Regulation of programmed cell death in maize endosperm by abscisic acid

Cereal endosperm undergoes programmed cell death (PCD) during its development, a process that is controlled, in part, by ethylene. Whether other hormones influence endosperm PCD has not been investigated. Abscisic acid (ABA) plays an essential role during late seed development that enables an embryo to survive desiccation. To examine whether ABA is also involved in regulating the onset of PCD during endosperm development, we have used genetic and biochemical means to disrupt ABA biosynthesis or perception during maize kernel development. The onset and progression of cell death, as determined by viability staining and the appearance of internucleosomal DNA fragmentation, was accelerated in developing endosperm of ABA-insensitive vp1 and ABA-deficient vp9 mutants. Ethylene was synthesized in vp1 and vp9 mutant kernels at levels that were 2–4-fold higher than in wild-type kernels. Moreover, the increase and timing of ethylene production correlated with the premature onset and accelerated progression of internucleosomal fragmentation in these mutants. Treatment of developing wild-type endosperm with fluridone, an inhibitor of ABA biosynthesis, recapitulated the increase in ethylene production and accelerated execution of the PCD program that was observed in the ABA mutant kernels. These data suggest that a balance between ABA and ethylene establishes the appropriate onset and progression of programmed cell death during maize endosperm development.     

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.     

Analysis of programmed cell death in wheat endosperm reveals differences in endosperm development between cereals

Although maize endosperm undergoes programmed cell death during its development, it is not known whether this developmental feature is common to cereals or whether it arose inadvertently from the selection process that resulted in the enlarged endosperm of modern maize. Examination of wheat endosperm during its development revealed that this tissue undergoes a programmed cell death that shares features with the maize program but differs in some aspects of its execution. Cell death initiated and progressed stochastically in wheat endosperm in contrast to maize where cell death initiates within the upper central endosperm and expands outward. After a peak of ethylene production during early development, wheat endosperm DNA underwent internucleosomal fragmentation that was detectable from mid to late development. The developmental onset and progression of DNA degradation was regulated by the level of ethylene production and perception. These observations suggest that programmed cell death of the endosperm and regulation of this program by ethylene is not unique to maize but that differences in the execution of the program appear to exist among cereals.     

Programmed cell death during embryogenesis in maize

Programmed cell death (PCD) in plants is considered an integral part of development. Evidence of DNA fragmentation, occurring at specific sites and times during embryo formation in maize (Zea mays L.), was obtained using terminal deoxyribonucleotidyl transferase-mediated dUTP-fluorescein nick end labelling (TUNEL) and by genomic DNA ladder detection. During the crucial period of elaboration of the primary shoot and root axis (14-20 d after pollination), TUNEL-positive nuclei are present in the scutellum, coleoptile, root cap and principally in the suspensor. Additional evidence of a form of programmed cell death occurring in these tissues comes from the detection of a DNA ladder. Upon completion of the differentiation process, all embryonic cells are TUNEL-negative, indicating that possible programmed cell death events during maize embryogenesis are confined to structures or organs that do not contribute to the adult plant body.     

细胞程序性死亡与生态适应

细胞程序性死亡是多细胞有机生命周期中正常的组成部分,细胞程序性死亡过程的存在对生物体是一种保护机制。它是在生物进化过程中形成的,也是生物对环境的适应方式之一。     

Apoptosis: Programmed cell death in health and disease

Apoptosis is a normal physiological cell death process of eliminating unwanted cells from living organisms during embryonic and adult development. Apoptotic cells are characterised by fragmentation of nuclear DNA and formation of apoptotic bodies. Genetic analysis revealed the involvement of many death and survival genes in apoptosis which are regulated by extracellular factors. There are multiple inducers and inhibitors of apoptosis which interact with target cell specific surface receptors and transduce the signal by second messengers to programme cell death. The regulation of apoptosis is elusive, but defective regulation leads to aetiology of various ailments. Understanding the molecular mechanism of apoptosis including death genes, death signals, surface receptors and signal pathways will provide new insights in developing strategies to regulate the cell survival/death. The current knowledge on the molecular events of apoptotic cell death and their significance in health and disease is reviewed.     

Programmed cell death in seeds of angiosperms

During the diversi fication of angiosperms, seeds have evolved structural, chemical, molecular and physiologically developing changes that specially affect the nucellus and endosperm. All through seed evolution, programmed cell death(PCD) has played a fundamental role. However,examples of PCD during seed development are limited. The present review examines PCD in integuments, nucellus,suspensor and endosperm in those representative examples of seeds studied to date.     

