INTERACTIONS OF NH4-GLUTAMATE WITH NO3- TRANSPORT PROCESSES OF NONMYCORRHIZAL FAGUS-SYLVATICA ROOTS( AND L)

The processes of NO3- uptake and transport and the effects of NH4+ or L-glutamate on these processes were investigated with excised non-myco rrhizal beech (Fagus sylvatica L,) roots, NO3- net uptake followed uni phasic Michaelis-Menten kinetics in a concentration range of 10 mu M t o 1 mM with an apparent K-m of 9.2 mu M and a V-max of 366 nmol g(-1) FW h(-1), NH4+, when present in excess to NO3- or 10 mM L-glutamate in hibited the net uptake of NO3-. Apparently, part of NO3- taken up was loaded into the xylem, Relative xylem loading of NO3- ranged from 3.2 +/- 1,6 to 6.4 +/- 5,1% of NO3- net uptake, It was not affected by tre atment with NH4+ or L-glutamate. N-15/N-13 double labelling experiment s showed that NO3- efflux from roots increased with increasing influx of NO3- and, therefore, declined if influx was reduced by NH4+ or L-gl utamate exposure, From these results it is concluded that NO3- net upt ake by non-mycorrhizal beech roots is reduced by NH4+ or L-glutamate a t the level of influx and not at the level of efflux.