduction is inadequate, and if the storage capacity of the vacuoles for protons and sulfate is exhausted, damage is unavoidable. Calculations indicate that trees with a low ratio of reduced S to C cannot tolerate long-term exposure to concentrations of SO2 as low as 0.02 or 0.03 μl·l(-1) which so far have been considered to be non-toxic to sensitive plant species.

CRITICAL LEAF CONCENTRATIONS FOR DEFICIENCIES OF NITROGEN, POTASSIUM, PHOSPHORUS, SULPHUR, AND MAGNESIUM IN PERENNIAL RYEGRASS

Critical leaf concentrations for deficiency of nitrogen, potassium, phosphorus, sulphur, and magnesium were estimated for perennial ryegrass (Lolium perenne L.) grown in sand culture. The values associated with a 10% reduction in dry matter yield were as follows (all results expressed as g kg^-1 DM except for the nitrate-nitrogen value which appears as μg^-1 DM): Kjeldahl-nitrogen 32; nitrate-nitrogen 500; potassium 28; phosphorus 2.1; sulphur 1.8; and magnesium 0.7. A major difference between the critical leaf concentrations estimated in this study and the tentative values published elsewhere was for potassium. Concentrations required in the shoot for near maximum growth were higher than previously reported. Differences in the nitrogen status of the plants probably account for this result. The depressing effect of potassium on the absorption of magnesium and calcium is discussed in relation to plant and animal nutrition. Sulphur was found to be inefficiently absorbed by phosphorus deficient plants despite non-limiting amounts of sulphur applied in the nutrient solution. A possible explanation for this effect may be linked to the observation that the transport of sulphate into the chloroplast was coupled with that of phosphate. The concentration of macroelements required in the nutrient solution to produce maximum shoot growth of perennial ryegrass was very much greater than that generally applied to plants grown in sand culture.