Metacaspase activity of Arabidopsis thaliana is regulated by S-nitrosylation of a critical cysteine residue.

Nitric oxide (NO) regulates a number of signaling functions in both animals and plants under several physiological and pathophysiological conditions. S-Nitrosylation linking a nitrosothiol on cysteine residues mediates NO signaling functions of a broad spectrum of mammalian proteins, including caspases, the main effectors of apoptosis. Metacaspases are suggested to be the ancestors of metazoan caspases, and plant metacaspases have previously been shown to be genuine cysteine proteases that autoprocess in a manner similar to that of caspases.

Caspase-like activity in the seedlings of Pisum sativum eliminates weaker shoots during early vegetative development by induction of cell death.

Activation of aspartate-specific cysteine proteases (caspases) plays a crucial role in programmed cell death (PCD) in animals. Although to date caspases have not been identified in plants, caspase-like activity was described in tobacco during a hypersensitive response to pathogens and in Arabidopsis and tomato cell cultures during chemical-induced PCD. Caspase-like activity was also detected in the course of plant development during petal senescence and endosperm PCD.

AtCYS1, a cystatin from Arabidopsis thaliana, suppresses hypersensitive cell death.

In plants, cysteine protease inhibitors are involved in the regulation of protein turnover and play an important role in resistance against insects and pathogens. AtCYS1 from Arabidopsis thaliana encodes a protein of 102 amino acids that contains the conserved motif of cysteine protease inhibitors belonging to the cystatin superfamily (Gln-Val-Val-Ala-Gly). Recombinant A.

Oxidative stress increased respiration and generation of reactive oxygen species, resulting in ATP depletion, opening of mitochondrial permeability transition, and programmed cell death.

Mitochondria constitute a major source of reactive oxygen species and have been proposed to integrate the cellular responses to stress. In animals, it was shown that mitochondria can trigger apoptosis from diverse stimuli through the opening of MTP, which allows the release of the apoptosis-inducing factor and translocation of cytochrome c into the cytosol. Here, we analyzed the role of the mitochondria in the generation of oxidative burst and induction of programmed cell death in response to brief or continuous oxidative stress in Arabidopsis cells.