Habituation in sugarbeet plant cells: Permanent stress or antioxidant adaptative strategy?

Summary Habituation is one of the four neoplastic diseases of plants and occurs spontaneously in plant cell cultures. To date, and even if an epigenetic origin has been previously postulated, the fundamental concept that underlies this neoplastic state remains obscure. Recently, a permanent stress hypothesis has been proposed, using habituated nonorganogenic (HNO) sugarbeet cell line (Beta vulgaris L.altissima) as a model. According to this proposal, the low catalase and peroxidase activities were supposed to be responsible for H₂O₂ accumulation. A supposed lipoxygenase activation would generate LOO° radicals. OH°, produced by the Fenton reaction would be responsible for a lipoperoxidation process, leading to malondialdehyde (MDA) accumulation. In this paper, the elements of this hypothesis have been examined using data previously obtained by several teams, and the permanent stress idea appears less sustainable. Several properties of the habituated nonorganogenic sugarbeet- and some other habituated-cell lines have been described. A more realistic concept emerging from this analysis is that habituated cells exhibit efficient scavenging properties (antioxidant and antilipoperoxidant) against deleterious free radicals produced during cell culture. This thesis is developed in this article.