【作者】 孙山；

【导师】 高辉远； 束怀瑞；

【作者基本信息】 山东农业大学 ， 植物学， 2009， 博士

【摘要】 苹果(Malus domestica Borkh.)果实灼伤是一种由高温、干旱和强光引起的生理伤害,每年在世界各主要苹果产区都有发生,尤其在气温偏高、雨水较少的地区果实日灼更为严重。日灼使果品的产量和质量均受到不同程度的影响,给果品生产造成巨大损失。目前对强光加重日灼的研究,均集中在光对果实的增温作用和紫外辐射的破坏方面。事实上在日光照射下,苹果绿色果实发生灼伤的临界温度比单纯高温低3-7℃,即在光照条件下,苹果绿色果实在相对较低的温度下就易发生灼伤。大量对植物叶片的研究表明,高温、强光均会引起光抑制,导致光合电子传递链产生活性氧;与叶片相比,苹果绿色果实的光能利用能力较低,高温强光下绿色果皮吸收的光能会远远超出其光合作用所能利用的范围。由于现有的各种光合作用研究的设施都是针对植物叶片所设计的,再加之果实的特殊形状、结构以及特殊的生长环境,人们对果实的光合作用的光抑制和光破坏的防御机制的研究非常有限。迄今为止,高温、强光胁迫对苹果绿色果实光合作用的影响以及苹果绿色果实光合作用的光抑制与氧化胁迫的关系仍不清晰。所以,从多角度探讨绿色果皮的光合作用以及果皮抗氧化系统对高温与强光的响应规律,了解果皮灼伤的生理生化机制,对改善预防果实日灼的措施具有重大的理论和实践意义。本研究从光合生理的角度出发,以当前国内外生产上广泛栽培的苹果品种新红星为试材,首先改进了苹果果实光合生理的研究方法,进而利用所建立的研究方法研究了苹果果实绿色发育阶段光合色素、光合能力、呼吸速率的动态变化以及苹果绿色果皮PSII原初光化学反应对自然高温、强光的响应;在上述基础上,探讨了高温、光胁迫条件下苹果绿色果皮光合机构的光抑制机理及光抑制对果皮氧化胁迫的影响。主要研究结果如下:1.建立了一套适合苹果绿色果实光合生理研究的方法⑴改进了果实光合作用的研究方法。利用改进的氧电极测定方法,比较了果实阴、阳面以及阳面纵向的光合放氧速率的差异,确立了果实阳面中央部位为果实光合测定的代表部位;通过测定果皮光合放氧的光、温响应曲线,找出测定果实光合放氧速率的适宜光强和温度分别为500μmol m-2 s-1和30℃。此外,设计并改进了用于苹果果实叶绿素荧光测定和反射光谱测定的专用探头适配器以及适宜整果和果皮高温光胁迫处理的专用装置。⑵建立了利用无损伤光谱测定技术研究苹果果皮色素含量的方法从众多的反射光谱指数中筛选出了适用于苹果果实叶绿素、花青素、类胡萝卜素无损伤动态估测的高光谱指数,并与传统的溶液提取法做了相关性分析,其中叶绿素、花青素的高光谱指数与化学方法测定含量之间的相关性均达到极显著水平;实验证明了从整果测得的光化学反射光谱指数(PRI)能较好地反映果皮组织的叶黄素循环变化。这种无损伤光谱测定技术可以成为研究苹果果实色素含量动态变化的有力工具。2.测定并分析了苹果果实发育过程中色素含量、光合能力和呼吸速率的动态变化新红星苹果果实的叶绿素含量随果实发育呈下降的趋势。在绿色果实发育前期(盛花后41天之前)果皮中的叶绿素含量处于较高水平,之后单位面积果皮的叶绿素含量随果实发育快速下降;类胡萝卜素的变化规律与叶绿素相似,伴随着叶绿素含量的下降也逐渐降低,但单位果皮面积类胡萝卜素总量与叶绿素总量的比值则随发育期而逐渐增加,说明果皮内叶绿素降解速度大于类胡萝卜素;果皮中花青素的变化,与叶绿素及类胡萝卜素含量的变化规律相反。花后25-61天之间含量一直保持较低水平,变化不显著,花后61-83天之间开始明显增加。与叶片展叶过程中光合能力的逐步提升完全不同,绿色果皮的光合放氧速率随着发育的进展一直下降。所以,在幼果发育早期,果实光合作用对于其自身碳需求的贡献最大。苹果果实的呼吸在着色之前的发育过程中,特别是花后33-53天之间,呼吸强度一直在下降,花后53天达到最低值,随后较为稳定。呼吸强度在绿色果实发育前期保持较高水平,此期果实细胞生理代谢较为活跃,抗氰呼吸途径占总呼吸的比率也相应较高,这可以在一定程度上减少呼吸途径中的活性氧(ROS)产生,提升细胞整体水平上防御氧化胁迫的能力。3.研究了苹果绿色果皮的原初光化学反应对自然条件下光、温变化的响应晴天条件下,苹果绿色果皮的原初光化学反应的日变化表明,随着光、温的增强,苹果果皮在12-14时存在较为严重的光抑制。PSII的放氧复合体(OEC)的活性在一天当中没有受到强光和高温的伤害;但是捕获的激子将电子传递到电子传递链中QA-下游电子受体的概率(ΨO)从8-12时逐渐下降,表明PSII反应中心受体侧的功能受到了抑制。强光降低了果皮单位面积上有活性的反应中心(RC/CS)的数量,导致单位反应中心吸收的光能(ABS/RC)增加。果皮的光化学反应(TRO/RC)不能完全利用所吸收的光能,使单位反应中心的热耗散(DIO/RC)增加。伴随着光抑制的出现,苹果果皮启动了叶黄素循环机制,以减轻过剩光能对光合机构的进一步伤害。该结果揭示了苹果绿色果皮与植物叶片相似,在自然条件下可以通过光化学效率的下调和依赖叶黄素循环的能量耗散机制保护果皮光合机构免受高温强光的破坏。这是自然条件下,果皮减轻氧化胁迫伤害的机制之一。4.探讨了高温与光交互作用下,苹果PSII反应中心活性、抗氧化系统对高温和光照的响应,以及光照对高温下果实氧化胁迫的影响为了避免自然条件下,光、温以外其它环境因子的交互影响,利用人工控制光、温条件处理,从多角度分析绿色果皮原初光化学反应、光破坏保护能力和果皮抗氧化系统对光、温的响应,结果表明,从30℃一直上升到44℃,苹果绿色果皮的光合速率变化不大,而48℃高温处理,引起了光合速率的显著下降,且各种光强处理均加重48℃下光合速率的下降。结合PSII最大光化学效率(Fv/Fm)、H2O2含量和MDA的变化,本研究表明,高温不仅可以直接伤害光合机构造成光抑制,还可通过各种途径间接地加剧光抑制,使得果皮在中等光强甚至弱光下即可发生光抑制。强光下44℃以上的高温处理可引起果皮的叶绿素降解,并引起部分PSⅡ反应中心失活,光强超过600μmol m-2 s-1的光温交互作用加剧了反应中心的失活。48℃以下高温、黑暗处理和30℃与1000μmol m-2 s-1以下光的交互处理,对苹果绿色果皮PSⅡ反应中心受体侧的影响均较小,但在光照条件下,44℃以上的高温即可对PSⅡ受体侧造成伤害。48℃高温与1000μmol m-2 s-1的光强交互处理造成抗氧化酶失活,使超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)、过氧化氢酶(CAT)的活性大幅度下降。高温强光使果皮的ROS清除能力显著降低,从而造成果皮中ROS含量的显著增加。过氧化物酶(POD)与多酚氧化酶(PPO)在苹果绿色果实的生长发育过程中,具有明显的发育阶段的特异性,与绿色果实的早期生长发育有着密切的关系。二者的活性分别于花后56天和84天后逐渐完全消失。在高温、光胁迫下,尽管PSII光化学效率下调,并启动了热耗散机制,但由于高温引起酶的失活,使ROS生成与清除的动态平衡被打破,光合电子传递链产生的活性氧增加,造成植物体内更多的活性氧(ROS)积累,加剧氧化胁迫,造成包括类囊体膜在内的细胞膜系统的破坏。48℃高温下,中度光照即可显著加剧对膜脂结构的破坏。本研究结果表明:高温造成苹果果皮氧化胁迫,而高温与强光的交互胁迫显著加重果皮的光抑制,导致过剩激发能的产生,造成光合电子传递链产生的活性氧增加,进一步加剧了高温条件下的氧化胁迫。因此,强光高温引起绿色果皮光合机构的光抑制与苹果的光下灼伤有着密切的关系,为苹果日灼的重要发生机理之一,同时也是光下灼伤阈值温度下降的原因所在。更多还原

