The Presence of DNA in Ribosome-Deficient Plastids of Heat-Bleached Rye Leaves

Abstract

In leaves of rye seedlings (Secale cereale L.) grown at 32°C the formation of plastid (70-S) ribosomes is specifically prevented. The resulting plastid-ribosome-deficient leaves can be used as a suitable system to identify chloroplast proteins which are translation products of cytosolic (80-S) ribosomes. The ribosome deficiency in plastids is accompanied by a bleaching of the leaves in light. In experiments aimed at finding the primary heat-sensitive event leading to ribosome deficiency the DNA of rye chloroplasts has been identified. Its properties are similar to those of chloroplast DNAs from other higher plants. The ribosome-deficient plastids isolated from heat-bleached rye leaves contained a DNA species which was indistinguishable from that of chloroplasts with regard to buoyant density in CsCl equilibrium gradients, reassociation properties and fragment patterns obtained upon cleavage by restriction endonucleases. Its quantity was comparable to that of chloroplast DNA of green leaves grown at a permissive temperature (22 "C). These results suggest that, unlike the effect in heat-bleached Euglena strains, lack of chloroplast DNA cannot be considered as the reason for the primary effect of high temperature on rye leaves but steps in the biosynthetic pathway of plastid ribosomes themselves must be affected more directly.In several higher plants, especially in cereal seedlings, the biogenesis of plastid ribosomes was found to be heat-sensitive [l]. When seedlings of these plants are grown at an appropriate non-permissive temperature, usually in the range between 32°C and 34 "C, the accumulation of plastid (70-S) ribosomes as well as that of plastid rRNA in leaves is prevented [2,3]. Consequently, defective plastids develop and the ribosome-deficient leaves grown in light are chlorotic [3,4]. In rye seedlings the interference of the high temperature was confined to events of plastid development and the high temperature apparently had no major damaging effects on the organization or functions of the rest of the cell [2-41.The high temperature appeared specifically to block the formation of the 70-S ribosomes in plastids and the defects observed seem to result primarily Abbreviations. NaCI/Cit, 0.15 M NaC1,0.015 M citrate, pH 7.2; cpDNA, chloroplast DNA, nDNA, nuclear DNA.

Effect of chloramphenicol and lincomycin on chloroplast DNA amplification in greening pea leaves

“…The present results, in agreement with earlier work with spinach leaf disk [7] and those with mutants [3,4,11,14], suggest that chloroplast genes are not important for light-induced chloroplast DNA amplification. In the complete sequences of chloroplast DNA [8,12], homologous sequences related to DNA replication have not been found, although about 30 open reading frames in the sequence have not yet been identified~ Probably, nuclear-encoded proteins are important for the amplification.…”

“…In wheat that lacks substantial portions of chloroplast genome, the chloroplast DNA still replicates [3]. Amplification of chloroplast DNA occurs in chloroplast ribosomedeficient mutants of maize [14], rye [4] and barley [11]. In cultured spinach leaf tissue, a single cycle of chloroplast division and chloroplast DNA synthesis is insensitive to chloramphenicol [7].…”

Unstable chloroplast ribosomes in the cold-sensitive barley mutanttigrina-o 34

“…The primary temperature-sensitive step for the formation of 70S ribosomes in rye is not yet known (12) although several biosynthetic reactions have been studied (3,17). From the electron microscopy data it is deduced that in the very young plastids ribosomes are present in tigrina-o 34 grown at 20 ~ in agreement with the small peak of 70S ribosomes obtained after isolation of ribosomes from the total leaf.…”

Loss of chloroplast transcripts for proteins associated with photosystem II: an early event during heat-bleaching in Euglena gracilis

“…To a large extent, these observations remind us of a 60 h partially bleached plastid in Euglena with one notable exception: bleached plastids in cereals retain their chloroplast DNA [19] and show remarkably strong levels of transcription by a presumably nuclear-encoded RNA polymerase [14,20]. Plastid transcription is not possible in fully bleached Euglena because transcription is template (chloroplast DNA)-limited [10].…”