ABSTRACT
University of Liège, Gembloux Agro-Bio Tech, Plant Biology Unit, Passage des Déportés, 2, 5030 Gembloux, Belgium, Fax: +32 (0)81 60 07 27, E-mails: pierre.delaplace@ulg.ac.be, marielaure.fauconnier@ulg.ac.be, patrick.dujardin@ulg.ac.be *Corresponding author
Introduction
At the organ level, ageing and senescence are often closely associated, mainly within the scope of human ageing physiology (De Magalhães 2006). However, when dealing with plant physiology, these concepts are quite distinct although they both refer to the metabolic changes that lead to the death of an organism or a part thereof in the short or middle term (Hartmann 1992). The difference between both concepts relies on the causing agents that induce such changes. The progressive and passive weakening of a living system, mainly due to attacks from the environment, is referred to as ageing while senescence implies qualitative changes that originate from programming of the genome expression. Senescence is indeed defi ned as the last developmental step where several-increasingly irreversible-events occur that lead to cellular breakdown and sometimes a programmed cell death at the organ level (Hartmann 1992, Gan and Amasino 1997, Thomas 2002, Dertinger et al. 2003, Yoshida 2003, Jones and Smirnoff 2005, Zentgraf 2007).