程序性细胞死亡与肿瘤

程序性细胞死亡（programmed cell death,PCD）是指由基因控制的细胞自主的有序性死亡方式,涉及一系列基因的激活、表达以及调控等。目前,经典细胞凋亡被称为Ⅰ型PCD,而自噬性细胞死亡称为Ⅱ型PCD,坏死样程序性细胞死亡则被称为Ⅲ型PCD,它们在肿瘤的发生、发展及治疗过程中起非常重要的作用。该文结合国内外最新研究进展主要针对不同细胞死亡模式及其相互作用、关键作用蛋白,细胞自噬与肿瘤发生,细胞自噬、凋亡与肿瘤治疗作一简要综述,并展望发展前景,提出在肿瘤治疗中如何利用不同死亡模式的协同作用最大限度地发挥其临床应用价值。     

Rice caryopsis development Ⅱ: Dynamic changes in the endosperm

The rice endosperm plays crucial roles in nourishing the embryo during embryogenesis and seed germination. Although previous studies have provided the general information about rice endosperm, a systematic investigation throughout the entire endosperm developmental process is still lacking. In this study, we examined in detail rice endosperm development on a daily basis throughout the 30‐day period of post‐fertilization development. We observed that coenocytic nuclear division occurred in the first 2 days after pollination (DAP), cellularization occurred between 3 and 5 DAP, differentiation of the aleurone and starchy endosperm occurred between 6 and 9 DAP, and accumulation of storage products occurred concurrently with the aleurone/starchy endosperm differentiation from 6 DAP onwards and was accomplished by 21 DAP. Changes in cytoplasmic membrane permeability, possibly caused by programmed cell death, were observed in the central region of the starchy endosperm at 8 DAP, and expanded to the whole starchy endosperm at 21 DAP when the aleurone is the only living component in the endosperm. Further, we observed that a distinct multi‐layered dorsal aleurone formed near the dorsal vascular bundle, while the single‐ or occasionally two‐cell layered aleurone was located in the lateral and ventral positions of endosperm. Our results provide in detail the dynamic changes in mitotic divisions, cellularization, cell differentiation, storage product accumulation, and programmed cell death that occur during rice endosperm development.     

Characterization of nuclease activities and DNA fragmentation induced upon hypersensitive response cell death and mechanical stress

Programmed cell death (PCD) is activated during the response of multicellular organisms to some invading pathogens. One of the key aspects of this process is the degradation of nuclear DNA which is thought to facilitate the recycling of DNA from dead cells. The PCD of tobacco plants (genotype NN) infected with tobacco mosaic virus (TMV) is accompanied by the induction of nuclease activities and the cleavage of nuclear DNA to fragments of about 50 kb. We examined the correlation between the increase in nuclease activities and the fragmentation of nuclear DNA during TMV- and bacteria-induced PCD in tobacco. We found that the increase in nuclease activities did not always correlate with fragmentation of nuclear DNA. Thus, in addition to pathogens that induce PCD, mechanical injury and infiltration of leaves with 1 M sucrose or bacteria that did not induce PCD also resulted in an increase in nuclease activities. Analysis of nuclease activities in total leaf extracts, nuclear extracts, and intercellular fluid (i.e., apoplast) revealed that at least four different nuclease activities are induced during PCD in tobacco; of these at least three appear to be secreted into the intercellular fluid. Although the latter were also induced in response to treatments that did not result in DNA fragmentation, they may function in the recycling of plant DNA during late stages of PCD when the integrity of the plasma membrane is compromised. This suggestion is supported by the finding that DNA degradation occurred late during TMV-induced PCD in tobacco. In addition, the finding of induced nuclease activities in the intercellular fluid raises the possibility that they may serve a protective function by degrading the DNA of invading pathogens.     

Programmed neuronal death in insect development

Programmed death in the developing nervous system of insects serves to remove obsolete neurons, generate segmental specializations and sexual dimorphism, as well as adjust neuronal number. This diversity is also reflected in the mechanisms which control the death of these neurons. In general, but not without exception, these deaths occur independent of target fate, while endocrine cues, segmental identity, and neural signalling often play critical roles. In addition, the programmed death of at least some neurons can be delayed by behavioral feedback. The study of neuronal death in Drosophila and the cloning of an ecdysteroid receptor bring the promise of understanding the genetic factors and molecular events that regulate this phenomenion. © 1992 John Wiley & Sons, Inc.     

Programmed cell death of tracheary elements as a paradigm in plants

Plant development involves various programmed cell death (PCD) processes. Among them, cell death occurring during differentiation of procambium into tracheary elements (TEs), which are a major component of vessels or tracheids, has been studied extensively. Recent studies of PCD during TE differentiation mainly using an in vitro differentiation system of Zinnia have revealed that PCD of TEs is a plant-specific one in which the vacuole plays a central role. Furthermore, there are recent findings of several factors that may initiate PCD of TEs and that act at autonomous degradation of cell contents. Herein I summarize the present knowledge about cell death program during TE differentiation as an excellent example of PCD in plants.     

Programmed cell death in cell cultures

In plants most instances of programmed cell death (PCD) occur in a number of related, or neighbouring, cells in specific tissues. However, recent research with plant cell cultures has demonstrated that PCD can be induced in single cells. The uniformity, accessibility and reduced complexity of cell cultures make them ideal research tools to investigate the regulation of PCD in plants. PCD has now been induced in cell cultures from a wide range of species including many of the so-called model species. We will discuss the establishment of cell cultures, the fractionation of single cells and isolation of protoplasts, and consider the characteristic features of PCD in cultured cells. We will review the wide range of methods to induce cell death in cell cultures ranging from abiotic stress, absence of survival signals, manipulation of signal pathway intermediates, through the induction of defence-related PCD and developmentally induced cell death.     

