Optimization of ammonium acquisition and metabolism by potassium in rice (Oryza sativa L. cv. IR-72).

ABSTRACT We present the first characterization of K(+) optimization of N uptake and metabolism in an NH(4)(+)-tolerant species, tropical lowland rice (cv. IR-72). (13)N radiotracing showed that increased K(+) supply reduces futile NH(4)(+) cycling at the plasma membrane, diminishing the excessive rates of both unidirectional influx and efflux.

NH4+-stimulated and -inhibited components of K+ transport in rice (Oryza sativa L.).

The disruption of K(+) transport and accumulation is symptomatic of NH(4)(+) toxicity in plants. In this study, the influence of K(+) supply (0.02-40 mM) and nitrogen source (10 mM NH(4)(+) or NO(3)(-)) on root plasma membrane K(+) fluxes and cytosolic K(+) pools, plant growth, and whole-plant K(+) distribution in the NH(4)(+)-tolerant plant species rice (Oryza sativa L.

Alleviation of rapid, futile ammonium cycling at the plasma membrane by potassium reveals K+-sensitive and -insensitive components of NH4+ transport.

Futile plasma membrane cycling of ammonium (NH4+) is characteristic of low-affinity NH4+ transport, and has been proposed to be a critical factor in NH4+ toxicity. Using unidirectional flux analysis with the positron-emitting tracer 13N in intact seedlings of barley (Hordeum vulgare L.), it is shown that rapid, futile NH4+ cycling is alleviated by elevated K+ supply, and that low-affinity NH4+ transport is mediated by a K+-sensitive component, and by a second component that is independent of K+.

Mechanism of CO2 acquisition in an acid-tolerant Chlamydomonas.

The acid-tolerant green alga Chlamydomonas (UTCC 121) grows in media ranging in pH from 2.5 to 7.0.