湿地匍灯藓（Plagiomnium acutum）的防御机制对镉胁迫的响应

采用浸没培养实验研究不同浓度镉溶液（0、2、5、50mg·L-1）对湿地匍灯藓（Plagiomnium acutum）的膜系统、光合系统的损伤情况及其抗氧化酶系统的影响。结果表明：湿地匍灯藓外表伤害症状随Cd胁迫浓度增加而加重;湿地匍灯藓对Cd有较强的生物富集能力,且藓体Cd累积量与溶液Cd浓度显著正相关（P〈0.05）;湿地匍灯藓的总叶绿素含量随Cd浓度增加显著降低,其含量与可溶性蛋白含量显著正相关（P〈0.05）;Cd胁迫引起湿地匍灯藓的丙二醛（MDA）积累,同时伴随可溶性糖和游离脯氨酸含量显著增加,其中可溶性糖含量与MDA含量显著正相关（P〈0.05）;可溶性蛋白含量和过氧化氢酶（CAT）活性随Cd浓度增加均持续下降,而超氧化物歧化酶（SOD）和过氧化物酶（POD）的活性却随Cd浓度增加而呈现逐渐上升趋势,其中可溶性蛋白和CAT活性均与MDA含量显著负相关（P〈0.05）,SOD活性则与MDA含量显著正相关（P〈0.05）,POD活性与MDA含量极显著正相关（P〈0.01）。Cd胁迫抑制或降解光合作用相关酶类、细胞膜质过氧化和蛋白质代谢紊乱可能是湿地匍灯藓遭受Cd毒害的主要原因;湿地匍灯藓通过增加可溶性糖含量、SOD和POD活性来抵御Cd的毒害,但由于CAT活性丧失,使湿地匍灯藓的防御系统崩溃,最终导致了湿地匍灯藓细胞的凋亡。可溶性糖、SOD和POD可以作为湿地匍灯藓防御Cd毒害的指标。

Response of Defense Mechanisms in Plagiomnium acutum Under Cd Stress

A submersion experiment was conducted to clarify the effects of Cd stress on membrane, photosynthetic and antioxidant enzyme of Plagiomnium acutum. P. acutum was exposed to four different Cd levels（0, 2, 5, 50 mg·L-1）. The results showed the following：（1）The obvi- ous toxic symptoms appeared on P. acutum with the increase of Cd levels. P. acutum exhibited a relatively strong ability to accumulate Cd from the solutions. The Cd concentrations in P. acutum were significantly positively correlated to the solution Cd（P〈0.05）（.2）The total chlorophyll content of P. acutum significantly decreased with the increasing solution Cd, it was significant positively correlated to the content of soluble protein（P〈0.05）（.3）Cd stress resulted the significantly higher contents of malondialdehyde（MDA）, soluble sugar and free proline contents compared to the controls, with the significant positively correlation between the soluble sugar content and the MDA content. In con - trast, the contents of soluble protein and the activity of catalase（CAT）decreased significantly with increasing solution Cd. Moreover, the ac- tivities of superoxide dismutase（SOD）and peroxidase（POD）exhibited a tendency of increase with increasing solution Cd. Of which, signifi- cant negatively correlation exhibited between CAT and MDA（P〈0.05）, significant positive correlation between SOD and MDA（P〈0.05）, and extreme positive correlation between POD and MDA（P〈0.01）. Therefore, Cd toxicity resulted inhibition or degradation of photosynthesis en- zymes, lipid peroxidation and disorder of protein metabolism in P. acutum. P. acutum mitigated the Cd toxicity by increasing soluble sugar, SOD and POD activities. However, the breakdown of the defense system in P. acutum resulted the cell apoptosis due to the loss of CAT activ- ity. The soluble sugar, SOD and POD may be considered as sensitive biomarkers of Cd toxicity in P. acutum.