Photosynthetic Physiology In The Macroaglae Ulva Prolifera And Porphyra Yezoensis

In order to assess the effects of UV radiation (UVR,280–400nm) on the relativesensitivity attachment, germination success and seedling growth of the zoospores of thegreen tide macroalga, Ulva prolifera, we exposed the cells to three different radiationtreatments (PAB:280–700nm, PA:320–700nm, P:400–700nm) under solar orartificial radiation. The experimental units were covered with three different cut-offfilters to obtain three treatments: PAB, PA and P under solar simulator, respectively. Thelight intensity was set at900μmol photons m-2s-1, while the irradiances of ultravioletradiation were UV-A:19.9W m-2, UV-B:0.68W m-2, respectively. Optimumphotosynthetic efficiency (Fv/Fm) of zoospores was measured as variable fluorescenceof PSII by using a water pulse amplitude modulation (PAM) fluorometer. After exposedto light treatments, the samples were then placed in the dark so that the zoosporesattached to the cover glass slices randomly. After24h the settled zoospores werecountered by microscope. The randomly settled zoospores on the cover glass slices wereplaced under different light treatments with cut-off filters. The germination success andgrowth were measured punctually. The results showed that:1) PA and PAB treatmentscould significantly inhibit the zoospores optimum photosynthetic efficiency (Fv/Fm)under900μmol photons m-2s-1, and the extension of inhibition increased with exposuretime. Moreover, the inhibitory of PAB treatment was more obvious than those of P andPA treatments.2) The hysteresis effects of zoospore settlement were observed undershort-term ultraviolet radiation, and the results showed that24h settlement rate of PAand PAB treatments after short-term exposure of ultraviolet radiations of5,10and15min were not significant from control (P).3) The significant differences among the groups of germination success of settled zoospores were found when the samples wereplaced under different solar radiations. The relative germination rates to P treatment at3rdday and6thday were: PA:57.0%and58.5%, PAB:39.1%and34.6%, respectively.There was no significant difference between first3d and6d, which implied zoosporesurvival depends on the initial3d.4) The seedling growth were significantly inhibitedby PA and PAB treatments. The rates of seedlings contained more than4cells were P:72.9%; PA:14.3%; PAB:10.1%respectively. The growth inhibition rates were46.2%and68.1%by PA and PAB treatments. Overall the data showed that optimumphotosynthetic efficiency, adhesion time, germination success and seedling growth ofzoospore were significantly inhibited by UVR, and the inhibitory of PAB was strongerthan that of PA. The results suggested that UVR could play the negative roles on theearly development and survival, and might have a major impact on the occurrence andrecruitment of U. prolifera populations.The mechanisms for acquisition of dissolved inorganic carbon (DIC) in the greenmacroalga Ulva prolifera and the red macroalga Porphyra yezoensis, which livetogether in the intertidal zone, have been investigated. Both Ulva prolifera andPorphyra yezoensis exhibited high pH compensation points (10.56,9.65respectively).These data indicate that Ulva prolifera and Porphyra yezoensis were able to use HCO3-as a source of DIC for photosynthesis. The relationship between photosynthetic O2evolution rates and DIC concentrations showed that the normal DIC composition innatural seawater could fully saturate photosynthesis of Ulva prolifera and Porphyrayezoensis at pH8.2or lower. However, the affinity for DIC and the carbonsaturatedmaximum photosynthesis were dramatically reduced at pH9.2. The capacity for HCO3-use by an extracellular carbonic anhydrase(CA; EC4.2.1.1), and by an anion exchangerwith similar properties to that of red blood cells, has been quantified in two algae. It wasillustrated by comparing O2evolution rates with those theoretically supported by CO2,as well as by photosynthesis-pH curves. Both external and internal CA, and a directuptake were involved in HCO3-use, since photosynthesis and pH evolution wereaffected by acetazolamide (AZ),6-ethoxyzolamide (EZ)(inhibitors of external and totalCA, respectively) and4,4’-diisothio-cyanatostilbene-2,2’-disulfonate,(DIDS; aninhibitor of HCO3-exchanger protein). Inhibitors caused a reduction in the pHcompensation points in pH-drift experiments, indicating a suppression of the pathways involved in the carbon-concentrating mechanism. The net photosynthesis rates as afunction of DIC concentration displayed a biphasic pattern that could be supported bythe occurrence of the two mechanisms of HCO3-use in Porphyra yezoensis. Our resultssuggest that the HCO3-use by Porphyra yezoensis is carried out by the two DIC uptakemechanisms especially at low DIC concentration. The contribution to HCO3-acquisitionby the DIDS-sensitive mechanism was higher at a low pH in Porphyra yezoensis,however, the anion exchanger inhibitor (DIDS) had weak inhibitory effects onphotosynthetic O2evolution at neither acidic nor alkaline pH values on Ulva prolifera..These operate simultaneously with different affinities for DIC, the indirect HCO3-useby an external CA activity being the main pathway in both algae. Oxygen evolution inseawater of pH8.2was sharply reduced with the increase of pH. However, the rates ofO2evolution at pH7.8and