Comparison between the effects of fusicoccin, Tunicamycin, and Brefeldin A on programmed cell death of cultured sycamore (Acer pseudoplatanus L.) cells

Ferulic acid is a putative surrender signal to stimulate programmed cell death in grapevines after infection with Neofusicoccum parvum

An apoplectic breakdown from grapevine trunk diseases (GTDs) has become a serious challenge to viticulture as a consequence of drought stress. We hypothesize that fungal aggressiveness is controlled by a chemical communication between the host and colonizing fungus. We introduce the new concept of a 'plant surrender signal' accumulating in host plants under stress and facilitating the aggressive behaviour of the strain Neofusicoccum parvum (Bt-67) causing Botryosphaeriaceae-related dieback in grapevines. Using a cell-based experimental system (Vitis cells) and bioactivity-guided fractionation, we identify trans-ferulic acid, a monolignol precursor, as a 'surrender signal'. We show that this signal specifically activates the secretion of the fungal phytotoxin fusicoccin A aglycone. We show further that this phytotoxin, mediated by 14-3-3 proteins, activates programmed cell death in Vitis cells. We arrive at a model showing a chemical communication facilitating fusicoccin A secretion that drives necrotrophic behaviour during Botryosphaeriaceae-Vitis interaction through trans-ferulic acid. We thus hypothesize that channelling the phenylpropanoid pathway from this lignin precursor to the trans-resveratrol phytoalexin could be a target for future therapy.

Genome-wide identification of 14-3-3 gene family and characterization of their expression in developmental stages of Solanum tuberosum under multiple biotic and abiotic stress conditions

GF14 proteins are a family of conserved proteins involved in many cellular processes including transport, growth, metabolism, and stress response. However, only few reports are available regarding the 14-3-3 genes in potato. In this study, twelve 14-3-3 genes were detected in the potato genome. Based on their phylogenetic relationships, the StGF14 family members were categorized into two classes. Gene expression analysis demonstrated that StGF14h, StGF14a, and StGF14k had the highest gene expression, induced by abiotic and biotic stresses in all three tissues. The number of exons in 14-3-3 genes ranged from four to seven and most of these genes in the same subfamily had similar exon-intron patterns. The results of our study showed that the conserved motifs are similar in most of the proteins in each group. The intron-exon patterns and the composition of conserved motifs validated the 14-3-3 gene phylogenetic classification. According to the genome distribution results, 14-3-3 genes were located unevenly on the 12 Solanum tuberosum chromosomes. We find out 97 orthologous gene pairs between potato and Arabidopsis as well as 15 paralogous genes among potato genomes. Our results showed that GF-14 genes have an effective role in functional and molecular mechanisms in response to environmental stresses.

Reactive oxygen species and nitric oxide as mediators in plant hypersensitive response and stomatal closure

Nitric oxide (NO) and reactive oxygen species (ROS) have attracted considerable interest from plant pathologists since they regulate plant defenses via the hypersensitive response (HR) and stomatal closure. Here, we introduce the regulatory mechanisms of NO and ROS bursts and discuss the role of such bursts in HR and stomatal closure. It showed that epidermal sections of leaves respond to pathogens by the rapid and intense production of intracellular ROS and NO. Oxidative stress and H₂O₂ induce stomatal closure. Catalase and peroxidase-deficient plants are also hyperresponsive to pathogen invasion, suggesting a role for H₂O₂ in HR-mediated cell death. The analysis reveals that ROS and NO play important roles in stomatal closure and HR that involves multiple pathways. Therefore, multi-disciplinary and multi-omics combined analysis is crucial to the advancement of ROS and NO research and their role in plant defense mechanism.

