JXB Advance Access originally published online on October 8, 2004
Journal of Experimental Botany 2004 55(408):2617-2623; doi:10.1093/jxb/erh275
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
RESEARCH PAPER |
Bcl-2 family members localize to tobacco chloroplasts and inhibit programmed cell death induced by chloroplast-targeted herbicides
Department of Plant Pathology, 406 Plant Sciences Hall, University of Nebraska, Lincoln, NE 68583-0722, USA
* To whom correspondence should be addressed. Fax: +1 402 472 2853. E-mail: mdickman{at}unlnotes.unl.edu
Received 7 April 2004; Accepted 11 August 2004
 |
Abstract |
|---|
 Top Abstract IntroductionMaterials and methodsResultsDiscussionReferences |
|---|
In mammalian cells, apoptosis is often mediated via organelles. While apoptotic-like cell death occurs in plants, the mechanistic details are unresolved. Transgenic tobacco plants have been generated that harbour selected animal anti-apoptotic genes. Subcellular fractionation followed by western blot analysis indicated that chloroplasts serve as a location for these animal anti-apoptotic proteins in addition to the established mitochondrial location. To explore the functional significance of this observation, tobacco plants were treated with three chloroplast-directed herbicides. Wild-type plants died and exhibited features associated with apoptosis. Transgenic plants survived and did not show any apoptotic-like characteristics. Moreover, the herbicide-induced apoptotic-like cell death was light requiring. It was concluded that chloroplasts may be involved in mediating certain types of plant programmed cell death.
Key words: Apoptosis, Bcl-2, chloroplast, herbicide
|
Introduction |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
In mammalian cells, programmed cell death (PCD) generally proceeds by one of two signalling pathways; intrinsic or extrinsic. In the latter, induction of apoptosis is mediated by extracellular receptors; binding of death ligands to these specialized death receptors (e.g. FAS, TNF) causes receptor oligimerization, recruitment of adaptor molecules, and activation of initiator caspases. Once activated, these upstream caspases activate downstream effector caspases which are involved in the execution of the cell (Earnshaw et al., 1999
). The intrinsic pathway is organellar; generally mediated by the mitochondrion, whereby following apoptotic stimulation, cytochrome c (and other apoptotic factors) are released. Cytochrome c and ATP or dATP form an oligomeric complex with the cytosolic adaptor protein, Apaf-1. Together, these proteins form a large multimeric complex termed the apoptosome which recruits and activates caspase 9, which is then released and processes the downstream executioner caspases 3, 6, and/or 7 (Ferri and Kroemer, 2001). PCD is characterized by a number of hallmark features including cell shrinkage, plasma membrane blebbing, nuclear condensation, internucleosomal DNA cleavage, and externalization of plasma membrane phosphatidylserine, which lead to fragmentation and coalescing of DNA into apoptotic bodies that migrate to the periphery of the cell for eventual phagocytosis by neighbouring macrophages. Thus, during the PCD process, unwanted cells are cleanly removed without inflammation. It is now well established that inappropriate cell death (too much, too little) significantly contributes to a number of important mammalian diseases (e.g. cancer, AIDS, stroke) (Cory and Adams, 2002).
In plants, PCD plays a normal physiological role in a variety of developmental processes including xylem formation, senescence, sloughing of root cap cells, and embryogenesis, among others (reviewed in Dickman and Reed, 2003). Plant cell death in response to pathogen challenge and in response to abiotic stresses has also been documented and, at least in some cases, is clearly genetically programmed (Li and Dickman, 2004; Navarre and Wolpert, 1999; Dickman et al., 2001). A question that has arisen is whether plant PCD and mammalian PCD share similar mechanistic features. A primary argument against this idea stems from the fact that homologues of the core machinery of apoptotic regulators (Bcl-2 family, caspases) have not been identified in plants, at either the sequence or functional levels. Although the biochemical mechanisms responsible for cell suicide in plants are largely unknown, an increasing number of reports suggest similarities to the programmed cell death that occurs in animal species. For example, PCD in plants typically requires new gene expression, and thus can be suppressed by cycloheximide and similar inhibitors of protein or RNA synthesis (Havel and Durzan, 1996). The morphological characteristics of plant cells undergoing PCD also bear some striking similarities to apoptosis in animals, although the presence of a cell wall around plant cells imposes certain differences. Akin to animal cells, PCD in plants is associated with internucleosomal DNA fragmentation (DNA ladders) and the activation of proteases (Ryerson and Heath, 1996; Stein and Hansen, 1999; Solomon et al., 1999). For instance, genes encoding cysteine proteases are induced during tracheary element development in Zinnia and during senescence in Arabidopsis and tomato plants (Groover and Jones, 1999; Nam, 1997; Fukuda, 1996). It should be noted, however, that PCD processes in plants do not always exhibit these hallmark characteristics (Heath, 1998).
