壳损伤及海水酸化对厚壳贻贝脲酶和碳酸酐酶的影响

Effects of Shell Damage and Seawater Acidification on Urease and Carbonic Anhydrase in Mytilus coruscus

海洋酸化是当前全球面临的最为紧迫的环境问题之一,已显现出对具生物矿化现象物种的严重影响。以往研究发现,贻贝表现出对海洋酸化较强的耐受性。为探究贻贝对海洋酸化耐受性的可能机制,选择两种对生物矿化具有重要影响的酶(碳酸酐酶和脲酶)为研究对象,分析其在壳损伤以及酸化海水条件下基因表达量和酶活力的变化;进一步对上述条件下的贻贝贝壳内表面开展了显微观察。研究结果表明,相比对照组,壳损伤或酸化海水处理诱导碳酸酐酶和脲酶的基因表达量产生不同程度的上调(P<0.05),酶活力测试与基因表达量分析结果具有类似特征,但存在时序性差异。而壳损伤叠加海水酸化处理则诱导碳酸酐酶和脲酶的基因表达量及酶活性在外套膜中均明显下调(P<0.05),但碳酸酐酶在血细胞中明显上调(P<0.05);在酸化海水中添加尿素则明显上调血细胞和外套膜中碳酸酐酶和脲酶的基因表达量以及酶活性(P<0.05)。贝壳内表面显微观察结果进一步表明,海水酸化及壳损伤导致损伤部位附近的贝壳内表面产生明显纹理质地改变,尿素可诱导海水酸化条件下壳损伤部位修复层的重新出现。上述结果表明,碳酸酐酶和脲酶可能参与了对壳损伤修复及海洋酸化条件下的壳保护过程。上述研究为深入了解海洋酸化背景下,贻贝的生物矿化过程及其对酸化海水的耐受机制提供了新的思路。

Ocean acidification is one of the most urgent environmental problems over the world and has shown serious impacts on the species with biomineralization process.Previous studies have revealed that Mytilus exhibits strong tolerance to ocean acidification.However,the mechanism behind this phenomenon is unclear so far.For exploring the possible mechanism of Mytilus on ocean acidification tolerance,two enzymes with important roles in biomineralization,carbonic anhydrase and urease,were selected as the target genes,and the expression profiles and the enzymatic activities of these two enzymes were evaluated in the mantle and hemocytes of Mytilus coruscus under shell damage and/or acidic sea water,respectively.In addition,the inner surface of mussel shell under the above conditions was further observed by light microscope and scanning electron microscope,respectively.The results showed that,comparing to the mussel with complete shell and raised in normal sea water,the shell damage or acidified seawater raising significantly up-regulated the gene expression levels of carbonic anhydrase and urease in mussels(P<0.05).The results of enzyme activity test showed a similar change to the results of gene expression analysis,whereas presenting a temporal difference.In addition,the gene expression and enzyme activity of carbonic anhydrase and urease were significantly inhibited in the mantle(P<0.05),while the carbonic anhydrase was significantly up-regulated in the hemocytes(P<0.05)for the mussel with damaged shell and raised in acidic sea water.In addition,the gene expression and enzyme activity of carbonic anhydrase and urease in hemocytes and mantle were significantly increased by urea supplementation(P<0.05).Further microscopic observation of the shell inner surface indicated that the shell inner surface near the damaged site had obvious texture change caused by seawater acidification and/or shell damage,and urea could induce the re-emergence of shell repair layer in the damaged site even under seawater acidification.These results indicate that both carbonic anhydrase and urease play important roles in shell damage repair and shell protection under ocean acidification,and may have different mechanisms in different tissues and under different conditions.Urea may contribute to the repair of the shell damage under acidification by lytic producing carbonate ions.These studies provide a new idea for understanding the biomineralization process of mussels under the background of ocean acidification,as well as the mechanism of their tolerance to acidified seawater.