Root Cell Death Research Articles

Biological responses of maize (Zea mays) plants exposed to chlorobenzenes. Case study of monochloro-, 1,4-dichloro- and 1,2,4-trichloro-benzenes

A 7-day-exposure time experiment was designed to investigate the phytotoxicity of chlorobenzenes (CBs) on Zea mays seedlings, focusing on the growth and generation of oxidative stress. Significant growth inhibition (based on biomass gain) was observed for exposure to monochlorobenzene (MCB), dichlorobenzene (DCB) and trichlorobenzene (TCB) concentrations higher than 10 mg l(-1). It would seem that CBs inhibit cell division, since the mitotic index decreased for roots exposed to DCB at 80 mg l(-1) dose (8%) and to all the TCB concentrations tested (20% inhibition). CBs exposure resulting in an increase in the oxidative stress response in maize seedlings [reactive oxygen species like H(2)O(2), antioxidant enzymes (POD, GR), lipid peroxidation] correlated to the compound's degree of chlorination, where damage increasing with the number of chlorine atoms (MCB < DCB < TCB). This biological response was also dependent on the dose-exposure. Z. mays exposed to CBs at concentrations <10 mg l(-1) did not induce sufficient oxidative damage to cause root cell death. Therefore, CBs at current environmental concentrations are unlikely to produce evident phytotoxic effects on Z. mays seedlings.

Ammonium affects cell viability to inhibit root growth in Arabidopsis

Ammonium (NH₄⁺) is an important form of nitrogen nutrient for most plants, yet is also a stressor for many of them. However, the primary events of NH₄⁺ toxicity at the cellular level are still unclear. Here, we showed that NH₄⁺ toxicity can induce the root cell death in a temporal pattern which primarily occurs in the cells of root maturation and elongation zones, and then spreads to the cells in the meristem and root cap. The results from the NH₄⁺-hypersensitive mutant hsn1 further confirmed our findings. Taken together, NH₄⁺ toxicity inhibits primary root growth by inhibiting cell elongation and division and inducing root cell death.

Characteristics of mitochondria and cell death in roots of Malus hupehensis var. pingyiensis under NaCl stress.

Aims Malus hupehensis var. pingyiensis with strong ability for apomixes is unique to China and is tolerant of waterlogged conditions and salt. There is little difference among its seedlings because of apomixes. Malus hupe-hensis var. pingyiensis is widely used as stocks of apple cultivars and ornamental apples and has important applied value in apple production and research. Our objective was to determine the response characteristic of cells and mitochondria in M. hupehensis var. pingyiensis roots under high saline conditions. Methods Pot seedlings with at least seven mature leaves were used in this experiment. In order to avoid irre-versible damage to roots caused by sudden exposure to high level saline condition, we first used a weak saline solution (0.051 mol·L–1 NaCl) to water seedlings every two days, for a total of three times. Then strong saline so-lution (0.085 mol·L–1 NaCl) was used to water seedlings. Tap water was used for control seedlings. H2O2 content, membrane potential of mitochondria (Δψm), ATP content, terminal deoxynucleotidyl transferase mediated dUTP nick end labelling (TUNEL) and caspase3/7 activity were determined every two days from the third day of 0.085 mol·L–1 NaCl treatment, altogether five times. Important findings Δψm of roots declined slowly in the first six days of 0.085 mol·L–1 NaCl treatment and thereafter declined rapidly. The H2O2 content in mitochondria decreased slowly in the first six days and then ac-cumulated quickly. ATP content in roots remained constant during the treatment of 0.085 mol·L–1 NaCl, but was low compared with that in control seedlings. The results of TUNEL assay showed that root paraffin slices dis-played distinct positive-reaction spots that became more numerous in the root paraffin slice of the ninth day. Cas-pase3/7 activity was examined with a detection kit; it remained at a low level for the first six days of 0.085 mol·L–1 NaCl treatment, and thereafter increased sharply. Results indicated that programmed cell death could be induced in roots of M. hupehensis var. pingyiensis by 0.085 mol·L–1 NaCl treatment, and this was closely related to the change of mitochondrial characteristics.