In addition to its role in developmental processes in plants, cell suicide plays an important role in the interactions of plants with pathogens, including bacteria, fungi, and viruses. One of the best studied of plant responses to pathogens is the hypersensitive response (HR). Upon exposure to certain pathogens, plant cells in the immediately affected area undergo a rapid cell suicide response that results in cell death at and near the site of infection, thereby limiting spread of pathogens (Dangl and Jones, 2001). The HR is associated with the expression of a variety of plant defence genes and the induction of programmed cell death. The HR is usually preceded by rapid and transient responses including ion fluxes, alterations in protein phosphorylation patterns, pH changes, changes in membrane potential, release of reactive oxygen species (ROS; oxidative burst), and oxidative cross-linking of plant cell wall proteins (Richberg et al., 1998; Bolwell and Wojtaszek, 1997). HR appears to be coupled to cysteine protease expression akin to animal PCD although it is unclear whether the analogy extends to caspase-like proteases. Parallels with the animal cell death machinery have been suggested by reports that (a) the HR induced by tobacco mosaic virus (TMV) in tobacco plants is associated with the generation of caspase-like protease activity; and (b) caspase-inhibitory peptides can block bacteria-induced PCD in Arabidopsis without significantly affecting the induction of HR-associated defence genes (del Pozo and Lam, 1998).
Previously, it has been shown that transgenic expression of anti-apoptotic Bcl-2 family members (Bcl-2, Bcl-xL, CED-9, Op-IAP) in tobacco plants conferred heritable disease resistance to several necrotrophic fungi, including Sclerotinia sclerotiorum and Botrytis cinerea (Dickman et al., 2001). Hallmark features of apoptosis have also been observed in plants that are sensitive to toxin-producing necrotrophic fungi, including Fusarium moniliforme (fumonisin), Alternaria alternata (AAL toxin), and Cochliobolus victoriae (victorin) (Navarre and Wolpert, 1999; Wang et al., 1996). When S. sclerotiorum was inoculated to wild-type tobacco, DNA fragmentation was observed in the form of a characteristic ‘ladder’ and by terminal deoxynucleotide transferase-mediated dUTP end labelling (TUNEL) of DNA 3'-OH groups, both common features of apoptotic responses. Importantly, when transgenic plants were inoculated with S. sclerotiorum, not only were the plants resistant, but there was no laddering nor were there any TUNEL positive cells. Wild-type and transgenic plant responses to selected abiotic stresses, including heat, cold, salt, drought, and oxidative stress, have recently been evaluated (Awada et al., 2003; Li and Dickman, 2004). Transgenic plants were protected from lethal levels of these stresses and sensitive wild-type tobacco during the death process exhibited features associated with mammalian apoptosis during the death process. Thus, at least in some cases, abiotic stress-induced cell death in plants can be accompanied by apoptotic-like features that are inhibited by expression of Bcl-2. These observations add to the growing body of evidence indicating transkingdom conservation of programmed cell death mechanisms.
In the following, the subcellular localization of the animal anti-apoptotic proteins in tobacco is described. It is shown that Bcl-2, Bcl-xL, and CED-9, not only localize to the mitochondrial and nuclear fractions as in mammals, but also to chloroplast membranes. The localization to chloroplasts may have functional significance. Selected chloroplast-directed herbicides killed tobacco cells in an apoptotic-like, light-requiring manner, but transgenic tobacco expressing anti-apoptotic genes survived and did not exhibit apoptotic characteristics. Taken together, these data suggest that under conditions of oxidative stress, chloroplasts can mediate plant apoptosis.
|
Materials and methods |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Plasmid construction and plant transformation
Separate binary plasmid vectors containing human Bcl-2; Bcl-2
BH4; chicken Bcl-xL, and Caenorhrabditis elegans CED-9 were constructed and introduced into wild-type tobacco (Nicotiana tabacum cv. Glurk NN) as described previously (Dickman et al., 2001).
