SummarySoluble adenosine triphosphatases (ATPases) from carrot, beetroot, and the fresh-water alga Ohara australi8 were activated by sodium and potassium chlorides, but not by choline chloride, and were inhibited by potassium sulphate and fluoride. Ouabain was not inhibitory, and Na+-K+ synergism of the type found with animal "transport" ATPases was not observed.The ATPases had acid pH optima and were not activated by Mg 2+; fractionation on Sephadex and electrophoresis in starch gel gave identical patterns of ATPase activity (with or without potassium chloride) and acid phosphatase. The identity of the salt-stimulated ATPases with acid phosphatase was supported by parallel inhibition by trypan blue and adenylyl methylene diphosphonate and by association of the activities during purification.Enzyme eluted from carrot cell-wall fractions at high ionic strength was indistinguishable from the soluble enzyme. Cell walls freed of enzyme with alkali took up the ATPase from a soluble preparation of carrot enzyme.Trypan blue at a concentration (14/-,M) causing marked inhibition of saltstimulated ATPase did not inhibit potassium chloride uptake in aged carrot slices.The specificity of salt stimulation and the possible involvement of saltstimulated ATPase in active transport of salt into plant cells is discussed.

SummaryThe time course during aging of carrot xylem disks for development of salt respiration and sensitivity of respiration to inhibition by L-ethionine was determined. 5 mM L-ethionine has no effect on the respiration of freshly cut disks, but sensitivity developed during the aging process and was maximal from 25 to 120 hr, falling to zero at 150 hr. Maximal inhibition (35-40%) coincided with the period of maximum basal respiratory rate.Rb+ uptake into carrot xylem disks aged for 77 hr was linear and at 80% of the control rate for nearly 2 hr in the presence of 5 mM L-ethionine, despite inhibition of salt respiration and a concomitant drop in the ATP level to 50% of control values during this period.5 mM L·ethionine failed to inhibit Rb+ and Cl-uptake into disks aged for 125 hr, although the ATP level fell to 40% of control after 2 hr and both basal and salt respiration were inhibited; 90% of the salt respiration was eliminated within 60 min. Cl-uptake from 40 mM NaCl into disks aged for 125 hr proceeded linearly at 85% of the control rate for over 2 hr despite a 60% drop in ATP level.A lag in the onset of oligomycin inhibition of K + and Cl-uptake into aged carrot disks and ofKCl uptake into aged beetroot disks was observed. Anaerobic conditions strongly inhibited Cl-uptake into aged carrot disks over 30 min, although the ATP level fell by only 30%.The results provide further evidence that salt accumulation into aged carrot xylem tissue is linked to electron transport rather than to hydrolysis of ATP, and indicate that a large proportion of salt respiration may be an indirect consequence of salt accumulation.

SummaryEffects of anaerobic conditions, uncouplers [2,4-dinitrophenol and carbonyl cyanide 3-chlorophenylhydrazone (OOOP)], inhibitors of oxidative phosphorylation (Dio-9 and oligomycin), and an ATP-trapping reagent (L-ethionine) on influx and net uptake of K+, Na+, and 01-from 0·5 mM KOI or NaOI solutions into aged beet parenchyma disks and on tissue ATP levels were determined.Anaerobic conditions inhibited K+ and 01-influx completely and Na+ influx by 85% after 30 min. After 1 hr of anaerobiosis the ATP level in aged beet disks was not significantly lower than the initial aerobic level.Dinitrophenol (0·25-1'0 X 10-3M) and OOOP (l'Ox 1O-5M) caused rapid net loss of K+ from aged beet disks. Dinitrophenol completely inhibited K+, Na+, and 01-influxes within 30 min and caused depression of the ATP level to 4% of the control level after 2 hr. In contrast, L-ethionine (0·5-1·0 mM) caused severe depression of the tissue ATP level without inhibiting K+, Na+, or 01-influxes by more than 50% after 1 hr.Dio-9 (10 iLg/ml) had little effect on Na+ or K+ influx into aged beet disks. Oligomycin (1 ·3-2·6 iLg/ml) caused a delayed inhibition of K + and N a + influxes and did not completely inhibit these fluxes over 2 hr.The results provide evidence against the concept of a direct involvement of ATP as energy source for Na+, K+, and 01-transport by the high-affinity ion accumulation systems of aged beet parenchyma cells.

The effects of cycloheximide and of cryptopleurine (two inhibitors of protein synthesis) on ion uptake and protein synthesis in beet disks are described