From compartmental analysis of 15N elution measurements, concentrationsand fluxes of NH+4 and NO3 were estimated for corticalcells in excised root segments, when bathed in a complete nutrientsolution, in which 20 mol m3 NH4+ or NO3 werethe single N sources. The results were compared with those fornutrient solution containing 20 mol m3 NH4NO3. No nitratereductase activity was detected in the roots but rapid assimilationof NH4+ occurred, due to glutamine synthetase activity. Theefflux curves for NH4+, on a 'µg 15N remaining againsttime' basis, deviated from the criteria determining conformityto first order kinetics, since the slowest rate constant wasan order of magnitude lower than that exhibited by the curvefor efflux versus time. The data were transformed to conformto the appropriate criteria, revealing a large slowly exchangingpool equated with assimilated NH4+. The presence of NO3had little effect on NH4+ uptake and exchange, but NH4+ suppressedNOj uptake and reduced exchange across plasmalemma and tonoplast.It was established that NH4+ absorption was an active process.However, NH4+ entering and leaving the vacuole was overestimated,since the flux equation used did not differentiate between total15NH4 influx at the plasmalemma and that at the tonoplast, afterassimilation. The only active NO3 transfer was influxat the plasmalemma. The results were compared with those ofothers using13N and 36C1O3 analogues to measure NH4+ and NO3fluxes in cereal roots. Key words: Ammonium, nitrate, compartmental analysis, 15N, active transport 相似文献
Polymerase chain reaction (PCR)‐based isolation of microsatellite arrays (PIMA) technique was used to isolate seven polymorphic microsatellite loci in sea bass, Lates calcarifer Bloch. A total of 62 samples of wild and cultivated sea bass collected from a few populations within Peninsular Malaysia were used in the study. For seven polymorphic loci, the number of alleles ranged from four to nine and locus heterozygosities ranged from 0.710 to 1.000. The loci will be useful for studying population structure, genetic variability of wild and hatchery stocks of L. calcarifer and broodstock management purposes. 相似文献