【Abstract】 Apple fruit sunburn, a common physiological disorder caused by high temperature, drought and strong sunlight, happens widely in main apple-producing areas around the world, especially in the areas with high temperature and drought stress, which results in a huge loss annually. At present, the study on effect of strong light on sunburn is mainly focused on its enhancement of fruit surface temperature or on UV damage. In fact, the threshold temperature was required for sunburn appears to be 3-7℃lower than that of thermal damage in the dark. Studies on plant leaves have shown that both high temperature and strong light can cause photoinhibition, which results in over production of Reactive Oxygen Species (ROS) in photosynthetic electronic chain. Compared with leaf, the photosynthetic capacity of apple green peel is lower, energy absorbed by green peel under high temperature and strong light conditions should be much more than its utilization. However, due to that nearly all of the instruments on study of photosynthesis are designed according to plant leaves and due to the special shape, structure and growth condition of apple fruits, studies on photoinhibition and photoprotection mechanisms in apple fruit peel is very limited up to now. The effect of high temperature and strong light on photosynthesis of apple green fruit as well as the relationship between photoinhibition and oxidation stress has not been clear yet Therefore, it is theoretically and practically important to elucidate the response of photosynthesis and antioxidation system in green peel to high temperature and strong light and to explore the physiological and biochemical mechanism of sunburn, which will help us to improve cultivation practice against sunburn in apple production.In this dissertation, Starkrimson cultivar (Malus domestica Borkh.), a broadly cultivated apple cultivar, were selected⑴to establish a series of approaches to study photosynthetic physiology in apple fruits;⑵to investigate the dynamic variations of relative pigment contents, photosynthetic capacity and respiration rate in apple fruit peel during development of the fruits;⑶to investigate the variations of primary photochemical reactions of apple green peel in response to diurnal changes of incident PFD and air temperature. Furthermore, mechanism of photoinhibition in apple green peel under the cross stress of strong light and high temperature, and the effect of photoinhibition on oxidative stress on apple green peel were also investigated. The main results are as follows:1. Approaches to study photosynthetic physiology in apple peel were established.⑴Approaches to study photosynthesis in apple fruit was improved.By the new approach, the difference of photosynthetic O2 evolution in sun peel, shade peel and longitudinally different parts were compared. It was proved that the central part of sun peel was the desirable representative one for measuring photosynthetic O2 evolution. 500μmol m-2 s-1 PFD and 30℃are optimal measurement condition for photosynthesis in apple peel. In addition, special probes for measuring spectral reflectance and chlorophyll a fluorescence of apple fruit and apparatus for the control of temperature and light for treatment of apple peel or fruit were designed and improved.