Plant Cell Cultures as a Tool to Study Programmed Cell Death

Programmed cell death (PCD) is a genetically controlled suicide process present in all living beings with the scope of eliminating cells unnecessary or detrimental for the proper development of the organism. In plants, PCD plays a pivotal role in many developmental processes such as sex determination, senescence, and aerenchyma formation and is involved in the defense responses against abiotic and biotic stresses. Thus, its study is a main goal for plant scientists. However, since PCD often occurs in a small group of inaccessible cells buried in a bulk of surrounding uninvolved cells, its study in whole plant or complex tissues is very difficult. Due to their uniformity, accessibility, and reproducibility of application of stress conditions, cultured cells appear a useful tool to investigate the different aspects of plant PCD. In this review, we summarize how plant cell cultures can be utilized to clarify the plant PCD process.

TGBp3 triggers the unfolded protein response and SKP1-dependent programmed cell death

The Potato virus X (PVX) triple gene block protein 3 (TGBp3), an 8-kDa membrane binding protein, aids virus movement and induces the unfolded protein response (UPR) during PVX infection. TGBp3 was expressed from the Tobacco mosaic virus (TMV) genome (TMV-p3), and we noted the up-regulation of SKP1 and several endoplasmic reticulum (ER)-resident chaperones, including the ER luminal binding protein (BiP), protein disulphide isomerase (PDI), calreticulin (CRT) and calmodulin (CAM). Local lesions were seen on leaves inoculated with TMV-p3, but not TMV or PVX. Such lesions were the result of TGBp3-elicited programmed cell death (PCD), as shown by an increase in reactive oxygen species, DNA fragmentation and induction of SKP1 expression. UPR-related gene expression occurred within 8 h of TMV-p3 inoculation and declined before the onset of PCD. TGBp3-mediated cell death was suppressed in plants that overexpressed BiP, indicating that UPR induction by TGBp3 is a pro-survival mechanism. Anti-apoptotic genes Bcl-xl, CED-9 and Op-IAP were expressed in transgenic plants and suppressed N gene-mediated resistance to TMV, but failed to alleviate TGBp3-induced PCD. However, TGBp3-mediated cell death was reduced in SKP1-silenced Nicotiana benthamiana plants. The combined data suggest that TGBp3 triggers the UPR and elicits PCD in plants.

TGBp3 triggers the unfolded protein response and SKP1-dependent programmed cell death

The Potato virus X (PVX) triple gene block protein 3 (TGBp3), an 8-kDa membrane binding protein, aids virus movement and induces the unfolded protein response (UPR) during PVX infection. TGBp3 was expressed from the Tobacco mosaic virus (TMV) genome (TMV-p3), and we noted the up-regulation of SKP1 and several endoplasmic reticulum (ER)-resident chaperones, including the ER luminal binding protein (BiP), protein disulphide isomerase (PDI), calreticulin (CRT) and calmodulin (CAM). Local lesions were seen on leaves inoculated with TMV-p3, but not TMV or PVX. Such lesions were the result of TGBp3-elicited programmed cell death (PCD), as shown by an increase in reactive oxygen species, DNA fragmentation and induction of SKP1 expression. UPR-related gene expression occurred within 8 h of TMV-p3 inoculation and declined before the onset of PCD. TGBp3-mediated cell death was suppressed in plants that overexpressed BiP, indicating that UPR induction by TGBp3 is a pro-survival mechanism. Anti-apoptotic genes Bcl-xl, CED-9 and Op-IAP were expressed in transgenic plants and suppressed N gene-mediated resistance to TMV, but failed to alleviate TGBp3-induced PCD. However, TGBp3-mediated cell death was reduced in SKP1-silenced Nicotiana benthamiana plants. The combined data suggest that TGBp3 triggers the UPR and elicits PCD in plants.

