1.2 Uptake of N and rhizosphere pH changes NH4+ assimilation: pH(acicl)-often whole root surface NO3 assimilation; pH often alkaline-sometimes in patches, may be also be pH patches elsewhere on same root Maize(in soil agar indicator) NO NH+ low no Marschner Romheld (1983) 60 1D
1.2 Uptake of N and Rhizosphere pH changes ▪ NH4 + assimilation: pH (acid) - often whole root surface ▪ NO3 - assimilation: pH often (alkaline) - sometimes in patches; may be also be pH patches elsewhere on same root Maize (in soil & agar + indicator) NO3 - NH4 + low NO3 - Marschner & Römheld (1983)
NH4 assimilation in roots (and pH regulation) protein etc light sucrose cO2 shoot Xylem phloem root Excess cation uptake amino-N NH4 Raven& Smith (1976); modified pH protein etc
NH4 + assimilation in roots (and pH regulation) amino-N NH4 + H+ protein etc protein etc sucrose CO2 shoot root xylem phloem pH light ‘Excess’ cation uptake Raven & Smith (1976); modified
NHy assimilation in roois (and pH regulation) protein etc light sucrose cO2 shoot xylem phloem root amino-N H protein etc
NH4 + assimilation in roots (and pH regulation) amino-N NH4 + H+ protein etc protein etc sucrose CO2 shoot root xylem phloem pH light ‘pH nonperturbing’ amino acids & amides
Ammonium cytoplasm outside High Affinity Trans port ve PD Systems: Km=20 NH4 40mmol/m As well as net efflux some ' re-cycles' by co transport NH transport with NH IIIEIIEIEIEE NH4+[& Kti Low Affinity TS channel NH4+ [&K+1? NH3?(Diffusion at high concentrations?) Energetics, kinetics, regulation, genes: Forde Clarkson(1999); Glass et al. (2002)
Ammonium cytoplasm outside -ve PD NH4 + H+ ) NH4 + ) H+ → NH4 + [& K+ ] NH4 + [& K+ ]? NH3? High Affinity Transport Systems; Km=20- 40mmol/m3 Low Affinity TS (Diffusion at high concentrations?) channel H+ cotransport As well as net H+ efflux, some H+ ‘re-cycles’ by cotransport with NH4 + Energetics, kinetics, regulation, genes : Forde & Clarkson (1999); Glass et al. (2002) pH
pH regulation during NO3 assimilation in roots protein etc light sucrose cO2 shoot xylem phloem root amino-N 2H+pH T protein etc
pH regulation during NO3 - assimilation in roots amino-N NO3 - 2H+ protein etc protein etc sucrose CO2 shoot root xylem phloem pH light ‘Excess’ anion uptake