calcimycin and propionic-acid

Self-incompatibility (SI) is an important genetically controlled mechanism to prevent inbreeding in higher plants. SI involves highly specific interactions during pollination, resulting in the rejection of incompatible (self) pollen. Programmed cell death (PCD) is an important mechanism for destroying cells in a precisely regulated manner. SI in field poppy (Papaver rhoeas) triggers PCD in incompatible pollen. During SI-induced PCD, we previously observed a major acidification of the pollen cytosol. Here, we present measurements of temporal alterations in cytosolic pH ([pH]cyt); they were surprisingly rapid, reaching pH 6.4 within 10 min of SI induction and stabilizing by 60 min at pH 5.5. By manipulating the [pH]cyt of the pollen tubes in vivo, we show that [pH]cyt acidification is an integral and essential event for SI-induced PCD. Here, we provide evidence showing the physiological relevance of the cytosolic acidification and identify key targets of this major physiological alteration. A small drop in [pH]cyt inhibits the activity of a soluble inorganic pyrophosphatase required for pollen tube growth. We also show that [pH]cyt acidification is necessary and sufficient for triggering several key hallmark features of the SI PCD signaling pathway, notably activation of a DEVDase/caspase-3-like activity and formation of SI-induced punctate actin foci. Importantly, the actin binding proteins Cyclase-Associated Protein and Actin-Depolymerizing Factor are identified as key downstream targets. Thus, we have shown the biological relevance of an extreme but physiologically relevant alteration in [pH]cyt and its effect on several components in the context of SI-induced events and PCD.

Topics: Actins; Apoptosis; Calcimycin; Calcium; Caspase 3; Cytosol; Hydrogen-Ion Concentration; Inorganic Pyrophosphatase; Ionophores; Papaver; Peptide Hydrolases; Plant Proteins; Pollen Tube; Propionates; Self-Incompatibility in Flowering Plants; Solubility; Vacuoles

The relationship between the chemotactic-factor-elicited changes in the intracellular pH and the shape of human neutrophils was investigated using simultaneous measurements of both parameters. The results demonstrate first that fMet-Leu-Phe and leukotriene B4 elicit qualitatively similar pH and shape change responses from the neutrophils. A relationship between the chemoattractant-elicited decrease in cytoplasmic pH and the shape changes is indicated by several findings including: 1) the similarities in the time courses of the two responses, 2) the ability of propionic acid to induce a transient and pertussis-toxin-sensitive shape change response, and 3) the ability of the calcium ionophore A23187 to similarly induce both responses under conditions when the degranulation is minimized. On the other hand, several other results indicate that the drop in pH is not a sufficient condition for the chemotactic-factor-stimulated shape changes. These include: 1) the ability of pertussis toxin to inhibit the shape changes induced by propionic acid and by A23187 without affecting the drop in pH, and 2) the observation that the drop in pH induced by propionic acid persists significantly longer than the shape change. Increasing the cytoplasmic pH by adding ammonium chloride was also found to cause shape changes in the neutrophils. The response to the base differs in two important aspects from that caused by propionic acid: it is pertussis-toxin-insensitive, and it is long-lived. Chemotactic factors have been found to induce a shape change under conditions when the internal pH was artificially increased or decreased, indicating that it is not the absolute cytoplasmic pH that represents the internal signalling parameter. The results are discussed in terms of the activation of the cytoskeletal network of the neutrophils by chemotactic factors.

Topics: Ammonium Chloride; Calcimycin; Calcium; Chemotactic Factors; Chemotaxis, Leukocyte; Humans; Hydrogen-Ion Concentration; Leukotriene B4; N-Formylmethionine Leucyl-Phenylalanine; Neutrophils; Pertussis Toxin; Propionates; Sodium; Virulence Factors, Bordetella