Defense/stress responses activated by chitosan in sycamore cultured cells

Chitosan (CHT) is a natural, non-toxic, and inexpensive compound obtained by partial alkaline deacetylation of chitin, the main component of the exoskeleton of crustaceans and other arthropods. The unique physiological and biological properties of CHT make this polymer useful for a wide range of industries. In agriculture, CHT is used to control numerous pre- and postharvest diseases on various horticultural commodities. In recent years, much attention has been devoted to CHT as an elicitor of defense responses in plants, which include raising of cytosolic Ca(2+), activation of MAP kinases, callose apposition, oxidative burst, hypersensitive response, synthesis of abscisic acid, jasmonate, phytoalexins, and pathogenesis-related proteins. In this work, we investigated the effects of different CHT concentrations on some defense/stress responses of sycamore (Acer pseudoplatanus L.) cultured cells. CHT induced accumulation of dead cells, and of cells with fragmented DNA, production of H(2)O(2) and nitric oxide, release of cytochrome c from the mitochondrion, accumulation of regulative 14-3-3 proteins in the cytosol and of HSP70 molecular chaperone binding protein in the endoplasmic reticulum, accompanied by marked modifications in the architecture of this cell organelle.

The environmental endocrine disruptor, bisphenol A, affects germination, elicits stress response and alters steroid hormone production in kiwifruit pollen

In vitro toxicity of the endocrine disruptor bisphenol A (BPA) to pollen, the male haploid generation of higher plants, was studied. BPA caused significant inhibition of both tube emergence and elongation of kiwifruit pollen in a dose-dependent manner, beginning at 10 mg · l(-1); morphological changes to tubes were also detected. Despite strong inhibition of pollen tube production and growth, a large percentage of treated cells remained viable. Immunoblotting experiments indicated that levels of BiP and 14-3-3, which are proteins involved in stress response, substantially increased in BPA-treated pollen compared to controls. The increases were dose-dependent in the range 10-50 mg · l(-1) BPA, i.e. even when germination ability was completely blocked. Steroid hormones (17 β-estradiol, progesterone and testosterone) were detected in kiwifruit pollen, and their levels increased during germination in basal medium. In a BPA treatment of 30 mg · l(-1), larger increases in both estrogen and testosterone concentrations were detected, in particular, a six-fold increase of 17 β-estradiol over control concentration (30 min). The increased hormone levels were maintained for at least the 90 min incubation. Increasing concentrations of exogenous testosterone and 17 β-estradiol increasingly inhibited pollen tube emergence and elongation. Current data for BPA-exposed kiwifruit pollen suggest a toxicity mechanism that is at least in part based on a dramatic imbalance of steroid hormone production during tube organisation, emergence and elongation. It may be concluded that BPA, a widespread environmental contaminant, can cause serious adverse effects to essential pollen functions. On a broader scale, this chemical poses a potential risk to the reproductive success of higher plants.

Ethylene is involved in stress responses induced by fusicoccin in sycamore cultured cells

The phytohormone ethylene is involved in many physiological and developmental processes of plants, as well as in stress responses and in the development of disease resistance. Fusicoccin (FC) is a well-known phytotoxin, that in sycamore (Acer pseudoplatanus L.) cultured cells, induces a set of stress responses, including synthesis of ethylene. In this study, we investigated the possible involvement of ethylene in the FC-induced stress responses of sycamore cells by means of Co(2+), a well-known specific inhibitor of ethylene biosynthesis. Co(2+) inhibited the accumulation of dead cells in the culture, the production of nitric oxide (NO) and of the molecular chaperone Binding Protein (BiP) in the endoplasmic reticulum induced by FC. By contrast, Co(2+) was ineffective on the FC-induced accumulation of cells with fragmented DNA, production of H(2)O(2) and release of cytochrome c from the mitochondrion, and only partially reduced the accumulation of regulative 14-3-3 proteins in the cytosol. In addition, we compared the effect of FC on the above parameters with that of the ethylene-releasing compound ethephon (2-chloroethane phosphonic acid). The results suggest that ethylene is involved in several stress responses induced by FC in sycamore cells, including a form of cell death that does not show apoptotic features and possibly involves NO as a signaling molecule.

Devil inside: does plant programmed cell death involve the endomembrane system?

