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Programmed Cell Death in Seeds

Current working model of biochemical pathways implicated in programmed cell death in seeds. Copyright: Elsevier (Taken from Kranner et al. 2006. Free Radic Biol Med DOI:10.1016/ j.freeradbiomed.2006.02.013).

This project is one of a series in the theme 'Science of Seed Ageing'.

Programmed cell death (PCD) is the mechanism by which multi-cellular organisms eliminate unwanted cells. While ~18,000 papers on PCD in humans and animals are published per year, our knowledge of the biochemical pathways that contribute to PCD in plants is rather limited. Even in mammals, the precise nature of signals that initiate PCD, often referred to as 'cell death triggers', is still under debate.

Our recent results show that PCD occurs in seeds when environmental stress becomes detrimental. Thus, the seed eliminates cells that are damaged beyond repair. This will benefit the seed if only a few cells are damaged when ageing (in orthodox seeds) or desiccation (in recalcitrant seeds) commences, but if too many cells undergo PCD, the whole seed will eventually die.

'DNA laddering' is a classic hallmark of the final, or execution phase, of PCD, in which DNA is cleaved into intra-nucleosomal fragments. Such fragments appeared with increasing intensity as seeds lost viability, suggesting that death during seed ageing in the low-hydrated state (in orthodox seeds) or during desiccation (in recalcitrant seeds) follows a controlled pattern of PCD. Seed treatment with the caspase inhibitor zVAD-fmk prior to ageing enhanced viability, confirming that caspase-like proteins contribute to viability loss in seeds. Based on our results (this and other projects) and previous publications on human and animal systems, we have put forward a model of biochemical pathways of PCD (Annex 1).  See Annex 2 for two papers emanating from this project.

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