above exceeded the theoretical calculated maximum ratessupported solely by the CO2supply from the spontaneous dehydration of HCO3-in thebulk seawater. The presence of a carbon-concentrating mechanism conferseco-physiological advantages in a fluctuating ecosystem subjected daily to high pHs andlow DIC concentrations.In order to assess the effects of ultraviolet radiation (UVR,280–400nm) on acommon and economically important rhodophyte, Porphyra yezoensis, we exposed thethalli to three different solar radiation treatments (PAB:295–700nm, PA:320–700nm,P:395–700nm). A significant decrease in the effective quantum yield (ΔF/Fm’) at noonduring a daily cycle was observed. In all experiments, photosynthetically activeradiation (PAR：395–700nm) was responsible for most of the observed inhibition;nevertheless, the thalli exposed to PAB had the lowest recovery in any condition, ascompared to the other radiation treatments. The incomplete recovery of effectivequantum yield under high ligh（tHL）suggests that photosynthetic apparatus are damagedby excess light, especially PAB treatment. As a result, UVB radiation drasticallyaffected the growth activity of both high light and low light (LL) conditions, furthermore, the growth activity was much worse inhibited by PAB treatment under HLcondition. However, there was a significant increase of the absorptance ofUV-absorbing compounds at334nm from0.9to1.6and1.5in samples exposed in thePAB and PA as compared to P treatment after7days treatment. Both UV radiation andirradiance affected the content of photosynthetic pigments in P. yezoensis. An increase was found in Chl a and phycobiliprotein [phycocyanin (PC) and phycoerythrin (PE)]content in P and PA treatments under LL conditions. Highest phycobiliproteinconcentrations were found in the PA treatments. However UVB radiation decreased Chla and phycobiliprotein levels much lower compared with P treatment at LL conditions.Dissimilarly, the content of carotenoids (Car) increased significantly in the PA and PABtreatments, compared to the P treatment at HL condition. Comparison between theacclimation conditions suggests that the increase of UV-absorbing compounds andcarotenoids attribute to protection of the photosynthetic apparatus. Thus, theseexperiments indicate that high light and UV radiation inhibited photosynthesis andgrowth and consequently affected the content of photosynthetic pigments in P.yezoensis. However P. yezoensis has a few basic physiological strategies seem to beactive during acclimation to high solar irradiance: dynamic photoinhibition, increasedconcentration of carotenoids, and accumulation of UV-absorbing compounds.Porphyra yezoensis, an intertidal macroalga, may be encountered acid rain underemersed state. In this study, the changes of optimum photochemical quantum yield (Fv/Fm) of photosystem Ⅱw ere investigated w hen P. yezoensis encountered the stress ofdesiccation and acid rain. The results showed that: after3hours of desiccation, thallilost94.5%of their water, and then photosynthesis stopped, but thalli had been shown toresume photosynthesis quickly during immersion in sea water. If the thalli encounteredacid rain just emersed, the maximum quantum yield decreased with pH and timeprolongation. Even6hours treatment in the lowest pH (4.0) experimental acid rain, thephotosynthetic capacity could recover after6h rehydration in sea water. However, ifencounter acid rain after desiccation, only the group of pH5.6could recover after24hour recovery, and the thalli treated with pH4.5couldn’t be restored within24hrecovery, and the thalli of pH4.0group turned to red and died after been treated withacid rain for one hour. If the thalli were treated for3hours, the pH5.6and pH4.5groups were seriously hurt, for their normal photosynthetic capacity couldn’t be restoredwithin24h, the pH4.0group toward death. Our results suggested that the doublestresses of desiccation and acid rain could endanger the survival of P. yezoensis severely,and might be cut the production of P. yezoensis seriously.The growth，photosynthesis，and the some biochemical components in Porphyrayezoensis to enriched nitrogen and phosphorus were investigated. The results showed that when N were supplied only there were significant effects on accumulation of tissueN, free amino acid, phycobiliprotein and soluble protein, and reduction of soluble sugar,but there were not significant effects on the growth, photosynthesis and the contents ofchlorophyll a and carotenoid. Moreover, when P were supplied only there weresignificant effects on the growth, photosynthesis and the accumulation of sugar, butthere were not significant effects on contents of pigments, tissue N, free amino acid andsoluble protein. However, when N and P were simultaneously supplied thephysiological biochemical characteristics were almost enhanced except soluble sugarcontent, especially the free amino acid phycoerythrin contents were enhancedsignificantly. It was found significant positive correlations between photosynthesis andgrowth, tissue N and soluble protein, free amino acid and soluble protein, chla and otherpigments, and significant negative correlations between soluble protein and solublesugar in P. yezoensis. These results indicate that relief of limit of N and P at the sametime can promote growth rapidly of P. yezoensis and be conducive to enhancing thequality of P. yezoensis.