高温及强光诱发绿水螅白化进程中共生藻数量动态、活性氧积累及抗氧化酶活性变化

Quantity dynamics of symbiotic algae, reactive oxygen accumulation,and antioxidant enzyme activities during bleaching induced by high temperature and strong light in Hydra sinensis

受全球暖化及光辐射增强的双重胁迫,珊瑚礁主成分刺胞动物-微藻共生体白化(共生藻数量减少)日趋严重.在中国绿水螅(Hydra sinensis)对异常环境因子的响应前期研究中筛选到一个“高温(33℃)-强光(6 000 lx)”双胁迫参数组合能诱发绿水螅白化,进一步在其基础上探讨高温单胁迫、强光单胁迫及高温-强光双胁迫诱发中国绿水螅白化进程中其共生藻的数量动态、活性氧(超氧阴离子自由基及丙二醛两个指标)的积累及抗氧化酶(超氧化物歧化酶、过氧化氢酶及过氧化物酶)活性的变化.结果显示,与高温单胁迫和强光单胁迫相比,高温-强光双胁迫下绿水螅共生藻数量下降幅度最高(双胁迫处理21 d后共生藻数量下降幅度接近90%);强光单胁迫下绿水螅仅在胁迫的起始阶段共生藻数量下降幅度略高于高温单胁迫,而其余时段均明显低于高温单胁迫;无论是单胁迫、还是双胁迫均导致绿水螅活性氧水平上调,但在强光单胁迫下绿水螅活性氧水平上调的起始时间明显早于高温单胁迫;在所有胁迫处理的中、后期绿水螅3种抗氧化酶活性动态总体趋势为上调,而在大部分时间段双胁迫条件下每种抗氧化酶活性高于单胁迫,并且强光单胁迫下绿水螅每种抗氧化酶活性上调的起始时间均早于高温单胁迫.综上所述,与高温单胁迫以及强光单胁迫相比,高温-强光联合胁迫显著加剧了绿水螅的白化程度,即高温胁迫及强光胁迫联合处理对绿水螅白化发生的促进具有协同效应;绿水螅对强光胁迫的响应较对高温胁迫的响应更敏感,但高温胁迫在促进绿水螅白化发生的进程中影响程度却大于强光胁迫,因此高温胁迫与强光胁迫之间在诱导绿水螅白化发生的作用方式上存在差异.

Under the combined stresses of global warming and enhanced light radiation, the bleaching(decrease in the number of symbiotic algae) of cnidarian-microalgae holobionts, the main component of the coral reef ecosystem, is increasingly prevalent. In our preliminary experiment, the combined stress conditions of hightemperature(33 ℃) and strong-light(6 000 lx) that could bleach Hydra sinensis were screened out;thus,H. sinensis could be used as an alternative model organism for the analogical study of bleaching cnidarianmicroalgae holobionts. Based on this, the present study explored the effects of single and combined hightemperature and strong light stress on the quantity dynamics of symbiotic algae, reactive oxygen accumulation,and antioxidant enzyme activities(superoxide dismutase, SOD;catalase, CAT;peroxidase, POD) in H. sinensis.The results indicated that the number of symbiotic algae in H. sinensis decreased more under combined hightemperature and strong light stress than under single stress of either high temperature or strong light. After 21 days of combined high-temperature and strong light stress, the number of symbiotic algae decreased by nearly 90%. In addition, the number of symbiotic algae under strong light stress decreased slightly more at the initial stress stage, but was low at the subsequent stage, compared with that under high-temperature stress.Both single and combined high-temperature and strong light stresses increased the active oxygen level in H.sinensis, and the start time of the upregulation of its active oxygen level under strong light stress was distinctly earlier than that under high-temperature stress. The activities of antioxidant enzymes SOD, CAT, and POD in H. sinensis were upregulated in the middle and late stages under single and combined high-temperature and strong light stresses. The activity of each antioxidant enzyme in H. sinensis under combined high-temperature and strong light stresses was higher than that under single high-temperature or strong light stress most of the time. Notably, the onset time for the upregulation of antioxidant enzyme activities in H. sinensis under strong light stress was earlier than that under high-temperature stress. Therefore, our study demonstrated that the combined high-temperature and strong-light stresses significantly aggravated the bleaching degree of H.sinensis compared with that under either high-temperature or strong light stress;in other words, the combined treatment of high temperature and strong light had a synergistic effect on the occurrence of bleaching in H.sinensis. Moreover, the response of H. sinensis to strong light stress was more sensitive than that to hightemperature stress, but the effect of high-temperature stress on the promotion of bleaching was greater than that of strong light stress, indicating that the mechanism by which H. sinensis bleaches under strong light stress was different from that under high-temperature stress.