水稻淀粉胚乳细胞编程性死亡中细胞核变化特征

应用透射电子显微镜技术,观察了水稻(Oryza sativa L.)淀粉胚乳细胞编程性死亡过程中核的变化特征.伴随胚乳的发育进程,淀粉胚乳细胞核表现出衰退特征:核变形、染色质凝缩、核膜多处被降解破坏、核基质外泄等.DNA Ladder显示核内大片段DNA呈严重的弥散状拖尾现象,而核内和胞质中在140～180 bp处有明显的条带.在核衰退的同时,其胞质中的粗面内质网、淀粉质体和线粒体等细胞器具有正常的代谢功能,细胞仍在合成并积累营养物质,淀粉胚乳细胞一边衰退一边行使其功能,直至死亡.这些结果表明,水稻淀粉胚乳在核衰退的同时,细胞仍在积极合成与积累贮藏产物,表现为一种特殊形式的植物细胞编程性死亡现象.此外,对淀粉胚乳细胞特有的核质关系、植物细胞编程性死亡过程中细胞核的变化等问题进行了讨论.     

小麦淀粉胚乳发育期间的程序性细胞死亡

小麦淀粉胚乳在发育过程中经历程序性细胞死亡(PCD).小麦淀粉胚乳的DNA在发育的特定阶段呈现梯状电泳条带,用乙烯处理使DNA片段化发生的时间提前,而且ABA处理虽然不能推迟DNA片段化的发生时间,但能减弱DNA片段化的程度.小麦淀粉胚乳细胞在PCD过程中出现某些动植物细胞凋亡的共同的结构变化特征,但也有一些独特的结构变化.如染色质凝聚后仅少数染色质块发生趋边化;细胞核在PCD过程中最先开始衰退,细胞核解体时胞质中有丰富的细胞器,细胞核解体后细胞并未死亡,在胞质中仍在合成和积累淀粉和储藏蛋白,直到细胞被淀粉充满,细胞才死亡;不形成凋亡小体,死亡的淀粉胚乳细胞成为营养物质的储藏库.因此小麦淀粉胚乳细胞的PCD是一种特殊形式的PCD.     

水稻淀粉胚乳程序性细胞死亡中的去核化

对水稻品种中籼8836淀粉胚乳细胞的去核化发育阶段的细胞超微结构变化和同期籽粒灌浆速率及相关酶活性的动态进行了观察和分析。开花受精后约在第3天胚乳完成细胞化,花后第5天少数淀粉胚乳细胞启动去核发育过程。核消亡是淀粉胚乳细胞程序性细胞死亡(PCD)的第一步。同一籽粒淀粉胚乳细胞的去核进程是不同步的。花后第13天所有淀粉胚乳细胞都已完成去核过程。在去核过程中,胚乳核的形态变化特征既有动植物PCD的共性又有其特殊性。伴随核降解过程,一部分线粒体解体,表明去核化与线粒体解体有一定联系。在去核化发育阶段,与PCD有关的酶类,如超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性非常高;与淀粉合成有关的酶类,如ADPG焦磷酸化酶、可溶性淀粉合成酶(SSS酶)、淀粉分支酶(或Q酶)也表现出很高的活性。去核化发育阶段籽粒灌浆速率最高,籽粒增重亦最快。淀粉胚乳细胞去核之后,细胞并未立即死亡,这些无核的细胞仍维持正常有序的代谢活动,继续进行淀粉和贮藏蛋白的合成与积累,但上述酶类的活性明显降低,灌浆速率也明显趋缓。淀粉胚乳细胞最终被贮藏物质充满时成为死细胞,完成其程序性死亡过程。Evan‘s blue染色鉴定表明淀粉胚乳细胞死亡不同步,细胞死亡在淀粉胚乳组织中是随机发生的。     