Eukaryotic cells have to constantly cope with environmental cues and integrate developmental signals. Cell survival or death is the only possible outcome. In the field of animal biology, tremendous efforts have been put into the understanding of mechanisms underlying cell fate decision. Distinct organelles have been proven to sense a broad range of stimuli and, if necessary, engage cell death signalling pathway(s). Over the years, forward and reverse genetic screens have uncovered numerous regulators of programmed cell death (PCD) in plants. However, to date, molecular networks are far from being deciphered and, apart from the autophagic compartment, no organelles have been assigned a clear role in the regulation of cellular suicide. The endomembrane system (ES) seems, nevertheless, to harbour a significant number of cell death mediators. In this review, the involvement of this system in the control of plant PCD is discussed in-depth, as well as compared and contrasted with what is known in animal and yeast systems.

Effect of heat stress on actin cytoskeleton and endoplasmic reticulum of tobacco BY-2 cultured cells and its inhibition by Co2+

Temperature stress such as heat, cold, or freezing is a principal cause for yield reduction in crops. In particular, heat stress is very common and dangerous for plants since this stress can impact several plant and cellular functions. In spite of their role in sensing local stress and in controlling fundamental processes including PCD, the responses of cellular structures and organelles to heat stress are poorly investigated. In this work, we investigated the possible changes induced by mild heat stress, medium heat stress, and heat shock (HS; 5 min at 35 degrees C, 45 degrees C, or 50 degrees C, respectively) on actin cytoskeleton and endoplasmic reticulum (ER) of tobacco BY-2 cultured cells. While mild and medium heat stresses are ineffective, HS induces depolymerization of actin microfilaments and changes in ER morphology accompanied by accumulation of the HSP70 binding protein (BiP). These effects of HS are prevented by the inhibitor of ethylene production Co(2+). While the analyzed cell structures do not seem to be involved in the establishment of mild and medium heat stresses at least in this experimental system, the strong modifications induced by the treatment at 50 degrees C suggest that actin cytoskeleton and ER may be involved in the responses to HS. Besides, the inhibiting effect of Co(2+) suggests a role for ethylene as a regulative molecule in the responses to HS here observed.

Programmed cell death of tobacco BY-2 cells induced by still culture conditions is affected by the age of the culture under agitation

Evans Blue staining indicated that actively growing tobacco BY-2 cells in the exponential phase died more rapidly than quiescent cells in the stationary phase when the cells cultured under agitation were placed under still conditions. Fifty percent cell death was induced at about 18, 26, 80 and 140 h for early, mid, late exponential- and stationary-phase cells, respectively. Actively growing cells became TUNEL (transferase-mediated dUTP nick end labelling)-positive more rapidly than quiescent cells, suggesting that the cell death evaluated by Evans Blue is accompanied by DNA cleavages. Electrophoresis of genomic DNA showed a typical 'DNA laddering' pattern formed by multiples of about 200 bp internucleosomal units. Chromatin condensation was first detected at least within 24 h by light microscopy, and then cell shrinkage followed. These findings suggest that the death of BY-2 cells induced by still conditions is PCD (programmed cell death).

The ER luminal binding protein (BiP) mediates an increase in drought tolerance in soybean and delays drought-induced leaf senescence in soybean and tobacco

The ER-resident molecular chaperone BiP (binding protein) was overexpressed in soybean. When plants growing in soil were exposed to drought (by reducing or completely withholding watering) the wild-type lines showed a large decrease in leaf water potential and leaf wilting, but the leaves in the transgenic lines did not wilt and exhibited only a small decrease in water potential. During exposure to drought the stomata of the transgenic lines did not close as much as in the wild type, and the rates of photosynthesis and transpiration became less inhibited than in the wild type. These parameters of drought resistance in the BiP overexpressing lines were not associated with a higher level of the osmolytes proline, sucrose, and glucose. It was also not associated with the typical drought-induced increase in root dry weight. Rather, at the end of the drought period, the BiP overexpressing lines had a lower level of the osmolytes and root weight than the wild type. The mRNA abundance of several typical drought-induced genes [NAC2, a seed maturation protein (SMP), a glutathione-S-transferase (GST), antiquitin, and protein disulphide isomerase 3 (PDI-3)] increased in the drought-stressed wild-type plants. Compared with the wild type, the increase in mRNA abundance of these genes was less (in some genes much less) in the BiP overexpressing lines that were exposed to drought. The effect of drought on leaf senescence was investigated in soybean and tobacco. It had previously been reported that tobacco BiP overexpression or repression reduced or accentuated the effects of drought. BiP overexpressing tobacco and soybean showed delayed leaf senescence during drought. BiP antisense tobacco plants, conversely, showed advanced leaf senescence. It is concluded that BiP overexpression confers resistance to drought, through an as yet unknown mechanism that is related to ER functioning. The delay in leaf senescence by BiP overexpression might relate to the absence of the response to drought.