Reagents
Bcl-2 and Bcl-xL antibodies were obtained from Santa Cruz Biotechnology (Santa Cruz, CA, USA), CED-9 antibody was kindly provided by Dr Robert Horvitz (MIT, Cambridge, MA, USA), the tobacco Rubisco large (RBSL) subunit antibody was obtained from Agrisera (Vännäs, Sweden), PEP carboxlase (PEPC) antibody was a gift from Dr Ray Chollet (University of Nebraska, USA), and plant porin antiobody was obtained from Dr Tom Elthon (University of Nebraska, USA). Methyl viologen (paraquat) was obtained from Sigma (St Louis, MO, USA), acifluorfen from Riedel-de Haën (Sedze, Germany), and sufentrazone from Du Pont (Wilmington, DE, USA).
Chloroplast and mitochondria isolation
All isolation and fractionation procedures were performed at 4 °C. Intact chloroplasts were isolated by Percoll gradient centrifugation (Palatnik et al., 1997). Intact mitochondria were isolated by a modified protocol (Curtis and Wolpert, 2002) using the same buffers and leaf material as for the chloroplast isolation. Briefly, the supernatant from the first differential centrifugation was further centrifuged at 10 500 rpm for 20 min. The pellet (crude mitochondrial fraction) was resuspended in 8 ml of the grinding buffer, layered onto a three-step Percoll gradient (21:26:47% Percoll) and centrifuged at 18 000 rpm for 45 min. The mitochondria banded between the 26% and 47% Percoll interface and were removed and diluted with an equal volume of grinding buffer. 16 ml of the mitochondrial fractions were layered onto a second discontinuous Percoll gradient (26:47% Percoll) and centrifuged at 18 000 rpm for 30 min. The presumably purified mitochondria located at the 26–47% Percoll interface were removed, washed twice with grinding buffer, and resuspended in 5 mM Tricine-KOH and 5 mM MgCl2, pH 7.9.
Subcellular localization of animal anti-apoptotic proteins
Preweighed leaf discs were ground in 0.5 M sucrose, 0.1% ascorbic acid, 0.1% cysteine-HCl, and 0.1 M TRIS-HCl, pH 7.5. Cleared supernatant was obtained by centrifuging for 15 min at 15 000 g. The cell-free protein extracts were used as a positive control. Chloroplast and mitochondrial proteins were subject to 12% SDS-PAGE and electroblotted to nitrocellulose. Bound proteins were probed with primary antibodies made against Bcl-2, Bcl-xL, CED-9, RBSL, porin, or PEPC followed by treatment with peroxidase-linked donkey anti-rabbit IgG or sheep anti-mouse IgG. Blots were developed by chemiluminescence according to the manufacturer's instructions (Amersham, Piscataway, NJ, USA).
Herbicide treatments
Measurements of the effects of herbicides on wild-type and transgenic tobacco plants essentially followed the methods of Aono et al. (1995). In brief, 7 mm circular leaf discs, from wild-type and transgenic leaves of equivalent developmental age, were immersed with their abaxial sides up in 10 ml of a 0.1% Tween 20 solution containing the selected herbicide at various (10–20 µM) concentrations. Leaf discs were then subjected to vacuum infiltration for 1 min, preincubated in the dark for 1 h, and incubated at 25 °C under continuous light conditions (300 µmol m–2 s–1) for 48 h. Following treatment, discs were visually inspected and chlorophyll concentrations were determined (Arnon, 1949).
Analysis of apoptotic markers
To determine whether DNA laddering occurred, genomic DNA was extracted from treated plant samples and run on 2% agarose gel as described by White and Kaper (1989). DNA fragmentation in situ was detected by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labelling (TUNEL) with fluorescein isothiocyanate (FITC)-conjugated dUTP (in situ cell death detection kit, Roche Biochemicals). Following TUNEL, sections were counterstained with propidium iodide and examined using a Bio-Rad MRC1024ES confocal microscope (Hercules, CA, USA). Confocal images of the FITC- or PI-labelled signals were collected simultaneously using a dual-line excitation/emission mode (488/520 nm for FITC and 560/598 nm for PI) using the Bio-Rad LaserSharp imaging program.