⑵Nondestructive measurement of pigment content in apple fruits using spectral reflectance was investigated.The results showed that the spectral indices chose in present study were better correlated to the pigment concentrations in fruit peel, the spectral indices were significantly correlated with contents of chlorophyll (a+b) or anthocyanin. It was demonstrated that the relationships of spectral indices to pigment concentrations can be well used for non-destructive and quickly estimating pigment concentrations in apple fruits. The result also showed that photochemical reflectance indices (PRI) was significantly negative correlated with de-epoxidation status of total xanthophylls pigment pool ((0.5A+Z)/( A+Z+V)).2. Dynamic variations of relative pigment contents, photosynthetic capacity and respiration rate in peel during apple green fruit development were investigated.Immature apple fruits had a high content of chlorophyll that gives them the characteristic green color. From the 25th to 83rd day after bloom, the content of both chlorophyll and carotenoid decreased, but the ratio of carotenoid to chlorophyll increased, which indicated that the degradation of chlorophyll was faster than that of carotenoid in green peel. The content of anthocyanin changed in an opposite way to chlorophyll and carotenoid, it was maintained unchanged during the period of 25-61 days after bloom, then increased gradually from the 61st day after bloom.Photosynthesis was higher in immature apple fruit peel. It declined with the progress of fruit development, changing in a similar to chlorophyll content. The contribution of fruit photosynthesis to the total carbon requirement of a fruit was the highest during early development.Before color up, especially in the interval of 33-53 days after bloom, the respiration rate decreased and was minimized 53 days after bloom, and then it leveled off. The total respiratory rate and the ratio of alternative pathway to the total respirations were higher during the early stage of fruit development. The increase of cyanide-resistant respiration could be in favor of reducing the production of ROS to alleviate oxidative stress in whole cell level.3. The response of PSII primary photochemical reactions and xanthophyll cycle in apple peel to diurnal changes of incident photon flux density (PFD) and air temperature were studied.In a sunny day, with increase of incident PFD, severe photoinhibition occurred from 12:00 to 14:00 in apple peel. Relative activity of oxygen evolving complex (OEC) indicated by a fluorescence index Wk did not change significantly through the day, efficiency that a trapped exciton can move an electron into the electron transport chain beyond QA- (ΨO) reduced from 12:00 to 14:00, indicating that acceptor side of PSⅡwas damaged in apple peel. High irradiance caused a decrease in the density of PSⅡreaction centers per excited cross-section(RC/CS) and resulted in an increase in absorption per active reaction centers(ABS/RC). Since the photochemical reaction in apple peel (TRO/RC) was not able to use excited energy completely at noon, the dissipation per active reaction center (DIO/RC) was increase during that time. Along with appearance of photoinhibition, the de-epoxidation level of xanthophyll pigment pool indicated by PRI markedly increased, indicating that xanthophyll cycle was initiated to prevent PSII reaction centers and electron transport chain against photodamage in apple peel.4. Activity of PSⅡreaction