Response Characteristics And Mechanisms Of Life History Of Gracilariopsis Lemaneiformis To UV-B Radiation

For comprehensive understanding the effects of global environmental changes,especially of increasing UV-B radiation, on the growth and development ofmacroalgae, the responses of different developmental stages of life history of G.lemaneiformis to the enhanced UV-B radiation were studied in the laboratory basedon the techniques and methods with experimental ecology.1. Study on sensitivities of different developmental stages of life history of G.lemaneiformis to UV-B radiationThere is a24h acute inhibitory effect on attachment ratio of carpospores andtetraspores of G. lemaneiformis by UV-B radiation. We used probit analysis to obtainthe24h-ED50of UV-B radiation which was244.9J·m-2·d-1and197.7J·m-2·d-1respectively. UV-B radiation had the There also is a96h acute inhibitory effects oncarpospores division stage of or tetraspores as well as multicellular disks, while the96h-ED50of UV-B radiation was837.1J·m-2·d-1,760.8J·m-2·d-1，1020.7J·m-2·d-1and931.2J·m-2·d-1, respectively. It was found that phycoerythrin contents of G.lemaneiformis reduced rapidly when exposed to UV-B radiation. And UV-B radiationalso had the96h acute inhibitory effects on phycoerythrin contents in both erect thalliand adult thalli. The96h-ED50of UV-B radiation for carpospore erect thalli,tetraspore erect thalli, tetrasporophyte, carposporophyte and male gametophyte was1274.6J·m-2·d-1,1228.1J·m-2·d-1,1815.4J·m-2·d-1,1745.0J·m-2·d-1and1734.5J·m-2·d-1, respectively. Comprehensive analysis of the experimental results showedthat the sensitivities of different developmental stages of life history of G.lemaneiformis to UV-B radiation were various. The general formulation isattchment> division stage> multicellular disk> erect thallus> adult thallus. The tetraspore was more sensitive than carpospore. As well as the carposporophyte andmale gametophyte was more sensitive than tetrasporophyte.2. Effects of UV-B radiation on the developments of G. lemaneiformisHigh doses of UV-B radiation could inhibit and even block the development of G.lemaneiformis accompanies with decreasing the development ratios and prolong thedevelopment time. The dose of UV-B radiation which could block the development ofG. lemaneiformis was discrepant in different life stages. It took1152J·m-2·d-1and768J·m-2·d-1of UV-B radiation to block the attachment of carpospores and tetraspores. Italso took240J·m-2·d-1of UV-B radiation to block the development of division stageof carpospores or tetraspores. The doses of UV-B radiation which could block thedevelopment of multicellular disks was288J·m-2·d-1for carpospore and244J·m-2·d-1for tetraspores. When exposed to more than3600J·m-2·d-1or2880J·m-2·d-1UV-Bradiation, the spores released form carposporophyte or tetrasporophyte would losetheir adhesive capacity.3. The response of the early developmental stages of G. lemaneiformis toenhanced UV-B radiationThe results showed that UV-B radiation had significant impacts on the earlydevelopment of carpospores and tetraspores. It indicated that lowest UV-B radiation(24J·m-2·d-1) showed accelerating effects on the growth and development ofcarpospores, making the diameter and the relative growth rate increased andshortening the time of early development. With a gradual increase of UV-B radiation(48~120J·m-2·d-1), the growth and development of carpospores were significantlylower than that of the control (PAR only), with decrescent diameters, decreasedrelative growth rates, diminished developmental ratios, prolonged development timeand increased abnormal ratios. The growth and development of tetraspores wereinhibited when exposed to UV-B radiation which does was larger than48J·m-2·d-1.The UV-B radiation reduced diameters, relative growth rates and developmental ratios,prolonged time of development and increased abnormal ratios of tetraspores. 4. Studies on the damage mechanisms of UV-B radiation to G. lemaneiformisAfter13days of treatment, the relative growth rates of G. lemaneiformis, unlike thecontrol, significantly reduced under UV-B radiation in the range of0.36~1.80KJ·m-2·d-1. Depigmentation and partial necrosis of the apical segments occurred toalgae when exposed to UV-B radiation. Results from analysis of pigment contentshowed that the content of phycoerythrin and chlorophyll remarkably decreased withthe increasing of UV-B radiation dose and exposure time. Moreover, this trend ismore obvious on phycoerythrin. Similarly, the photosynthetic activity of G.lemaneiformis was also inhibited by UV-B radiation, leading to the decrease ofphotosynthetic parameters, such as Fv/Fm, Y(II), rETRmax,, Ekand Rubisco content.When exposed to UV-B radiation in the range of0.36~1.80KJ·m-2·d-1, the activity ofnitrate reductase increased at first and then decreased, indicating that the utilization ofN nutrient had been altered by UV-B radiation. With low dose and short time of UV-Bradiation，the content ofO-2and H2O2changed marginally. However, with theincrease of dose and exposure time, UV-B radiation induced excessive production ofand H2O2which eliciting a marked cellular membrane damage and lipidperoxidation. As a strategy to prevent the damaging effects of excess ROS, the SOD,CAT, GPx and GR activities as well as the AsA content and T-AOC increased.However, with the increase of dose and exposure time, the activities of GPx and GR,the contents of AsA, and T-AOC declined. It demonstrated that the antioxidant systemmight be damaged by the excessive ROS. In addition, with the increase of dose andexposure time, CPDs significantly accumulated in the thalli, while the content ofultraviolet absorption compounds was significantly reduced. This indicated that thedefense system of G. lemaneiformis did not have the capacity to against UV-Bradiation. Observed by transmission electron microscopy, UV-B radiation has changedthe cellular structure of G. lemaneiformis, making gelatinous layer thinned, cell wallthickened, floridean starch grain and chloroplasts reduced, chloroplast structuredestroyed and plastoglobuli increased.