Morphophysiological responses and programmed cell death induced by cadmium in Genipa americana L. (Rubiaceae)

Cadmium (Cd) originating from atmospheric deposits, from industrial residues and from the application of phosphate fertilizers may accumulate in high concentrations in soil, water and food, thus becoming highly toxic to plants, animals and human beings. Once accumulated in an organism, Cd discharges and sets off a sequence of biochemical reactions and morphophysiological changes which may cause cell death in several tissues and organs. In order to test the hypothesis that Cd interferes in the metabolism of G. americana, a greenhouse experiment was conducted to measure eventual morphophysiological responses and cell death induced by Cd in this species. The plants were exposed to Cd concentrations ranging from 0 to 16 mg l(-1), in a nutritive solution. In TUNEL reaction, it was shown that Cd caused morphological changes in the cell nucleus of root tip and leaf tissues, which are typical for apoptosis. Cadmium induced anatomical changes in roots and leaves, such as the lignification of cell walls in root tissues and leaf main vein. In addition, the leaf mesophyll showed increase of the intercellular spaces. On the other hand, Cd caused reductions in the net photosynthetic rate, stomatal conductance and leaf transpiration, while the maximum potential quantum efficiency of PS2 (Fv/Fm) was unchanged. Cadmium accumulated in the root system in high concentrations, with low translocation for the shoot, and promoted an increase of Ca and Zn levels in the roots and a decrease of K level in the leaves. High concentrations of Cd promoted morphophysiological changes and caused cell death in roots and leaves tissues of G. americana.

An endoplasmic reticulum response pathway mediates programmed cell death of root tip induced by water stress in Arabidopsis

Drought induces root death in plants; however, the nature and characteristics of root cell death and its underlying mechanisms are poorly understood. Here, we provide a systematic analysis of cell death in the primary root tips in Arabidopsis during water stress. Root tip cell death occurs when high water deficit is reached. The dying cells were first detected in the apical meristem of the primary roots and underwent active programmed cell death (PCD). Transmission electron microscopic analysis shows that the cells undergoing induced death had unambiguous morphological features of autophagic cell death, including an increase in vacuole size, degradation of organelles, and collapse of the tonoplast and the plasma membrane. The results suggest that autophagic PCD occurs as a response to severe water deficit. Significant accumulation of reactive oxygen species (ROS) was detected in the stressed root tips. Expression of BAX inhibitor-1 (AtBI1) was increased in response to water stress, and atbi1-1 displayed accelerated cell death, indicating that AtBI1 and the endoplasmic reticulum (ER) stress response pathway both modulate water stress-induced PCD. These findings form the basis for further investigations into the mechanisms underlying the PCD and its role in developmental plasticity of root system architecture and subsequent adaptation to water stress.

Intracellular consequences of SOS1 deficiency during salt stress

A mutation of AtSOS1 (Salt Overly Sensitive 1), a plasma membrane Na+/H+-antiporter in Arabidopsis thaliana, leads to a salt-sensitive phenotype accompanied by the death of root cells under salt stress. Intracellular events and changes in gene expression were compared during a non-lethal salt stress between the wild type and a representative SOS1 mutant, atsos1-1, by confocal microscopy using ion-specific fluorophores and by quantitative RT-PCR. In addition to the higher accumulation of sodium ions, atsos1-1 showed inhibition of endocytosis, abnormalities in vacuolar shape and function, and changes in intracellular pH compared to the wild type in root tip cells under stress. Quantitative RT-PCR revealed a dramatically faster and higher induction of root-specific Ca2+ transporters, including several CAXs and CNGCs, and the drastic down-regulation of genes involved in pH-homeostasis and membrane potential maintenance. Differential regulation of genes for functions in intracellular protein trafficking in atsos1-1 was also observed. The results suggested roles of the SOS1 protein, in addition to its function as a Na+/H+ antiporter, whose disruption affected membrane traffic and vacuolar functions possibly by controlling pH homeostasis in root cells.

