Morgan M A, Volk R J, Jackson W A
Department of Soil Science, North Carolina State University, Raleigh, North Carolina 27695-7619.
Plant Physiol. 1985 Mar;77(3):718-21. doi: 10.1104/pp.77.3.718.
Roots of decapitated maize seedlings (Zea mays L.) were exposed for 12 hours to 1.0 millimolar KNO(3) (98.5 atom per cent (15)N) in the presence and absence (control) of 0.1 millimolar p-fluorophenylalanine (FPA), an analog of the amino acid phenylalanine. FPA decreased nitrate uptake but had little effect on potassium uptake. In contrast, accumulation of both ions in the xylem exudate was greatly restricted. The proportion of reduced (15)N-nitrogen that was translocated at each time was also restricted by FPA. These observations are interpreted as indicating that synthesis of functional protein(s) is required for nitrate uptake and for transport of potassium, nitrate, and reduced-(15)N from xylem parenchyma cells into xylem elements. The effect of FPA on nitrate reduction is less clear. Initially, FPA limited nitrate reduction more than nitrate uptake, but by 8 hours the cumulative reduction of entering nitrate was similar ( approximately 35%) in both control and FPA-treated roots. A relationship between nitrate uptake and nitrate reduction is implied. It is suggested that nitrate influx regulates the proportion of nitrate reductase in the active state, and thereby regulates concurrent nitrate reduction in decapitated maize seedlings.
将去头玉米幼苗（玉米）的根在存在和不存在（对照）0.1毫摩尔对氟苯丙氨酸（FPA，一种氨基酸苯丙氨酸的类似物）的情况下，暴露于1.0毫摩尔硝酸钾（98.5原子百分比的¹⁵N）中12小时。FPA减少了硝酸盐的吸收，但对钾的吸收影响很小。相比之下，木质部渗出液中这两种离子的积累都受到极大限制。每次转运的还原态¹⁵N-氮的比例也受到FPA的限制。这些观察结果被解释为表明，硝酸盐吸收以及钾、硝酸盐和还原态¹⁵N从木质部薄壁细胞转运到木质部成分中需要功能性蛋白质的合成。FPA对硝酸盐还原的影响不太清楚。最初，FPA对硝酸盐还原的限制比对硝酸盐吸收的限制更大，但到8小时时，对照根和经FPA处理的根中进入硝酸盐的累积还原量相似（约35%）。这暗示了硝酸盐吸收与硝酸盐还原之间的关系。有人提出，硝酸盐流入调节处于活性状态的硝酸还原酶的比例，从而调节去头玉米幼苗中同时发生的硝酸盐还原。
