Signal Transduction Events Mediating Chitosan Stimulation of Anthraquinone Synthesis In Rubia tinctorum.

VASCONSUELO, ANDREA ANAHÍ; ANA GIULLIETTI,; RICARDO BOLAND,

PLANT SCIENCE

ELSEVIER IRELAND LTD

Año: 2004 vol. 166 p. 405 - 413

0168-9452

The signalling mechanism by which chitosan increases anthraquinones in Rubia tinctorum L. is largely unknown. We recently showed that the effects of the elicitor require activation of the PLC/PKC cascade. In view of the intrincate network of pathways mediating extracellular stimuli, in this study we investigated whether mitogen activated protein kinase (MAPK), a pathway known to be a PKC target, also participates in chitosan action. Immunoblot analysis revealed a marked stimulation of the MAPK in elicited cells. In presence of the PKC inhibitor calphostin C, lack of activation of MAPK paralleled by a 90% suppression of the chitosan-dependent increase in anthraquinones were observed. Moreover, the elicitor action was decreased 65% by MAPK kinase inhibitor PD 98059. Also, we tested whether the adenylyl cyclase (AC)/cAMP/PKA messenger system plays a role in elicitation. Forskolin, which stimulates AC, and the PKA activators adenosine 3Œ,5Œ-cyclic monophosphorothioate-Sp (Sp-cAMPS) or 8-Br-cAMP, were not able to mimic the induction of anthraquinone synthesis in R. tinctorum cells by the elicitor. In addition, the PKA inhibitor adenosine 3Œ,5Œ-cyclic monophosphorothiolate-Rp (Rp-cAMPS) did not block chitosan effects. On the other hand, phosphoinositide 3Œ-OH-kinase (PI3K) inhibitors LY204002 and wortmannin blocked chitosan stimulation of PKC activity and anthraquinone synthesis. These results involve PI3K-mediated activation of PKC and in turn of MAPK in chitosan elicitation.