Aerenchyma formation: programmed cell death in adventitious roots of winter wheat (Triticum aestivum) under waterlogging

This study determined the characteristics of cortical cell death in wheat (Triticum aestivum L.) roots during programmed cell death (PCD) and the relationship between PCD and acid phosphatases. An examination of morphological development by light microscrope revealed that aerenchyma formed in roots waterlogged for 24 h and well developed aerenchyma formed in roots waterlogged for 120 h. The first detectable events were observed by electron microscopy and included plasma membrane invagination and the appearance of vesicles between the plasma membrane and the cell wall. Later, chromatin condensation and double-membrane-bound structures resembling autophagosomes were observed. The activity of acid phosphatases gradually increased during waterlogging and was present during the entire process of cell death. These observations suggest that cortical cell death during aerenchyma formation induced by waterlogging was a form of PCD. Acid phosphatases play an important role in PCD induced by waterlogging, being responsible for the hydrolysis of cell components at the later stages of PCD.

Cell death in wheat roots induced by the powdery mildew fungus Blumeria graminis f. sp. tritici

Inoculation of wheat (Triticum aestivum L. cv. Huamai 8) leaves with wheat powderly mildew fungus (Blumeria graminis f. sp. tritici) induced cell death in wheat adventitious roots, where no fungal structures were observed. The cytological and molecular characterization of this cell death was shown as following: cell nuclei were TUNEL positive labeled; genomic DNA was fragmented and showed DNA laddering; chromatin condensed and formed peripheral conglomeration in nuclei; and perinuclear spaces partly dilated. These results suggested that, without pathogen spread, the infection could induce systemic PCD in adventitious roots. Comparison with a leaf-cutting experiment (LC)enabled us to speculate that lack of assimilates was not the only reason for the systemic PCD in wheat roots in powdery mildew experiment and that such systemic PCD might be mediated by long-distance signals. In addition, reactive oxygen species (ROS) and Ca2+ were related to the systemic PCD.

Carbon monoxide mitigates salt-induced inhibition of root growth and suppresses programmed cell death in wheat primary roots by inhibiting superoxide anion overproduction

In our experiments, treatment of wheat seedling roots with varying concentrations of NaCl caused the inhibition of primary root growth in a dose-dependent manner, which was consistent with the progressive DNA laddering in the primary root tips. Upon 100, and 200 mM NaCl stress, the increase of carbon monoxide (CO) release and heme oxygenase (HO) activity was observed. By contraries, treatment with 400 mM NaCl is otherwise, that the result displays a decreasing tendency. Besides DNA laddering, 200 mM NaCl treatment exhibited the induction of other programmed cell death (PCD) associated with phenomenon in the primary root tips, such as TUNEL staining, nuclear condense and deformation. Further, HO's catalytic product CO was able to dose-dependently mitigate 200 mM NaCl-induced inhibition of root growth and delay PCD. These effects were prevented strongly by incubation with DETC (a Cu/Zn-SOD inhibitor), and differentially influenced by Tiron (a scavenger of superoxide anion) and apocynin (an inhibitor of NADPH oxidase). Meanwhile, 50% CO aqueous solution inhibited the overproduction of superoxide anion, NADPH oxidase activities and corresponding transcript, and enhanced superoxide dismutase (SOD) activity, Mn-SOD and Cu/ Zn-SOD transcript. Taken together, the results suggested that CO might be involved in plant tolerance against salinity stress, and its alleviation of PCD and inhibition of root growth was related to the decrease of superoxide anion overproduction partially via up-regulation of SOD and down-regulation of NADPH oxidase expression.

