Proteolytic Enzymes in Plant Programmed Cell Death

Abstract

Programmed cell death (PCD) is required for the development and morphogenesis of almost all multicellular
eukaryotic organisms. In cell death mechanisms proteolytic enzymes have very diverse roles. The recent fi ndings
point to the existence of different plant caspase-like proteolytic activities involved in cell death. Cysteine
proteases, specifi cally caspases, have emerged as key enzymes in the regulation of animal PCD. Although plants
do not have true caspase homologues, several instances of caspase-like proteolytic activity with aspartate-specifi c
cleavage have been demonstrated in connection with PCD in plants. Because of the caspase-like activity in plants,
the researcher’s main goal is to determine which molecular components may be used in the execution of PCD in
plants that have been conserved during evolution. In the present review, examples of serine, cysteine, aspartic,
metallo- and threonine proteinases are explained which provide background information about their roles as
regulators of animal PCD, and linked to plant PCD in developing fl owers, senescing organs, differentiating
tracheary elements and in response to stress.