Biomedical subjects

D W Rains

Publications and source records attributed to D W Rains.

27 records · Page 2Linked to original sources

PubMed1969

Sodium and potassium absorption by bean stem tissue.

The effect of various periods of pretreatment in CaSO(4) solutions (aging) on the absorption of Na and K by bean stem slices was investigated. Freshly sliced tissue absorbed Na over the entire range of concentrations studied (0.02-50 mm). Potassium absorption by fresh tissue was nil at concentrations below 0.5 mm but at higher concentrations was similar to that of Na. When tissue was aged by aerating slices for 20 hr in 0.5 mm CaSO(4), K absorption was substantial over the entire range (0.01-50 mm), with evidence of a dual mechanism of absorption, whereas Na absorption was nil at concentrations below 0.2 mm. The formation of K-absorbing capacity with aging, and the loss of Na-absorbing capacity at low concentrations, were temperature-dependent and did not result from significant changes in rates of efflux of either ion. The absorption of Na by fresh tissue and K by aged tissue was sensitive to antimetabolites, with K uptake the more sensitive. Benzyladenine, an analog of kinetin, suppressed the formation of K-absorbing capability in aged tissue but did not prevent the loss of Naabsorbing capacity. Possible mechanisms for this alteration in ion-specificity of transport mechanisms are discussed.

Journal Article↗

PubMed1968

Kinetics and Energetics of Light-enhanced Potassium Absorption by Corn Leaf Tissue.

The effect of illumination on the absorption of K(+) by leaf tissue of Zea mays was investigated. The rate of K(+) absorption was enhanced by exposure of slices of corn leaf tissue to light, even of relatively low intensities. Potassium was transported inward, with virtually no efflux of previously accumulated K(+). The evidence indicates that the transport mechanism for absorption of K(+) is the same in the light as in the dark, but that the source of energy for absorption of K(+) is different in the light from that in the dark. Various anti-metabolites were used to establish that the energy utilized for active ion transport in the light came partly from ATP supplied by cyclic photophosphorylation. Expenditure of ATP was required in the dark too, but this ATP was formed by oxidative phosphorylation. Establishing the ultimate source of energy for active ion uptake by higher plants might be facilitated by demonstration of an ion-transport process that is not linked directly with the transfer of electrons in the mitochondrial cytochrome chain.

Journal Article↗

PubMed1967

Light-enhanced potassium absorption by corn leaf tissue.

The rate of absorption of potassium by slices of corn leaf in the light was about twice the rate in the dark. When the light was turned on or off, changes in the rate of absorption took place some minutes after the change in illumination. Experiments with the antimetabolites, 2,4-dinitrophenol and cyanide, indicated that the source of energy for active accumulation of potassium by green tissue in the light was different from that in the dark. In the light, energy was closely linked to photosynthetic reactions; in the dark, it was linked to respiratory processes.

Absorption↗

PubMed1967

Sodium absorption by barley roots: role of the dual mechanisms of alkali cation transport.

Radioactively labeled Na(+) absorbed by barley roots was sequestered in an intracellular compartment or compartments ("inner" spaces) in which it was only very slowly exchangeable with exogenous Na(+). Absorption of this fraction proceeded at a constant rate for at least 1 hour.When the rate of Na(+) absorption was examined over the range of concentrations, 0.005 to 50 mm, the isotherm depicting the relation showed dual kinetics as follows. Over the range, 0.005 to 0.2 mm, a single Michaelis-Menten term describes the relation between the concentration of Na(+) and the rate of its absorption. The mechanism of Na(+) absorption operating over this range of concentrations, mechanism 1 of alkali cation transport, is severely inhibited in the presence of Ca(2+) and virtually rendered inoperative for Na(+) transport by the combined presence of Ca(2+) and K(+). The mechanism is equally effective in Na(+) transport whether Cl(-) or F(-) is the anion, but is somewhat inhibited when the anion is SO(4) (2-).Over the high range of concentrations, 0.5 to 50 mm Na(+), a second, low-affinity mechanism of Na(+) absorption comes into play. In the presence of Ca(2+) and K(+), this mechanism 2 is the only one to transport Na(+) effectively, since Na(+) absorption via mechanism 1 is virtually abolished under these conditions.Anaerobic conditions, low temperature, and the uncoupler, 2,4-dinitrophenol, inhibit Na(+) absorption both at low and high Na(+) concentrations.

Journal Article↗

PubMed1967

Sodium absorption by barley roots: its mediation by mechanism 2 of alkali cation transport.

When barley roots absorb Na(+) at concentrations ranging from 1 to 50 mm, in the presence of low concentrations of Ca(2+) and K(+), absorption of Na(+) is mediated by carrier mechanism 2 of alkali cation transport, mechanism 1 being unavailable for Na(+) transport under these conditions. The absorption isotherm depicting the rate of Na(+) absorption as a function of the external Na(+) concentration, over the 1 to 50 mm range of concentrations, shows several inflections. This stepwise response occurs whether Cl(-) or SO(4) (2-) is the counterion, but actual rates of Na(+) absorption are lower in the latter case.When the concentration of Na(+) is 50 mm, and the concentration of either K(+) or Ca(2+) is increased from nil to 50 mm, the rate of absorption of Na(+) is diminished not as a smooth function of increasing concentrations of the interfering ions but stepwise. Similarly, when the concentration of K(+) is 50 mm, and the concentration of either Na(+) or Ca(2+) is increased from nil to 50 mm, the rate of absorption of K(+) is diminished not as a smooth function of increasing concentrations of the interfering ions but stepwise.Together, this evidence supports the previous conclusion to the effect that mechanism 2 of alkali cation transport possesses a spectrum of carrier sites with different ionic affinities.When both K(+) and Na(+) are presented at equivalent concentrations over the 1 to 50 mm range, mechanism 2 transports Na(+) almost exclusively, and mechanism 1 K(+) almost exclusively. These findings support previous conclusions to the effect that the active sites of mechanism 2 have higher affinity for Na(+) than for K(+), whereas the reverse is true for mechanism 1.

Journal Article↗

PubMed1965