|
Results |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Subcellular fractionation of transgenic tobacco lines harbouring animal anti-apoptotic genes followed by western blotting was performed to determine the cellular location of selected Bcl-2 family anti-apoptotic proteins. The purity of each preparation was confirmed by immunobloting with the following specific markers: PEP carboxlase for cytoplasm; maize porin for mitochondria, and the tobacco RBSL for the chloroplast (Fig. 1A). These studies indicated that all three selected transgenes (Bcl-2, Bcl-xL, CED-9) localize not only to both mitochondrial and cytosolic fractions, as might be expected, but also to the chloroplast (Fig. 1B).
|
These anti-apoptotic proteins all contain transmembrane binding domains, thus, the organellar associations are not entirely surprising. Mitochondrial localization of Bax, a Bcl-2 family member, has been shown to occur in tobacco (Lacomme and Santa Cruz, 1999
); thus there was particular interest in determining whether chloroplast localization was of functional significance. To address this question, herbicides were used whose mode of action is coupled to impairment of chloroplast function. Biperidyl herbicides such as methyl viologen (MV) or paraquat, are redox-active contact compounds that become reduced within the cell and subsequently catalyse the photoreduction of O2 forming 
and H2O2 (Asada and Takahashi, 1987; Halliwell and Gutteridge, 1989). Herbicide activity is light-dependent, and the ROS that is generated is lethal to the plant cell. The diphenyl-ether herbicide acifluorfen is an inhibitor of protoporphyrinogen oxidase (PPO). PPO is a chloroplast enzyme that oxidizes protoporphyrinogen to produce protoporphyrix IX. This product is a precursor for both chlorophyll (photosynthesis) and haem (electron transfer). When PPO is inhibited, substrate accumulation occurs and, in the presence of light, protoporphyrin excites to the triplet state and interacts with molecular O2 to produce singlet oxygen which is toxic (Lermontova and Grimm, 2000). Sulfentrazone, a member of the aryetriczolinone family, also inhibits PPO.
Herbicide treatment of wild-type tobacco at concentrations used under field conditions was lethal to whole plants, detached leaves, and leaf discs (Fig. 2A). However, when transgenic tobacco plants harbouring Bcl-2, Bcl-xL, or CED-9 were treated in an identical manner, the plants survived and appeared similar to control plants, treated with buffer alone. Chlorophyll levels of the treated plants were consistent with these observations (Fig. 2B). To confirm that specific transgene expression was responsible for these phenotypes, a tobacco line harbouring Bcl-2BH4 was generated. This mutant has a deletion of the BH4 domain rendering it null for anti-apoptotic activity in mammalian cells (Hanada et al., 1995). As shown in Fig. 2A, tobacco leaf discs carrying Bcl-2BH4, lost cytoprotection following herbicide treatment. Thus, transgenic expression of anti-apoptotic genes inhibits herbicide-induced plant cell death. To confirm that these results are chloroplast-dependent, the same experiments were conducted in the dark by covering the plants with aluminium foil. Herbicide treatments had no effect on dark-grown plants, indicating that herbicide-induced cell death is light-dependent (data not shown).
|
Since anti-apoptotic gene expression prevented herbicide-induced cell death, the mechanism of this protection was explored next by evaluating whether a programmed type of apoptotic cell death was occurring. DNA was extracted from herbicide-treated leaf tissue. Figure 3A shows the presence of DNA laddering in MV, AC, and ST-treated wild-type leaves; however, DNA appears to be intact and not fragmented in treated transgenic leaves. As a control, tobacco expressing Bcl-2
BH4 was also herbicide treated and, as shown in Fig. 3A, DNA laddering occurred. There was no evidence for DNA fragmentation in chloroplasts, based on evaluating isolated chloroplast DNA as well as using chloroplast DNA as a probe in DNA blots from DNA laddering gels (data not shown). Moreover using fluorescence microscopy, it is evident that TUNEL positive nuclei are present in the herbicide-treated wild-type leaves (Fig. 3B). It therefore appears that these herbicides kill plants via the generation of toxic levels of ROS, in an apoptotic-like manner. Such programmed cell death is inhibited by the expression of animal anti-apoptotic genes. Moreover, when the chloroplast-directed herbicide glyphosate was administered to tobacco, cell death occurred, but there was no generation of ROS, DNA fragmentation did not occur, nor was protection afforded by the transgenes (data not shown). Thus, based on the available evidence, the localization of the anti-apoptotic proteins to the chloroplast may be relevant for protection in certain facets of plant PCD.
|
|
Discussion |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Apoptosis is often mediated via organelles (Ferri and Kroemer, 2001
). While the mitochondrion has received the bulk of the attention, evidence has shown that the endoplasmic reticulum, nucleus, lysosomes, and Golgi can also be involved in the triggering of the death programme (Ferri and Kroemer, 2001). In this report, evidence is presented to show that plant chloroplasts, not only associate with Bcl-2 family members, but importantly this interaction may have functional significance.
