Morgan M A, Volk R J, Jackson W A
Department of Soil Science, North Carolina State University, Raleigh, North Carolina 27607.
Plant Physiol. 1973 Feb;51(2):267-72. doi: 10.1104/pp.51.2.267.
Experiments with intact plants of Lolium perenne previously grown with (14)NO(3) (-) revealed significant efflux of this isotopic species when the plants were transferred to solutions of highly enriched (15)NO(3) (-). The exuded (14)NO(3) (-) was subsequently reabsorbed when the ambient solutions were not replaced. When they were frequently replaced, continual efflux of the (14)NO(3) (-) was observed. Influx of (15)NO(3) (-) was significantly greater than influx of (14)NO(3) (-) from solutions of identical NO(3) (-) concentration. Transferring plants to (14)NO(3) (-) solutions after a six-hour period in (15)NO(3) (-) resulted in efflux of the latter. Presence of Mg(2+), rather than Ca(2+), in the ambient (15)NO(3) (-) solution resulted in a decidedly increased rate of (14)NO(3) (-) efflux and a slight but significant increase in (15)NO(3) (-) influx. Accordingly, net NO(3) (-) influx was slightly depressed. A model in accordance with these observations is presented; its essential features include a passive bidirectional pathway, an active uptake mechanism, and a pathway for recycling of endogenous NO(3) (-) within unstirred layers from the passive pathway to the active uptake site.
对先前用(14)NO(3) (-)培养的多年生黑麦草完整植株进行的实验表明，当将这些植株转移到高度富集(15)NO(3) (-)的溶液中时，这种同位素形态会有显著外流。当环境溶液不更换时，渗出的(14)NO(3) (-)随后会被重新吸收。当频繁更换环境溶液时，会观察到(14)NO(3) (-)持续外流。在相同NO(3) (-)浓度的溶液中，(15)NO(3) (-)的内流显著大于(14)NO(3) (-)的内流。在(15)NO(3) (-)中培养6小时后将植株转移到(14)NO(3) (-)溶液中，会导致后者外流。环境(15)NO(3) (-)溶液中存在Mg(2+)而非Ca(2+)，会使(14)NO(3) (-)的外流速率明显增加，(15)NO(3) (-)的内流略有但显著增加。因此，净NO(3) (-)内流略有降低。本文提出了一个符合这些观察结果的模型；其基本特征包括一个被动双向途径、一个主动吸收机制，以及一个在内源NO(3) (-)从被动途径到主动吸收位点的非搅拌层内进行循环的途径。