水稻淀粉胚乳程序性细胞死亡中的去核化

对水稻品种中籼8836淀粉胚乳细胞的去核化发育阶段的细胞超微结构变化和同期籽粒灌浆速率及相关酶活性的动态进行了观察和分析。开花受精后约在第3天胚乳完成细胞化,花后第5天少数淀粉胚乳细胞启动去核发育过程。核消亡是淀粉胚乳细胞程序性细胞死亡(PCD)的第一步。同一籽粒淀粉胚乳细胞的去核进程是不同步的。花后第13天所有淀粉胚乳细胞都已完成去核过程。在去核过程中,胚乳核的形态变化特征既有动植物PCD的共性又有其特殊性。伴随核降解过程,一部分线粒体解体,表明去核化与线粒体解体有一定联系。在去核化发育阶段,与PCD有关的酶类,如超氧化物歧化酶(SOD)过氧化氢酶(CAT)活性非常高;与淀粉合成有关的酶类,如ADPG焦磷酸化酶、可溶性淀粉合成酶(SSS酶)、淀粉分支酶(或Q酶)也表现出很高的活性。去核化发育阶段籽粒灌浆速率最高,籽粒增重亦最快。淀粉胚乳细胞去核之后,细胞并未立即死亡,这些无核的细胞仍维持正常有序的代谢活动,继续进行淀粉和贮藏蛋白的合成与积累,但上述酶类的活性明显降低,灌浆速率也明显趋缓。淀粉胚乳细胞最终被贮藏物质充满时成为死细胞,完成其程序性死亡过程。Evan’s blue染色鉴定表明淀粉胚乳细胞死亡不同步,细胞死亡在淀粉胚乳组织中是随机发生的。     

洋葱花粉母细胞细胞内、细胞间微染骨架的超微结构观察

以洋葱（Allium cepa L.）花粉母细胞为材料,采用DGD包埋去包埋原位技术,对花粉母细胞不同发育时期的细胞内、细胞间微染骨架的超微结构进行了电镜观察。结果发现,花粉母细胞核内存在的粗细不等的微染骨架,与核仁和染色体紧密相连,随着发育的推移,其均一性发生改变。在核周有核纤层样的结构存在,与细胞核和胞质中的微染骨架紧密相连,到前期结束时解体。洋葱花粉母细胞内具有发达的胞质微染骨架,这种结构在减数分裂前期Ⅰ变化不明显。在胞间连接（胞间连丝和胞质通道）内,也有精细的微染骨架分布,并且与两端细胞中的骨架相连。在凝线期的花粉母细胞中观察到细胞融合现象,有胞质或核内微梁骨架与穿壁转移的胞质小球和核小球内骨架相连。此时细胞核偏向一边,但细胞的基余部位仍充满了胞质微染骨架,初步探讨了核微染骨架与核仁和染色体之间的关系,核纤层与细胞核之间的关系。以及细胞内、细胞间微染骨架与细胞融合之间的关系。     

洋葱花粉母细胞细胞内、细胞间微梁骨架的超微结构观察(英文)

以洋葱(AlliumcepaL.)花粉母细胞为材料,采用DGD包埋去包埋原位技术,对花粉母细胞不同发育时期的细胞内、细胞间微梁骨架的超微结构进行了电镜观察。结果发现,花粉母细胞核内存在粗细不等的微梁骨架,与核仁和染色体紧密相连,随着发育的推移,其均一性发生改变。在核周有核纤层样的结构存在,与细胞核和胞质中的微梁骨架紧密相连,到前期结束时解体。洋葱花粉母细胞内具有发达的胞质微梁骨架,这种结构在减数分裂前期Ⅰ变化不明显。在胞间连接(胞间连丝和胞质通道)内,也有精细的微梁骨架分布,并且与两端细胞中的骨架相连。在凝线期的花粉母细胞中观察到细胞融合现象,有胞质或核内微梁骨架与穿壁转移的胞质小球和核小球内骨架相连。此时细胞核偏向一边,但细胞的其余部位仍充满了胞质微梁骨架。初步探讨了核微梁骨架与核仁和染色体之间的关系,核纤层与细胞核之间的关系,以及细胞内、细胞间微梁骨架与细胞融合之间的关系     