Chloroplasts are green photosynthetic plastids that are responsible for energy capture during the process of converting light energy to chemical energy. Thus, chloroplasts are potentially the major source of toxic oxygen derivatives in plant tissue (Foyer et al., 1994). Accumulation of active oxygen species is an unavoidable consequence of photosynthesis. Under high doses of illumination, singlet oxygen is generated through the interaction of triplet-state chlorophyll with ground-state oxygen which can also produce the superoxide radical (). Chloroplasts are particularly sensitive to damage by ROS because electrons that escape from the photosynthetic electron transfer system are able to react with the relatively high concentrations of O2 in chloroplasts.
Chloroplasts have been previously suggested to play significant roles in the programmed death of plant cells. For example, on epidermal peels of pea leaves, CN– induces guard cell death (containing chloroplasts and mitochondria), but not epidermal cell death (containing mitochondria only) and only in the presence of light (Samuilov et al., 2002, 2003). The association of Bcl-2, Bcl-xL, and CED-9 with chloroplast membranes should not be unexpected. These proteins all have transmembrane domains at their C termini and have been previously reported to associate with numerous membrane-bound structures. Thus, the key question is whether chloroplast localization has functional importance in modulating cell death responses. The evidence that plant chloroplasts are causally involved in plant programmed cell death is based on the following. (i) Treatment of tobacco with herbicides whose primary site of action is the chloroplast result in a plant cell death that is typified by apoptotic-like features. It should be noted that expression of these transgenes did not protect against the herbicide glyphosate (‘Round-up’), which is also a chloroplast-targeted herbicide that does not generate ROS. In addition, cell death induced by glyphosate did not exhibit apoptotic-like features. (ii) Light is required for cell death to occur. (iii) Transgenic tobacco harbouring animal anti-apoptotic genes inhibit herbicide-mediated plant cell death and apoptotic-like characteristics are not observed. (iv) Null mutations in the transgenes no longer confer cytoprotection.
A common theme shared by these chemical stresses is the induction of toxic levels of reactive oxygen. Bcl-2 and Bcl-xL have been shown in mammalian systems to confer tolerance to oxidative stress, although the precise manner by which this occurs is not clear (Hockenbery et al., 1993). Previously, it has been shown that these anti-apoptotic genes, including CED-9 can protect yeast from lethal levels of oxidative stress induced by menadione and H2O2 (Chen et al., 2003). Paraquat has often been used as an inducer of photo-oxidative stress and the site of action has generally been associated with the chloroplast. When isolated chloroplasts were illuminated in the presence of paraquat, both stromal and thylakoid-bound ascorbate peroxidases were rapidly inactivated (Mano et al., 2001). The chloroplastic glutamine synthetase, a key enzyme that catalyses the rate-determining step in the photorespiratory pathway, also showed rapid decline when exposed to paraquat (Palatnik et al., 1999). Thus, the association of paraquat activating with chloroplasts is well documented. However, paraquat also functions in mammalian systems presumably generating toxicity via mitochondrial electron transport (Kelner et al., 1995). Therefore, two additional chloroplast-targeted herbicides were used to confirm these studies. In all cases, an apoptotic-like cell death occurred in wild-type tobacco that was light requiring and inhibitable by transgene expression. It was determined that the source of DNA laddering was not from the chloroplast (data not shown). Thus, chloroplast-directed PCD is mediated via the nucleus.
Light is known to be required for the development of a number of plant diseases and chloroplasts are a well established site of action for certain diseases. For example, in the compatible interaction between tobacco mosaic virus and its host, chlorosis is observed as the virus replicates and spreads. In the incompatible hypersensitive response, a programmed cell death occurs that involves morphological changes in the chloroplast prior to chromatin cleavage and death (Mitter et al., 1997). Chloroplasts appear to be the key mediators of cell death in maize lesion mimic lls1 mutants (Gray et al., 2002) and a tobacco salicylic acid binding protein was found to be a chloroplast carbonic anhydrase that was shown to harbour antioxidant activity in plants and yeast. Further, when this gene was silenced, the HR was suppressed (Slaymaker et al., 2002).