Extracellular alkaline phosphatase is a sensitive marker for cellular stimulation and exocytosis in heterotroph cell cultures of Chenopodium rubrum

We investigated the response of extracellular phosphatase to heat shock in heterotrophic Chenopodium rubrum L. cell cultures. Surprisingly, in contrast to the generally used acid phosphatase, an extracellular alkaline phosphatase showed the most sensitive response. This phosphatase was characterized as a marker for cellular stimulation by its high correlations with induced changes of extracellular pH: 10microM nigericin (correlation coefficient r=0.91), 100microM salicylic acid (r=0.84), heat shock 5min 37 degrees C (r=0.79), and heat shock after pre-treatment with 5microM fusicoccin (r=0.92) or 0.5% ethanol (r=0.90). Cellular stimulation was estimated with concentrations of acids and bases, yielding similar levels of pH change (0.5 pH) in cell-free supernatant: salicylic acid (200microM), benzoic acid (600microM), HCl (140microM), NaOH (100microM), and KOH (100microM). The Golgi apparatus inhibitor Brefeldin A (200microM) reduced the heat-shock-induced phosphatase (-33%). The pH optimum of heat-shock-induced phosphatase was 3; however, there the proportion of constitutive phosphatase was higher than at pH 8-9.5, indicating different pH dependence of constitutive and induced activity. Thus, heat-shock-induced phosphatase was characterized by alkaline activity with inhibitors (10microM molybdate: -52%, 2.5mM phosphate: -64%, 10microM ZnCl(2): -82%), substrates (2.5mM, tyrosine phosphate: 255pkat g(-1), p-nitrophenyl phosphate: 92pkat g(-1), serine phosphate: 0, threonine phosphate: 0), Hill coefficient (nH=1.4) indicating two binding sites, and the extent of heat-shock stimulation (p-nitrophenyl phosphate: +190%, tyrosine phosphate: +180%). SDS-PAGE showed a correlation of alkaline phosphatase with the heat-shock-induced release of highly N-glycosylated 53kDa protein, detected by peroxidase-labeled concanavalin A affinoblotting after endoglycosidase H treatment. The 53kDa protein showed no in-gel phosphatase activity after SDS-PAGE and regeneration treatment, in contrast to a putative dimer (105kDa).

Inhibitors of protein glycosylation or secretion change the pattern of extracellular proteins in suspension-cultured cells of Arabidopsis thaliana

Cell walls are essential for plant development and morphogenesis. The majority of wall proteins are glycosylated, either as N- or O-glycans. Various inhibitors of glycosylation and secretion are used to determine the importance of wall proteins for the functioning of the walls. Tunicamycin is an inhibitor of the first enzyme in the N-glycosylation pathway, 3,4-dehydroproline inhibits peptidyl proline hydroxylation, and Brefeldin A is an inhibitor of vesicle trafficking, disrupting the delivery of wall polymers to the apoplast. In inhibitor-treated suspension-cultured Arabidopsis thaliana cells, qualitative and quantitative differences in the extracellular proteome were observed for both proteins secreted into medium or ionically-bound in the walls. Lack of O-glycosylation resulted in the selective protein loss from the extracellular compartments. Following tunicamycin treatment the secretion of additional proteins as well as ER-resident chaperones from the Hsp70 and Hsp90 families outside the protoplasts was noted. Moreover, changes in the proteolytic degradation pattern of culture filtrate proteins were also observed. Application of Brefeldin A resulted in transient and selective loss of individual proteins from the extracellular compartments of A. thaliana cell suspension. We conclude that post-translational modifications are vital for the proper functioning of wall proteins. N-glycosylation is crucial for their proper folding and stability. Extracellular compartments could also serve as a sink for improperly folded proteins during the unfolded protein response.

