Identification of Indole-3-Acetic Acid in the Basidiomycete Schizophyllum commune

Indole-3-acetic acid (IAA) was detected in the ether extracts of culture filtrates of indigotin-producing strains of the basidiomycete Schizophyllum commune. Several solvents, known to give distinctly different R(F) values for IAA, and 3 location reagents gave identical results with synthetic IAA and IAA found in the extract. Confirmation was obtained by the Avena straight growth test, split pea test, and ultraviolet absorption spectrum.

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.

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.

Preferential Absorption of Potassium by Leaf Tissue of the Mangrove, Avicennia Marina: An Aspect of Halophytic Competence in Coping with Salt

One aspect of the salt tolerance of the mangrove, Avicennia marina, was investigated: the preferential absorption of potassium by leaf tissue in the presence of high concentrations of salt (sodium chloride). The rate of absorption of potassium, over the concentration range 0�02 to 1�5 mM, follows the Michaelis-Menten relation, approaching the theoretical maximum, V max, at 1� 5 mM. The apparent Michaelis constant is 0�20 mM. At higher concentrations, up to 50 mM potassium, the rate of potassium absorption reaches values several times higher than the theoretical maximum calculated on the basis of the relation applying over the low range of concentrations, indicating the operation of a second mechanism of absorption. At both low (1 mM) and high (10 mM) concentrations of potassium, its absorption was little affected by sodium chloride concentrations up to 200 mM. At 10 mM potassium, sodium chloride at concentrations up to and including 500 mM (more than its concentration in sea.water) failed to interfere with the absorption of potassium.