【作者】 曹慧；

【导师】 韩振海； 许雪峰；

【作者基本信息】 中国农业大学 ， 果树学， 2003， 博士

【摘要】 本实验以平邑甜茶和新疆野苹果幼苗为试材，研究了水分胁迫诱导苹果属植物的衰老机理。实验结果表明，苹果属植物幼苗在水分胁迫下，随着胁迫时间的延长，Chl降解加剧，活性氧O₂^、H₂O₂、脂质过氧化产物（MDA）含量明显增加及细胞质膜相对透性（PMP）明显增大。其中，抗旱性较强的新疆野苹果幼苗降低的幅度均低于抗旱性较弱的平邑甜茶。Chl含量的降低和O₂^、H₂O₂、MDA含量增高及PMP升高之间均呈显著负相关。说明水分胁迫下苹果属植物幼苗Chl降解与活性氧损伤密切相关。 水分胁迫引起苹果属植物幼苗核酸代谢的变化，DNase、RNase活性上升，O₂^、H₂O₂含量增高；DNA、RNA含量下降，其中DNA含量下降的幅度小于RNA含量下降的幅度，DNase活性上升的幅度小于RNase活性上升的幅度。表明RNA比DNA对水分胁迫更敏感。水分胁迫下苹果属植物幼苗叶片的DNA、RNA含量与RWC、O₂^、H₂O₂含量间均呈显著相关。表明水分胁迫下活性氧自由基累积引起植物组织衰老的启动，进而影响核酸代谢的变化。 平邑甜茶叶片在水分胁迫下内肽酶活力的变化可分为低值缓降期和速升期，对应于叶绿素含量的缓降期和速降期。水分胁迫引起叶片老化过程中存在3种以上的内肽酶（巯基蛋白酶、丝氨酸蛋白酶和金属蛋白酶），但在蛋白质降解中起主要作用的是巯基蛋白酶。其中在叶片衰老过程中起主要作用的是酸性蛋白水解酶；且内肽酶的最适温度为45℃。另外，不同浓度放线菌酮、激素、H₂O₂处理实验结果表明，放线菌酮和BA抑制内肽酶的活性，而ABA和H₂O₂可促进内肽酶活力的提高。 水分胁迫下对与光系统Ⅱ原初光能转化（Fv／Fo、Fv／Fm、q_p＼q_N、yield、Ca／Fo）和膜脂过氧化作用有关的生理指标的测定结果表明：叶绿素荧光参数的变化程度与不同苹果属植物的抗旱性相关；平邑甜茶和新疆野苹果叶绿素荧光参数的变化程度与MDA含量及质膜相对透性呈显著相关。因此，水分胁迫下PSⅡ原初光能转化受抑程度与膜脂过氧化间存在一定关系。 水分胁迫引起苹果属植物幼苗叶片的P_n与Chl、Car、Chl-Pro、O₂^、H₂O₂、¹O₂、Gs、ASA、SOD、POD、CAT的变化，且在水分胁迫下这些参数变化程度与抗旱性程度相一致。同时，水分胁迫下苹果属植物幼苗叶片的 Pn的变化与其 Chl、Chl－Pro、O。’、H。O。、‘O。、Gs的变化间均呈显著相关。表明水分胁迫对苹果属植物光合速率的影响除受气孔因素限制之外，与由活性氧代谢失调所诱导的非气孔因素高度相关。同时，水分胁迫下不同苹果属植物的叶肉细胞的超微结构发生了不同程度的变化，且这种叶肉细胞结构的变化过程与抗旱性相一致，进一步从细胞生物学角度证明了水分胁迫下非气孔因素所导致的光合速率的降低成为限制光合作用的主要因素。更多还原

【Abstract】 The physiological metabolism of leaf senescence in M. hupehensis and M. sieversii seedlings under water stress was studied with polyethylene glycol （PEG 6000） treatment. The results showed as follow:Under water stress, the chlorophyll in both seedlings degraded greatly with the increase of stress time, however, the contents of O₂ , H₂O₂, MDA and PMP increased significantly. The declining extents of these results in the drought tolerant variety （M. sieversii） were lower than the non-drought variety （M. hupehensis）. The results indicated that there existed high significant correlation between O₂^, H₂O₂, MDA, PMP and chlorophyll in both Mains seedlings. So it is concluded that Chi degradation in Malus seedlings induced by water stress had significant relationship with the damage of active oxygen.The results of nucleic acid metabolisms under water stress indicated that the activities of DNase and RNase, the contents of O₂ and H₂O₂ increased gradually in both seedlings with the increasing time of water stress. However, the contents of DNA and RNA declined significantly. The further study showed that the less decrease in DNA content was accompanied with high increase of DNase activity. So it is concluded that RAN was more sensitive to water stress compared with DNA. On the other hand, There existed high significant correlation between DNA, RNA and DNase, RNase, RWC, (V, H₂O₂ contents.Therefore it is the accumulation of free radical and active oxygen that promote the leaf senescence process and further influence the nucleic acid metabolisms.The changes of endopeptidases activities in M. hupehensis leaves under water stress could be divided into two phases: relatively low steady phase and rapid increase phase, which consisted with the varieties of chlorophyll contents. It is inferred that there were more than three subclasses of endopeptidases during leaf aging process, namelythiol-proteinases, serine proteinases and metallo-proteinases. Among of them, thiol-proteinases was the most active one in the process of protein degradation. However, the acid endopeptidases played a key role in leaf senescence during aging process. The optimum temperature for endopeptidases were all 45℃. The results also showed that BA and actidione inhibited endopeptidases activity. However, ABA and H₂O₂ could enhance its activity.The physiological results related to the primary conversion of light system II （including Fv/Fo, Fv/Fitu qp, qN, yield and Ca/Fo） and the peroxidation of membrane in both seedling leaves under water stress showed that the changes of chlorophyll fluorescence parameters were closely related to the difference of Malus seedlings to drought resistance. Moreover, there existed significant correlation between the changes of these chlorophyll fluorescence parameters and MDA, plasma membrane permeability in both M. hupehensis and M. sieversii seedlings. So it can be concluded that the inhibition degree of primary conversion of light energy was closely related to membrane lipid peroxidation in both seedling under water stress.Water stress caused changes in the contents of chlorophyll （Chi）, carotenoid （Car）, antioxidants ASA, Chl-Pro, photosynthetic rate （Pn）, stomatal conductance （Gs）, intercellular CO2 concentration （Ci） and the activities of SOD, POD, CAT in both Malus seedlings. Moreover, the changing extents of these parameters were consistent with the ability of drought resistance. On the other hand, there existed significant correlation between photosynthetic rate and Chi, Chl-Pro O2-, H2O2, 1O2, Gs in these seedlings. So it is indicated that the decline of photosynthetic rate in Malus seedlings under water stress had significant relationship with non-stomatal factors induced by metabolic obstacle of active oxygen beside the limitation of stamatal factors. Moreover, the ultrastructure of mesophyll cell in M. hupehensis and M. sieversii seedling leaves were examined with transmission electron microscope. The results showed that the ultrastructure of mesophyll cell revealed some changes und更多还原