ISSN:
1399-3054
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
The blue light-elicited monovalent anion-dependent alkalinization of the medium of Monoraphidium braunü (Legnerová, 202–7d) was characterized for the NO-3 and Cl- uptake. The maximal H+ uptake rates for these two anions have a similar optimum pH around 8.5, and quite similar Ks values for high (38 üM for Cl- and 35üM for NO-3) and low (320 üM for Cl- and 335 üM for NO-3) affinities. The steady H+ uptake associated with the uptake and reduction of NO-3 showed a Ks of 125 üM. which in this alga corresponds to the NO-3 reductase (EC 1.6.6.2) Km for NO-3. The only and striking difference found in the uptake properties of these anions was the delay time between the switching on of the blue light and the start of the alkalinization, which increased from 10 to 90 s as the initial pH decreased from 8.5 to 6.5 in the presence of NO-3, whereas for Cl- uptake this delay time (10s) did not vary in relation to the initial pH. When the NO-3 concentration in the medium was low (100 üM), the presence of relatively high concentrations of Cl- (3 üM), on the one hand, greatly stimulated the maximal alkalinization rates but, on the other, Cl- severely reduced the steady NO-3-dependent rate of alkalinization. The data indicate that Cl- inhibits competitively NO-3 uptake with a Ki of 750 üM. Moreover, high concentrations of NO-3 (above 5 üM) reduced its own maximal, but not the steady, uptake rates. The above results allow us to propose that most of the components of the individual NO-3 and Cl- transport systems are under identical light control and, as the competition data suggest, that these two anions may be taken up by the same transport system.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1399-3054.1995.tb00966.x
Permalink
