title: Intercellular localization of nitrate reductase in roots.
abstract: Experiments were conducted with segments of corn roots to investigate whether nitrate reductase (NR) is compartmentalized in particular groups of cells that collectively form the root symplastic pathway. A microsurgical technique was used to separate cells of the epidermis, of the cortex, and of the stele. The presence of NR was determined using in vitro and enzyme-linked immunosorbent assays. In roots exposed to 0.2 millimolar NO(3) (-) for 20 hours, NR was detected almost exclusively in epidermal cells, even though substantial amounts of NO(3) (-) likely were being transported through cortical and steler cells during transit to the vascular system. Although NR was present in all cell groups of roots exposed to 20.0 millimolar NO(3) (-), the majority of the NR still was contained in epidermal cells. The results are consistent with previous observations indicating that limited reduction of endogenous NO(3) (-) occurs during uptake and reduction of exogenous NO(3) (-). Several mechanisms are advanced to account for the restricted capacity of cortical and stelar cells to induce NR and reduce NO(3) (-). It is postulated that (a) the biochemical system involved in the induction of NR in the cortex and stele is relatively insensitive to the presence of NO(3) (-), (b) the receptor for the NR induction response and the NR protein are associated with cell plasmalemmae and little NO(3) (-) is taken up by cells of the cortex and stele, and/or (c) NO(3) (-) is compartmentalized during transport through the symplasm, which limits exposure for induction of NR and NO(3) (-) reduction.
authors: United States Department of Agriculture, Agricultural Research Service, Oxford, North Carolina 27565.
authors: T W
authors: TW
authors: Rufty
authors: J F
authors: JF
authors: Thomas
authors: J L
authors: JL
authors: Remmler
authors: W H
authors: WH
authors: Campbell
authors: R J
authors: RJ
authors: Volk