【作者】 马增岭；

【导师】 高坤山；

【作者基本信息】 汕头大学 ， 海洋生物学， 2008， 博士

【摘要】 螺旋藻,作为重要经济蓝藻,其形态特征及代谢机理与环境变化的关系一直是该藻研究的热点。螺旋藻的螺旋丝状结构,受环境因子变化的调控,但有关阳光辐射变化对其影响的机制尚不清楚;同时,阳光紫外辐射(UVR)如何影响其光合作用与生长的问题也有待于进一步探讨。为此,本文研究了可见光(PAR)和紫外辐射对螺旋藻形态、生长以及光合作用的影响,并探讨了其它关键环境因子(如温度、ROS、无机碳等)变化与阳光辐射变化的耦合效应。主要研究结果如下:螺旋藻的螺旋结构,受PAR和UVR的影响,而该影响又受温度变化的调控。在较低温度(20 oC以下)条件下,PAR和UVR耦合效应导致藻丝螺距明显变小(螺旋变紧);而在适合其生长的温度范围(25-35 oC)内,仅仅PAR就能使得其螺旋变紧,UVR的存在虽然会加速藻丝螺旋变紧,但是在没有PAR存在的情况下UVR却不能引起藻丝螺旋结构的变化。通过对螺旋结构变化前后及不同辐射处理条件下的蛋白分析,发现分子量为52.0 kDa的胞膜蛋白与螺旋结构变化有关。对螺旋结构变化与生理过程关系的研究显示,螺旋结构变紧,细胞彼此遮挡程度增加,使得藻丝具有较高耐受强光(PAR和UVR)的能力,降低了PSII的损伤,也有效地阻止了藻丝的断裂,起到了明显的光保护作用。对可见光作用光谱的分析显示,可见光的任何波段均可以引起螺旋变紧,蓝光(波长400-500 nm)和红光(610-700 nm)对形态的诱导作用最强,而波长大于700 nm的红外光对藻丝形态没有任何影响。不同波段的可见光对细胞的生长和光合作用也产生了不同影响,也是蓝光和红色光对生长最有效。光照对藻丝形态的效应,可能与其驱动光合作用能力有关,引起与形态变紧相关的蛋白量增加,导致螺距变小。较高水平的PAR和UVR条件下,螺旋藻藻丝发生断裂,该断裂与细胞内活性氧自由基(ROS)的积累有关。高PAR和UVR处理,使得消除ROS的超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性下降,导致细胞内ROS量升高,损伤叶绿素、藻胆体和PSII并降低了光合电子传递速率。ROS的积累加速了细胞质膜的氧化(生成氧化产物丙二醛,MDA),同时引起了藻丝的断裂和解体。水体中,溶解无机碳(DIC)不足也会引起藻丝形态变化。将培养溶液的DIC浓度降低至0.3~4.0 mM范围内,培养螺旋藻时,其螺旋结构崩溃并出现变小的个体,藻蓝蛋白(PC)和别藻蓝蛋白(APC)的含量降低了,类胡萝卜素(Car)的含量却有所上升,最大光合作用速率下调了25%,其对无机碳的表观亲和力(K0.5DIC)增加了近14倍。另外,螺旋藻的浮性,受光合作用的调控,并非是逃避强光或获取营养的一种机制。藻丝的浮性,随着PAR的增强,与光合作用速率成负相关,光合作用速率越高,浮性越小。把强光下下沉的藻丝转到暗处或者低光下后,其浮性能够得到恢复。阳光UVR抑制藻丝的光合作用,增加其浮性,其作用与PAR相反。结果分析表明,螺旋藻没有主动逃避有害辐射的能力,其下沉与上浮受光合生产量的调控,在碳水化物累积较多时下沉,反之上浮;在自然界或养殖池中,早晨或傍晚阳光辐射光合生产量较低时上浮,而中午时下沉,被动性的逃避了有害UVR的影响。更多还原

