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 ...

Plastids of Cuscuta reflexa Roxb., C. subinclusa D. et H., C. gronovii Willd. and C. campestris Yunck. possess thylakoids and contain both chlorophyll a and b in a ratio similar to that of stem tissue of the systematically closely related but 'normal' green Ipomoea tricolor. In contrast, plastids of C. odorata R. et P. and C. grandiflora H.B.K. do not contain any chlorophyll or possess thylakoids. Light-driven electron transport, as measured by oxygen evolution and indicated by analysis of chlorophyll fluorescence, was present in all chlorophyll-containing species. The photosystem II efficiency was low and ranged from 0.511 to 0.687. The plastid rbcL gene could not be detected in C. odorata, but was present in all other tested species. Neither rbcL transcripts nor the large subunit of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) could be detected in C. odorata and C. grandiflora. Low amounts of the large subunit of Rubisco were detected immunologically in all other Cuscuta species. Apparently, the genus Cuscuta comprises species with different degrees of plastid functionality, ranging from intact chloroplasts, via plastids with impaired protein production and gene expression to plastids with reduced plastome gene content.

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Electron microscopical investigations of primary haustoria of Orobanche crenata parasitizing the roots of the highly compatible host, Vicia narbonensis, reveal an uninterrupted phloem system connecting both partners. Individual sieve elements belonging to the host and parasite could be identified by the cell markers: plastids, mitochondria and P-protein, which in the present system turned out to have species-specific fine structure.Sieve pores of normal structure interconnect the sieve elements of host and parasite. They origmate from interspecific plasmodesmata.

Phloem proteins of the sieve tube exudate from Cucurbita maxima Duch. and Cucurbita pepo L. were investigated as to their filament forming ability in vitro. From the two main proteins (116000 dalton, 30000 dalton) only the 116000 dalton protein was found to form reversibly distinct filaments of 6-7 nm diameter upon removal of SH-protecting agents from the buffer, whereas the 30000 dalton protein was precipitated as amorphous material under these conditions. The protein filaments were similar to the filaments ocurring within the sieve tube cells in vivo.