SummaryThe mangrove Rhizophora mucronata grows in an intertidal region and exchfdes salt from its xylem (17 m·equiv. chloride per litre of sap) more efficiently than does the salt· secreting mangrove AegialitiB annulata (85-122 m·equiv. chloride per litre of sap). From the transpiration stream each leaf of Rhizophora receives about 17 p.·equiv. chloride each day, but the chloride concentration of the growing leaf remains approximately constant (510-560 m·equiv. chloride per litre of sap water). In Aegialiti8 input of chloride to a mature leaf is about 100 p..equiv. per day and this input is balanced by secretion (mainly of sodium chloride) from the salt glands. Secretion collected under oil contains chloride, 450 p.-equiv/ml, sodium, 355 p.-equiv/ ml, and potassium, 27 p.-equiv/ml. Secretion rates from leaves on the tree, based on leaf area, vary from 93 p-equiv. cm-2 sec-1 during the day to 3 p-equiv. cm-2 sec-1 in darkness; the secretion in light, based on an effective gland area, is about 25,000 p-equiv. cm-2 sec-I. The water potential of the secretion is close to that in the leaf suggesting that secretion involves active transport of salt and passive movement of water by local osmosis. Salt secretion is inhibited by carbonyl cyanide 3-chlorophenyThydrazone applied ·to the cut petiole or to the leaf surface. Out leaves secrete salt in darkness at approximately the same rate as in light, in contrast to leaves on the tree.With infused radioactive chloride, the specific activity of chloride in the secretion reached a higher value than the mean value in the leaf, suggesting that some chloride passes freely from the leaf veins to the salt glands without equilibrating with the main chloride pool of the leaf.Light-and electron-microscope studies of the glands of AegialitiB are described.

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.

Isolated pea chloroplasts undergo both cyclic and non-cyclic electron flow. Both processes are coupled to photophosphorylation. During non-cyclic flow the rate of oxygen production showed ADP-governed ;photosynthetic control' analogous to respiratory control of isolated mitochondria. Measurements of ADP/O and photosynthetic control ratios yielded values of 1-1.3 and 2-5.7 respectively. ;Photosynthetic control' was shown to be dependent on the intactness of the chloroplasts.

SummanyOhaetomorpha darwinii is a marine alga with large coenocytic cells. The cell sap contains about 540 mM potassium, 25 mM sodium, and 600 mM chloride, and the vacuole is 10 mY positive to the sea water. The potassium selectivity is due to an active inward pump and an outward sodium pump at the plasmalemma. The fluxes of potassium at the plasmalemma and tonoplast were about 100 and 150 pmoles/cm2/sec, and the fluxes of sodium at these membranes were about 100 and 4 pmoles/cms/sec, respectively. The potential differences at these boundaries were -35 mY and +45 mY. The cytoplasmic phase contained about 18 p.-equiv/g of potassium and 0·5-1·0 p.-equiv /g of sodium.Dinitrophenol reduced the flux of potassiuni at the plasmalemma, and the content of the cytoplasm fell to about 0·5 p.-equiv/g, but it did not induce a net flux from the vacuole. Sodium influx was not affected by dinitrophenol, but the content of the cytoplasm rose from 0·5 to 7 p.-equiv/g, due to inhibition of the sodium efflux.There were some anomalies in the results, i.e. the high potassium content of the cytoplasm, the high potential difference at the tonoplast, and the lack of any effect of dinitrophenol on the net fluxes. These problems are considered to be due to the organization of the cytoplasm.

SummaryA comparative study has been made of the effects of four metabolic inhibitors on chloride uptake and photosynthetic 14C02 fixation by cells of O. corallina, and on oxygen evolution by chloropl<1sts isolated from the cells. Low concentrations of phlorizin and Dio-9 inhibited chloride uptake, but this was not accompanied by an inhibition of photosynthesis in vivo, and could not be correlated with the measured inhibition of electron flow in vitro. Low concentrations of imidazole stimulated the chloride influx in light, but there was again no effect on photosynthetic 14C0 2 fixation, although imidazole did uncouple electron flow in vitro. The effect of imidazole was dependent on the pH of the external solution. Increasing concentrations of carbonyl cyanide m-chlorophenylhydrazone progressively reduced the chloride influx and 14C02 fixation, and uncoupled electron flow in vitro. The work provides no evidence to support the view that chloride uptake is directly linked to electron flow rather than phosphorylation.The work is discussed with reference to previous studies of ion transport in giant algal cells, and the possible significance of direct effects of metabolic inhibitors on ion transport processes is stressed.