Components of chlorophyll biosynthesis were investigated in the plastid-ribosome-deficient albostrians mutant of barley (Hordeum vulgare L.). Compared with green leaves, white leaves lacked chloroplast tRNA(Glu) and 16S ribosomal RNA, but contained a much higher level of the mRNA for glutamate 1-semialdehyde aminotransferase. Substantial amounts of protochlorophyllide were accumulated when the mutant was incubated in a solution of δ-aminolevulinic acid. The level of protochlorophyllide oxidoreductase mRNA (PCOR, EC 1.6.99.1.) in etiolated albostrians plants reached only about 50% of the level in wild-type plants. In addition the content of PCOR protein and the activity of chlorophyll synthetase were distinctly lower than in the wild-type. Mutant and wild-type barley seedlings which were grown under a daily light/dark regime and were therefore nonetiolated both possessed PCOR mRNA. The data presented may help explain the albino phenotype of this mutant. The results are discussed in relation to biosynthesis of tetrapyrrols in higher plants, regulation of chlorophyll biosynthesis and the action of a plastidderived signal involved in the expression of certain nuclear genes.

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A cDNA clone for NADPH: protochlorophyllide oxi­doreductase from barley was subcloned for production of antisense-mRNA. This enabled heterologous hybridi­ zation with RNA from cress seedlings (Lepidium sativum L.). The m RNA level for NADPH: protochlorophyllide oxidoreductase did not decrease in cress seedlings during irradiation with continuous far-red or white light up to 12 h. The amount of NADPH: protochlorophyllide oxi­ doreductase protein, identified by Western blot de­ creased 5-fold after continuous irradiation with white light for 12 h. Species differences for light regulation of RNA are discussed.

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