Morphological classification of plant cell deaths

Abstract

Programmed cell death (PCD) is an integral part of plant development and of responses to abiotic stress or pathogens. Although the morphology of plant PCD is, in some cases, well characterised and molecular mechanisms controlling plant PCD are beginning to emerge, there is still confusion about the classification of PCD in plants. Here we suggest a classification based on morphological criteria. According to this classification, the use of the term 'apoptosis' is not justified in plants, but at least two classes of PCD can be distinguished: vacuolar cell death and necrosis. During vacuolar cell death, the cell contents are removed by a combination of autophagy-like process and release of hydrolases from collapsed lytic vacuoles. Necrosis is characterised by early rupture of the plasma membrane, shrinkage of the protoplast and absence of vacuolar cell death features. Vacuolar cell death is common during tissue and organ formation and elimination, whereas necrosis is typically found under abiotic stress. Some examples of plant PCD cannot be ascribed to either major class and are therefore classified as separate modalities. These are PCD associated with the hypersensitive response to biotrophic pathogens, which can express features of both necrosis and vacuolar cell death, PCD in starchy cereal endosperm and during self-incompatibility. The present classification is not static, but will be subject to further revision, especially when specific biochemical pathways are better defined. Research on plant cell death has grown considerably in the past few years, owing to the importance of cell death for plant development and defense. Just as animal cells engage several mechanisms leading to death, the road to cell demise in plants can also vary. The long evolutionary distance and distinct cellular architecture between the two kingdoms may account for the differences between the mechanisms of plant and animal cell death. It is therefore appropriate to assess the relevance of animal cell death nomenclature 1 to plants. At present, there is confusion in cell death terminology in plant biology, which drives our attempt to formulate a more logical classification. Although our molecular understanding of plant cell death regulation and execution is insufficient to create definitive classifications based on precise biochemical pathways, it is possible to begin classifying plant cell death scenarios based on morphological criteria, as was initially the case in animal cell death research 2,3 and is still used for the classification of cell death in animal science. 1 This document attempts to provide a classification of plant cell death. We urge authors, reviewers and editors to follow this classification to facilitate communication between scientists and accelerate research in this field.

Genome-wide gene expression profiling of introgressed indica rice alleles associated with seedling cold tolerance improvement in a japonica rice background

“…Strikingly, ten genes with higher basal expression in K354 were related to PCD (GO: 0012501), and all of them were disease-resistance related genes with an NBS domain (Table 3). It has been reported that cell death pathways in plants can be activated not only by successful recognition of a pathogen during hypersensitive responses but also by a range of abiotic stresses [22]. In addition, PCD has been reported to be activated in tobacco cells in response to cold stress [23].…”

Reactive oxygen species and plant resistance to fungal pathogens

“…PCD is a highly genetically controlled and orchestrated process that leads to the degradation of proteins, lipids and DNA, destruction of the plasma membrane and phosphatidylserine externalisation, that ends with the destruction of the cell (Dickman and de Figueiredo, 2013). During the last years, PCD in plants has been extensively characterised and several molecular players have been recently described, including the endoplasmic reticulum (ER), Ca 2+ , nitric oxide (NO) and ROS (reviewed in Agurla et al, in press;Garcion et al, 2014;van Doorn et al, 2011;Williams et al, 2014). In plants, PCD takes place during leaf senescence, photosynthesis and as part of the innate immune response triggered by plant-pathogen interactions, called hypersensitive response (HR).…”

Endosperm and Nucellus Develop Antagonistically in Arabidopsis Seeds

“…In plants, different cell death programs have been classified according to morphological features and grouped into two major types: necrotic and vacuolar PCD (van Doorn et al, 2011). To understand which type of PCD happens in the Arabidopsis nucellus, we analyzed seeds at 4 DAF by transmission electron microscopy ( Figure 1M).…”