Cyclophilins, which catalyses protein folding and other transconformational reactions in the cell, might be needed in greater amounts to accelerate protein maturation during stress conditions. Alterations in gene expression are not only related to developmental conditions, but are also induced in response to endogenous signals in various stress responses (Marivet
et al.
1992, 1995). In infected potato plants CyP might function as a chaperone-like molecule in order to decrease the risk of proteolytic degradation or to avoid aggregation, reactions that take place during the stress condition. In plants launching an active defense, higher amounts of CyP might also be needed to process mRNA (Romano
et al.
2004), accelerate the protein folding steps and therefore the maturation process of newly synthesized pathogenesis related (PR)-proteins and others known to be induced during defense and believed to play protective functions. In this regard it is interesting that in potato cell suspension cultures CyP is induced by salicylic acid, a signalling molecule in the induction of defense responses, specifically those associated with infection