PLANT PHYSIOLOGY , Vol 109, Issue 1 177-185, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
1-Chloro-2,4-Dinitrobenzene-Elicited Increase in Vacuolar Glutathione-S-Conjugate Transport Activity
Z. S. Li, R. G. Zhen and P. A. Rea
Plant Science Institute, Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018
Unlike most other characterized organic solute transport in plants, uptake
of the model compound S-(2,4-dinitrophenyl)glutathione (DNP-GS) and related
glutathione-S-conjugated by vacuolar membranes is directly energized by
MgATP. Here we show that exogenous application of the DNP-GS precursor
1-chloro-2,4-dinitrobenzene (CDNB) to seedlings of Vigna radiata (mung
bean) increases the capacity of vacuolar membrane vesicles isolated from
hypocotyls for MgATP-dependent DNP-GS transport in vitro. Our findings are
4-fold: (a) Pretreatment of seedlings with CDNB causes a progressive
increase in MgATP-dependent DNP-GS uptake by vacuolar membrane vesicles,
whereas the same range of CDNB concentrations causes only marginal
stimulation when the compound benoxacor
[4-(dichloroacetyl)-3,4-dihydro-3-methyl-2H-1,4-benzoxazine] is included in
the pretreatment solution. (b) Increased DNP-GS uptake is accompanied by a
proportionate and selective increase in Vmax(DNP-GS) but not in Km(DNP-GS)
or Km(MgATP). (c) CDNB-enhanced DNP-GS uptake is not accompanied by a
change in the density profile or sidedness of the vacuolar membrane
fraction. (d) Basal and CDNB-enhanced DNP-GS uptake are indistinguishable
in terms of their inhibitor profiles. On the basis of these findings, it is
inferred that pretreatment with CDNB increases the amount or recruitment of
functional transporter into the vacuolar membrane and that agents such as
benoxacor antagonize the effects otherwise seen with CDNB in this sytem.