A new branch of endoplasmic reticulum stress signaling and the osmotic signal converge on plant-specific asparagine-rich proteins to promote cell death

NRPs (N-rich proteins) were identified as targets of a novel adaptive pathway that integrates endoplasmic reticulum (ER) and osmotic stress signals based on coordinate regulation and synergistic up-regulation by tunicamycin and polyethylene glycol treatments. This integrated pathway diverges from the molecular chaperone-inducing branch of the unfolded protein response (UPR) in several ways. While UPR-specific targets were inversely regulated by ER and osmotic stresses, NRPs required both signals for full activation. Furthermore, BiP (binding protein) overexpression in soybean prevented activation of the UPR by ER stress inducers, but did not affect activation of NRPs. We also found that this integrated pathway transduces a PCD signal generated by ER and osmotic stresses that result in the appearance of markers associated with leaf senescence. Overexpression of NRPs in soybean protoplasts induced caspase-3-like activity and promoted extensive DNA fragmentation. Furthermore, transient expression of NRPs in planta caused leaf yellowing, chlorophyll loss, malondialdehyde production, ethylene evolution, and induction of the senescence marker gene CP1. This phenotype was alleviated by the cytokinin zeatin, a potent senescence inhibitor. Collectively, these results indicate that ER stress induces leaf senescence through activation of plant-specific NRPs via a novel branch of the ER stress response.

Dolichol biosynthesis and its effects on the unfolded protein response and abiotic stress resistance in Arabidopsis

Dolichols are long-chain unsaturated polyisoprenoids with multiple cellular functions, such as serving as lipid carriers of sugars used for protein glycosylation, which affects protein trafficking in the endoplasmic reticulum. The biological functions of dolichols in plants are largely unknown. We isolated an Arabidopsis thaliana mutant, lew1 (for leaf wilting1), that showed a leaf-wilting phenotype under normal growth conditions. LEW1 encoded a cis-prenyltransferase, which when expressed in Escherichia coli catalyzed the formation of dolichol with a chain length around C(80) in an in vitro assay. The lew1 mutation reduced the total plant content of main dolichols by approximately 85% and caused protein glycosylation defects. The mutation also impaired plasma membrane integrity, causing electrolyte leakage, lower turgor, reduced stomatal conductance, and increased drought resistance. Interestingly, drought stress in the lew1 mutant induced higher expression of the unfolded protein response pathway genes BINDING PROTEIN and BASIC DOMAIN/LEUCINE ZIPPER60 as well as earlier expression of the stress-responsive genes RD29A and COR47. The lew1 mutant was more sensitive to dark treatment, but this dark sensitivity was suppressed by drought treatment. Our data suggest that LEW1 catalyzes dolichol biosynthesis and that dolichol is important for plant responses to endoplasmic reticulum stress, drought, and dark-induced senescence in Arabidopsis.

Role of nitric oxide in actin depolymerization and programmed cell death induced by fusicoccin in sycamore (Acer pseudoplatanus) cultured cells

