Sodium and Potassium Transport in the Marine Alga Chaetomorpha Darwinii

Abstract

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.

Comparison of Photassium and Sodium Uptake by Barley Roots at High and Low Salt Status

“…Using roots of plants grown on solutions containing full nutrients and 10 m-equivjl of potassium plus sodium, Pitman and Saddler (1967) found that uptake was consistent with a model similar to that suggested for giant algal cells such as Nitella (MacRobbie 1962) and Chaetomorpha (Dodd, Pitman, and West 1966), i.e. there appeared to be active potassium transport into the cells and active sodium extrusion.…”

Ionic Relations and Ultrastructure in Ulva Lactuca

“…Similar explanations have ,been suggested tQ account for potassium' selectivity in a number of othe'l' algae -NiteUopsisobtusaJ (MacRobbie and Dainty 1958), Ohara australis (Hope and Walker 1960;Hope 1963); Nitella'translucens (MacRobbie 1962), Ohaetomorpha darwinii (Dodd, Pitman, and West 1966). In these examples it was possible to measure tracer fluxes at the plasmalemma and at the tonoplast.…”

Uptake and Transport of Ions in Barley Seedlings I. Estimation of Chloride Fluxes in Cells of Excised Roots

“…Fluxes can be calculated from the kinetics of tracer exchange with plant cells. This approach has been used for giant algal cells (MacRobbie and Dainty 1958;Hope 1963;Dodd, Pitman, and West 1966); for homogeneous plant tissues such as beet (Pitman 1963) and carrot (Cram 1968); and for some roots (Pitman and Saddler 1967;Pallaghy and Scott 1969). It is assumed in calculating fluxes in this way that the cells can be treated as three phases in series: free space, cytoplasm, and vacuole.…”