Effect of Ca2+ on programmed death of guard and epidermal cells of pea leaves

Mitochondria-targeted quinones suppress the generation of reactive oxygen species, programmed cell death and senescence in plants

This work focuses on the effect of mitochondria-targeted quinones (SkQs) on plants. SkQs with antioxidant properties are accumulated in the mitochondria of pea cells and suppress the generation of reactive oxygen species. At nanomolar concentrations, SkQs prevented the death of pea leaf epidermal or guard cells caused by chitosan, bacterial lipopolysaccharide or KCN. The protective effect of SkQs was removed by a protonophoric uncoupler. SkQs at micromolar concentrations inhibited the O2 evolution by illuminated chloroplasts and stimulated the respiration of mitochondria. SkQs slowed down the senescence and the death of Arabidopsis thaliana leaves and improved the wheat crop structure.

Plant cell death caused by fungal, bacterial, and viral elicitors: protective effect of mitochondria-targeted quinones

Chitosan (partially deacetylated chitin), a component of fungal cell walls, caused epidermal cell (EC) death in the leaves of pea (Pisum sativum L.) and tobacco Nicotiana tabacum or Nicotiana benthamiana detected by destruction of cell nuclei. The mitochondria-targeted quinone SkQ1 prevented the destruction of EC nuclei induced by chitosan. Chitosan increased and SkQ1 suppressed the activity of protein kinases in N. benthamiana and P. sativum and eliminated the effect of chitosan. Chitosan induced the generation of reactive oxygen species (ROS) in the guard cells (GC) of pea plants. Treatment with chitosan or H2O2 did not cause destruction of GC nuclei; however, it resulted in disruption of the permeability barrier of the plasma membrane detected by propidium iodide fluorescence. Treatment with bacterial lipopolysaccharide but not peptidoglycan caused destruction of pea EC nuclei, which was prevented by SkQ1. Leaves of tobacco plants containing the N gene responsible for resistance to tobacco mosaic virus (TMV) were infiltrated with Agrobacterium tumefaciens cells. These cells contained a genetic construct with the gene of the helicase domain of TMV replicase (p50); its protein product p50 is a target for the N-gene product. As a result, the hypersensitive response (HR) was initiated. The HR manifested itself in the death of leaves and was suppressed by SkQ3. Treatment of tobacco epidermal peels with the A. tumefaciens cells for the p50 gene expression stimulated the destruction of EC nuclei, which was inhibited by SkQ1 or SkQ3. The p50-lacking A. tumefaciens cells did not induce the destruction of EC nuclei. The protective effect of mitochondria-targeted antioxidants SkQ1 and SkQ3 demonstrates the involvement of mitochondria and their ROS in programmed cell death caused by pathogen elicitors.

Dual Role of Hydrogen Peroxide in Arabidopsis Guard Cells in Response to Sulfur Dioxide

Sulfur dioxide (SO2) is a major air pollutant and has significant impacts on plant physiology. Plant can adapt to SO2 stress by controlling stomatal movement, gene expression, and metabolic changes. Here we show clear evidences that SO2-triggered hydrogen peroxide (H2O2) production mediated stomatal closure and cell death in Arabidopsis leaves. High levels of SO2 caused irreversible stomatal closure and decline in guard cell viability, but low levels of SO2 caused reversible stomatal closure. Exogenous antioxidants ascorbic acid (AsA) and catalase (CAT) or Ca2+ antagonists EGTA and LaCl3 blocked SO2-induced stomatal closure and decline in viability. AsA and CAT also blocked SO2-induced H2O2 and [Ca2+]cyt elevation. However, EGTA and LaCl3 inhibited SO2-induced [Ca2+]cyt increase but did not suppress SO2-induced H2O2 elevation. These results indicate that H2O2 elevation triggered stomatal closure and cell death via [Ca2+]cyt signaling in SO2-stimulated Arabidopsis guard cells. NADPH oxidase inhibitor DPI blocked SO2-induced cell death but not the stomatal closure triggered by low levels of SO2, indicating that NADPH oxidase-dependent H2O2 production plays critical role in SO2 toxicity but is not necessary for SO2-induced stomatal closure. Our results suggest that H2O2 production and accumulation in SO2-stimulated plants trigger plant adaptation and toxicity via reactive oxygen species mediating Ca2+ signaling.

Sulfur dioxide induced programmed cell death in Vicia guard cells

Sulfur dioxide (SO(2)) induced nuclear condensation and nuclear fragmentation and rapid loss of guard cell viability in detached epidermis of Vicia leaves at concentrations of 1 mM and higher (3 h exposure). Caspase inhibitors Z-Asp-CH(2)-DCB (0.1 mM) and TLCK (0.1 mM) markedly suppressed SO(2)-induced cell death. The typical nuclear morphological changes and the inhibition effects of caspase inhibitors suggest the activation of a programmed cell death (PCD) pathway. SO(2)-induced cell death can be blocked by either antioxidants (0.1 mM AsA or 200 U/mL CAT) or Ca(2+) antagonists (0.1mM EGTA or LaCl(3)). AsA and CAT also blocked SO(2)-induced ROS production and [Ca(2+)](cyt) increase. However, EGTA and LaCl(3) can inhibit SO(2)-induced [Ca(2+)](cyt) increase, but cannot suppress SO(2)-induced ROS production. Our results indicate that high concentrations of SO(2) induce guard cell death via a PCD pathway through ROS mediating [Ca(2+)](cyt) elevation, which causes harmful effects to plants.

Programmed cell death in plants: protective effect of tetraphenylphosphonium and tetramethylrhodamine cations used as transmembrane quinone carriers

Tetraphenylphosphonium (TPP(+)) and tetramethylrhodamine ethyl ester (TMRE(+)) cations used as transmembrane carriers of ubiquinone (MitoQ) and plastoquinone (SkQ, SkQR) in mitochondria prevented at nanomolar concentrations the chitosan- or H(2)O(2)-induced destruction of the nucleus in epidermal cells of epidermis isolated from pea leaves. The protective effect of the cations was potentiated by palmitate. Penetrating anions of tetraphenylboron (TB(-)) and phenyl dicarbaundecaborane also displayed protective effects at micromolar concentrations; the effect of TB(-) was potentiated by NH(4)Cl. It is proposed that the protective effect of the penetrating cations and anions against chitosan is due to suppression of the generation of reactive oxygen species in mitochondria as a result of the protonophoric effect of the cations plus fatty acids and the anions plus NH(4)(+). Phenol was suitable as the electron donor for H2O2 reduction catalyzed by horseradish peroxidase, preventing the destruction of cell nuclei. The penetrating cations and anions, SkQ1, and SkQR1 did not maintain the peroxidase or peroxidase/oxidase reactions measured by their suitability as electron donors for H(2)O(2) reduction or by the oxidation of exogenous NADH.