1,2-Dioctanoylglycerol accelerates or retards mitotic progression in Tradescantia stamen hair cells as a function of the time of its addition

Phospholipase C signaling involvement in macrotubule assembly and activation of the mechanism regulating protoplast volume in plasmolyzed root cells of Triticum turgidum

The role of phosphoinositide-specific phospholipase C (PI-PLC) signaling in the macrotubule-dependent protoplast volume regulation in plasmolyzed root cells of Triticum turgidum was investigated. At the onset of hyperosmotic stress, PI-PLC activation was documented. Inhibition of PI-PLC activity by U73122 blocked tubulin macrotubule formation in plasmolyzed cells and their protoplast volume regulatory mechanism. In neomycin-treated plasmolyzed cells, macrotubule formation and protoplast volume regulation were not affected. In these cells the PI-PLC pathway is down-regulated as neomycin sequesters the PI-PLC substrate, 4,5-diphosphate-phosphatidyl inositol (PtdInsP(2)). These phenomena were unaffected by R59022, an inhibitor of phosphatidic acic (PA) production via the PLC pathway. Taxol, a microtubule (MT) stabilizer, inhibited the hyperosmotic activation of PI-PLC, but oryzalin, which disorganized MTs, triggered PI-PLC activity. Taxol prevented macrotubule formation and inhibited the mechanism regulating the volume of the plasmolyzed protoplast. Neomycin partly relieved some of the taxol effects. These data suggest that PtdInspP(2) turnover via PI-PLC assists macrotubule formation and activation of the mechanism regulating the plasmolyzed protoplast volume; and the massive disorganization of MTs that is carried out at the onset of hyperosmotic treatment triggers the activation of this mechanism.

When microspores decide to become embryos — cellular and molecular changesThis review is one of a selection of papers published in the Special Issue on Plant Cell Biology

Cultured microspores can be induced to develop into fully functional haploid embryos instead of mature pollen. The ability of these cells to change their development in response to environmental stimuli is an exceptional example of totipotency in plants. Discovering the triggers of embryo development in microspore cultures could lead to a greater understanding of the early stages of embryogenesis in plants and might be used to increase the range of crop plants to which microspore culture can be applied for the production of double haploid homozygous lines. The information might also help to define the general characteristics of pluripotent cells in any organism. In this review, the changes that occur in cellular organization and gene expression in early-stage microspore cultures of several species are discussed. Responding cells in these cultures enlarge, their nuclei are repositioned to their cell centres, and their cytoplasms become filled with fragmented vacuoles. We used flow cytometry to track cellular changes in canola ( Brassica napus L.) microspore cultures as well as microarray analyses and real-time PCR to compare gene expression in embryogenic and nonembryogenic cells. A model for embryogenic cell activation in plants that involves alkalinization, Ca2+ signaling, and changes in GTPase activity that lead to significant changes in gene expression is discussed.

Abscisic acid signal transduction in the barley aleurone is mediated by phospholipase D activity

The plant hormones abscisic acid (ABA) and gibberellic acid (GA) are important regulators of the dormancy and germination of seeds. In cereals, GA enhances the synthesis and secretion of enzymes (principally alpha-amylases) in the aleurone cells of the endosperm, which then mobilize the storage reserves that fuel germination. ABA inhibits this enhanced secretory activity and delays germination. Despite the central role of ABA in regulating germination, the signal transduction events leading to altered gene expression and cellular activity are essentially unknown. We report that the application of ABA to aleurone protoplasts increased the activity of the enzyme phospholipase D (PLD) 10 min after treatment. The product of PLD activity, phosphatidic acid (PPA), also increased transiently at this time. The application of PPA to aleurone protoplasts led to an ABA-like inhibition of alpha-amylase production, and induction of the ABA up-regulated proteins ASI (amylase subtilisin inhibitor) and RAB (responsive to ABA). Inhibition of PLD activity by 0.1% 1-butanol during the initial 20 min of ABA treatment resulted in inhibition of ABA-regulated processes. This inhibition coincided with the timing of PLD activation by ABA and was overcome by simultaneous addition of PPA. These results suggest that ABA activates the enzyme PLD to produce PPA that is involved in triggering the subsequent ABA responses of the aleurone cell.

The plant phosphoinositide system

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Bombesin impairs spindle function in mitotic V79 Chinese hamster cells by a receptor-dependent mechanism

Bombesin belongs to a family of peptides acting as local hormones with roles in growth regulation, neural function and secretion. Upon binding to its receptor bombesin primarily elicits an increase of inositolphosphates and diacylglycerol, events leading to increased [Ca2+]i and activation of protein kinase C. When asynchronously growing V79 Chinese hamster cells were treated with bombesin in the 10(-9)-10(-7) M concentration range their content of inositolphosphates increased and so did the frequency of mitotic cells with abnormal chromosomal arrangements (c-mitoses). Both effects were abolished by simultaneous addition of the synthetic peptide antagonist D-Arg1,D-Phe5,D-Trpu7,9-Leu11-substance P that binds to certain bombesin receptors. These results demonstrate that the V79 cells most probably have receptors for bombesin and that the weak but significant c-mitotic effect is mediated by such receptors.