Search

Similar NH[SUB4,SUP+] and NO[SUB3,SUP-] uptake kinetic patterns were observed in Neoagardhiella baileyi (Harvey ex Kützing) Wynne & Taylor and Gracilaria foliifera (Forsskål) Borgesen. NO[SUB3,SUP-] was taken up in a rate-saturating fashion described by the Michaelis-Menten equation. NH[SUB4,SUP+] uptake was multicomponent: a saturable component was accompanied by a diffusive or a high K component showing no evidence of saturation (at ⩽50 μM [NH[SUB4,SUP+]). Nitrogen starved plants (CIN atom ratios >ca. 10) showed higher transient rates of NH[SUB4,SUP+] uptake at a given concentration than plants not N-limited. Only plants with high N content transient rates of NH[SUB4m,SUP+] uptake rates, and showed transient rates of NH[SUB4,SUP+] accumulation which did not greastly exceed the capacity to incorporate N in steady-state growth. NH[SUB4,SUP+] was preferred over NO[SUB3,SUP-], even in plants preconditioned on NO[SUB3,SUP-] as the sole N source. NO[SUB3,SUP-] uptake was suppressed at 5 μM [NH[SUB4,SUP+]. But simulataneous uptake occurred at unsurpressed rates at lower concentrations. Potential for N accumultion was greater via NH[SUB4,SUP+] uptake than via NO[SUB3,SUP-] uptake. Changing capacity for NH[SUB4,SUP+] uptake with N content appears to be a mechanism whereby excessive accumulation of N was abvoided by N-satiated plants but large accumulation was possible for N-depleted plants. [ABSTRACT FROM AUTHOR]