Photosynthetic Responses Of Edible Cyanobacteria Nostoc Spaeroides And Nostoc Commune Vauch To Water Stress And Salt Stress

Both Nostoc Spaeroides and Nostoc Commune Vauch are edible cyanobacteria,which are very close in evolutionary relationship.N.Spaeroides grows in rice fields,whereas semi-terrestrial N.Commune,is worldwidely distribution.In this paper,the effects of water and salt stress on photosynthetic activities of N.Spaeroides and N.Commune were studied in order to investigate the differences of photosynthetic responses of the two species of Nostoc to environmental stress and make a through exploration in the adaptation mechanism of cyanobacteria from aquatic to terrestrial environment,and provide a theoretical basis for the artificial culture of these two species.In this experiment,BGllo with different concentrations of sorbitol were used to simulate the water stress.In order to study the response mechanisms of photosynthesis of two species to water stress.With the rise of sorbitol concentration,the Fv/Fm of PSII of two species were decreasad,and the IC50 concentration of F,/Fm of N.Commune was 1.22 M,while that of N.Spaeroides was 1.03 M.When the concentration of sorbitol was less than or 1 M,there was no significant difference in the Pn,of both PSI.When the concentration of sorbitol reached 1.5 M,the Pm of N.Spaeroides and N.Commune decreased by 78.62%and 63.25%respectively.These results suggested that PSII were more sensitive to the water stress than PSI of both species,and PS? and PSI of N.Commune were more tolerant to water stress than that of N.Spaeroides.The rapid light response experiment of photosynthetic electron transfer rate showed that N.Commune also had higher photosynthetic potential under water stress.With the increase of sorbitol concentration,the heat dissipation mechanism Y(NPQ)of two species was strongly stimulated.When the concentration of sorbitol reached 1.5 M,the Y(NPQ)of N.Spae,roides and N.Commune increased by about 6.5 times and 11 times respectively.The cyclic photosynthetic electron transfer quantum efficiency Y(CEF)/Y(?)of both species were also strongly stimulated.When the concentration of sorbitol reached 1.5 M,Y(CEF)/Y(?)of N.Commune and N.Spaeroides increased by about 17 times and 13 times respectively.These results suggested that both photosynthetic protection mechanisms were effectively activated under water stress,but the protection mechanism of N.Commune was more effective than that of N.Spaeroides.BG110 supplemented with NaCl of different concentrations were used in order to study the response mechanisms of photosynthesis to salt stress for artificial liquid cultured and wild growed N.Commune.The results showed that there were significant differences in morphology between wild and artificial cultured colonies.Photosynthetic experiments showed that under salt stress,the PSI of N.Commune in both states was more stable than PSII,but the wild growed colonies had higher photosynthetic potential than that in artificial cultured colonies under lower salt stress.The rapid light response experiment of photosynthetic electron transfer rate showed that the cultured colonies was very sensitive to high light whether it was suffered salt stress or not,while wild colonies still had a high photosynthetic potential under 0.2 M NaCl.The photosynthetic protection mechanism under response to salt stress for the wild colonies was more effective than that of cultured colonies.