咖啡的硝酸还原酶活性及其对根外追肥的反应

用体内法测定小粒种咖啡植株硝酸还原酶活性及分析其对根外追肥反应的结果表明:①漂浮于低浓度NO_8~-诱导液中的咖啡叶片,NO_8~-积累量少,硝酸还原酶体内测定的活性是保温介质中NO_8~-浓度的函数,硝酸还原酶米氏方程模拟良好,双倒数作图在高底物浓度下近乎直线(r=0.9396)。②直接从田间采样的咖啡叶片,不需经硝态氮诱导就有可测定的酶活性。沙培的咖啡籽苗通过根部进行硝态氮诱导,其硝酸还原酶活性以根中为最强,叶和茎中次之,移栽了3个月的小苗,其根、茎、叶中酶活性的强弱相差不大;2—3年生成龄植株的酶活性以叶中的为最强,而且植株外围成熟阳叶的要比内层阴叶的强,枝梢幼叶的最弱。③施用钼酸铵和螯合稀土钼能增强田间咖啡叶片的硝酸还原酶活性,但对硝态氮诱导的最大酶活性没有增益效应;施用硝酸稀土也能增强田间咖啡叶片的硝酸还原酶活性,而且对硝态氮诱导的最大酶活性仍有增益效应;施用尿素对咖啡叶片的硝酸还原酶活性及其硝态氮诱导的最大酶活性都不具增效作用。

NITRATE REDUCTASE ACTIVITY IN COFFEE TREE AND ITS CHANGES AFTER LEAF FERTILIZATION

In vivo assay was applied in the determination of nitrate reductase activity(NRA) in Coffea arabica and of response of the enzyme to leaf fertilization. The results obtained showed that in those coffee leaves floating on low concentration of NO_3~- solution, the accumulation of NO_3~- was negligible, the NRA was the function of NO_3~- concentration in the solution, Michaelis's equation simulation fitted very well into the NRA, and the bireciprocal figure presented approximately in linear pattern(r=0.9396). The results also revealed that in those leaves obtained directly from the field, NRA was detectable without any induction of nitric nitrogen. In the case of supply of nitric nitrogen to the roots of coffee seedling in pot culture, NRA was highest in roots, followed by leaves and stems. NRA didn't show big difference between roots, stems and leaves of young coffee seedlings transplanted for three months. On mature coffee plants of 2-3 years old, NRA was highest in leaves, hut higher in mature unshady outer leaves than inner shady leaves and lowest in young leaves on shoot top. It was found that application of ammonium molybdate and chelated rare earth molybdate could increase the NRA in leaves of coffee trees in field, but no benificiary effects could be seen by such increase to the peak NRA already induced by nitric nitrogen. On the contrary, application of rare earth nitrate not only could increase the NRA in leaves of coffee trees in field, but also give beneficiary effects to the peak NRA induced by nitric nitrogcn. Application of urea didn't bring about any increase in NRA in coffee leaves or any beneficiary effect to the peaks NRA induced by nitric nitregon.