Project description:Arabidopsis thaliana cell suspension cultures (ACSC) were subjected to 30-min, mild chemical treatments with three different singlet oxygen elicitors at low-medium light conditions (150 µE m–2 s–1) with the aim of getting a better understanding of singlet oxygen-mediated defence responses in plants. The three elicitors Indigo Carmine (IC), Methylene Violet (MV) and Rose Bengal (RB) at a concentration of 0.5 µM were chosen because they exhibited different abilities to permeate the plasma membrane and to accumulate in the cell soma or organelles such as chloroplasts. In addition, ACSC were treated with 500 µM H2O2 for comparison. Confocal image analysis of Arabidopsis cells revealed that IC was not retained in cells, whereas MV and RB permeated the plasma membrane and accumulated in the chloroplast envelope and inside chloroplasts, respectively. As a consequence of their different cellular location, the physiological, transcriptional and photosynthetic responses of Arabidopsis cells to singlet oxygen production varied from each other and the activation of programmed cell death (PCD) was observed in ACSC treated with 0.5 µM RB, but not with the other elicitor nor with 500 µM H2O2. The role of chloroplasts in the activation of PCD was further investigated when this physiological response was analyzed in dark-grown cell cultures containing undifferentiated plastids. Interestingly, PCD was only activated in light-grown, but not in dark-grown, Arabidopsis cell cultures, suggesting that singlet oxygen-mediated defence responses were initiated inside chloroplasts. Genome-wide transcriptional profile analyses were performed as well and the results proved that there were only statistically significant changes in the transcript expression of light-grown ACSC treated with 0.5 µM RB and 500 µM H2O2, but not with IC nor with MV. Functional enrichment analyses revealed that GO/Biological process terms associated with defence responses were common in the treatments with 0.5 µM RB and 500 µM H2O2; however, resistance response to pathogen and PCD terms were only significantly over-represented in the RB treatment. Moreover, the analysis of the up-regulated transcripts in ACSC treated with 0.5 µM RB brought out that both specific markers for singlet oxygen from the conditional fluorescence (flu) mutant of Arabidopsis and transcripts with a key role in hormone-activated PCD (i.e. ethylene and jasmonic acid) were present, although there was no evidence for the up-regulation of EDS1 encoding the ENHANCED DISEASE SUSCEPTIBILITY PROTEIN 1. Finally, a co-regulation analysis proved that ACSC treated with 0.5 µM RB exhibited higher correlation with the flu family mutants than with other singlet oxygen producer mutants of Arabidopsis or wild-type plants of Arabidopsis subjected to high light treatments, where singlet oxygen was produced in photosystem II and an acclimatory response was activated instead of PCD.

