摘要
以不同外源KNO_3培养C_3和C_4禾本科作物幼苗,发现在2.5mmoL·L^(-1)以下时,7天龄大麦幼苗比同龄玉米幼苗有较低的NO_3^-吸收;但在5.0mmol·L^(-1)以上时,则是大麦幼苗比玉米幼苗有较高的NO_3^-吸收。另一方面,对从相同5.0mmol·L^(-1)KNO_3溶液里吸收NO_3^-的时间进程(0-24h)来看,5天龄和7天龄大麦幼苗都比同龄玉米幼苗有较高NO_3^-吸收。原因可能在于大麦幼苗根系比玉米幼苗根系有较低数量的构成型NO_3^-离子载体,但却具有较强的为外源NO_3^-所诱导的合成诱导型NO_3^-离子载体的能力。
In 1978 Brown (3) published the hypothesis that C_4plants have a greater nitrogen use efficiency, expressed as biomass production per unit of nitrogen in the plants, than C_3plants. Several experiments (2, 12, 11) support the hypothesis and the data indicate C_4species not only have greater nitrogen use efficiency but make more efficient use of chlorophyll, soluble protein, Rubisco and PEPC. Martin et al (9) found that NO_3^-3 accumulation was significantly higher in C_3cereals (barley and wheat) than in C_4cereals (corn and sorghum). This indicated to us that C_3cereals may accumulate NO_3^-3 in the vacuole rather than channelling it to nitrogen assimilation pro- ceses. Generally, Tubisco accounts for 30 to 60% of the soluble protein in C_3plants (14, 15, 5, 8), but only 5 to 20% in C_4plants (1, 6, 12, 13) . Typically, soluble protein accounts for about half of the organic leaf nitrogen. That means C_4plants have higher nitrogen converting efficiency than C_3do. In this investigation we have examined this point in detail. Levels of nitrate reductase (NRA), tissue NO_3^-3 and soluble protein in 1 week- and 3 week-old plants have been compared. The C_3cereals were barley, wheat, oats and rice; the C_4cereals, corn, teosinte, sorghum and sugarcane. We found that NRA and tissue NO_3^-3 levels were higher in C_3cereals whereas protein nitrogen was higher in C_4cereals. This trend was more apparent when the plant were irrigated with high levels of KNO3 (20mM).Similar trends are seen when plants are grown in Kimpack, sand+vermiculite and soil. These results suggest that C_4plants were more effi- cient than C_3plants in the converting of NO_3^-3-N to protein. In all tests, generally C_3cereals, whether grown for 1 week or 3, accumulated higher leves of NO_3^-3 than C_3cereals; but the accumulation of protein relative to NO_3^-3 was higher in the C_4cereals than in C_3cereals. Where assays were possible NRA relative to NO_3^-3 showed a similar trend. To the benefit of temperature (20℃) on C_3plants, we are currently doing the same experiments above and testing the uptake of NO_3^-3 in barley and corn seedings to see whether this aspect of N-assimilation is similar or different. We expect these experiments will contribute to increase the N-use efficiency in plants.
出处
《云南师范大学学报（自然科学版）》
1992年第4期72-77,共6页
Journal of Yunnan Normal University:Natural Sciences Edition
关键词
禾本科
作物
氮素
利用效率
C_3 and C_4 cereals
nitrate reductase
NO_3^-3
soluble protein
nitrogen conversion
nitrogen us efficiency
