光周期对中国水螅种群增长、无性出芽生殖及抗氧化酶活力的影响

摘要

The symbiotic system of endodermal epithelial cell in Chinese green hydra (Hydra sinensis) and unicellular eukaryotic green algae is a special biological model which has a high scientific value.Hydra host cell provides CO2,nitrogen and minerals for symbiotic algae,and symbiotic algae could provide carbohydrate from photosynthesis for their host cells.Therefore,it's clear that metabolic flux between green hydra and its symbiotic algae centres on photosynthesis in symbiotic algae,but the interaction mechanism based on metabolic flow between green hydra and its symbiotic algae has not been elucidated at present.In general,nutrient accumulation results in asexual budding reproduction of hydra,and the number of buds falling off parent body could indirectly reflect the relative amount of nutrient accumulation in hydra.Illumination time can affect photosynthesis of symbiotic algae in green hydra,and if symbiotic algae could indeed transfer some products of photosynthesis to hydra host cell,then illumination time should be able to indirectly affect nutrition accumulation in green hydra,thereby further affect asexual budding reproduction of green hydra.In order to confirm the hypothesis,the effect of photoperiod on population growth,asexual budding reproduction and activities of two antioxidant enzymes (SOD and CAT) of H.sinensis was observed by the method of population accumulative culture.The photoperiod had obvious impact on population growth of green hydra.Hydra populations in all experimental groups increased positively 15 days after the onset of the experiment,and hydra population density was the biggest at 8 h light/16 h dark cycle,while it is lowest at 0 h light/24 h dark cycle.In addition,activities of SOD and CAT had a decreasing trend with increasing illumination time.The results show that,from the view of the effect of photoperiod on asexual budding reproduction and activities of two antioxidases,the physiological response of H.sinensis is rather sensitive to photoperiod due to the fact that the symbiotic algae can provide some products of photosynthesis as nutritional supplements of green hydra.%单细胞真核绿藻在中国水螅(Hydra sinensis)内胚层皮肌细胞中共生是有较高科研价值的特殊生物学现象.水螅宿主细胞为共生藻提供CO2、氮源及矿物质,而共生藻通过光合作用可能为宿主提供碳水化合物等有机物营养,因此水螅与共生藻间代谢流是以共生藻光合作用为中心,但基于代谢流二者间的互作机制目前尚未阐明.水螅通过营养积累进行出芽生殖,从母体脱落的芽体数量间接反映水螅营养积累的相对量.而光暴露时长能影响共生绿藻光合作用,如果共生藻的确能向水螅细胞转移光合作用产物,那光暴露时长应该能间接影响水螅的营养积累、从而进一步影响水螅无性出芽生殖.为证实该假说,本研究应用种群累积培养法,观察了光周期对中国水螅种群增长、无性出芽生殖及抗氧化酶(SOD和CAT)活力的影响.结果显示,光周期对中国水螅种群增长具有明显的影响.培养15 d后,所有实验组水螅的种群密度均为正增长,其中8L:16D(在一个24 h周期内光暴露8 h、黑暗16 h)实验组种群密度最大、而0L:24D(持续黑暗)实验组种群密度最小.另外,随着光暴露时长的增加,中国水螅SOD及CAT活力整体均呈下降趋势.结果表明,从光周期对中国水螅无性出芽生殖及两种抗氧化酶活力的影响来看,中国水螅对光周期的生理学响应较为敏感,这个现象可能源于共生绿藻能通过向宿主细胞转移光合作用产物的方式为水螅提供营养补充.