The role of mitochondria and PCD has been extensively discussed from an evolutionary perspective (Blackstone and Green, 1999). Considerable evidence indicates a bacterial origin for mitochondria and chloroplasts, which resemble and appear to be descended from photosynthetic bacteria. Mitochondria and chloroplasts have several common features including (i) they arise by growth and division not by de novo synthesis, (ii) they are not inherited in a Mendelian manner, (iii) have different DNA organization, (iv) are generally devoid of introns, (v) are involved in energy metabolism, and (vi) are semi-autonomous, containing the genetic machinery required to synthesize some of their own proteins. All of these designations are consistent with the endosymbiont theory. Thus it is postulated that these bacteria evolved into the modern day mitochondria (and chloroplasts), which provided not only critical antioxidants, but also a source of ROS as a by-product of oxidative phosphorylation. It has been hypothesized that the endosymbiotic origins of mitochondria and the evolution or aerobic metabolism in eukaryotes formed the basis of active cell death that is illustrated by apoptosis in metazoans (Kroemer, 1997). While mitochondria (and chloroplasts) are not involved in all forms of cell death (e.g. apoptosis can occur in the absence of mitochondria), roles for mitochondrial involvement in apoptosis have been clearly established. It is suggested that regulation of oxidative stress in chloroplasts is a means by which certain programmed cell death events are manifested in plants.
|
Acknowledgements |
|---|
This work was supported by National Science Foundation Grant IBN 0133078.
|
References |
|---|
|
TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
|---|
Aono M, Saji H, Sakamoto A, Tanaka K, Kondo N. 1995. Paraquat tolerance of transgenic Nicotiana tabacum with enhanced activities of glutathione reductase and superoxide dismutase. Plant Cell Physiology 36, 1687–1691.
Arnon DI. 1949. Copper enzymes in isolated chloroplasts and polyphenol oxidase in Beta valgaris. Plant Physiology 24, 1–15.
Asada K, Takahashi M. 1987. Production and scavenging of active oxygen in photosynthesis. In: Kyle DJ, Osmond CB, Arntzen CJ, eds. Photoinhibition. Amsterdam: Elsevier Science Publishers, 227–287.
Awada T, Dunigan DD, Dickman MB. 2003. Animal anti-apoptotic genes ameliorate the loss of turgor in water-stressed transgenic tobacco. Canadian Journal of Plant Science 83, 499–506.
Blackstone NW, Green DR. 1999. The evolution of a mechanism of cell suicide. Bioessays 21, 84–88.[CrossRef][ISI][Medline]
Bolwell GP, Wojtaszek P. 1997. Mechanisms for the generation of reactive oxygen species in plant defence—a broad perspective. Physiological and Molecular Plant Pathology 51, 347–366.
Chen SR, Dunigan DD, Dickman MB. 2003. Bcl-2 family members inhibit oxidative stress-induced programmed cell death in Saccharomyces cerevisiae. Free Radical Biology and Medicine 34, 1315–1325.[CrossRef][ISI][Medline]
Cory S, Adams JM. 2002. The Bcl-2 family: regulators of the cellular life-or-death switch. Nature Reviews Cancer 2, 647–656.[CrossRef][ISI][Medline]
Curtis MJ, Wolpert TJ. 2002. The oat mitochondrial permeability transition and its implication in victorin binding and induced cell death. The Plant Journal 29, 295–312.[CrossRef][ISI][Medline]
Dangl JL, Jones IDG. 2001. Plant pathogens and integrated defence responses to infection. Nature 411, 826–833.[CrossRef][Medline]
del Pozo O, Lam E. 1998. Caspases and programmed cell death in the hypersensitive response of plants to pathogens. Current Biology 8, 1129–1132.[CrossRef][ISI][Medline]
Dickman MB, Park YK, Oltersdorf T, Li W, Clemente T, French R. 2001. Abrogation of disease development in plants expressing animal antiapoptotic genes. Proceedings of the National Academy of Sciences, USA 98, 6957–6962.
Dickman MB, Reed JC. 2003. Paradigms for programmed cell death in animals and plants In: Gray J, ed. When plant cells die. Chapter 2, UK: Blackwell Publishing, 26–43.
Earnshaw WC, Martins LM, Kaufmann SH. 1999. Mammalian caspases: structure, activation, substrates, and functions during apoptosis. Annual Reviews of Biochemistry 68, 383–424.
