Programmed cell death of the nucellus during Sechium edule SW seed development is associated with activation of gaspase-like proteases

The nucellus is a maternal tissue that embeds and feeds the developing embryo and secondary endosperm. During seed development, the cells of the nucellus suffer a degenerative process soon after fertilization as the cellular endosperm expands and accumulates reserves. Nucellar cell degeneration has been considered to be a form of developmentally programmed cell death (PCD). It was investigated whether or not this degenerative process is characterized by apoptotic hallmarks. Evidence showed that cell death is mostly localized in the border region of the tissue adjacent to the expanding endosperm. Cell death is accompanied by profound changes in the morphology of the nuclei and by a huge degradation of nuclear DNA. Moreover, an increase of activity of different classes of proteinases is reported, and the induction of caspase-like proteases sensitive to specific inhibitors was detected. Nucellar caspase-like proteases are characterized by an acid pH optimum suggesting a possible localization in the vacuole

Hydrolysis of gliadin during germination of wheat seeds

The in vivo degradation of gliadin has been studied using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and reversed-phase high performance liquid chromatography. Both analyses show the appearance of a small number of degradation products and the early disappearance of some gliadin components during the course of germination. These components thus appear to be subject to preferential breakdown, the w-gliadin fraction being the first to be degraded. The in vitro degradation of total gliadin or selected gliadin fractions, performed by the main endopeptidase appearing during wheat germination, reveals a transient accumulation of intermediates, which were subsequently degraded to small peptides. These data suggest that the relatively small amount of intermediates formed during wheat germination might be due to the concerted action of the cysteine proteinase and of the carboxypeptidases. Since these enzymes have high activities during the course of seed germination, they might cause a rapid degradation of intermediates before they can accumulat

Changes in Histones/DNA Ratio in Scutellum Nuclei During Ageing of Triticum Durum

SUMMARYColumnar epithelium and parenchyma cells of the scutellum of Triticum durum caryopses show different quiescence models: while epithelium cells display a DNA content per nucleus of 2C, the parenchyma cells undergo poli- ploidization. Furthermore, in old seeds, the distribution of the histones/DNA ratio shifts much more in parenchyma cells than in columnar epithelium cells. It may thus be concluded that different tissues of the same organ (scutellum) are affected in a different way by damaging effect of ageing factors

Session 08 Germination and dormancy

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