【Abstract】 The relationship of morphological characteristics and metabolisms of filamentous Arthrospira (Spirulina) platensis with environmental changes has been the focus of this economically important cyanobacterium. Spiral structure of A. platensis is known to alter according to environmental changes, however, little has been documented on the mechanisms about the effects of solar radiation changes on its morphology. In addition, effects of solar ultraviolet radiation (UVR) on its photosynthesis and growth also need to be further studied. Therefore, impacts of photosynthetic active (PAR) and UV radiations as well as their combined effects with temperature and DIC on its morphology, growth and photosynthesis were investigated in this study. The main results are as following:The spiral structure was affected by PAR and UVR, but such effects of PAR and UVR were dependant on temperature. At temperature levels lower than 20 oC, the helix pitch of A. platensis (D-0083) became smaller due to the interactive effect of PAR and UVR, however, at temperature levels (25-35 oC) suitable for its growth, irradiation with PAR alone resulted compressed spirals. Although change of the compressed helix pitch happened faster in existence of UVR, UVR alone did not tighten the helix. With the technique of SDS-PAGE for separation of the proteins washed off from the cellular membrane, it was found that a protein of 52.0 kDa was responsible for the compression of the spirals. The tightened spiral structure played a protective role against high levels of UVR or PAR by increasing shelf-shading among the cells, alleviating the photo-damage of PSII and reducing the breakage of trichomes. The compression of the helix pitch did not depend on specific wavebands of PAR, nevertheless, the blue (400-500 nm) and red light (610-700 nm) were the most effective components. The infrared radiation (>700 nm) had no effect on its morphology at all. Furthermore, different wavebands of PAR showed discrepant effects on the growth and photosynthesis, blue and red light was more effective for its growth too. The efficiency of blue and red light on the spiral compression might be due to its higher efficiency for driving higher rate of photosynthesis, which runs the biochemical machinery for generation of proteins.The spiral filaments of A. platensis broke when irradiated with high levels of PAR and/or UVR. This was proved to link to the accumulation of reactive oxygen species (ROS) in the cells. High PAR and UVR suppressed the activity of superoxide dismutase (SOD) and catalase (CAT), leading to an increase of ROS in the cells. The accumulated ROS damaged chlorophyll a, phycobilisome and PSII, decreased the photosynthetic electrode transfer rate (ETR) and accelerated the oxidation of cell membrane (with an increased production of malondialchehyche, MDA), which was thought to result the spiral breakage.The limitation of dissolved inorganic carbon (DIC) could change the filaments’morphology too. When the DIC concentration in the culture medium was reduced to 0.3-4.0 mmol/L, the spiral filaments broke even under moderate levels of PAR and the trichomes with much smaller size appeared. DIC limitation decreased the contents of phycocyanin (PC) and allophycocyanin (APC) in the cells, however, the contents of carotenoid (CAR) increased. Compared with filaments cultured with normal Zarrouk medium, the maximal photosynthetic rate of adapted cells in medium with much lower DIC concentration decreased by 25% and the apparent affinity for DIC (K1/2(DIC)) increased about 14 times.Buoyancy provided by gas vesicles has been suggested to play important roles in regulating vertical distribution and nutrient acquisition in cyanobacteria. However, little is known about how PAR (400-700 nm) as well as UV radiation (UVR, 280-400 nm) which change with day time and depth would affect the buoyancy. In this study, it was demonstrated that the floatation activity of A. platensis decreased with increased photosynthetic rates associated with increased PAR, but it decreased less in the presence of UVR that resulted inhibitory effects. When the cells were grown under isoenergetic levels of solar PAR or UVR alone, they migrated downward under the PAR but maintained buoyant under the UVR. The buoyancy regulation of A. platensis depended on the exposed levels of PAR as well as UVR, which affected photosynthesis and growth in an antagonistic way. The buoyancey of A. platensis in water columns is much likely to be dependant on diurnal photosynthetic performance regulated by solar radiation, and can hardly be considered as an active strategy to gain more energy during sunrise/sunset or to escape from harmful irradiations during noon period.更多还原