Ferri KF, Kroemer G. 2001. Organelle-specific initiation of cell death pathways. Nature Cell Biology 3, E255–263.[CrossRef][ISI][Medline]
Foyer CH, Descourvieres P, Kunert KJ. 1994. Protection against oxygen radicals: an important defence mechanism studied in transgenic plants. Plant, Cell and Environment 17, 507–523.[CrossRef]
Fukuda H. 1996. Xylogenesis: initiation, progression, and cell death. Annual Review of Plant Physiology and Plant Molecular Biology 47, 299–325.[CrossRef][ISI]
Gray J, Janick-Buckner D, Buckner B, Close PS, Johal GS. 2002. Light-dependent death of maize lls1 cells is mediated by mature chloroplasts. Plant Physiology 130, 1894–1907.
Groover A, Jones AM. 1999. Tracheary element differentiation uses a novel mechanism coordinating programmed cell death and secondary cell wall synthesis. Plant Physiology 119, 375–384.
Halliwell B, Gutteridge JMC. 1989. Free radicals in biology and medicine, 2nd edn. Oxford, UK: Clarendon Press.
Hanada M, Aime-Sempe C, Sato T, Reed JC. 1995. Structure–function analysis of Bcl-2 protein. Identification of conserved domains important for homodimerization with Bcl-2 and heterodimerization with Bax. Journal of Biological Chemistry 270, 11962–11969.
Havel L, Durzan DJ. 1996. Apoptosis in plants. Botanica Acta 109, 268–277.
Heath MC. 1998. Apoptosis, programmed cell death and the hypersensitive response. European Journal of Plant Pathology 104, 117–124.[CrossRef]
Hockenbery DM, Oltvai ZN, Yin XM, Milliman CL, Korsmeyer SJ. 1993. Bcl-2 functions in an antioxidant pathway to prevent apoptosis. Cell 75, 241–251.[CrossRef][ISI][Medline]
Kelner MJ, Bagnell RD, Uglik SF, Montoya MA, Mullenbach GT. 1995. Heterologous expression of selenium-dependent glutathione peroxidase affords cellular resistance to paraquat. Archives of Biochemistry and Biophysics 323, 40–46.[CrossRef][ISI][Medline]
Kroemer G. 1997. Mitochondrial implication in apoptosis towards an endosymbiont hypothesis of apoptosis evolution. Cell Death and Differentiation 4, 443–456.[CrossRef][ISI][Medline]
Lacomme C, Santa Cruz S. 1999. Bax-induced cell death in tobacco is similar to the hypersensitive response. Proceedings of the National Academy of Sciences, USA 96, 7956–7961.
Lermontova I, Grimm B. 2000. Overexpression of plastidic protoporphyrinogen IX oxidase leads to resistance to the diphenyl-ether herbicide acifluorfen. Plant Physiology 122, 75–84.
Li W, Dickman MB. 2004. Abiotic stress induces apoptotic-like features in tobacco that is inhibited by expression of human Bcl-2. Biotechnology Letters 26, 87–95.[CrossRef][ISI][Medline]
Mano J, Ohno C, Domae Y, Asada K. 2001. Chloroplastic ascorbate peroxidase is the primary target of methylviologen-induced photo-oxidative stress in spinach leaves: its relevance to monodehydroascorbate radical detected with in vivo ESR. Biochimica et Biophysica Acta 1504, 275–287.[Medline]
Mittler R, Simon L, Lam E. 1997. Pathogen-induced programmed cell death in tobacco. Journal of Cell Science 110, 1333–1344.[Abstract]
Nam HG. 1997. The molecular genetic analysis of leaf senescence. Current Opinion in Biotechnology 8, 200–207.[CrossRef][ISI][Medline]
Navarre DA, Wolpert TJ. 1999. Victorin induction of an apoptotic/senescence-like response in oats. The Plant Cell 11, 237–249.
Palatnik JF, Carrillo N, Valle EM. 1999. The role of photosynthetic electron transport in the oxidative degradation of chloroplastic glutamine synthetase. Plant Physiology 121, 471–478.
