INTERNAL NITRATE CONCENTRATIONS IN SINGLE CELLS OF LARGE PHYTOPLANKTON FROM THE SARGASSO SEA1

Nitrate concentrations within individual cells of Ethmodiscus, Pyrocystis, and Halosphaera and chains of Rhizosolenia were determined from samples collected in the Sargasso Sea. In all cases, field populations exhibited a wide range of internal nitrate concentrations (INCs) within a single sampling date. Halosphaera INCs reached 100 mM, in contrast to diatom and dinoflagellate INCs, which did not exceed 22 mM. Sinking Rhizosolenia, Ethmodiscus and Pyrocystis had significantly lower internal NO₃- pools than did floating cells (P< 0.05). Ethmodiscus incubations in surface seawater resulted in a dramatic reduction in the proportion of high INC cells concurrent with decreases in average INCs and an increased proportion of sinking cells. Population buoyancy was inversely related to INC, and negatively buoyant cells rarely exceeded I mM INC, suggesting that a critical INC threshold may exist. The photosynthetic parameters P_max and α decreased with time as internal NO₃-_- Pools were depleted. Internal nitrate depletion rates were consistent with oxygen production rates during this time. Based on the known characteristics of Pyrocystis and Ethmodiscus, we conclude that virtually all of the > 100 μm-sized phytoplankton present in the Sargasso Sea can vertically migrate. However, the appropriate time scale for migrators such as Halosphaera that reproduce by swarmer formation is unclear and may be significantly different than the other taxa studied. Changes in the frequency distributions, buoyancy-internal pool relationships, and general P-1 photosynthesis-irradiance time series data in Ethmodiscus suggest that nutrient limitation is related to these migrations. High INC appears to be a fundamental property of the largest microalgal cells present in oligotrophic seas and suggests that nitrate transport by these nonmotile cells is widespread.     

THE EQUIVALENCE OF AGE IN ANIMALS

1. A method of plotting growth curves is presented which is considered more useful than the usual method in bringing out a number of important phenomena such as the equivalence of age in different animals, difference in the shape and duration of corresponding growth cycles in different animals, and also in determinating the age of maxima without resorting to complicated mathematical computations. 2. It is suggested that after the third cycle is past the conceptional age of the maximum of the third cycle may be taken as the age of reference for estimating the equivalent physiological ages in different animals. Before the age of the third cycle, the maxima of the second and first cycles are most conveniently used as points of reference. 3. It is shown that the product of the conceptional age of the maximum of the third cycle by 13, gives a value which is, with the possible exception of man, very near to the normal duration of life of animals under the most favorable conditions of life. In other words, the equivalent physiological ages in different animals bear an approximately constant linear relation to the duration of their growth periods. 4. Attention is called to certain differences in the shape and duration of the corresponding growth cycles in different animals and of the effect of sex on these cycles.     

THE ACCUMULATION OF ELECTROLYTES : IV. INTERNAL VERSUS EXTERNAL CONCENTRATIONS OF POTASSIUM

Lowering the potassium in the sea water from 0.011 M to 0.006 M caused an exit of potassium from cells of Valonia macrophysa. Sodium continued to penetrate and the ratio K ÷ Na fell off. The cells ceased to grow but there was no evidence of injury. Increasing the external potassium brought about an increase of the internal concentration of potassium, of halide, of total cations, and of the ratio K ÷ Na inside. These phenomena are to be expected on theoretical grounds.     

EFFECTS OF MEDIA OF DIFFERENT IONIC COMPOSITION ON THE ACTIVATION POTENTIAL OF ANURAN EGG CELLS

Activation potentials of the eggs of two anuran species, Bufo vulgaris formosus and Rana rugosa , were measured in media of different ionic composition, and the mechanism of their generation is discussed. The same trends of ionic effects upon the activation potential were consistently obtained in both species.
The membrane potential of the unactivated eggs was negative with respect to tap water, Ringer's solution, and the media described below except isotonic KCl and KNO₃, in which the potentials were nearly zero or sometimes slightly positive. Upon activation induced by pricking in tap water, isotonic Na₂SO₄, or 42 mM or 63 mM buffered sodium phosphate solution, depolarization followed by reversal of the membrane potential took place, associated with a decrease in the effective resistance. Then the potential gradually decreased and returned to the initial value.
On the other hand, in Ringer's solution, or in isotonic NaBr, NaNO₃, KCl or KNO₃, the activation potential occurred in a hyperpolarizing direction, associated with a decrease in the effective resistance.
These results suggest that the ooplasmic membrane of the anuran egg surface during activation is selectively permeable to NO₃⁻ and Br⁻ as well as Cl⁻, but not to SO₄⁻ and phosphate ions, or alternatively, that the activation potential is due to this selective permeability and to the concentration gradients of these monovalent anions across the ooplasmic membrane.     

HYDROGEN ION CONCENTRATIONS IN THE BLOOD OF INSECTS

The range of pH values for the blood of grasshoppers and of houseflies is 7.2 to 7.6. The range of values for roaches is 7.5 to 8.0. The range for Malacosoma americanum is 6.4 to 7.4; and the range for Bombyx mori is 6.4 to 7.2. From the work of other investigators and from the writer''s results, it is apparent that the pH of insect blood, in general, may vary between 6.4 and 8.0. In the forms observed no correlation exists between blood pH and age, nor between pH and metamorphosis.     

ELEVATED CONCENTRATIONS OF HISTAMINE IN THE RAT BRAIN

—Whole brain concentrations of histamine (Hm) in the rat were measured with a sensitive and specific single-isotope enzymatic microassay and found to be elevated about 2-fold in rats killed by focused microwave irradiation compared with rats killed by decapitation. However, regardless of the method of killing, whole brain Hm concentrations were elevated about 4-fold when the brains were homogenized in 12.5 vol vs 2.5 vol of water or phosphate buffer. Homogenization of brain regions in 12.5 vol of water resulted in Hm concentrations that were about 10 times greater than previously reported values (except in the hypothalamus). Since (1) the‘extra’Hm could be extracted from pellets of low volume homogenates, and (2) synthesis of Hm is not likely to occur through an increase in the volume of water or buffer used for homogenization, we suggest that the elevated concentrations of Hm seen after high volume homogenization of brain tissue are due to a more complete extraction of Hm from brain tissue, and not to an artifactual production of this amine from its precursor (histidine) or some other compound(s).