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Glycosylation of endogenous secondary plant products and abiotic substances such as herbicides increases their water solubility and enables vacuolar deposition of these potentially toxic substances. We characterized and compared the transport mechanisms of two glucosides, isovitexin, a native barley flavonoid C-glucoside and hydroxyprimisulfuron-glucoside, a herbicide glucoside, into barley vacuoles. Uptake of isovitexin is saturable (K m ‫؍‬ 82 M) and stimulated by MgATP 1.3-1.5-fold. ATP-dependent uptake was inhibited by bafilomycin A1, a specific inhibitor of vacuolar H ؉ -ATPase, but not by vanadate. Transport of isovitexin is strongly inhibited after dissipation of the ⌬pH or the ⌬⌿ across the vacuolar membrane. Uptake experiments with the heterologue flavonoid orientin and competition experiments with other phenolic compounds suggest that transport of flavonoid glucosides into barley vacuoles is specific for apigenin derivatives. In contrast, transport of hydroxyprimisulfuron-glucoside is strongly stimulated by MgATP (2.5-3 fold), not sensitive toward bafilomycin, and much less sensitive to dissipation of the ⌬pH, but strongly inhibited by vanadate. Uptake of hydroxyprimisulfuron-glucoside is also stimulated by MgGTP or MgUTP by about 2-fold. Transport of both substrates is not stimulated by ATP or Mg 2؉ alone, ADP, or the nonhydrolyzable ATP analogue 5-adenylyl-␤,␥-imidodiphosphate. Our results suggest that different uptake mechanisms exist in the vacuolar membrane, a ⌬pH-dependent uptake mechanism for specific endogenous flavonoid-glucosides, and a directly energized mechanism for abiotic glucosides, which appears to be the main transport system for these substrates. The herbicide glucoside may therefore be transported by an additional member of the ABC transporters.

In carotenoid-deficient albina mutants of barley and in barley plants treated with the herbicide Norflurdzon the light-dependent accumulation of the mRNA for the light-harvesting chlorophyll a/h protein (LHCP) is blocked. Thus, the elimination of a functional chloroplast, either as a result of mutation or as a result of herbicide treatment, can lead to the specific suppression of the expression of a nuclear gene encoding a plastid-localizcd protein. These results confirm and extend earlier observations on maize Euv. J.Biochem. 144, 79 -841. The inhibition of mRNA accumulation appears to be specific for the LHCP; the mRNAs encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and the NADPH : protochlorophyllide oxidoreductase are relatively unaffected. The failure of the albina mutants and of Norflurazon-treated plants to accumulate the LHCP mRNA is not exclusively caused by an instability of the transcript but rather by the inability of the plants to enhance the rate of transcription of the LHCP genes during illumination. Several chlorophyll-deficient xantha mutants of barley, which are blocked after protoporphyrin IX or Mg-protoporphyrin, and the chlorophyll-h-less mutant chlorina f 2 accumulate the LHCP mRNA to almost normal levels during illumination. Thus, if any of the reactions leading to chlorophyll formation is involved in the control of LHCP mRNA accumulation it should be one between the formation of protochlorophyllide and the esterification of chlorophyllide a.While the nature of the regulatory factor(s) has not been identified our results suggest that, in addition to phytochrome (Pfr), plastid-dependent factors are required for a continuous light-dependent transcription of nuclear genes encoding the LHCP.The light-induced transformation of etioplasts into chloroplasts in higher plants depends on an intimate interaction of the nuclear and plastid genomes [I -31. Many plastidlocalized proteins are nucleus-encoded and synthesized on cytoplasmic 80s ribosomes [4]. Some of these nucleus-encoded proteins form functional complexes with chloroplast-encoded proteins. Polypeptides comprising a given complex generally accumulate in a coordinate fashion. The basis of this apparent coordinate genc expression is unknown.One of the most prominent nucleus-encoded plastid membrane proteins, whose appearance is controlled by light, is the light-harvesting chlorophyll a/h protein (LHCP) [5 -71. While the assembly of the complete chlorophyll protein complex depends on the cooperation of at least two distinct photoreceptors, phytochrome and protochlorophyllide [8, 91, a rapid increase of the mRNA encoding the apoprotein of the LHCP can be induced by phytochrome alone [lo, 111. Similar phytochrome-induced changes in the concentration of specific niRNAs have been found for other nuclear-encoded plastid proteins, namely the small subunit of the ribulose-1,5-bisphosphate carboxylase and the NADPH: protochlorophyllide oxidoreductase 112-171. In all three cases it has been demonstrated that the photoreceptor is ...