Abstract
Programmed cell death (PCD) is a universal event experienced by all eukaryotes and is an essential process for the maintenance of regular homeostasis. The careful regulation of PCD pathways is beneficial to all organisms and a better understanding of various PCD components and their interactions may enhance overall quality of life and increase longevity of defective organisms. Since a boom of interest was shown towards the study of PCD approximately thirty years prior, a comprehensive understanding of the underlying mechanisms of apoptosis currently exists. Many of the key features involved in PCD have been shown to be conserved across the animal and plant kingdoms and although the overall process of cell death appears to occur in a similar manner in both plants and animals, subtle variations have been identified between these two kingdoms regarding various mechanisms of apoptosis. The major component of cell death in plants and animals appears to be the mitochondria where most of the PCD points of control converge. Heat shock proteins (Hsps) play a vital role in the regulation of PCD and act at an array of points along the PCD pathway. One of the crucial events of PCD is the release of cytochrome c from the mitochondria which proceeds to activate the protease cascade. Hsp70 has been shown to attenuate apoptosis by specifically preventing cytochrome c release into the cytosol of animal cells. A similar correlation between increases of Hsp70 and decreased PCD has been identified in plants, the mechanism of which remains unclear. The objective of this study was to investigate the interaction between increased Hsp70 accumulation and decreased PCD, as indicated by reduced cytochrome c translocation and DNA laddering. The major observations of this study proceeded to show that an increased expression of Hsp70, induced by a mild heat shock, was able to protect tobacco cells against H2O2-mediated cell death. This protection appeared to commence at a mitochondrial level as cytochrome c translocation was clearly inhibited and was confirmed by the absence of downstream DNA laddering. The major findings obtained from this study provided a clearer picture of the mechanisms surrounding the cytoprotective properties of thermotolerant cells, the implications of which are beneficial to post harvest industries, as the ability to postpone PCD provides an advantage enables prolonged shelf lives of various crops.
Dr. Marianne J. Cronjé