荞麦胚和胚乳的发育及贮藏营养物质的积累

荞麦原胚期,胚乳为游离核期。球形胚晚期,胚乳开始细胞化。心形胚期,胚囊中部形成一层“开放细胞”。鱼雷形胚期,胚囊中部有５－７层胚乳细胞。子叶弯曲胚期,胚乳全部形成胚乳细胞,具传递细胞特征的合点胚乳吸器形成。胚乳细胞的初始垂周壁来自于自由生长壁和胞质分裂形成的细胞板;初始平周壁由自由生长垂周壁分友相接形成,及有丝分裂的细胞板形成。开花后９ｄ,胚乳细胞积累淀粉,比胚细胞积累早６ｄ。开花后１５ｄ,胚乳最     

水稻(Oryza sativa L.)×狼尾草(Pennisetum sp.)胚胎发育的细胞学观察

1.狼尾草花粉可以在水稻柱头上萌发并能长入胚囊,但受精过程缓慢而且不正常,单受精现象经常出现。2.胚胎发育滞缓,长时间停留在球状胚阶段,很难进一步分化,而且不时败育,只在传粉后16—24天的一些胚囊中看到有简单分化的胚胎。3.胚乳发育异常,由游离核形成细胞的时间推迟到传粉后第八天。整个胚乳组织由形状及功能上均有很大差异的细胞团块组成。其中一部分细胞缺乏合成淀粉的能力,胚乳在发育过程中不时出现解体现象。4.在反足细胞附近的一些珠心细胞中出现多量淀粉积累,反映因杂交而出现的胚囊代谢上的某些变化。讨论了胚和胚乳发育困难的原因和得到杂种种子的可能性。     

水稻胚乳发育中淀粉体和蛋白体ATPase活性的动态变化

利用ATPase定位技术,对水稻品种(Oryza sativa L.cv．Minghui 63)胚乳细胞发育中后期淀粉体和蛋白体的ATPase活性进行了超微细胞化学定位。结果表明,在淀粉体内外膜上、淀粉粒间的通道上和淀粉体四周的无定形物上呈现显著的ATPase活性。蛋白体Ⅰ和蛋白体Ⅱ的膜上和四周的囊泡、小泡上均出现ATPase活性产物。另外,胚乳细胞的胞壁和质膜,糊粉层和亚糊粉层细胞的胞壁、质膜、细胞核和胞间连丝上也有定位的ATPase活性产物分布。根据ATPase活性产物分布特点,推测淀粉体内的网状通道是便于养分进入淀粉体内部的转运通道。淀粉体膜和蛋白体膜上的ATPase主要是为养分进入内部提供跨膜动力。     

被子植物胚乳细胞化的形态学研究

被子植物进行双受精 ,2个极核或次生核与 1个精子结合后形成 1个三倍体的初生胚乳核 ,初生胚核经多次分裂形成多个胚乳游离核。有些植物的初生胚乳核和胚乳游离核分裂后紧跟着壁的形成 ,称为细胞型胚乳 ,如番茄等 ;有些植物初生胚乳核和胚乳游离核分裂时不伴随着壁的形成 ,而是形成多核体 ,到胚乳发育后期由胚囊的边缘向中央逐步细胞化 ,这种胚乳发育类型称为核型胚乳 ,如玉米、小麦、水稻等 ;还有一些中间类型的植物 ,称为双型胚乳 ,这种类型的植物仅见于某些单子叶植物。无论是核型胚乳植物还是双型胚乳植物的胚乳发育都涉及到从胚乳游离…     

The scutellum of germinated wheat grains undergoes programmed cell death: identification of an acidic nuclease involved in nucleus dismantling

