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This paper considers the problem of allocating pushback times to departing aircraft, specifying the time 1 at which they will be given permission to push back from their allocated stand, [...]

An unusual form of leaf morphogenesis occurs in the aquatic, lace plant, Aponogeton madagascariensis (Aponogetonaceae). Early in development, discrete patches of cells undergo programmed cell death (PCD) and form perforations during leaf expansion. In addition to the protoplasts, walls of the dying cells are degraded during PCD. The cuticle of the perforation site is eroded first, followed by dissolution of cell wall matrix components, so that walls appear as loose fibrillar networks as perforations form. Gel diffusion assays of wall-degrading enzyme activity indicated that pectinases are active throughout leaf development, while cellulase activity was restricted to early stages of perforation formation. Alcian blue staining showed that degrading walls remain rich in pectin, and immunolocalization of pectin epitopes indicated that the proportions of esterified and de-esterifed pectins do not change significantly. Walls of perforation border cells are modified by suberin deposition late in development, and reactive oxygen species, thought to have a role in polymerization of phenolin suberin monomers, are present at the same stage. This timing suggests that suberization may limit the spread of PCD and provide an apoplastic barrier against microbial invasion but does not initiate PCD. Key words: Aponogeton; cell wall degradation; cellulose; lace plant; pectin; pectinase; programmed cell death; suberin.

Although London Heathrow is one of the busiest airports in the world, it has only one runway for use by departing aircraft at any time. Separations are required between each [...]

Abstract: Programmed cell death (PCD) is a requisite, genetically controlled process in plants resulting in the death of particular cells and tissues and the recycling of the cellular constituents back [...]

Abstract: Cysteine proteinases are ubiquitously involved in programmed cell death (PCD) in multicellular organisms. In animals, one group of cysteine proteinases, the cysteine-dependent aspartate-specific proteinases (caspases), are involved in a [...]

The ricinosome (precursor protease vesicle) is an organelle found exclusively in plant cells. Ricinosomes contain a 45-kDa pro-cysteine endopeptidase (CysEP) with a C-terminal KDEL endoplasmic reticulum retention signal. CysEP is a member of a unique group of papain-type cysteine peptidases found specifically in senescing and ricinosome-containing tissues. During seed development in the castor oil plant (Ricinus communis L.), the cells of the nucellus are killed as the major seed storage organ, the cellular endosperm, expands and begins to accumulate reserves. The destruction of the maternal seed tissues is a developmentally programmed cell death. Terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling revealed that nuclear DNA fragmentation occurs in the nucellar cells adjacent to the expanding endosperm. These cells exhibit ultrastructural features consistent with programmed cell death, including vesiculation of the cytosol, development of irregularly shaped nuclei, vacuolar collapse, and shrinkage of the cytoplasm. Ricinosomes containing the CysEP were identified in the nucellar cells by light and electron microscopy and immunocyto-chemistry. Both proCysEP and mature CysEP are present in protein extracts of the nucellar tissues during seed development. Upon collapse of the nucellar cells, the content of the ricinosomes is released into the cytoplasm, where the activated CysEP digests the remaining proteinaceous cellular debris. Digestion products of the nucellar cells are presumed taken up by the outermost cells of the endosperm, which have labyrinthine ingrowths of the outer walls typical of transfer cells. castor bean | papain-type KDEL peptidase | seed maturation