中文摘要：

【目的】作物选择性吸收铵态氮或硝态氮是导致根际pH发生变化的主要原因,本文探索旱地作物根系细胞膜质子泵对铵硝营养及pH的反应机制。【方法】采用水培方法,分别用NH＋4-N和NO-3-N培养高粱幼苗,并控制营养液的pH。高粱生长三周以后,用葡聚糖两相法分离根系细胞膜,测定细胞膜质子泵的水解活性、酶动力学特征,利用免疫杂交方法测定质子泵蛋白浓度。【结果】培养三周后,供给铵态氮的高粱根际pH下降到3,质子泵活性最高,达到Pi 8．81μmol/（mg·min）；供给硝态氮的高粱根际pH上升至7,质子泵活性最低,为Pi 3．82μmol/（mg· min）。将铵态氮处理的营养液pH人为上调到7,而将硝态氮处理下调到3后发现,铵态氮培养的高粱根系细胞膜质子泵活性在pH 7时低于pH 3,但仍高于pH 3时硝态氮处理。酶动力学特征的测定结果表明,铵态氮营养（ pH 3）时,酶反应最大速率最高,亲和性也最高,而硝态氮营养（pH 7）时酶反应最大速率最小,亲和性也最低。质子泵活性与其蛋白浓度之间具有正相关性。【结论】无论是铵还是硝态氮处理,根际pH降低都会导致高粱根系细胞膜质子泵活性升高,这说明,质子泵具有适应根际酸化而提高自身活性的基本功能。但是,在相同的pH下,铵态氮都导致高粱根系细胞膜质子泵活性比硝态氮处理更高,这说明铵态氮在根系细胞中同化产生氢离子,而硝态氮的还原不产生氢离子,因此,吸收铵态氮的细胞需要进一步提高细胞膜质子泵的活性将氢离子排出体外。这很可能是高粱根系在铵态氮营养下的一种反应机制。

英文摘要：

[Objectives]Ammonium and nitrate nutrition strongly affect the rhizosphere pH. The response of upland crop to the different pH in root with ammonium and nitrate supplies was studied. [Methods] Using a hydroponic experiment, sorghum（ Sorghum bicolor） was supplied with NH＋4-N or NO-3-N as sole nitrogen nutrition. After 3 weeks’ cultivation, the plasma membrane vesicles of sorghum roots were isolated using a two-phase system with poly-glucose. The rhizosphere pH and the plasma membrane H＋-ATPase hydrolytic activity were measured, and the enzyme concentration was tested by immune hybridizes.[Results] The activity of H＋-ATPase in the plasma membrane of sorghum roots supplied with NH＋4-N（pH3）is 8. 81 μmol Pi/（mg·min）and is markedly higher than that supplied with NO-3-N（pH 7）（3. 82 μmol Pi/（mg·min）. If the pH was adjusted to 7 in the medium with ammonium nutrition, the activity of H＋-ATPase is decreased. In contrast, if the pH was adjusted to 3 in the medium with nitrate nutrition, the activity of H＋-ATPase is increased, and the activity of H＋-ATPase in sorghum roots treated by ammonium nutrition related to the protein concentration. These results indicate that the higher activity of plasma membrane H＋-ATPase in sorghum roots is affected by the rhizosphere pH. However, ammonium＆amp;nbsp;has stronger influence on the activity of plasma membrane H＋-ATPase, even at the same medium pH.[Conclusion]Plasma membrane H＋-ATPase could adapt to the rhizosphere acidification by enhancing its activity, either under ammonium or nitrate application. In contrast to the H＋ consumption after nitrate reduction, the H＋production after ammonium assimilation should be pumped outside the root cell with further enhancement of the plasma membrane H＋-ATPase activity. This might be the mechanism of adaptation to ammonium nutrient by sorghum roots.