Metabolic Factors Influencing the Sodium and Potassium Distribution in Ulva Lactuca

Abstract

1. Methods for the use of the marine green alga, Ulva lactuca, in studies on electrolyte metabolism are described. 2. The effect of illumination and iodoacetate on the potassium and sodium content, as well as the influence of light and running sea water on the iodoacetate effect was investigated. The rate of exchange of cellular potassium ion for K42 under conditions of light and dark at 20 and 30°C. was studied. 3. Ulva maintained in the dark for long periods loses some potassium and gains sodium, both effects being reversed upon illumination. The presence of 0.001 M iodoacetate in the dark causes a marked progressive loss of potassium and gain of sodium, phenomena which do not occur when the alga is illuminated. Evidence for the penetration of the inhibitor into the cell in the presence of light is presented. The iodoacetate effect on potassium and sodium content, once established, can be "washed out" of the alga when the plant is placed in light and running sea water without the inhibitor. Illumination and increased temperature each favor a more rapid exchange of tissue for environmental potassium ion. 4. In the interpretation of these findings it is emphasized that metabolic work, perhaps in the form of ion transports, must be done by the cell to compensate for the continual flow of potassium ion and sodium ion with their respective concentration gradients and thus maintain homeostasis within the cell. Evidence is presented which indicates separate mechanisms for the distribution of sodium and potassium in this organism. It is further suggested that the degradation of phosphoglyceric acid, an important glycolytic and photosynthetic intermediate, or one of the products of its metabolism supplied the energy for these ion transports(s). The role of permeability per se is considered.

Ionic Relations and Ultrastructure in Ulva Lactuca

“…In measurements of changes of net flux, such as those made by Scott and Hayward (1953a) the net flux of sodium would have been limited by this boundary, but the net uptake of potassium would have been limited by the plasmalemma, as we have seen. Here, then, is a simple explanation for the differences they found in the kinetics of sodium and potassium exchange.…”

“…~ronds of U. lactuca grown in the light contain about 300-360 fL-equivjg fresh weight of potassium; when kept in the dark for about 4 days this level falls to 260-280 Wequivjg fresh weight and stays steady at this level (see Scott and Hayward 1953a). When fronds are put into sea-water labelled with 42K there is a rapid uptake of tracer and within 10 hr the specific activity of potassium is the same within the tissue as in the sea-water.…”

“…'The tissue contains about 350 fG-equiv/g of potassium and 50 ",,-equiv/g of sodium, while sea-water contains 10 and 500 ",,-equiv/ml respectively of these ions. Scott and Hayward (1953a, 1953b, 1953c showed that this selectivity was maintained by metabolically linked processes; an active potassium uptake and'an active sodium excretion.…”

Sodium and Potassium Transport in the Marine Alga Chaetomorpha Darwinii

“…The KINa ratio in the cells was not altered by transferring tissue from the light to darkness, nor did this reduction in photosynthesis immediately alter the apparent potassium uptake, i.e. the cation ion-transport mechanism was not critically dependent on photosynthesis, as in Ulva (Scott and Hayward 1953). Potassium uptake by cells in nitrogen was unaffected if the tissue was in the light, but in the dark there was a rapid loss of potassium and uptake of sodium (Fig.…”

Trace Element Regulation in the Marine Alga Caulerpa Racemosa

“…Laboratory studies on ionic equilibria between algae and surrounding media have demonstrated that certain elements are selectively absorbed by algae as a result of special physiological functions. Scott and Hayward (1953) observed a metabolic control on the sodium and potassium distribution in Ulva lactuca. Scott (1954) found, for several algal species, that the accumulation of caesium is dependent upon the fixation of carbon dioxide and rate of photosynthesis.…”