CHITOSAN-INDUCED CELL DEATH IN SYCAMORE CULTURED CELLS

Programmed cell death (PCD) plays a pivotal role in many developmental plant processes and in defence mechanisms against biotic and a-biotic stresses. At least three different forms of PCD have been reported in plants: a “nuclear” (apoptotic-like) form, a “chloroplastic” form and a “vacuolar” form1. In sycamore (Acer pseudoplatanus L.) cultured cells different stress conditions induce cell death that only in a fraction of the dead cells presents the typical morphological hallmarks of apoptosis, i.e. cell shrinkage, chromatin condensation, DNA fragmentation2,3. Recently, our attention has been focused on chitosan (CHT). CHT is a natural, non-toxic and inexpensive compound obtained by partial alkaline deacetylation of chitin, the main component of the exoskeleton of crustaceans and other arthropods (Kurita, 2006). Although the exact mode of action of CHT is still unknown, in agriculture it has been shown to be a versatile compound that controls numerous pre and postharvest diseases on various horticultural commodities4. In sycamore culture cells CHT rapidly induces a set of defense/stress responses that include accumulation of dead cells and of cells with fragmented DNA accompanied by release of cytochrome c from the mitochondrion5. In this work we further investigated the cell death process induced by CHT. In particular, we tested the capability of CHT to induce oxidative stress (superoxide anion and malondialdehyde production) and caspase3-like activity.