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.

The nature and location of the light-stimulated active transport of chloride to the epidermal bladders of A. 8pongio8a leaves was examined. Chloride transport to the bladder vacuole was found to have properties similar to those for light-dependent

The apparent unidireotional transport of sugars and ions in isolated onion epidermis was shown to be due to the presenoe of a outiole on the outer surfaoe of the epidermis. The outiole probably is partially permeable for ions and impermeable for hexoses. Sugar transport aoross the inner surfaoe of isolated epidermis had a temperature ooeffioient (k20°C/klOoC) of 2·4, the oorresponding activation energy was 14·5 koal/mole, and the permeability coeffioient was approximately 10-8 cm/sec. Sugar transport was not inhibited by oarbonyl oyanide m-chlorophenylhydrazone, potassium cyanide, or sodium azide.

Leaf slices of two sets of M. crystallinum plants were used in the present study. The first set were plants grown in 400 mM NaCl and showing diurnal oscillations of malate levels typical of crassulacean acid metabolism (CAM). The second set were plants grown in non-saline media and exhibiting no CAM-like diurnal malate fluctuations. Both sets of leaf slices accumulated malate during a 12-h light or dark period, depending on the osmotic pressure of the incubation medium. Highest malate accumulations were obtained when media were isotonic or slightly hypertonic. These osmotic characteristics are similar to those of leaf slices of the CAM plant Kalanchoe daigremontiana as reported elsewhere. However, discrepancies are observed in light and temperature dependence. Unlike in K. daigremontiana leaf slices and in intact leaves with CAM (i.e. also in intact leaves of M. crystallinum grown on highly saline media), in both sets of M. crystallinum leaf slices used here light stimulated malate accumulation. Compared to 15°C, 25°C had either no effect on malate accumulation or stimulated malate accumulation. After leaf slices had accumulated malate in the dark in isotonic or slightly hypertonic media, malate accumulation continued in the light when the osmolarity of the medium remained unchanged. When the osmotic pressure of the medium was lowered considerably, however, malate accumulation in the light was much reduced or else there was a loss of malate from the tissue. Mechanisms different from CAM may be partially involved in the changes of malate levels in these experiments. The significance of the experimental results for the interpretation of the balance between net carbon gain via C3 pathway and CAM in M. crystallinum is discussed.

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