摘要
NO_3^-亏缺能使叶片硝酸还原酶活性(NRA)和NO_3^-总量降低,而根部NO_3^-吸收及上运能力提高,以亏缺2d的幼苗最为明显,该幼苗经12hNO_3^-吸收,叶片的NRA高于未经亏缺的幼苗,但NO_3^-含量以后者为高,代谢库中NO_3^-含量前者高于后者。提高营养液中NO_3^-浓度,NO_3^-上运速率升高,叶片内NRA增加。叶片组织暗中无氧保温40min后,代谢库体积渐大,液泡内NO_3^-有外流产生;Cl^-可促使液泡内NO_3^-外流,代谢库中NO_3^-量增加,NRA升高。NRA在体内测定条件下,保温3h后,NO_2^-产生趋于稳值,NRA降至最低;系统中加KCl或KNO_3使NO_2^-产生趋于稳值的时间延长,且能提高NO_2^-积累总量。
The role of nitrate transport from root to shoot in the regulation of nitrate reductase activity (NRA) in vivo was investigated with seedlings of wheat Yangmai 3. When the seedlings were deprived of nitrate, both NRA and nitrate content in leaves decreased, but the former decreased more slowly than the latter. Once nitrate was supplemented to the culture solution, the rates of nitrate uptake and transport to shoot became higher, and the NRA increased. With an increase of the nitrate concentration in nutrient solution, the rates of nitrate uptake and transport increased with the rise of the NRA. The seedlings with higher rate of nitrate transport had higher NRA and nitrate contents in metabolic pool (MPS). This suggested that the rate of nitrate transport from root to shoot could regulate the NRA in leaves by changing the MPS of nitrate.
During the incubation period of lea. tissues, the volume of metabolic pool grew larger after 40 min. This indicated that the nitrate in vacuoles (storage pool) could leak to cytoplasm fot reduction when the contents of nitrate in cytoplasm decreased.
Pretreatment of leaf tissues with 50 mmol/L Cl^- for 2 h stimulated the efflux of nitrate from vacuole and enlarged the MPS of nitrate, and thus increased the NRA. When wheat leaf slices were incubated at 30℃ in darkness, nitrite production ceased after 3 h. Addition of KCl or KNO_3 to the incubation medium could delay the cessation of nitrite production, and the amount of accumulated nitrite increased.
The mechanism of nitrate efflux in vacuoles was discussed.
关键词
小麦
代谢库
上运
外流
硝酸还原酶
wheat, metabolic pool, upward transport, vacuolar efflux, nitrate reductase
