ISWC OpenIR  > 水保所2018--届毕业生论文
单半乳糖甘油二酯的光保护机理
李倩
Subtype硕士
Thesis Advisor殷俐娜
2018-05-24
Degree Grantor中国科学院大学
Place of Conferral北京
Keyword单半乳糖甘油二酯 光保护 叶黄素循环 膜脂
Abstract单半乳糖甘油二酯(monogalactosyldiacylglycerol, MGDG)是类囊体膜的重要组分,约占类囊体膜糖脂含量的50%,对于植物的光合作用至关重要。光照是光合作用不可或缺的条件,而光合系统多层次光保护和修复机制是植物应对高光胁迫做出的反应,在这个机制中存在两条防线:热耗散阻抑机制和光有毒产物清除机制。目前关于MGDG在盐胁迫、干旱胁迫和冷害胁迫过程所起作用的研究较多,但是,高光胁迫下MGDG在光保护过程的作用不甚明了。本实验以转水稻MGDOsMGD)基因烟草(M2、M5)和野生型烟草(SR)为实验材料,根据前期光合曲线的测定选择两组处理光强,通过测定高光处理前后烟草的表型参数、光合参数、光有毒产物的生成、叶黄素循环效率、膜脂含量等指标,探索MGDG的在两条防线上的光保护机理。实验结果如下:
(1)在对光响应曲线进行分析时表明,与野生型SR烟草相比转基因株系M2和M5的净光合速率分别提高了28%和29%,光饱和点分别提高了38%和25%。高光处理1天后M2和M5的叶片鲜重分别比SR高19%和21%,全株鲜重分别比SR高11%和11%;叶绿素含量分别比SR高23%和18%;净光合速率分别比SR高173%和172%。从表型上可以看出,高光处理后SR叶片出现漂白斑,叶片变小变薄,颜色微黄,而M2和M5株系的叶片受损较轻。综上可知,高光处理对SR、M2、M5均造成了光抑制,但是转基因株系具有更强的高光耐受性。
(2)对高光处理后烟草的荧光参数进行分析发现,高光处理后SR、M2和M5的热耗散分别增加37%、81%和75%;但SR的光合电子传递速率降低30%,而M2和M5却分别升高了23%和25%;SR的光化学淬灭系数降低32%,而M2和M5却升高了24%和18%。SR、M2和M5的超氧阴离子自由基含量分别升高239%、99%和71%,过氧化氢含量分别升高57%、25%和33%,丙二醛含量分别升高27%、3%和3%。以上结果说明,高光胁迫时转基因株系的相对电子传递效率、光化学淬灭系数的提高使能量更快速的通过光反应转化成同化力用于暗反应,另一方面转基因株系具有更高的热耗散能力,能够快速的将过剩激发能转化成热量散失,从而降低了光有毒产物的生成。
(3)对叶黄素循环的研究发现高光胁迫后SR、M2和M5的紫黄素含量分别降低11%、41%和43%,环氧玉米黄素含量分别降低27%、32%和56%,玉米黄素含量分别增加5311%、26945%和19616%,叶黄素循环效率分别提高2008%、5874%和4658%。说明高光胁迫时超表达OSMGD提高了叶黄素循环效率,在第一防线增强了热耗散能力。玉米黄素的大量生成,在第二防线清除活性氧,增强了转基因株系的高光耐受力。
(4)高光耐受性的差异来源于MGD基因的过表达,随后我们对膜脂进行了研究。结果表明高光处理后SR、M2和M5的MGDG含量分别降低34%、19%和18%,DGDG含量分别升高11%、38%和24%,PL含量分别降低42%、15%和19%,总脂含量分别降低10%、2.4%和3.9%;MGDG脂肪酸不饱和度分别降低9%、4%和4%,DGDG脂肪酸不饱和度分别降低26%、11%和15%,PL脂肪酸不饱和度分别降低28%、7%和10%; MGDG/叶绿素分别升高了28%、19%和12%,DGDG/叶绿素分别升高了9%、6%和4%,PL/叶绿素分别升高了22%、16%和8%;DGDG/MGDG升高,但是转基因型比野生型高。说明高光处理导致膜脂发生了降解,膜脂的不饱和度降低,类囊体蛋白堆叠密度降低,但是转基因株系的表现优于野生型。
综上所述,高光胁迫时单半乳糖甘油二酯含量的增加提高了叶黄素循环效率,在第一防线提高了能量的耗散,增强了植物的高光耐受性;玉米黄素的大量合成清除了活性氧,从而在第二防线清除了已生成的活性氧,提高了植物的高光耐受性;热耗散效率的提高,降低了光合系统的压力,促进了光合电子传递速率和CO2同化率,使能量通过光合作用固定,降低过剩激发能对光合结构的损害,提高了植物的高光耐受性。
光抑制造成膜脂降解,膜的流动性和通透性遭到破坏;类囊体膜的结构和功能受损,叶片的光合功能受到破坏。单半乳糖甘油二酯向双半乳糖甘油二酯的转化是生物膜应对高光胁迫的响应之一,通过双半乳糖甘油二酯的双层结构部分补偿膜的损伤,维持膜的结构和功能,提高了植物对高光胁迫的耐受性。
Other AbstractMonogalactosyldiacylglycerol (MGDG) is an important component of the thylakoid membrane, accounting for approximately 50% of the thylakoid membrane lipid content, and is essential for plant photosynthesis. Illumination is an indispensable condition for photosynthesis. Photosynthesis systems' multi-level photoprotection and repair mechanism is a response of plants to high-light stress. There are two defense lines in this mechanism: heat dissipation suppression mechanism and phototoxic product removal mechanism. At present, there are many studies on the role of MGDG in salt stress, drought stress and chilling stress. However, the role of MGDG in photoprotection under high-light stress is not clear. In this experiment, rice MGD (OsMGD) gene tobacco (M2, M5) and wild-type tobacco (SR) were used as experimental materials. The light intensity of the two groups was selected according to the measurement of the early photosynthetic curve, and the phenotypic parameters of the tobacco before and after high-light treatment were determined. The photosynthetic parameters, the formation of phototoxic products, xanthophyll cycle efficiency, and membrane lipid content were used to explore the photoprotective mechanism of MGDG on two defense lines. The experimental results are as follows:
(1) When the light response curve was analyzed, the net photosynthetic rate of the transgenic lines M2 and M5 was increased by 28% and 29%, respectively, and the light saturation point was increased by 38% and 25%, respectively, compared with the wild-type SR tobacco. After one day of high-light treatment, the leaf fresh weights of M2 and M5 were 19% and 21% higher than those of SR respectively. The fresh weight of the whole plant was 11% and 11% higher than that of SR, respectively; the chlorophyll content was 23% and 18% higher than SR, respectively; the net photosynthetic rate are 173% and 172% higher than SR, respectively. From the phenotype, it can be seen that after the high-light treatment, the SR leaves have bleaching spots, the leaves become smaller and thinner, and the color is yellowish, while the leaves of the M2 and M5 lines are less damaged. In summary, the high-light treatment caused photoinhibition of SR, M2, and M5, but the transgenic strain had a stronger high-light tolerance.
