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。     

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.     

Positional cues specify and maintain aleurone cell fate in maize endosperm development

A genetic analysis of maize aleurone development was conducted. Cell lineage was examined by simultaneously marking cells with C1 for anthocyanin pigmentation in the aleurone and wx1 for amylose synthesis in the starchy endosperm. The aleurone and starchy endosperm share a common lineage throughout development indicating that positional cues specify aleurone fate. Mutants in dek1 block aleurone formation at an early stage and cause peripheral endosperm cells to develop as starchy endosperm. Revertant sectors of a transposon-induced dek1 allele showed that peripheral endosperm cells remain competent to differentiate as aleurone cells until late in development. Ds-induced chromosome breakage was used to generate Dek1 loss-of-function sectors. Events occurring until late development caused aleurone cells to switch fate to starchy endosperm indicating that cell fate is not fixed. Thus, positional cues are required to specify and maintain aleurone fate and Dek1 function is required to respond to these cues. An analysis of additional mutants that disrupt aleurone differentiation suggests a hierarchy of gene functions to specify aleurone cell fate and then control aleurone differentiation. These mutants disrupt aleurone differentiation in reproducible patterns suggesting a relationship to endosperm pattern formation.     

Endosperm differentiation in barley wild-type and sex mutants

The cereal endosperm is a storage organ consisting of the central starchy endosperm surrounded by the aleurone layer. In barley, endosperm development is subdivisible into four main stages, i.e. the syncytial (I), the cellularization (II), the differentiation (III) and the maturation stage (IV). During stage I, a multinucleate syncytium is formed, which in stage II develops into the undifferentiated cellular endosperm. During stage III the cells of the endosperm differentiate into two types of aleurone cells (peripheral and modified) and three different starchy endosperm cell types (irregular, prismatic and subaleurone). To elucidate the ontogenetic relationship between the endosperm tissues, the phenotypes of sex (shrunken endosperm mutants expressing xenia) mutant endosperms were studied. These mutants can be classified into two groups, i.e. those in which development is arrested at one of the four wild-type stages described above, and those with abnormal development with new organizational patterns in the endosperm or with novel cell types. Based on these studies, it is suggested that the two endosperm halves represent cell lines derived from the two daughter nuclei of the primary endosperm nucleus, and that the prismatic starchy endosperm cells arise from a peripheral endosperm meristematic activity during stage III. Finally, a model for the main molecular events underlying the morphogenetic processes is discussed.     

Endosperm Development in Barley: Microtubule Involvement in the Morphogenetic Pathway

An immunofluorescence study of sectioned barley endosperm imaged by confocal laser scanning microscopy provided three-dimensional data on the relationship of microtubules to the cytoplasm, nuclei, and cell walls during development from 4 to 21 days after pollination (DAP). Microtubules play an important role throughout endosperm ontogeny. The syncytium is organized into units of nuclear-cytoplasmic domains by nuclear-based radial microtubule systems that appear to control the pattern of the first anticlinal walls at 5 to 6 DAP. After 7 DAP, phragmoplasts of two origins (interzonal and cytoplasmic) guide wall formation. Large compartments formed by the "free growing" walls in association with cytoplasmic phragmoplasts formed adventitiously at interfaces of opposing microtubule systems are subsequently subdivided by interzonal phragmoplast/cell plates to give rise to the starchy endosperm. During development of the aleurone layer from 8 to 21 DAP, the microtubule cycle is typical of plant histogenesis; cortical microtubules are hooplike, and preprophase bands of microtubules predict the division plane.     

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 (OryzasativaL .)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。DNALadder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 14 0～ 180bp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。