| With deterioration of the environment conditions such as marine pollution and greenhouse effect in recent years, the breeding of kelp face rising temperature conditions that undermine the growth and development of kelp. Laminaria japonica live in cold water and its gametophyte form live through high water temperature period in summer, so cultivating and screening high temperature resistant varieties is conducive to practical breeding. Some physiological indexes including the content of chlorophyll a, proline, soluble sugar, MDA and the activity of POD of the gametophyte of Laminaria japonica were measured under different high temperatures (20, 25, 28, 30℃) according to different times (1, 3, 5, 7d) , the control at 15℃. The result shows that all of the measured contents and activity of gametophyte of Laminaria japonica had little change under 20℃; When the gametophyte were cultured at 25℃, the cellular shrunk slightly, the contents of physiological indexes ascended except for chlorophyll a; When the gametophyte cultured under 28℃and 30℃, the cellular content shrunk and separated, the pigment of the cell faded, the cytomembrane ruptured, the content overflowed, cells died in quantity after 1d, cells almost died in 5~7d, the content of MDA ascended gradually, the content of chlorophyll a and the activity of POD descended, the conents of proline and soluble sugar first ascended and then descended. S-adenosyl-L-metnionine synthetase (SAMS) catalyzes the synthesis ofS-adenosyl-L-methionine which is an important substance in metabolism pathway from ATP and L-methionine. SAMS is significantly induced by oxidative stress, salt stress, low temperature stress and ethylene, different SAMS has different expression pattern. SAMS plays an important role in anti-stress, aging, metabolism and regulation of plant. By the methods of RT-PCR technology, we isolated a SAMS gene fragment from gametophyte generation of Laminaria japonica (LjSAMS gene fragment) : it contains 612bp nucleotides which encode 204 amino acids, the molecular weight of deduced protein is 22136.26Da and its theoretical isoelectric point is 5.08; The strongest Hydrophobic amino acid is leucine (NO.62 bit) , the strongest hydrophilic amino acids are glycine (NO.167 bit) and isoleucine (NO.168 bit) ; It has rich protein secondary structure that is composed of random coils (40.69%) , alpha helix (27.45%) , beta corner (11.76%) , extensions chain (20.10%) ; Nuclear export signal expression is on leucine (NO.111 bit) ; There is no signal peptide, transmembrane domain and introns; There are two conservative domains, N end comes from 1～70 bit amino acid residues and the middle end comes from 83~204 bit; The sequence consistency is 62.069% between LjSAMS gene fragment of 1~203 bit amino acid residues and SAMS protein crystal structure of Homo sapiens, we build a three-dimensional structure model of LjSAMS gene fragment with 2p02A as templates; The deduced amino acid sequences of LjSAMS gene fragment have 74.67% identity comparing with those of other 10 species SAMS genes; MEGA analysis shows that LjSAMS gene fragment is homology with Ectocarpus siliculosus and Porphyra yezoensis.The results provide some references for further researching the mechanism and cultivating and screening new varieties of Laminaria japonica to high temperature resistance. It contributes to a better understanding about the functions of SAMS gene and its expression regularity and metabolic pathways in kelp. |
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