Early signalling pathways in rice roots under vanadate stress

Vanadate is beneficial to plant growth at low concentration. However, plant exposure to high concentrations of vanadate has been shown to arrest cell growth and lead to cell death. We are interested in understanding the signalling pathways of rice roots in response to vanadate stress. In this study, we demonstrated that vanadate induced rice root cell death and suppressed root growth. In addition, we found that vanadate induced ROS accumulation, increased lipid peroxidation and elicited a remarkable increase of MAPKs and CDPKs activities in rice roots. In contrast, pre-treatment of rice roots with ROS scavenger (sodium benzoate), serine/threonine protein phosphatase inhibitor (endothall), and CDPK antagonist (W7), reduced the vanadate-induced MAPKs activation. Furthermore, the expression of a MAPK gene (OsMPK3) and four tyrosine phosphatase genes (OsDSP3, OsDSP5, OsDSP6, and OsDSP10) were regulated by vanadate in rice roots. Collectively, these results strongly suggest that ROS, protein phosphatase, and CDPK may function in the vanadate-triggered MAPK signalling pathway cause cell death and retarded growth in rice roots.

Quinclorac-induced cell death is accompanied by generation of reactive oxygen species in maize root tissue

The importance of reactive oxygen species for herbicide quinclorac (3,7-dichloro-8-quinolinecarboxylic acid)-induced cell death in roots was investigated. This was in order to understand its mode of action in grass species grown in the dark. Under these dark conditions, quinclorac suppressed the shoot and root growth of maize ( Zea mays L. cv. Honey Bantam) in a concentration-dependent manner (⩽50 μM), although the inhibition level was less than that observed under growth conditions in the light. Analysis of cell viability using Evans blue or fluorescein diacetate–propidium iodide (FDA–PI) staining showed that the maize root cells significantly lost their viability after 14 h root treatment with 10 μM quinclorac, but not 10 μM 2,4-dichlorophenoxyacetic acid (2,4-D). Determination of reactive oxygen species (ROS) in maize roots using a superoxide anion ( O 2 - )-specific indicator, dihydroethidium (DHE), indicated that 50 μM quinclorac induced a high level of O 2 - production in maize roots after 14 h root treatment than that of either the control (non-treated) or with 50 μM 2,4-D. Moreover, either cell death or ethane evolution, an indicator of lipid peroxide formation, in maize root segments was significantly enhanced by 50 μM quinclorac, but not by 50 μM 2,4-D. On the other hand, the 50 μM 2,4-D treatment induced much higher ethylene and cyanide production in the root segments than with the 50 μM quinclorac. These results suggest that quinclorac-induced cell death in maize roots may be caused by ROS and lipid peroxidation, but not by ethylene and its biosynthetic pathway-related substances including cyanide, which have been thought to be the causative factor of quinclorac-induced phytotoxicity in susceptible grass weeds such as Echinochloa, Digitaria, and Setaria.

Does salicylic acid regulate antioxidant defense system, cell death, cadmium uptake and partitioning to acquire cadmium tolerance in rice?

