龙须菜在不同盐度胁迫下的琼胶积累及相关生理生化变化的研究

AGAR ACCUMULATION AND PHYSIOLOGY AND BIOCHEMISTRY CHANGES OF GRACILARIOPSIS LEMANEIFORMIS UNDER DIFFERENT SALINITY STRESSES

为了探究不同盐度对龙须菜生长、琼胶合成及相关基因表达的影响,研究了15、25和35三种盐度条件下龙须菜的生长速率、琼胶含量、琼胶合成酶α-半乳糖苷酶(GLA)、半乳糖苷转移酶(GAT)、α-1,3-糖脂磺基转移酶(GST)、半乳糖-2,6-硫酸化酶(GAS)的基因表达。结果表明,盐度25时龙须菜生长速率最高,为7.17%/d,高于低盐(15)时的6.27%/d和高盐(35)时的3.57%/d,低盐和高盐都表现出明显的暗呼吸速率上升和光合速率下降。龙须菜培养15d后,在低盐条件下琼胶含量为9.27%,盐度25和高盐分别为6.91%和8.09%。培养第3天时在低盐和高盐下龙须菜中gla基因表达量和酶活都显著高于盐度25的表达量;15d后在盐度25条件下gla基因表达量仍然最低,但GLA酶活无显著差异。gat基因在低盐条件下先降低后升高,在高盐条件下表达量始终最高,为盐度25的3.03倍。在低盐条件下gst和gas基因都在短期内出现显著下降,但15d后恢复到与正常盐度无显著差异。龙须菜半乳糖含量在高盐条件下相对盐度25显著升高,达到其3.27倍,而在低盐条件下各种单糖含量相对较低,半乳糖含量极低。研究结果说明过高和过低盐度都会对龙须菜造成一定程度的胁迫,并促进琼胶的合成,但其促进琼胶积累的机制存在差异,α-半乳糖苷酶和半乳糖苷转移酶在其中扮演着非常重要的角色。

In order to investigate the effects of different salinities on the growth and agar synthesis genes of marine macroalgae Gracilariopsis lemaneiformis,three different salinities(15,25 and 35)were applied to evaluate correlations between agar content and the expression of genes related to agar synthesis includingα-galactosidase(gla),galactose transferase(gat),α-1,3-glycolipid sulfotransferase(gst),and galactose-2,6-sulfurylases(gas).As results,under salinity 25,the growth rate of G.lemaneiformis was the highest with the RGR of 7.17%/d,which was higher than 6.27%/d of salinity 15 and 3.57%/d of salinity 35.Both adverse salinities showed significant increase in dark respiration rate and decrease in photosynthetic rate during the experimental period.After 15 days of culture,the agar content of G.lemaneiformis under low salt conditions was 9.27%,while that in high salt conditions was 8.09%and in normal salinity 25 was only 6.91%.On the 3rd day of culture,the gene expression level and enzyme activity of galactosidase at low and high salinity was significantly higher than that of salinity 25.After 15 days of culture,the gla gene expression in salinity 25 was still the lowest one,while the GLA enzyme activity in different salinity showed no significant difference.Under low salt condition,the expression of gat gene decreased first and then increased.Under high salt condition,the expression of gat gene was always the highest one,which was 3.03 times of that in salinity 25.For three days of low salinity cultivation,the expression of gst and gas genes decreased significantly,but it recovered to normal level in a long term of 15 days.The content of galactose in high salinity was 3.27 times of that in salinity 25,and the monosaccharide contents of low salinity were relatively low,among them,the galactose content was extremely low.In conclusion,our research indicated that either too high or too low salinity would cause a certain degree of stress and increase of agar content in G.lemaneiformis,but the mechanism of promoting agar accumulation is different whileα-galactosidase and galactose transferase played an important role in this process.