Defining senescence and death

Abstract

This article evaluates features of leaf and flower senescence that are shared with, or are different from, those of other terminal events in plant development. Alterations of plastid structure and function in senescence are often reversible and it is argued that such changes represent a process of transdifferentiation or metaplasia rather than deterioration. It may be that the irreversible senescence of many flowers and some leaves represents the loss of ancestral plasticity during evolution. Reversibility serves to distinguish senescence fundamentally from programmed cell death (PCD), as does the fact that viability is essential for the initiation and progress of cell senescence. Senescence (particularly its timing and location) requires new gene transcription, but the syndrome is also subject to significant post- transcriptional and post-translational regulation. The reversibility of senescence must relate to the plastic, facultative nature of underlying molecular controls. Senescence appears to be cell-autonomous, though definitive evidence is required to substantiate this. The vacuole plays at least three key roles in the development of senescing cells: it defends the cell against biotic and abiotic damage, thus preserving viability, it accumulates metabolites with other functions, such as animal attractants, and it terminates senescence by becoming autolytic and facilitating true cell death. The mechanisms of PCD in plants bear a certain relation to those of apoptosis, and some processes, such as nucleic acid degradation, are superficially similar to aspects of the senescence syndrome. It is concluded that, in terms of physiological components and their controls, senescence and PCD are at best only distantly related.

Cell death in grape berries: varietal differences linked to xylem pressure and berry weight loss

“…In later stages of berry development, the mesocarp cells of Traminer have lost internal membranes and cell contents including lipids, starches and polyphenols were mixed within (Hardie et al 1996). Autolysis of vacuoles is likely to be indicative of cell death (Thomas et al 2003) and no functioning cytosol clearly means a cell is dead. Both mitochondria and plasma membranes appeared intact in mesocarp cells late in the ripening of fruit of the table grape V. vinifera  V. labrusca cv.…”

Large‐scale identification of leaf senescence‐associated genes

“…In general, vacuolar cys proteases are the most predominant proteases in senescing leaves. As the vacuole plays a signi®cant role in defense against pathogens and pests, a defense rather than re-mobilization role has been suggested for several of the senescencerelated proteases (Thomas et al, 2003). Vacuolar proteases may not have even a role in the process of chloroplast (and/or other organelle) protein degradation until the very late lytic stages of the vacuole following tonoplast disintegration.…”

The Acropetal Wave of Developmental Cell Death of Tobacco Corolla Is Preceded by Activation of Transglutaminase in Different Cell Compartments

“…In plant biology there is still confusion, especially centered on the application of the terms senescence and PCD (van Doorn and Woltering, 2004), which according to the different authors, may be considered separate, partially overlapping, or even identical events (Noodén et al, 1997;Thomas et al, 2003;van Doorn and Woltering, 2005;van Doorn, 2005;Rogers, 2006).…”