Project description:Arabidopsis thaliana cell suspension cultures (ACSC) were subjected to 30-min, mild chemical treatments with three different singlet oxygen elicitors at low-medium light conditions (150 µE m–2 s–1) with the aim of getting a better understanding of singlet oxygen-mediated defence responses in plants. The three elicitors Indigo Carmine (IC), Methylene Violet (MV) and Rose Bengal (RB) at a concentration of 0.5 µM were chosen because they exhibited different abilities to permeate the plasma membrane and to accumulate in the cell soma or organelles such as chloroplasts. In addition, ACSC were treated with 500 µM H2O2 for comparison. Confocal image analysis of Arabidopsis cells revealed that IC was not retained in cells, whereas MV and RB permeated the plasma membrane and accumulated in the chloroplast envelope and inside chloroplasts, respectively. As a consequence of their different cellular location, the physiological, transcriptional and photosynthetic responses of Arabidopsis cells to singlet oxygen production varied from each other and the activation of programmed cell death (PCD) was observed in ACSC treated with 0.5 µM RB, but not with the other elicitor nor with 500 µM H2O2. The role of chloroplasts in the activation of PCD was further investigated when this physiological response was analyzed in dark-grown cell cultures containing undifferentiated plastids. Interestingly, PCD was only activated in light-grown, but not in dark-grown, Arabidopsis cell cultures, suggesting that singlet oxygen-mediated defence responses were initiated inside chloroplasts. Genome-wide transcriptional profile analyses were performed as well and the results proved that there were only statistically significant changes in the transcript expression of light-grown ACSC treated with 0.5 µM RB and 500 µM H2O2, but not with IC nor with MV. Functional enrichment analyses revealed that GO/Biological process terms associated with defence responses were common in the treatments with 0.5 µM RB and 500 µM H2O2; however, resistance response to pathogen and PCD terms were only significantly over-represented in the RB treatment. Moreover, the analysis of the up-regulated transcripts in ACSC treated with 0.5 µM RB brought out that both specific markers for singlet oxygen from the conditional fluorescence (flu) mutant of Arabidopsis and transcripts with a key role in hormone-activated PCD (i.e. ethylene and jasmonic acid) were present, although there was no evidence for the up-regulation of EDS1 encoding the ENHANCED DISEASE SUSCEPTIBILITY PROTEIN 1. Finally, a co-regulation analysis proved that ACSC treated with 0.5 µM RB exhibited higher correlation with the flu family mutants than with other singlet oxygen producer mutants of Arabidopsis or wild-type plants of Arabidopsis subjected to high light treatments, where singlet oxygen was produced in photosystem II and an acclimatory response was activated instead of PCD. 18 Samples total. Six Samples are controls, 3 Samples each treated with Rose Bengal, Hydrogen Peroxide, Methyl Violet, and Indigo Carmine.

Project description:BACKGROUND:Thaxtomin A (TA) is a natural cellulose biosynthesis inhibitor (CBI) synthesized by the potato common scab-causing pathogen Streptomyces scabies. Inhibition of cellulose synthesis by TA compromises cell wall organization and integrity, leading to the induction of an atypical program of cell death (PCD). These processes may facilitate S. scabies entry into plant tissues. To study the mechanisms that regulate the induction of cell death in response to inhibition of cellulose synthesis, we used Arabidopsis thaliana cell suspension cultures treated with two structurally different CBIs, TA and the herbicide isoxaben (IXB). RESULTS:The induction of cell death by TA and IXB was abrogated following pretreatment with the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) and the natural auxin indole-3-acetic acid (IAA). The addition of auxin efflux inhibitors also inhibited the CBI-mediated induction of PCD. This effect may be due to intracellular accumulation of auxin. Auxin has a wide range of effects in plant cells, including a role in the control of cell wall composition and rigidity to facilitate cell elongation. Using Atomic Force Microscopy (AFM)-based force spectroscopy, we found that inhibition of cellulose synthesis by TA and IXB in suspension-cultured cells decreased cell wall stiffness to a level slightly different than that caused by auxin. However, the cell wall stiffness in cells pretreated with auxin prior to CBI treatment was equivalent to that of cells treated with auxin only. CONCLUSIONS:Addition of auxin to Arabidopsis cell suspension cultures prevented the TA- and IXB-mediated induction of cell death. Cell survival was also stimulated by inhibition of polar auxin transport during CBI-treatment. Inhibition of cellulose synthesis perturbed cell wall mechanical properties of Arabidopsis cells. Auxin treatment alone or with CBI also decreased cell wall stiffness, showing that the mechanical properties of the cell wall perturbed by CBIs were not restored by auxin. However, since auxin's effects on the cell wall stiffness apparently overrode those induced by CBIs, we suggest that auxin may limit the impact of CBIs by restoring its own transport and/or by stabilizing the plasma membrane - cell wall - cytoskeleton continuum.

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Programmed cell death activated by Rose Bengal in Arabidopsis thaliana cell suspension cultures requires functional chloroplasts.

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Programmed cell death activated by Rose Bengal in Arabidopsis thaliana cell suspension cultures requires functional chloroplasts.

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