We present the first characterization of K+ optimization of N uptake and metabolism in an NH4+-tolerant species, tropical lowland rice (cv. IR-72). 13N radiotracing showed that increased K+ supply reduces futile NH4+ cycling at the plasma membrane, diminishing the excessive rates of both unidirectional influx and efflux. Pharmacological testing showed that low-affinity NH4+ influx may be mediated by both K+ and non-selective cation channels. Suppression of NH4+ influx by K+ occurred within minutes of increasing K+ supply. Increased K+ reduced free [NH4+] in roots and shoots by 50-75%. Plant biomass was maximized on 10 mM NH4+ and 5 mM K+, with growth 160% higher than 10 mM NO3--grown plants, and 220% higher than plants grown at 10 mM NH4+ and 0.1 mM K+. Unlike in NH4+-sensitive barley, growth optimization was not attributed to a reduced energy cost of futile NH4+ cycling at the plasma membrane. Activities of the key enzymes glutamine synthetase (GS) and phosphoenolpyruvate carboxylase (PEPC) were strongly stimulated by elevated K+, mirroring plant growth and protein content. Improved plant performance through optimization of K+ and NH4+ is likely to be of substantial agronomic significance in the world’s foremost crop species.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/18163 |
| Date | 16 December 2009 |
| Creators | Balkos, Konstantine Dino |
| Contributors | Kronzucker, Herbert |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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