SummaryThe epidermal bladders of several Atriplex species contain high concentrations of ions. Chloride was secreted from the solution or the lamina to the bladders, against a concentration gradient. Transfer of 36CI to the bladders was strongly light stimulated, but uptake to the lamina was much less sensitive.Electrical potential measurements showed that the vacuole of the bladder cell was highly electronegative with respect to the bathing solution. Switching from dark to light and vice·versa resulted in transient changes in potential. In some instances the potential settled to a level which was more negative in the light than in the dark. These observations suggest that uptake of chloride into the bladders is an active process.Autoradiographs of intact and sectioned bladders after exposure to K.35S04 and K36CI showed that radioactivity was concentrated in the stalk cell and peripheral cytoplasm of the large vacuolated bladder cell. Electron microscopy showed that the stalk cell and peripheral cytoplasm of the bladder cell contained chloroplasts, numerous mitochondria, much endoplasmic reticulum, and many small vesicles. The stalk cell has the submicroscopic characteristics of a salt gland and, as it is con· nected to the bladder cell and the epidermal cells by plasmodesmata, may secrete ions from the leaf symplasm to the bladder cell.

An attempt is made to apply the Ussing-Teorell criterion for passive ion movement to root cells of young broad bean seedlings. This requires the estimation of ion concentrations in the cells, ion fluxes between cellular compartments and the external medium, and membrane potential differences.

Light-induced changes in chloroplasts of detached leaves of E. densa were investigated either by fixing leaves in 6% glutaraldehyde or by snap-freezing leaves and isolating chloroplasts after freeze-substitution in acetone. Individual chloroplasts were examined by electron probe analysis.Upon illumination (450 lux green light) chloroplasts in detached leaves flattened, with a reduction in volume of about 30% within the first second. During this initial phase of chloroplast contraction the calculated osmotic potential of chloroplasts fell from about -17 bars in the dark to -21 bars after 1 s of illumination, suggesting that the rapid contraction was not the result of an osmotic mechanism of water efflux brought about by an efflux of chloride, potassium, sodium, or calcium ions from chloroplasts. During the next hour of illumination chloroplast volume was reduced by only a further 5%, but the chloroplasts lost approximately 50% of their original ion content. The calculated osmotic potential of the chloroplasts rose to approximately -11 bars.During the first hour of illumination the average net efflux of ions (± standard error of the mean) across the chloroplast envelope was 32·6 ± 3·5 for chloride, 8·7 ± 0·8 for potassium, and 21·24 ± 1·4 p-equiv.cm-2 s-1 for sodium. The estimated efflux for calcium was approximately 8 p-equiv. cm-2 S-1. Typical concentrations of chloride, potassium, and sodium respectively in chloroplasts were 0·53, 0'24, and 0·31 equiv/l of chloroplast volume in dark-treated leaves and 0·32, 0·20, and 0·17 equiv/l in light-treated leaves. The chloride content of chloroplasts represents at least 20% of the total chloride content of dark-treated leaves. In the light the corresponding proportion is approximately 8%. The effects of CO2, ammonia, brucine, ouabain, and 3-p-chlorophenyl-1,I-dimethylurea on the in vivo ion and volume relations of E. densa chloroplasts are described.

The specific locations of the evaporating surfaces in the leaf are not yet known. However, Maercker (1965) repeated successfully the early experiments of Stahl (1894) and concluded from her evidence that the cuticular component oftranspiration could be further divided into "cuticular" and "peristomatal" transpiration, where the latter term refers to transpiration from the surfaces of the guard cells and their subsidiary cells. Peristomatal transpiration has been the subject of considerable recent interest (e.g. Lange et al. 1971).Using the method of Stahl (1894), Maercker (1965) placed cut leaves of Zea mays into 3% thallium sulphate solution and allowed the leaves to transpire in light or darkness, and in either normal air or CO2-depleted air. Under conditions which led to stomatal opening (Le. in light or in darkness in CO2-free air), TI+ was found exclusively in the guard cells, whereas it was located exclusively in the subsidiary cells of leaves with closed stomata. This evidence, in conjunction with experiments using tritiated water, led her to suggest that the terminal site of transpiration was in the guard cells when stomata are open and in the subsidiary cells when stomata are closed. Raschke (personal communication) suggested, however, that these observations merely indicate that Tl+ ions follow the shuttle of K + between the guard and subsidiary cells which occurs during stomatal movement in Z. mays (Pallaghy 1971;Raschke and Fellows 1971). The results briefly reported in this communication prove that TI+ cannot be employed as an indicator to locate the terminal sites of transpiration. Results and DiscussionThe leaf material (Z. mays) used was that described by Pallaghy (1971). Experiments, lasting 2-5 hr, were carried out using 0'5% thallium sulphate solution. Leaves were kept in distilled water for about 15 min prior to each experiment. Localization of Tl+ in the leaf epidermis was observed as a black precipitate of thallium chloride when the leaf was submerged for about 5 min into a solution of 3% NaCI in 50% methanol. Control experiments were carried out in the manner according to Maercker (1965). Similar experiments, but employing either normal or CO2-free aerated solutions, were carried out with leaves entirely submerged in the solution to prevent transpiration.The results obtained with both transpiring and submerged leaves (Fig. 1) were similar to those described by Maercker (1965), proving that Tl+ localization is independent of transpiration. The method of micro-autoradiography using tritiated water to localize transpiration sites near the stomatal pore is also subject to doubt. The topography of the stomatal apparatus is considerably different between the open and closed states, as has been well demonstrated in an extreme situation for Z. mays * Manuscript

Plants grown in uncovered pots and watered daily with either 350 mM KCl or NaCl showed a net uptake of CO2 during the day followed by CO2 release during the night, whereas plants grown under identical conditions, but in polyethylene-covered soil (covered pots) showed net CO2 accumulation and acidification during the night phase (CAM expression). Spraying the tops of plants with 5 mM ouabain either induced CAM in the case of plants grown in uncovered pots or enhanced CAM in plants grown in covered pots. This effect of ouabain and some aspects of the gross ion relations of M. crystallinum are discussed.