INVESTIGATION OF THE APPARENT INDUCTION OF NITRATE UPTAKE IN BARLEY (HORDEUM-VULGARE L) USING NO3--SELECTIVE MICROELECTRODES - MODULATION COARSE REGULATION OF NO3- UPTAKE BY EXOGENOUS APPLICATION OF DOWNSTREAMMETABOLITES IN THE NO3- ASSIMILATORY PATHWAY
Gh. Henriksen et Rm. Spanswick, INVESTIGATION OF THE APPARENT INDUCTION OF NITRATE UPTAKE IN BARLEY (HORDEUM-VULGARE L) USING NO3--SELECTIVE MICROELECTRODES - MODULATION COARSE REGULATION OF NO3- UPTAKE BY EXOGENOUS APPLICATION OF DOWNSTREAMMETABOLITES IN THE NO3- ASSIMILATORY PATHWAY, Plant physiology, 103(3), 1993, pp. 885-892
The influence of a 12-h pretreatment with either NO3-, NH4+, glutamine
, or glutamate (300 mu M) on the apparent induction of NO3- uptake was
investigated. Net fluxes of NO3- into roots of intact, 7-d-old barley
(Hordeum vulgare L. cv Prate) seedlings in solution culture were esti
mated from ion activity gradients measured with NO3--selective microel
ectrodes in the unstirred layer of solution immediately external to th
e root surface. Control plants, pretreated with nitrogen-free nutrient
solution, exhibited a sigmoidal increase in net NO3- uptake, reaching
a maximum rate between 8 and 9 h after first exposure to NO3-. Plants
pretreated with NH4+ or Glu exhibited a delay of several hours in the
initiation of the induction process after they had been exposed to NO
3-. In Gln-pretreated plants, however, responses ranged from no delay
of the induction process to delays comparable to those observed follow
ing NH4+ or Glu pretreatments. Only treatment with NO3- resulted in th
e induction of NO3- uptake, whereas pretreatments with NH4+, Gln, or G
lu tended to delay induction of NO3- uptake upon subsequent exposure t
o NO3-.