Photosynthetic Changes And Response Towards Signaling Molecule Nitric Oxide During The Sporulation Of Ulva Prolifera

Ulva prolifera is a macroscopic green alga that can grow and reproduce fast.In natural environment,U.prolifera can grow in fixing or floating status.Fixing alga can grow and develop according to the life history.However,floating alga can accumulate a large amount of biomass under appropriate environments.This accumulation can cause the outbreak of the green tide.When the green tide outbreaks,there is a disaster resulted from a tremendous amount of biomass by the accumulation of floating thallus of U.prolifera.Since 2007,the green tide outbreaks in China Yellow Sea in every year.U.prolifera mainly reproduces by spores during outbreak of the green tide.Therefore it is significant to study sporulation of U.prolifera to uncover the mechanism of biomass accumulation in green tide and find a way to prevent outbreak.Sporogenesis is a process of cell differentiation.There are many changes in biochemical reaction and physiological performance during sporogenesis.These changes can respond to many factors and result in regulation towards sporogenesis.To study the regulation towards sporulation in U.prolifera can pave a road to comprehend regulation mechanism and networks of cell differentiation in algae and plants.The main research is below:Firstly,it is studied what changes of photosynthetic electron transport happen during entire sporulation process.Combined microscopic observation with determination in photosynthetic parameters,it is found that prominent linear electron flow(LEF)and moderate cyclic electron flow(CEF)is in operation before sporulation onset.The cooperation of LEF and CEF may help the Calvin cycle reach its optimal performance to support sporulation.When sporulation onset occurs,CEF is enhanced whereas LEF is sharply declined.These results suggests that photosynthetic electron transport may be tightly related with sporulation especially onset.The treatment of DCMU and DBMIB,which both have different inhibit mechanism to photosynthetic electron transport chain,can result in inhibition towards sporulation of U.prolifera,even though there are distinct different between their effect of inhibition.The inhibition effect of DBMIB is independent from treatment period whereas the effect of DCMU is dependent on treatment period.There is little effect on inhibition of the treatment of DCMU in or after sporulation onset.The changes of photosynthesis resulted from the limitation of CO2 acquisition could stimulate sporulation onset.All results demonstrate that enhanced cyclic electron flow(CEF)and oxidation of the plastoquinone pool are essential for sporangia formation onset.Photosynthesis regulates sporulation by the changes in photosynthetic electron transport chain.Early stage of sporulation is dependent on Calvin-Cycle.When the process reaches the stage of sporulation onset,the operation of Calvin-Cycle is no more needed.Secondly,it is studied what effect and side-effect of different NO donors in different concentrations influence sporulation.It is suggested that NO,which was reckoned as inhibitor towards sporulation,has little effect on inhibition.Inhibition of sporulation resulted by NO scavenger means that sporulation can not be in progress without NO.The result that nitric oxide synthase inhibitor can not successfully constrain sporulation suggests NO production by NOS is only a little proportion in total NO production in U.prolifera.The result that the culture without calcium can lead to unavailable sproulation suggested calcium in extracellular environment is essential to sproulation.Ryanodine inhibition towards sporulation indicates that calcium release from intracellular store mediated by ryanodine receptor calcium release channels is key process that can influence sporulation.To determine NO concentration in cells under different treatments(normal,treated by NO scavenger,and treated by ryanodine),it can draw two conclusions.On one hand NO is an essential messenger to activate the process of sporulation.NO concentration in cell shows a negative correlation with inhibition effect towards sporulation.On the other hand there is an interesting and important link between NO concentration and calcium release mediated by ryanodine receptor calcium release channels.According to inhibition towards sporulation by DTT and other results,it is demonstrated that NO can regulate sporulation by modifying Cys residue in the ryanodine receptor to form S-nitrosylation in vivo.S-nitrosylation acting as posttranslational protein modification can activate ryanodine receptor calcium release channel and then allow calcium release from intracellular store into cytoplasm.Meanwhile calcium release also can induce NO production to high level.These results show that cross talk between NO and calcium regulates efficiently sporulation of U.prolifera and even cell differentiation of algae and plants.Finally,the proteome and transcriptome of thallus disks that are induced to sporulation of U.prolifera under different culture period are studied.The proteome analysis shows that abundances of proteins related with stress response,cytoskeleton,protein synthesis and folding increase during the process of sporulation.This result demonstrates that in early stage of sporulation many processes to support cell division and cell differentiation are in progress.Meanwhile,abundances of proteins related with Calvin-Cycle declined.This result is consistent with the results of photosynthetic regulation towards sporulation.The transcriptome analysis shows that in very early stage of sporulation the transcription of genes related with ryanodine receptor enhanced at a large scale.Meanwhile,transcription of genes related with calcium homeostasis,receptor activity,and ion channels changes drastically.These results testify regulation mechanism of cross talk between NO and calcium towards sporulation.All experimental results show that many biochemical and physiological changes including photosynthesis occurs during sporulation.Meanwhile many signaling molecule regulate sporulation together with these changes.This result demonstrates that the entire sporulation process is under multi-dimensional and network-like coordinative regulation.