Salicylic acid (SA) may accelerate the cell death of cadmium-stressed roots to avoid cadmium (Cd) uptake by plants or may play positive roles in protecting the stressed roots from Cd-induced damage. To test these hypotheses, we performed a series of split-root hydroponic experiments with one-half of rice (Oryza sativa L. cv. Jiahua 1) roots exposed to 50 microM Cd and the other half not exposed. The objectives were to elucidate the effects of SA pretreatment on the time-dependent changes of H(2)O(2) levels in roots, antioxidant defense system in different organs, root cell death and the dynamic distribution of Cd in the plants. In the split-root system, a higher Cd uptake rate was observed in the Cd-stressed portions of roots compared with the treatment with the whole roots exposed to Cd. Furthermore, an appreciable amount of Cd was translocated from the Cd-exposed roots to the unexposed roots and trace amounts of Cd were released into the external solution. The split-root method also caused the two root portions to respond differently to Cd stress. The activities of major antioxidant enzymes (superoxide dismutase, SOD; peroxidase, POD; and catalase, CAT) were significantly suppressed in the Cd-treated roots, hence leading to H(2)O(2) burst, lipid peroxidation, cell death and growth inhibition. By contrast, in the non-Cd-treated roots, the activities of enzymes (SOD, CAT, and POD) and root growth were persistently stimulated during the experimental period. The H(2)O(2) accumulation and lipid peroxidation were also induced in the non-Cd-treated roots, but they were significantly lower than those of the Cd-treated roots. The concentrations of glutathione (GSH) and non-protein thiols (NPT) in the Cd-treated roots were significantly higher than those of the untreated roots. SA pretreatment elevated enzymatic and non-enzymatic antioxidants, and the concentrations of GSH and NPT in roots and shoots, hence leading to alleviation of the oxidative damage as indicated by the lowered H(2)O(2) and MDA levels. Furthermore, SA pretreatment mitigated the Cd-induced growth inhibition in both roots and shoots and increased transpiration compared with non-SA-pretreatment under Cd exposure. It is concluded that Cd can be partly transferred from the Cd-exposed roots to Cd-unexposed roots and that cell death can be accelerated in the Cd-stressed roots in response to Cd stress. The SA-enhanced Cd tolerance in rice can be attributed to SA-elevated enzymatic and non-enzymatic antioxidants and NPT, and to SA-regulated Cd uptake, transport and distribution in plant organs.

Role of EDTA in alleviating lead toxicity in accumulator species of Sedum alfredii H.

The effects of Pb chelater (EDTA–Pb) and ionic Pb (Pb(NO 3) 2) on root cell death, Pb accumulation, changes of ROS, activities of antioxidant enzymes and uptake of mineral elements in response to Pb toxicity in Sedum alfredii H. were compared. Loss of plasma membrane integrity became serious by increasing Pb concentration in the medium, 200 μM Pb + 200 μM EDTA has alleviated the root cell death. The biomass was significantly affected by high concentration of Pb, and root growth was also affected by EDTA–Pb compared with ionic Pb. Lead accumulation was higher in the samples treated with ionic lead than that of the control. The concentration of reactive oxygen species (ROS) was determined by fluorescence microscopy, which indicates that the Pb stress increased the content of ROS significantly, whereas the EDTA–Pb decreased the burst of H 2O 2. High Pb concentrations increase the activity of SOD and LOX. The Cu concentration in root increased significantly under Pb and EDTA–Pb treatment, and 200 μM Pb markedly increased the Fe content in roots. Under ionic Pb condition, the contents of Mg, Ca and K in shoots decreased, whereas they were significantly increased in case of EDTA–Pb. These results suggested that accumulating ecotype of S. alfredii roots were inefficient in uptake of higher concentration of EDTA-chelated Pb for long treatment duration, and that lead toxicity could be alleviated by EDTA.

ROS and CDPK-like kinase-mediated activation of MAP kinase in rice roots exposed to lead

Lead (Pb2+) is a cytotoxic metal ion in plants, the mechanism of which is not yet established. The aim of this study is to investigate the signalling pathways that are activated by elevated concentrations of Pb2+ in rice roots. Root growth was stunted and cell death was accelerated when exposed to different dosages of Pb2+ during extended time periods. Using ROS-sensitive dye and Ca2+ indicator, we demonstrated that Pb2+ induced ROS production and Ca2+ accumulation, respectively. In addition, Pb2+ elicited a remarkable increase in myelin basic protein (MBP) kinase activities. By immunoblot and immunoprecipitation analysis, 40- and 42-kDa MBP kinases that were activated by Pb2+ were identified to be mitogen-activated protein (MAP) kinases. Pre-treatment of rice roots with an antioxidant and a NADPH oxidase inhibitor, glutathione (GSH) and diphenylene iodonium (DPI), effectively reduced Pb2+-induced cell death and MAP kinase activation. Moreover, calcium-dependent protein kinase (CDPK) antagonist, W7, attenuated Pb2+-induced cell death and MAP kinase activation. These results suggested that the ROS and CDPK may function in the Pb2+-triggered cell death and MAP kinase signalling pathway in rice roots.

