Programmed cell death in plants and caspase-like activities

Abstract

The development of multicellular

organisms involves an important balance between cell growth, cell

division and cell death. In animals, programmed cell death (PCD) plays a

key role by forming and deleting structures, controlling cell numbers and eliminating abnormal damaged cells. Caspases were found to be the key executioner of the cell suicide pathway. In plants, PCD plays an important role in development and in the responses to pathogens and abiotic stresses. Some common features of PCD were found to be conserved in both plants and animals (cytoplasm shrinkage, cytochrome c leakage out of mitochondria, chromatin condensation, altered nuclear morphology, DNA fragmentation in large fragments and DNA laddering). This indicates that a similar apoptotic machinery may be present in plants. After the elucidation of the complete sequences of Arabidopsis and rice, it has become clear that no genes for the caspases are present in plants. In this thesis, three model systems are described to determine the existence of caspase-like activities in plants during PCD. The first model used is a T-DNA integration arabidopsis mutant that shows necrotic spots on its leaves. The second model used is barley, during the transition from multicellular structures to globular embryos during androgenesis. The third model used was an artificial model of rice suspension cells with heat-shock as a PCD inducer. In these models, PCD was described and caspase-like activity was measured. In addition, the development and implementation of the protocol to purify plant caspase-3 like activity is described.