Programmed cell death in plants: distinguishing between different modes

Programmed cell death (PCD) in plants is a crucial componentof development and defence mechanisms. In animals, differenttypes of cell death (apoptosis, autophagy, and necrosis) havebeen distinguished morphologically and discussed in these morphologicalterms. PCD is largely used to describe the processes of apoptosisand autophagy (although some use PCD and apoptosis interchangeably)while necrosis is generally described as a chaotic and uncontrolledmode of death. In plants, the term PCD is widely used to describemost instances of death observed. At present, there is a vastarray of plant cell culture models and developmental systemsbeing studied by different research groups and it is clear fromwhat is described in this mass of literature that, as with animals,there does not appear to be just one type of PCD in plants.It is fundamentally important to be able to distinguish betweendifferent types of cell death for several reasons. For example,it is clear that, in cell culture systems, the window of timein which ‘PCD’ is studied by different groups varieshugely and this can have profound effects on the interpretationof data and complicates attempts to compare different researcher'sdata. In addition, different types of PCD will probably havedifferent regulators and modes of death. For this reason, inplant cell cultures an apoptotic-like PCD (AL-PCD) has beenidentified that is fairly rapid and results in a distinct corpsemorphology which is visible 4–6 h after release of cytochromec and other apoptogenic proteins. This type of morphology, distinctfrom autophagy and from necrosis, has also been observed inexamples of plant development. In this review, our model systemand how it is used to distinguish specifically between AL-PCDand necrosis will be discussed. The different types of PCD observedin plants will also be discussed and the importance of distinguishingbetween different forms of cell death will be highlighted. Key words: Apoptosis, apoptosis-like programmed cell death (AL-PCD), Arabidopsis, autophagy, mitochondria, necrosis, programmed cell death (PCD) Received 5 June 2007; Revised 13 September 2007 Accepted 20 September 2007     

Programmed cell death and tissue remodelling in plants

The use of programmed cell death (PCD) to remodel plants at the cellular, tissue, and organ levels is particularly fascinating and occurs in such processes as tracheary element differentiation, lysigenous aerenchyma formation, development of functionally unisexual flowers from bisexual floral primordia, and leaf morphogenesis. The formation of complex leaf shape through the use of PCD is a rare event across vascular plants and occurs only in a few species of Monstera and related genera, and in the lace plant (Aponogeton madagascariensis). During early development, the lace plant leaf forms a pattern of equidistantly positioned perforations across the surface of the leaf, giving it a lattice-like appearance. Due to the accessibility and predictability of this process, the lace plant provides highly suitable material for the study of developmentally regulated PCD in plants. A sterile lace plant culture system has been successfully established, providing material free of micro-organisms for experimental study. The potential role of ethylene and caspase-like activity in developmentally regulated PCD in the lace plant is currently under investigation, with preliminary results indicating that both may play a role in the cell death pathway.     

Programmed cell death during pigment gland formation in Gossypium hirsutum leaves

Ultrastructural studies have shown that the formation of pigment glands in Gossypium hirsutum L. leaves is a lysigenous process, originating from a cluster of cells in the ground meristem. Various techniques were used here to investigate whether programmed cell death (PCD) plays a critical role in this developmental process. Nuclei of internal cells in the pigment gland‐forming tissue were TUNEL‐positive and DAPI‐negative, suggesting that DNA cleavage is an early event and complete DNA degradation is a late event. Smeared bands and a lack of laddering after gel electrophoresis indicate that DNA cleavage is random. Ultrastructurally, secretory cells in the pigment glands become distorted, nuclei are densely stained, and chromosomes become condensed until completely degraded at late stages. Vacuoles with electron‐dense bodies and membrane‐bound autophagosomes are seen in both secretory and sheath cells, suggesting that autophagy plays a key role in PCD during cytoplasm degradation. Buckling of cell walls, seen at early stages, later leads to a complete breakdown of the walls. Together, these results suggest that PCD plays a critical role in the lysigenous development of pigment glands in G. hirsutum leaves.     

Programmed cell death in spinal cord injury pathogenesis and therapy

Spinal cord injury (SCI) always leads to functional deterioration due to a series of processes including cell death. In recent years, programmed cell death (PCD) is considered to be a critical process after SCI, and various forms of PCD were discovered in recent years, including apoptosis, necroptosis, autophagy, ferroptosis, pyroptosis and paraptosis. Unlike necrosis, PCD is known as an active cell death mediated by a cascade of gene expression events, and it is crucial for elimination unnecessary and damaged cells, as well as a defence mechanism. Therefore, it would be meaningful to characterize the roles of PCD to not only enhance our understanding of the pathophysiological processes, but also improve functional recovery after SCI. This review will summarize and explore the most recent advances on how apoptosis, necroptosis, autophagy, ferroptosis, pyroptosis and paraptosis are involved in SCI. This review can help us to understand the various functions of PCD in the pathological processes of SCI, and contribute to our novel understanding of SCI of unknown aetiology in the near future.