Physiological basis of different allelopathic reactions of cucumber and figleaf gourd plants to cinnamic acid

To provide an insight into the mechanism of interspecific interactions mediated by allelochemicals, cucumber and figleaf gourd seedlings were compared on their response to cinnamic acid, an autotoxin from root exudates of cucumber. Reactive oxygen species metabolism and plasma membrane H(+)-ATPase activity were examined in roots upon exposure to cinnamic acid. This exposure resulted in significant increases in activities of NADPH oxidase, superoxide dismutase, guaiacol peroxidase, and catalase, as well as in O(2)(.-) production and H(2)O(2) content, in cucumber roots but not in figleaf gourd roots. Notably, the cucumber roots produced significant amount of reactive oxygen species (ROS) immediately after cinnamic acid treatment, consequently increasing membrane peroxidation, decreasing membrane H(+)-ATPase activity, and losing root viability. By contrast, no such changes were observed in figleaf gourd roots. All these results indicated that there was an interspecies difference in the recognition of allelochemicals, which induced oxidative stress accompanied by root cell death in cucumber, an autotoxic plant, but not in figleaf gourd, a cucumber relative.

Characterization of reactive oxygen species‐involved oxidative damage in Hapalosiphon species crude extract‐treated wheat and onion roots

Crude extract‐induced oxidative damage using the cyanobacterium, Hapalosiphon sp., was investigated in wheat seedlings (Triticum aestivum L. cv. Norin 61) and onion seedlings (Allium cepa L. cv. Raputa II). The analysis of root cell viability or cell death using Evans blue uptake showed that the root‐tip cells of wheat and onion lost viability after 24 h and 48 h treatment with 3 g dry weight (DW) L−1 of the crude extract, respectively. Lipid peroxidation was induced in the roots of both species and the shoots of onion, whereas no increase in lipid peroxide formation was observed in the wheat shoots. In onion, the degree of random DNA fragmentation increased with the increasing concentration of the extract and laddering of the DNA was observed with 6 g DW L−1 of the extract, but no apparent DNA ladder formation occurred in the wheat. Pretreatment for 1 h with the NADPH oxidase inhibitors, diphenyleneidonium or imidazole, reduced the crude extract‐induced root cell death in both species. From the results, we suggest that the Hapalosiphon sp. crude extract might enhance reactive oxygen species (ROS) production, which causes membrane lipid damage and fragmentation of the DNA of plant cells, resulting in cell death and growth inhibition. The crude extract‐mediated phytotoxic damage might be caused by ROS, triggered by NADPH oxidase.

Root cell death and systemic effects ofPiriformospora indica: a study on mutualism

The root systems of most terrestrial plants are confronted with a huge variety of invasive microorganisms that either can cause detrimental effects or in case of mutualistic symbiosis provide benefits for the host. In either case, establishment of the parasitic or mutualistic interaction is the result of a highly sophisticated cross-talk between the partners. Despite the ecological importance of mutualistic symbioses, the molecular events accompanied by this phenomenon are far from being understood. Piriformospora indica represents a recently discovered fungus that transfers considerable beneficial impact to its host plants. In this review, the current knowledge on this novel symbiosis is summarized by focusing on its biological effects in hosts and the role of programmed cell death in the establishment of the mutualistic interaction.

Protein tyrosine dephosphorylation during copper-induced cell death in rice roots

Early signalling events that control the process of heavy metal-induced cell death are largely unknown in plants. In mammals protein tyrosine phosphorylation plays an important role in the activation of programmed cell death. We thus examined the involvement of tyrosine phosphorylation in Cu-induced rice cell death. This investigation demonstrates that Cu induces cell death and DNA fragmentation in rice root cells. In the presence of Cu, the level of phosphotyrosine accumulation declined in the band of 45 kDa, p45. To analyze the role of tyrosine dephosphorylation for the regulation of Cu-induced cell death more precisely, we increased levels of tyrosine phosphorylation using the protein tyrosine phosphatase inhibitor, sodium orthovanadate (Na 3VO 4). Treatment of rice roots with Na 3VO 4 blocked Cu-induced cell death and protein tyrosine dephosphorylation. In addition, the antioxidant GSH and the calcium chelator EGTA significantly abolished Cu-induced cell death and protein tyrosine dephosphorylation. These results provide evidence that dephosphorylation of a tyrosine-phosphorylated protein, p45, is an important step in the Cu-triggered signalling transduction pathway.

