1-CHLORO-2,4-DINITROBENZENE-ELICITED INCREASE IN VACUOLAR GLUTATHIONE-S-CONJUGATE TRANSPORT ACTIVITY

Unlike most other characterized organic solute transport in plants, up take of the model compound S-(2,4-dinitrophenyl)glutathione (DNP-CS) a nd related glutathione-S-conjugates by vacuolar membranes is directly energized by MgATP. Here we show that exogenous application of the DNP -CS precursor 1-chloro-2,4-dinitrobenzene (CDNB) to seedlings of Vigna radiata (mung bean) increases the capacity of vacuolar membrane vesic les isolated from hypocotyls for MgATP-dependent DNP-CS transport in v itro. Our findings are 4-fold: (a) Pretreatment of seedlings with CDNB causes a progressive increase in MgATP-dependent DNP-GS uptake by vac uolar membrane vesicles, whereas the same range of CDNB concentrations causes only marginal stimulation when the compound benoxacor roacetyl )-3,4-dihydro-3-methyl-2H-1,4-benzoxazine] is included in the pretreat ment solution. (b) Increased DNP-CS uptake is accompanied by a proport ionate and selective increase in V-max(DNP-GS) but not in K-m(DNP-GS) or K-m(MgATP) (c) CDNB-enhanced DNP-CS uptake is not accompanied by a change in the density profile or sidedness of the vacuolar membrane f raction. (d) Basal and CDNB-enhanced DNP-GS uptake are indistinguishab le in terms of their inhibitor profiles. On the basis of these finding s, it is inferred that pretreatment with CDNB increases the amount or recruitment of functional transporter into the vacuolar membrane and t hat agents such as benoxacor antagonize the effects otherwise seen wit h CDNB in this sytem.