Characterization And Spectroscopic Property Studies Of Red-shifted Chlorophyll Producing Cyanobacteria In Subtropic Forest Ecosyetem

Chlorophyll plays an important role in energy capture and energy transfer of photosynthesis.So far,chlorophyll a,b,c,d,f have been found in higher and lower plants.Since chlorophyll d(Chl d)and chlorophyllf(Chl f)can absorb far-red light,they are known as red-shifted chlorophyll.The discoveries of red-shifted chlorophylls challenged the traditional photosynthesis theory,which breaks through the physical limits of photosynthesis and extends the available light range to far-red light region of 700-800 nm.Until now,red-shifted chlorophyll has only been found in several cyanobacteria.However,the ecological distribution of red-shifted chlorophyll containing cyanobacteria in the natural terrestrial ecosystem are still unclear,and no red-shifted chlorophyll containing cyanobacteria has been reported in China.In this paper,the species and spectroscopic property of red-shifted chlorophyll producing cyanobacteria were surveyed in the subtropical forest ecosystem in Wuhan region.The following results were obtained:1.In Mulan Tianchi Scenic Area,the Central China Normal University campus and Wuhan Botanical Garden,samples were extensively collected in some habitats with few visible but ample far-red light such as moist moss,dry moss,streams,marshes and ponds.Through far-red light enrichment culture and pigment analysis,over 80%of samples were found produced Chlf and Chld.In these enriched samples,eight strains Chl f-containing cyanobacteria were isolated and belonged to three genera of Chroococcidiopsis,Leptolyngbya,and Aphanocapsa.The Chroococcidiopsis spp were not only found together with desiccated mosses on limestone,but also occupied aquatic environments or wet limestone surrounded with mosses as Leptolyngbya spp and Aphanocapsa spp.In addition,a chlorophyll d-producing cyanbacteria Acaryochloris sp.CCNUM4 was also isolated and purified,and Chld was the main chlorophyll,while the Chl a was less.Acaryochloris sp.CCNUM4 was isolated from the roots of aquatic plants in the stream.These results show that the red-shifted chlorophyll containing cyanobacteria were widely distributed in the subtropical forest ecology and the species are diverse.2.The spectroscopic properties of red-shifted chlorophyll producing cyanobacteria were studied.The cell absorption spectra,pigment absorption spectra and low temperature fluorescence emission spectra of the red-shifted chlorophyll producing cyanobacteria grown under white light and far-red light were compared.Results show that far-red light induced the production of Chl f in the Chl f-containing cyanobacteria.When Chl f-containing cyanobacteria grow under far-red light,the phycobiliprotein reduced and the content of various carotenoids increased,the fluorescence emission peak of photosystem I shifted from?720 nm to?740 nm.In addition,the differences in cell morphology,ultrastructure,and pigment fluorescence under white light and far-red light were compared,and it was found that the Chl f-producing cyanobacteria have different shapes,and the intracellular thylakoid membranes were arranged more closely under far-red light.The isolation of phycobiliproteins in Leptolyngbya sp.CCNUW1 revealed that far-red light induced the appearance of a red-shifted phycobilisomes component.However,there is no significant difference between cells cultured under white light and far-red light of the Chi d-containing cyanobacteria Acaryochloris sp.CCNUM4.These results show that the Chl-containing cyanobacteria have a significant adaptive change in both pigments and proteins grown under far-red light when compared with cell grown under white-light conditions.These induced changes are probably necessary for its survival under far-red light conditions.