Programmed cell death (PCD) is a crucial phenomenon in the life cycle of cereal grains. In germinating grains, the scutellum allows the transport of nutrients from the starchy endosperm to the growing embryo, and therefore it may be the last grain tissue to undergo PCD. Thus, the aim of this work was to analyse whether the scutellum of wheat grains undergoes PCD and to perform a morphological and biochemical analysis of this process. Scutellum cells of grains following germination showed a progressive increase of DNA fragmentation, and the TUNEL assay showed that PCD extended in an apical-to-basal gradient along the scutellum affecting epidermal and parenchymal cells. Electron-transmission microscopy revealed high cytoplasm vacuolation, altered mitochondria, and the presence of double-membrane structures, which might constitute symptoms of vacuolar cell death, whereas the nucleus appeared lobed and had an increased heterochromatin content as the most distinctive features. An acid- and Zn(2+)-dependent nucleolytic activity was identified in nuclear extracts of scutellum cells undergoing PCD. This nuclease was not detected in grains imbibed in the presence of abscisic acid, which inhibited germination. This nucleolytic activity promoted DNA fragmentation in vitro on nuclei isolated from healthy cells, thus suggesting a main role in nucleus dismantling during PCD.     

Spatial and temporal progress of programmed cell death in the developing starchy endosperm of rice

Programmed cell death (PCD) is the genetically regulated disassembly of cells, and occurs in the endosperm of cereals during seed maturation. Since PCD determines the lifetime of cells, it can affect endosperm growth and, therefore, cereal yield. However, the features and mechanisms of PCD in the developing starchy endosperm in the Poaceae remain unclear. In the present study, we investigated the characteristics of PCD in developing starchy endosperm of rice (Oryza sativa L.) by fluorescence microscopy, focusing on the spatial and temporal progress of PCD-associated responses. Cell death commenced in the central region of starchy endosperm, and then spread to the peripheral region. PCD-associated responses, such as mitochondrial membrane permeabilization and activation of the protease that cleaves the amino acid sequence VEID, showed similar spatial patterns to that of cell death, but preceded cell death. Degradation of nuclear DNA could not be detected in developing starchy endosperm by the TUNEL assay. These results indicated that PCD in developing starchy endosperm of rice proceeds via a highly organized pattern. In addition, these results suggested that PCD in developing starchy endosperm of rice is characterized by the involvement of mitochondrial signaling and the activity of a caspase-like protease that cleaves the VEID sequence.     

Endosperm degradation during seed development of Echinocystis lobata (Cucurbitaceae) as a manifestation of programmed cell death (PCD) in plants

Programmed cell death (PCD) is an active, genetically controlled process that ultimately leads to elimination of unnecessary or damaged cells from multicellular organism. It occurs during normal growth and development or in response to a variety of environmental triggers and is indispensable for survival of the organism. In Echinocystis lobata the endosperm, an ephemeral tissue in angiosperm plants, undergoes distinct cytological, physiological and molecular changes during seed development and maturation. As a result, mature seeds are deprived of this tissue. The endosperm was analyzed at the consecutive stages of seed development. The morphological changes of cells were studied at light and electron microscope levels. In this paper we report that endosperm cells undergo morphological and biochemical changes characteristic of apoptosis, a particular type of PCD, i.e. cell shrinkage, chromatin condensation, nuclear fragmentation, and cytoplasm degradation, while the ultrastructure of mitochondria seems to be less changed. Furthermore, the progression of DNA degradation has been shown by agarose gel electrophoresis (ladder pattern of DNA fragmentseparation), TUNEL and comet assay. It isconcluded that during seed maturation, endosperm degradation process is accompanied by typical PCD-related changes of cell morphology and internucleosomal DNA cleavage.     

The release of cytochrome c and the regulation of the programmed cell death progress in the endosperm of winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) under waterlogging