center, antioxidative system in response to strong light and high temperature and the effect of light on oxidative stress under high temperature were explored in apple fruit.To avoid effects of other factors except light and temperature, activity of PSⅡreaction center, antioxidative system in response to strong light and high temperature and the effect of light on oxidative stress under high temperature in apple fruit were explored under controlled light and temperature condition. The results showed that photosynthetic O2 evolution rates in apple peel did not change significantly between 30℃to 44℃, but distinctly declined at 48℃, and every combination of different light intensity with 48℃aggravated the decrease. Analysis of changes in Fv/Fm, H2O2 and MDA indicated that high temperature not only directly damaged photosynthetic apparatus to cause photoinhibition but also aggravated photoinhibition by affecting other biochemical metabolic processes, so high temperature caused photoinhibition under moderate light even under weak light.Under strong light, temperature over 44℃resulted in chlorophyll degradation and deactivation of PSⅡreaction centers. Over 600μmol m-2 s-1 light combined with high temperature accelerated the deactivation of PSⅡreaction centers. Treatments with 48℃in the dark or 30℃combined with 1000μmol m-2 s-1 light did not affect the accept side of PSII. While the combination of 44℃with various light intensity would inhibit the activity of the accept side of PSII.Along with appearance of photoinhibition caused by high temperature combined with light, xanthophyll cycle was initiated to prevent PSII reaction centers and electron transport chain against photodamage in apple peel.The treatment of 44℃combined with 1000μmol m-2 s-1 light greatly reduced the activities of antioxidant enzymes such as SOD, APX and CAT, resulting in over accumulation of ROS in apple peel.The activity of POD and PPO manifested stage heterogeneity, which correlated with the development of apple green fruit. The activity of POD and PPO minimized 56 and 84 days after bloom respectively.The high concentrations of H2O2 and MDA in apple peel treated with high temperature combined with strong light indicated that the antioxidant system was unable to cope with the photooxidation triggered by high temperature coupled with strong light. Under the stress of high temperature combined with light, although down- regulation of photochemistry and xanthophyll cycle were initiated, the ROS was over accumulated due to the broken equilibrium between the scavenging and production of ROS, which enhanced oxidative stress to damage membranes of peel cells including the membranes of thylakoids in apple peel.In conclusion, high temperature brought out oxidative stress in apple green peel; strong light coupled with high temperature caused severe photoinhibition, resulting in over production of ROS in photosynthetic electron chain, which increased the accumulation of ROS in whole cell to accelerate photooxidative damage of apple green peel at high temperature. Severe photoinhibition caused by strong light coupled with high temperature was one of important reasons to cause sunburn under light as well as a key reason to cause the decrease in threshold temperature required for sunburn by 3-7℃lower than that of thermal damage in the dark.更多还原