Palatnik JF, Valle EM, Carrillo N. 1997. Oxidative stress causes ferredoxin-NADP+ reductase solubilization from the thylakoid membranes in methyl viologen-treated plants. Plant Physiology 115, 1721–1727.[Abstract]
Richberg MH, Aviv DH, Dangl JL. 1998. Dead cells do tell tales. Current Opinion in Plant Biology 1, 480–485.[CrossRef][ISI][Medline]
Ryerson DE, Heath MC. 1996. Cleavage of nuclear DNA into oligonucleosomal fragments during cell death induced by fungal infection or by abiotic treatments. The Plant Cell 8, 393–402.[Abstract]
Samuilov VD, Lagunova EM, Dzyubinskaya EV, Izyumov DS, Kiselevsky DB, Makarova YV. 2002. Involvement of chloroplasts in the programmed death of plant cells. Biochemistry (Moscow) 67, 627–634.[CrossRef][Medline]
Samuilov VD, Lagunova EM, Gostimsky SA, Timofeev KN, Gusev MV. 2003. Role of chloroplast photosystems II and I in apoptosis of pea guard cells. Biochemistry (Moscow) 68, 1113–1118.
Slaymaker DH, Navarre DA, Clark D, del Pozo O, Martin GB, Klessig DF. 2002. The tobacco salicylic acid-binding protein 3 SABP3 is the chloroplast carbonic anhydrase, which exhibits antioxidant activity and plays a role in the hypersensitive defence response. Proceedings of the National Academy of Sciences, USA 99, 11640–11645.
Solomon M, Belenghi B, Delledonne M, Menachem E, Levine A. 1999. The involvement of cysteine proteases and protease inhibitor genes in the regulation of programmed cell death in plants. The Plant Cell 11, 431–444.
Stein JC, Hansen G. 1999. Mannose induces an endonuclease responsible for DNA laddering in plant cells. Plant Physiology 121, 71–80.
Wang H, Jones C, Zanella JC, Holt T, Gilchrist DG, Dickman MB. 1996. Fumonisins and Alternaria alternata lycopersici toxins: sphinganine analog mycotoxins induce apoptosis in monkey kidney cells. Proceedings of the National Academy of Sciences, USA 93, 3461–3465.
White JL, Kaper JM. 1989. A simple method for detection of viral satellite RNAs in small plant tissue samples. Journal of Virological Methods 23, 83–93.[CrossRef][ISI][Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  L. Zhang and D. Xing Methyl Jasmonate Induces Production of Reactive Oxygen Species and Alterations in Mitochondrial Dynamics that Precede Photosynthetic Dysfunction and Subsequent Cell Death Plant Cell Physiol., July 1, 2008; 49(7): 1092 - 1111. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. Bonneau, Y. Ge, G. E. Drury, and P. Gallois What happened to plant caspases? J. Exp. Bot., February 13, 2008; (2008) erm352v1. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. He, G. E. Drury, V. I. Rotari, A. Gordon, M. Willer, T. Farzaneh, E. J. Woltering, and P. Gallois Metacaspase-8 Modulates Programmed Cell Death Induced by Ultraviolet Light and H2O2 in Arabidopsis J. Biol. Chem., January 11, 2008; 283(2): 774 - 783. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Zuppini, C. Andreoli, and B. Baldan Heat Stress: an Inducer of Programmed Cell Death in Chlorella saccharophila Plant Cell Physiol., July 1, 2007; 48(7): 1000 - 1009. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 F. Van Breusegem and J. F. Dat Reactive Oxygen Species in Plant Cell Death Plant Physiology, June 1, 2006; 141(2): 384 - 390. [Full Text] [PDF]
|
|
|
|
|
|
H Vanacker, L. Sandalio, A Jimenez, J. Palma, F. Corpas, V Meseguer, M Gomez, F Sevilla, M Leterrier, C. Foyer, et al. Roles for redox regulation in leaf senescence of pea plants grown on different sources of nitrogen nutrition. J. Exp. Bot., May 1, 2006; 57(8): 1735 - 1745. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Y. Graham The Diphenylether Herbicide Lactofen Induces Cell Death and Expression of Defense-Related Genes in Soybean Plant Physiology, December 1, 2005; 139(4): 1784 - 1794. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
V. Pavet, E. Olmos, G. Kiddle, S. Mowla, S. Kumar, J. Antoniw, M. E. Alvarez, and C. H. Foyer Ascorbic Acid Deficiency Activates Cell Death and Disease Resistance Responses in Arabidopsis Plant Physiology, November 1, 2005; 139(3): 1291 - 1303. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. H. Foyer and G. Noctor Redox Homeostasis and Antioxidant Signaling: A Metabolic Interface between Stress Perception and Physiological Responses PLANT CELL, July 1, 2005; 17(7): 1866 - 1875. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||