It has been shown in mammalian systems that the mitochondria can play a key role in the regulation of apoptosis by releasing intermembrane proteins (such as cytochrome c) into the cytosol. Cytochrome c released from the mitochondria to the cytoplasm activates proteolytic enzyme cascades, leading to specific nuclear DNA degradation and cell death. This pathway is considered to be one of the important regulatory mechanisms of apoptosis. Previous studies have shown that endosperm cell development in wheat undergoes specialized programmed cell death (PCD) and that waterlogging stress accelerates the PCD process; however, little is known regarding the associated molecular mechanism. In this study, changes in mitochondrial structure, the release of cytochrome c, and gene expression were studied in the endosperm cells of the wheat (Triticum aestivum L.) cultivar “huamai 8” during PCD under different waterlogging durations. The results showed that waterlogging aggravated the degradation of mitochondrial structure, increased the mitochondrial permeability transition (MPT), and decreased mitochondrial transmembrane potential (ΔΨm), resulting in the advancement of the endosperm PCD process. In situ localization and western blotting of cytochrome c indicated that with the development of the endosperm cell, cytochrome c was gradually released from the mitochondria to the cytoplasm, and waterlogging stress led to an advancement and increase in the release of cytochrome c. In addition, waterlogging stress resulted in the increased expression of the voltage-dependent anion channel (VDAC) and adenine nucleotide translocator (ANT), suggesting that the mitochondrial permeability transition pore (MPTP) may be involved in endosperm PCD under waterlogging stress. The MPTP inhibitor cyclosporine A effectively suppressed cell death and cytochrome c release during wheat endosperm PCD. Our results indicate that the mitochondria play important roles in the PCD of endosperm cells and that the increase in mitochondrial damage and corresponding release of cytochrome c may be one of the major causes of endosperm PCD advancement under waterlogging.     

Programmed cell death in cereal aleurone

Progress in understanding programmed cell death (PCD) in the cereal aleurone is described. Cereal aleurone cells are specialized endosperm cells that function to synthesize and secrete hydrolytic enzymes that break down reserves in the starchy endosperm. Unlike the cells of the starchy endosperm, aleurone cells are viable in mature grain but undergo PCD when germination is triggered or when isolated aleurone layers or protoplasts are incubated in gibberellic acid (GA). Abscisic acid (ABA) slows down the process of aleurone cell death and isolated aleurone protoplasts can be kept alive in media containing ABA for up to 6 months. Cell death in barley aleurone occurs only after cells become highly vacuolated and is manifested in an abrupt loss of plasma membrane integrity. Aleurone cell death does not follow the apoptotic pathway found in many animal cells. The hallmarks of apoptosis, including internucleosomal DNA cleavage, plasma membrane and nuclear blebbing and formation of apoptotic bodies, are not observed in dying aleurone cells. PCD in barley aleurone cells is accompanied by the accumulation of a spectrum of nuclease and protease activities and the loss of organelles as a result of cellular autolysis.     

The nucellus degenerates by a process of programmed cell death during the early stages of wheat grain development

The nucellus, which is the maternal tissue of the wheat grain, degenerates during the early stages of development. We have investigated whether or not this degenerative process may be considered as programmed cell death (PCD). The analysis of DNA of tissues dissected from developing wheat (Triticum aestivum L. cv Chinese Spring) grains at 5-20 days post anthesis (dpa) showed the presence of DNA laddering, which is indicative of internucleosomal fragmentation of nuclear DNA, in maternal tissues but not in the endosperm. The TUNEL assay showed in-situ internucleosomal fragmentation of DNA in nuclei of parenchymal and epidermal cells of the nucellus, as well as in the pericarp, during the early stages of grain development (5 dpa). Furthermore, internucleosomal fragmentation of nuclear DNA was observed in nucellar projection cells in the middle stages of grain development (13-18 dpa), thus showing a process of PCD in these maternal tissues. Electron-transmission microscopy analysis allowed the morphology of PCD to be characterized in this plant tissue. Initially, fragmentation of the cytoplasm was observed, the nuclear envelope appeared dilated and to be forming vacuoles, and the content of heterochromatin increased. A progressive degradation of the cytosolic contents and organelles was observed, and the plasma membrane was disrupted. However, the Golgi apparatus remained intact and apparently functional even in the final stages of cell death.     

杜仲胚乳衰退过程中程序性细胞死亡的研究

杜仲胚乳在衰退过程中显示出了程序性细胞死亡的特征：细胞质出现原位自溶,细胞器呈现不同程度的解体;环状片层吞噬并分隔细胞组分;细胞核形态异常,并出现环状核仁和致密型核仁;DNA解体,电泳显示出拖尾状的条带。胚根端和非胚根端胚乳细胞在进入程序性死亡的时间上有先后。