| Porphyra yezoensis Ueda is a precious seaweed owing to its nutritional and health merits, it has the highest value of any cultivated seaweed, and have already been one of the most important aquaculture species of China.Porphyra yezoensis is abundant in cold-temperate and boreal shores of Northern Hemispheres, its conchocelis matured and release spores when conditions become appropriate on later autumn, the appropriate seawater temperature of foliose stage is 18-20℃. Higher temperature will decrease biomass yield of cultured Porphyra.In recent years, the global warming has seriously effect natural and agricultural terrestrial plant communities, as well as seaweed. Sustained high temperature during the seeding period and the temperature rebound phenomenon happened in late autumn negatively affect P.yezoensis blades. In that case, the Porphyra blades are prone to disease and can easily decay. It is therefore of high importance to select high-temperature-resistant strains of P.yezoensis in order to reduce economic lose.Firstly, the temperature-tolerance-ability of wild type in P. yezoensis was tested, the results shows that the survival rates and the rhizoid germination rates decreased 21.3% and 22.3% respectively compared with the control group (18℃) at the temperature of 23℃; the abnormal rates of conchospore germlings increased 31.3% at the temperature of 22℃, compared with the control group (18℃).This paper improved that TM-18 strain which isolated from the monospores that released from the double 60Co-γ-irradiation and heat treated WT blades is a high-temperature-resistant strain; HT strain which isolated from the blades that regenerated from single somatic cells of double 60Co-γ-irradiation treated WT blades is a high-temperature-resistant strain too.High-temperature-resistant ability of the blade discs of YZ-4, TM-18, HT and TM-32 were tested at 24, 25℃, the results showed that TM-32 was not a high-temperature-resistant strain, meanwhile the other 3 strains had the potential. For further selection, high-temperature-resistant ability of their somatic cells were tested at the same temperature, data shows that the division rates of TM-18 and HT somatic cells were significantly higher than those of WT when cultured at 18, 24 and 25℃. After two weeks of cultivation at 24℃, the survival rate and the division rate of WT were only 39.3 % and 100 %, YZ-4 were 62.1 % and 100 %, TM-18 were 71.9 % and 100 %, HT were 61.4 % and 100 %, respectively. After two weeks of cultivation at 25℃, the survival rate and the division rate of WT were only 8.8 % and 100 %, YZ-4 were 49.2 % and 99.1 %, TM-18 were 65.4 % and 100 %, HT were 54.6 % and 95 %, respectively. Although the regenerated germlings of TM-18 and HT displayed some degree of abnormality in shape and darkening in color, their high-temperature-resistant ability were better than those of the WT and YZ-4.After being cultured at 22, 24, 25℃for two weeks, the survival rates of conchospores of each strain showed apparently difference. At 22℃, the survival rates of WT, YZ-4, TM-18 and HT strains were 85.9%, 88.1%, 90.8% and 89.9% respectively, and their division rates were all reached 100%; at 24℃, the survival rates of each strain were 20.6%, 63.1%, 77.1% and 66.5%,and their division rates all reached 100%; at 25℃, the survival rates were 16.7%, 48.2%, 66.1% and 49.9% respectively, the division rates were 94.6%、98.8%、99.5%'100% respectively. Combined with their rhizoid germination rates and abnormal rates, the temperature tolerant ability of TM-18 were significantly higher than the other strains.When the 50-day-old gametophytic blades of WT, YZ-4, TM-18 and HT were transferred and cultured at 18, 22 and 24℃for 30 days, the mean length of WT strain increased 5.2, 4.3, 2.4 times, YZ-4 strains increased 11.0, 8.2 and 5.7 times, TM-18 strains increased 12.4, 8.6 and 6.1 times, HT strains increased 10.4, 6.5 and 5.1 times. When cultured at 25℃for 15 days, their mean length of blades increased 1.4, 1.9, 2.3 and 1.9 times.WT strains prematured about 10 days when cultured at 22℃, stop growing and begin to decay when cultured at 24℃for 15 days and 25℃for 10 days;YZ-4 strains did not matured even cultured for 30 days at 22℃, but its blades begin to decay when cultured at 24℃for 25 days and 25℃for 15 days; TM-18 strain showed excellent characteristics when cultured at 22℃for 30 days,24℃for 25 days and 25℃for 15 days; the temperature resistant ability of blades of HT strain are familiar with YZ-4 strains.Contents of Chl.a、PE and PC in the gametophytic blades ( aged for 50 days, at 18℃) of WT, YZ-4, TM-18 and HT strains all increased after being cultured at 22, 24 and 25℃for another 15 days. At the same time, the absorption peaks of in vivo absorption spectra also increased significantly along with the raise of temperature. The maximum absorption peak of WT, YZ-4 strains cultured at 25℃increased remarkably and showed 2-3 new apparent absorption peaks, meanwhile TM-18 increased smoothly and had only a gentle new peak at the similar wavelength, HT strain had no additional peaks.In conclusion, the high-temperature-resistant ability of TM-18 and HT strains of P. yezoensis is much better than that of YZ-4, especially TM-18 strain. Their conchospores can germinate and develop normally at the high temperature, and their blades also show ed high resistance to the temperature rebound. It is hoped that TM-18 and HT can be used to establish stable cultivar with high-temperature-resistance which are suitable for the production of P. yezoensis in the industry. |
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