Programmed cell death (PCD) plays a vital role in plant development and is involved in defence mechanisms against biotic and abiotic stresses. Different forms of PCD have been described in plants on the basis of the cell organelle first involved. In sycamore (Acer pseudoplatanus L.) cultured cells, the phytotoxin fusicoccin (FC) induces cell death. However, only a fraction of the dead cells shows the typical hallmarks of animal apoptosis, including cell shrinkage, chromatin condensation, DNA fragmentation and release of cytochrome c from the mitochondrion. In this work, we show that the scavenging of nitric oxide (NO), produced in the presence of FC, by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) and rutin inhibits cell death without affecting DNA fragmentation and cytochrome c release. In addition, we show that FC induces a massive depolymerization of actin filaments that is prevented by the NO scavengers. Finally, the addition of actin-depolymerizing drugs induces PCD in control cells and overcomes the inhibiting effect of cPTIO on FC-induced cell death. Vice versa, the addition of actin-stabilizing drugs to FC-treated cells partially inhibits the phytotoxin-induced PCD. These results suggest that besides an apoptotic-like form of PCD involving the release of cytochrome c, FC induces at least another form of cell death, likely mediated by NO and independent of cytochrome c release, and they make it tempting to speculate that changes in actin cytoskeleton are involved in this form of PCD.

Cellular response to unfolded proteins in the endoplasmic reticulum of plants

Secretory and transmembrane proteins are synthesized in the endoplasmic reticulum (ER) in eukaryotic cells. Nascent polypeptide chains, which are translated on the rough ER, are translocated to the ER lumen and folded into their native conformation. When protein folding is inhibited because of mutations or unbalanced ratios of subunits of hetero-oligomeric proteins, unfolded or misfolded proteins accumulate in the ER in an event called ER stress. As ER stress often disturbs normal cellular functions, signal-transduction pathways are activated in an attempt to maintain the homeostasis of the ER. These pathways are collectively referred to as the unfolded protein response (UPR). There have been great advances in our understanding of the molecular mechanisms underlying the UPR in yeast and mammals over the past two decades. In plants, a UPR analogous to those in yeast and mammals has been recognized and has recently attracted considerable attention. This review will summarize recent advances in the plant UPR and highlight the remaining questions that have yet to be addressed.

Both trivalent and hexavalent chromium strongly alter in vitro germination and ultrastructure of kiwifruit pollen

Due to its widespread industrial use, chromium is considered a dangerous environmental pollutant. It is known to inhibit plant growth and development. The present study provides the first evidence of the toxicity of this metal on the male haploid generation of a higher plant. Both Cr(III) and Cr(VI) species, supplied as CrCl(3) and CrO(3), respectively, exerted a strong dose-dependent inhibitory effect on kiwifruit pollen tube emergence and growth. Cr(III) resulted more effective than Cr(VI) in the 16-75microM interval; moreover, complete inhibition of germination was attained at much lower doses than Cr(VI). Also tube morphology was affected. While the plasma membrane was still undamaged in the large majority of the treated pollen grains, dramatic ultrastructural alterations were induced by chromium including chromatin condensation, swelling of mitochondria, cytoplasmic vacuolization, and perturbed arrangement of endoplasmic reticulum cisternae. Thus, it seems that the impact of the two chromium species on kiwifruit pollen may result in severe compromission of both essential structures and functions of the male gametophyte.

Cyclosporin A inhibits programmed cell death and cytochrome c release induced by fusicoccin in sycamore cells

Programmed cell death plays a vital role in normal plant development, response to environmental stresses, and defense against pathogen attack. Different types of programmed cell death occur in plants and the involvement of mitochondria is still under investigation. In sycamore (Acer pseudoplatanus L.) cultured cells, the phytotoxin fusicoccin induces cell death that shows apoptotic features, including chromatin condensation, DNA fragmentation, and release of cytochrome c from mitochondria. In this work, we show that cyclosporin A, an inhibitor of the permeability transition pore of animal mitochondria, inhibits the cell death, DNA fragmentation, and cytochrome c release induced by fusicoccin. In addition, we show that fusicoccin induces a change in the shape of mitochondria which is not prevented by cyclosporin A. These results suggest that the release of cytochrome c induced by fusicoccin occurs through a cyclosporin A-sensitive system that is similar to the permeability transition pore of animal mitochondria and they make it tempting to speculate that this release may be involved in the phytotoxin-induced programmed cell death of sycamore cells.