Sequence Determination Of Light Harvesting Complexes Of Photosystem ? Of Bryopsis Corticulans And Study On The Effect Of High Light On Photosystem ? Pigment Composition Of Chlamydomonas Reinhardtii

Bryopsis corticulans is a macroalgae green alga living in intertidal zones.During floodtime,the light environment is dominated by blue-green light and green light and the light intensity is low,under which the algae is able to absorb a limiting amount of photons to perform photosynthesis;during low tides,the algae can adapt to the prolonged high light intensity stress by non-photochemical quenching(NPQ)mechanism.Photosystem I(PS?)is an efficient light energy converter in nature.We have found that the structure of Light harvesting complex I(LHCI)of this green alga is more complicated than that of higher plants,which may be related to the particularity in the living environment and the evolutionary level of the algae.Based on the study on separation,purification and characterization of PS?-LHCI from Bryopsis corticulans,we cooperated with the Institute of Botany of the Chinese Academy of Sciences and Tsinghua University to carry out the project of cryo-electron microscopy structure of Bc.PS?-LHCI.Due to the absence of the gene sequence of Bryopsis corticulans,as well as the high sequence similarity among the various Lhca proteins,the structural identification of Bc.PS?-LHCI was blocked.Therefore,the purpose of this study is structure identification of Bc.PS?-LHCI,based on the sequence of all the Lhca proteins obtained by molecular biology.Furthermore,the variance of photosynthesis pigment and related NPQ mechanism under high light stress in Chlamydomonas will be studied.Major results are as follows:1.The amino acid sequences of eight Lhca antenna proteins were obtained by homologous sequence amplification and transcriptome sequencing.Sequence alignment and evolution analysis suggested that the amino acid sequences of this eight Lhca proteins were exactly similar,and the amino acid sequences of Lhca proteins between different species were very conservative.2.Each Lhca in the Bc.PS?-LHCI super-complex was identified by matching the amino acid sequences with the electron density of the antenna proteins.It provides important information for the structure analysis of freeze electron microscope,and finally the structure of PS?-LHCI from Bryopsis corticulans was reported at a resolution of 3.49 ?.3.The C.reinhardtii cells were grown under two differents light conditions: normal light and high light.The thylakoid membrane was separated by sucrose density gradient centrifugation.In order to study the NPQ mechanism of Cr PS?-LHCI under high light stress,the ?-DDM was used to solubilize the thylakoid membrane to separate and purify the PS?-LHCI complex.4.After high light treatment,the pigment components of the xanthophyll cycle Antheraxanthin and Zeaxanthin were detected by the HPLC analysis in the C.reinhardtii cells,thylakoid membranes and isolated PS?-LHCI complexes respectively.These two pigments were not founded in the normal light treatment samples.Comparing the variance of pigment content in algae cells and in thylakoid membranes before and after high-light treatment,the results showed that the Violaxanthin was transformed into Zeaxanthin under high-light conditions.The conversion ratio of zeaxanthin was 54 % in the LHCII complex,33 % in PS?I complex,and about 13 % in PS?-LHCI complex.This result showed that the xanthophyll cycle exists in the PS?-LHCI complex under high light stress.