RNAi silencing of genes for elicitation or biosynthesis of 5-deoxyisoflavonoids suppresses race-specific resistance and hypersensitive cell death in Phytophthora sojae infected tissues.

Isoflavonoids are thought to play an important role in soybean (Glycine max) resistance to Phytophthora sojae. This was addressed by silencing two genes for their biosynthesis and a third gene controlling their elicitation. Silencing of genes for isoflavone synthase (IFS) or chalcone reductase (CHR) was achieved in soybean roots through an Agrobacterium rhizogenes-mediated RNAi approach. Effectiveness of silencing was followed both by quantitative reverse transcriptase-polymerase chain reaction and high-performance liquid chromatography analyses. Silencing either IFS or CHR led to a breakdown of Rps-mediated resistance to race 1 of P. sojae in 'W79' (Rps 1c) or 'W82' (Rps 1k) soybean. Loss of resistance was accompanied by suppression of hypersensitive (HR) cell death in both cultivars and suppression of cell death-associated activation of hydrogen peroxide and peroxidase. The various results suggest that the 5-deoxyisoflavonoids play a critical role in the establishment of cell death and race-specific resistance. The P. sojae cell wall glucan elicitor, a potent elicitor of 5-deoxyisoflavonoids, triggered a cell death response in roots that was also suppressed by silencing either CHR or IFS. Furthermore, silencing of the elicitor-releasing endoglucanase (PR-2) led to a loss of HR cell death and race-specific resistance to P. sojae and also to a loss of isoflavone and cell death responses to cell wall glucan elicitor. Taken together, these results suggest that in situ release of active fragments from a general resistance elicitor (pathogen-associated molecular pattern) is necessary for HR cell death in soybean roots carrying resistance genes at the Rps 1 locus, and that this cell death response is mediated through accumulations of the 5-deoxyisoflavones.

An in vivo analysis of Schwann cell programmed cell death in embryonic mice: the role of axons, glial growth factor, and the pro‐apoptotic gene Bax

Building upon previous in vitro studies, the present investigation involves an in vivo examination of Schwann cell programmed cell death (PCD) and development in the brachial spinal ventral roots of embryonic mice. The period of Schwann cell PCD was found to occur between embryonic days (E) 11.5 and 18.5, which is in close coincidence with the PCD period of associated brachial motoneurons (E13.5-E18.5). Additionally, Schwann cells exhibited a peak in proliferation at E11.5, and differentiation from the precursor to the immature Schwann cell stage between E12.5 and E14.5. Axon-mediated Schwann cell survival was demonstrated in vivo by excitotoxic elimination of motoneurons and their axons, via NMDA treatment in utero. This treatment increased apoptotic Schwann cell death within degenerating ventral roots. Conversely, in utero co-treatment of glial growth factor (GGF) with NMDA resulted in decreased Schwann cell death, a finding which supports previous reports of the promotion of Schwann cell survival by GGF. Analysis of mice lacking Bax, a pro-apoptotic Bcl-2 protein, revealed that Schwann cell PCD occurred independently of Bax. However, owing to the lack of motoneuron PCD in Bax-knockout mice, and the corresponding increase in the number of ventral root axons, a decrease in Schwann cell PCD was observed during the normal period of motoneuron PCD. In conclusion, our findings regarding the regulation of Schwann cell development in vivo are consistent with the conclusions from in vitro studies, including a dependency on axons for survival and proliferation signals, timing of differentiation, and a dependency on GGF.