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Biomedical subjects

P E Gamble

Publications and source records attributed to P E Gamble.

6 recordsLinked to original sources
PubMed1989

Translation and stability of proteins encoded by the plastid psbA and psbB genes are regulated by a nuclear gene during light-induced chloroplast development in barley.

We have characterized a nuclear mutant of barley, viridis-115, lacking photosystem II (PSII) activity and compared it to wild-type seedlings during light-induced chloroplast development. Chloroplasts isolated from wild-type and viridis-115 seedlings illuminated for 1 h synthesized similar polypeptides and had similar protein composition. After 16 h of illumination, however, mutant plastids exhibited reduced ability to radiolabel D1, CP47, and several low Mr membrane polypeptides, and by 72 h, synthesis of these proteins was undetectable. Immunoblot analysis showed that plastids of dark-grown wild-type barley lacked several PSII proteins (D1, D2, CP47, and CP43) and that 16 h of illumination resulted in the accumulation of these polypeptides. In contrast, these polypeptides did not accumulate in illuminated viridis-115 seedlings, although mutant plastids accumulated two PSII proteins that participate in oxygen evolution, oxygen-evolving enhancers 1 and 3. Northern analysis showed that the levels of psbA and psbB mRNA in mutant plastids were equal to or greater than levels in wild-type plastids throughout the developmental period examined here. These results indicate that the nuclear mutation present in viridis-115 affects the translation and stability of the chloroplast-encoded D1 and CP47 polypeptides and that its influence is expressed after the onset of light-induced chloroplast development.

Blotting, Northern↗
PubMed1989

Blue light regulates the accumulation of two psbD-psbC transcripts in barley chloroplasts.

Synthesis of D2, a Photosystem II reaction center protein encoded by psbD, is differentially maintained during light-induced chloroplast maturation. The continued synthesis of D2 is paralleled by selective light-induced accumulation of two psbD-psbC transcripts which share a common 5' terminus. In the present study, we examine the nature of the photoreceptor and the fluence requirement for psbD-psbC transcript induction. The light-induced change in psbD-psbC RNA population can be detected between 1 and 2 h after 4.5 day old dark-grown barley seedlings are transferred to the light. Light-induced transcript accumulation occurs normally in the chlorophyll-deficient barley mutant, xan-f10, indicating that light-activated chlorophyll formation and photosynthesis are not required for RNA induction. High fluence blue light fully induces psbD-psbC transcript accumulation; low or high fluence red or far-red light do not. However, psbD-psbC transcript accumulation elicited by blue light pulses can be partially attenuated if far-red light is given immediately following the blue light treatment. Thus, although blue light is needed to initiate transcript accumulation, phytochrome modulates the amplitude of the response. Pretreatment of dark-grown plants with cycloheximide blocks light-induced psbD-psbC transcript accumulation. This could implicate a blue-light responsive nuclear gene in the light-induced accumulation of the two psbD-psbC transcripts.

4-Aminobutyrate Transaminase↗
PubMed1988

Light-dependent changes in psbD and psbC transcripts of barley chloroplasts: accumulation of two transcripts maintains psbD and psbC translation capability in mature chloroplasts.

The psbD and psbC genes encode two polypeptides of Photosystem II. These genes are adjacent in the barley chloroplast genome and are part of a 5.7 kbp transcription unit. In dark-grown barley, four large transcripts hybridize to psbD and psbC; two additional transcripts hybridize to psbC. Illumination of 4.5-day-old dark-grown seedlings causes a decrease in the six psbD--psbC transcripts found in etioplasts and the accumulation of two different transcripts of 4.0 and 3.2 kb which hybridize to psbD and psbC. The light-induced transcripts have a common 5' end approximately 600 nt upstream of psbD and 3' ends 1175 and 175 nt downstream of psbC. The shift in psbD--psbC transcript population occurs during a phase of chloroplast maturation when transcript levels and translation of chloroplast genes such as psaA--psaB and psbB decline approximately 3- to 5-fold. In contrast, translation of the psbD and psbC gene products declines to a lesser extent, suggesting that the light-induced accumulation of the 4.0 and 3.2 kb psbD--psbC transcripts is required to maintain psbD and psbC gene product translation in mature chloroplasts.

Chlorophyll↗
PubMed1987

Characterization of the barley chloroplast transcription units containing psaA-psaB and psbD-psbC.

Four plastid genes, psaA, psaB, psbD and psbC, were localized on the barley plastid genome. PsaA was adjacent to psaB in one transcription unit and psbD was adjacent to psbC in a second transcription unit. The transcription units containing psaA-psaB and psbD-psbC are separated by approximately 25 kbp on the barley plastid genome and are transcribed convergently. Transcripts hybridizing to each transcription unit were characterized by northern blot analysis, S1 protection experiments and primer extension analysis. Two 5.3 kb transcripts hybridize to psaA-psaB. The two transcripts have a common 5' end but differ at their 3' ends by about 26 nucleotides. The transcription unit which contains psbD-psbC also includes trnS(UGA), trnG(GCC), and an open reading frame which codes for a 62 amino acid protein. Six large transcripts ranging from 5.7 kb to 1.7 kb hybridize to the psbD-psbC transcription unit as well as several RNAs of tRNA size. The large transcripts arise from three 5' ends and two clusters of 3' ends. The 3' ends map near trnG(GCC) and trnS(UGA) and could be generated by RNA processing or termination of transcription. Two of the six transcripts hybridize to psbC but not psbD suggesting that translation of psbD and psbC could occur on separate RNAs.

Biological Evolution↗
PubMed1986

Inhibition of carotenoid accumulation and abscisic acid biosynthesis in fluridone-treated dark-grown barley.

Treatment of dark-grown barley with 0.1 mM fluridone inhibited carotenoid accumulation but did not alter plastid biogenesis. Plastids isolated from dark-grown control and dark-grown fluridone-treated plants were similar in size and protein compositions. Dehydration of dark-grown control barley caused abscisic acid levels to increase 30-40-fold in 4 h, while plants treated with 0.1 mM fluridone accumulated very little abscisic acid in response to dehydration. These results suggest that fluridone-treated plants do not accumulate abscisic acid because of carotenoid deficiency rather than plastid dysfunction. Dark-grown barley plants treated with 0.31 microM fluridone accumulated low levels of carotenoids. Dehydration of these plants resulted in a 4-8-fold increase in abscisic acid and a decrease in antheraxanthin, violaxanthin and neoxanthin, but no change in beta-carotene or lutein plus zeaxanthin levels. This result is consistent with the suggestion that xanthophylls are precursors to abscisic acid in dehydrated plants.

Abscisic Acid↗