The Light-adaptive Regulation Of Periphera Light-harvesting Complex(LH2) In Rhodopseudomonas Palustris CGA009

Rhodopseudomonas palustris(Rps. palustris) is a model organism for the mechanism study of photosynthesis. Absorption spectral diversity of periphera light-harvesting complex(LH2) is an important embodiment of the adaptability of purple bacteria to light environment. Explaining the mechanism of LH2 spectral diversity is of great significance for understanding the adaptability to the light environment and the photosynthesis mechanism of purple bacteria. As the representative of purple bacteria, Rhodopseudomonas palustris(Rps. palustris) can synthesis typical LH2 and abnormal LH2(called LH4) when grown under high light and low light respectively. The root cause of LH2 spectral diversity is the multi-copy genes pucBA encoding α/β polypeptide in Rps. palustris. However, low resolution structures, amino acid similarities between the complexes, and a lack of transcription analysis have made it difficult to determine the contributions of different pucBA operons to the composition and function of different LH complexes. In view of this problem, our study taking Rps. palustris CGA009 as the research material investigated the the relationship between the changes of pigments content in CGA009 grown under different light intensities and the LH2 spectral diversity. The main results were as follows:Different light intensity had significant effects on the cell growth, spectral type of peripheral light harvesting complex and pigment metabolism of CGA009 strain. The cell growth rate are maximum under 2500 lux, minimum under 50 lux; More higher light(4500 lux) inhibited the accumulation of biomass, and the strain can not grow under more lower light(7 Lux) Under high light, cells synthesised LH2 complexes, and under low light, LH4 was synthesized. BChl a and six Cars were accumulated in CGA009 strains grown under different lights but the accumulation amount showed differences. Under low light, the lycopene and rhodopin with lower conjugate were mainly accumulated, and the spirilloxanthin with higher conjugate were mainly accumulated under low light.Rps. palustris CGA009 pucBA showed selective expression in different light intensity, Under low and intermediate light, genes(pucBAa, pucABb and pucBAe)encoding LH2 polypeptide and gene(pucABd) encoding LH4 polypeptide were transcripted and co-transcription, and the transcription level is the highest under low light.Only pucBa, pucAb, pucBc, pucAd and pucBAe were transcripted under high light. Light intensity influenced the pucBA gene transcription and the assembly of light harvesting complexes, but the sensitive response of pucBA gene transcription to light priored to the assembly of light harvesting complexes.The study about stability of non-growth CGA009 cells under different light and oxygen conditions showed: the stability of C-800 light-harvesting structure in LH2 cells was poorer under anaerobic and high light intensity, while C-850 was most stable under the same condition. Both C-800 and C-850 light-harvesting structure in LH4 cells were degraded rapidly under anaerobic and high light. The stability of C-850 light harvesting structure was worse than that of C-800 under anaerobic and low light. It can be seen that the stability of peripheral light-harvesting complex is a potential factor for the LH2 spectral diversity.