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PubMed1954

Evidence for the presence of separate mechanisms regulating potassium and sodium distribution in Ulva lactuca.

1. The methods employed in these and preceding (25-27) studies were shown to allow analysis of true cellular sodium and potassium concentrations. 2. The rate of reaccumulation of potassium by potassium-deficient cells is independent of the presence or absence of sodium in the external medium. 3. Phenylurethane (10(-3)M), a photosynthetic and metabolic inhibitor, causes a marked progressive loss of potassium and gain of sodium, both of which changes are completely reversible on transferring the samples to running sea water. 4. Iodoacetate, while not effective in causing potassium and sodium shifts in the light, effects a loss of potassium and a gain of sodium in the light in the presence of phenylurethane. 5. Arsenate (5 x 10(-3)M) completely protects Ulva against the potassium loss usually observed with iodoacetate in the dark while it affords no protection against the sodium influx under the same conditions. Arsenate given after 18 to 20 hours in iodoacetate gives significant protection against potassium loss in the dark, and allows a slight net reaccumulation of potassium in the light. Arsenate in the dark after iodoacetate affords no protection against the sodium uptake caused by iodoacetate in the dark, while in the light under the same conditions sodium is rapidly secreted to the control level within a few hours. This resecretion of sodium is thought to be primarily an effect of light, the presence of arsenate being incidental. 6. The "decoupling agent" 4,6-dinitro-o-cresol causes a marked progressive increase in cellular sodium and a drop in cellular potassium, though the kinetics of these two movements are distinctly different from each other. 7. Pyruvate (50 mg. per cent) given with iodoacetate (2 x 10(-3)M) for 5 hours in the dark completely prevents the sodium increase caused by iodoacetate, while affording less protection against the potassium loss. Phosphoglycerate, on the other hand, offers more protection against potassium loss, and essentially none against the sodium gain. 8. ATP added in small amounts at short intervals to samples maintained in 10(-3)M iodoacetate in the dark affords significant protection against the potassium loss observed in iodoacetate. Cellular sodium is somewhat higher in the ATP-iodoacetate samples than in the iodoacetate samples. 9. In the discussion of the data presented two major points are emphasized: (1) the close correlation between cellular metabolism and normal cation control; (2) two mechanisms must be operative in cation regulation in this organism: one for moving potassium inwards and the other for transporting sodium outwards. These mechanisms are independent of each other.

Eukaryota↗
PubMed1980

Influence of After-ripening on Phytochrome Control of Seed Germination in Two Varieties of Lettuce (Lactuca sativa L.).

The reversible photoreaction on seed germination of two varieties of lettuce differs remarkably not only with the variety but also with the germination temperature and the physiological conditions of seeds caused by after-ripening.Grand Rapids showed reversible photoreaction at 25 C with 0 to 6 months and at 30 C with 5 to 6 months after-ripening. MSU 16 did not show any reversible photoreaction at 30 C with 0 to 6 months or at 25 C with 0 to 3 months after-ripening although they were completely reversible with 4 to 6 months after-ripening.These two varieties of lettuce seeds, however, showed reversible photoreaction at 20 C when they were sown immediately after harvest or after 1 and 2 months after-ripening. The photoreversion decreased after the 4-to 6-month stage.

Journal Article↗
PubMed1981

Oxidative Phosphorylation in Germinating Lettuce Seeds (Lactuca sativa) during the First Hours of Imbibition.

Experiments with lettuce seeds during the first hours of imbibition showed that oxygen is necessary to sustain high adenine nucleotide ratios and consequently, energy charge values are higher than 0.8 as is usually the case in normally metabolizing tissues.The energy charge value (0.2) of dry seeds soaked in aerated water increased to normal values (0.8) within 30 minutes. The energy charge value of seeds imbibed under cyanide or nitrogen stayed at low values, about 0.3 for 30 minutes. Nitrogen and cyanide treatment of seeds imbibed in aerated water produced a decrease of energy charge to low values within 3 minutes. During the first minutes of imbibition, the oxygen uptake is cyanide-sensitive. The effect of the uncoupler carbonyl cyanide p-trifluoromethoxyphenyl hydrazone was not as clear-cut. However, results were obtained which agree with the occurrence of oxidative phosphorylation during the first hours of imbibition. These results indicate that a normal cytochromic pathway synthesizes ATP during the first minutes and hours following the imbibition of lettuce seeds.

Journal Article↗