(2) After analyzing the fluorescence parameters of tobacco after high-light treatment, the heat dissipation of SR, M2 and M5 after high-light treatment increased by 37%, 81% and 75% respectively; however, the photosynthetic electron transfer rate of SR decreased by 30%. M2 and M5 increased by 23% and 25%, respectively; the photochemical quenching coefficient of SR decreased by 32%, while that of M2 and M5 increased by 24% and 18%. The content of superoxide anion radicals in SR, M2, and M5 increased by 239%, 99%, and 71%, respectively, and the hydrogen peroxide content increased by 57%, 25%, and 33%, respectively, and the malondialdehyde content increased by 27%. 3% and 3%. The above results indicate that the relative electron transfer efficiency and photochemical quenching coefficient of the transgenic strains under high-light stress increase the energy to be converted into assimilating force for dark reaction more quickly through light reaction, and the transgenic strain has higher heat on the other hand. The dissipative ability can quickly convert excess excitation energy into heat loss, thereby reducing the formation of phototoxic products.
(3) Study on the xanthophyll circulation found that the content of violaxanthin in SR, M2, and M5 decreased by 11%, 41%, and 43% after high-light stress, and the content of antheraxanthin decreased by 27%, 32%, and 56% respectively, zeaxanthin content increased 5311%, 26945% and 19916% respectively, and the xanthophyll cycle efficiency increased by 2008%, 5874% and 4658%, respectively. It shows that over-expression of OSMGD in high-light stress enhances the xanthophyll cycle efficiency, and enhances heat dissipation capacity in the first line of defense. The massive production of zeaxanthin scavenges active oxygen at the second line of defense, enhancing the high-light tolerance of transgenic lines.
(4) The difference in high-light tolerance results from the overexpression of the MGD gene. We subsequently studied membrane lipids. The results showed that the MGDG content of SR, M2, and M5 after high-light treatment decreased by 34%, 19%, and 18%, respectively; the DGDG content increased by 11%, 38%, and 24%, respectively, and the PL content decreased by 42%, 15%, and 19%, respectively. The total lipid content decreased by 10%, 2.4%, and 3.9%, respectively; MGDG fatty acid unsaturation decreased by 9%, 4%, and 4%, respectively, and DGDG fatty acid unsaturation decreased by 26%, 11%, and 15%, respectively. PL fatty acid unsaturation decreased by 28%, 7%, and 10%, respectively; MGDG/chlorophyll increased by 28%, 19%, and 12%, DGDG/chlorophyll increased by 9%, 6%, and 4%, respectively; PL/chlorophyll increased by 22%, 16%, and 8%. DGDG/MGDG increased, but the transgenic version was higher than the wild type. The results showed that the high-light treatment resulted in the degradation of membrane lipids, the unsaturation of membrane lipids, and the decrease in thylakoid protein packing density, but the transgenic lines performed better than the wild type
In summary, the increase in monogalactosyl diacylglycerol content in high-light stress increases the xanthophyll cycle efficiency, increases energy dissipation in the first line of defense, and enhances the plant's high-light tolerance; The massive synthesis of zeaxanthin removes the active oxygen, so that the generated reactive oxygen species are eliminated at the second line of defense, and the plant's high light tolerance is improved; the heat dissipation efficiency is increased, the pressure of the photosynthetic system is reduced, and the photosynthetic electron transfer rate and CO2 are promoted. The assimilation rate makes the energy fixed by photosynthesis, reduces the damage of the excess excitation energy to the photosynthetic structure, and improves the plant's high-light tolerance.
Photoinhibition caused membrane lipid degradation, membrane fluidity and permeability were destroyed; thylakoid membrane structure and function were impaired, and photosynthetic function of the leaf was destroyed. The conversion of monogalactosyl diglyceride to digalactosyl diglyceride is one of the biofilm response to high-light stress. The double-galactose diglyceride double structure partially compensates for membrane damage and maintains the structure and function of the membrane, increased plant tolerance to high-light stress.
Language中文
Document Type学位论文
Identifierhttp://ir.iswc.ac.cn/handle/361005/8124
Collection水保所2018--届毕业生论文
Affiliation中国科学院教育部水土保持与生态环境研究中心
Recommended Citation
GB/T 7714
李倩. 单半乳糖甘油二酯的光保护机理[D]. 北京. 中国科学院大学,2018.
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