ELICITOR-INDUCED CHANGES OF WALL-BOUND AND SECRETED PEROXIDASE-ACTIVITIES IN SUSPENSION-CULTURED SPRUCE (PICEA-ABIES) CELLS ARE ATTENUATED BY AUXINS

In ectomycorrhizae auxins are proposed to attenuate elicitor-induced d efence reactions in the host plant. To examine this hypothesis we comp ared the elicitor-induced accumulation of peroxidase isoforms between suspension-cultured spruce (Picea abies [L.] Karst.) cells incubated i n media with and without auxins. In spruce cells changes in ionically and covalently wall-bound as well as symplasmic peroxidase (EC 1.11.1. 7) activities were observed when elicitors from the following fungal s pecies were applied: (1) Hebeloma crustuliniforme, an ectomycorrhizal partner of spruce; (2) Suillus variegatus, an ectomycorrhizal fungus i ncompatible with spruce; (3) Heterobasidion annosum, a spruce pathogen . Activity staining after SDS-PAGE and western blotting showed an accu mulation of an ionically wall-bound 38-kDa peroxidase isoform. In addi tion, two covalently wail-bound isoforms (34 and 53 kDa) that could be released from spruce cell walls by cellulase and pectinase treatment were also induced by elicitors from these fungi. Moreover, in cells cu ltured without auxins all the elicitors triggered a rapid and transien t accumulation of ionically wall-bound peroxidases, which reached a ma ximum activity 48 h after elicitor application. This early and transie nt peroxidase accumulation was diminished and delayed in cells culture d in the presence of auxins. In contrast, activity of peroxidases rele ased into the culture medium of spruce cells or into the medium of pro toplasts was suppressed by the elicitors of Hebeloma crustuliniforme. However, this suppression was attenuated by the action of auxins. It i s suggested that under natural conditions, in infected spruce roots, t he elicitors of the compatible fungus cause both suppression of the pe roxidase (which is secreted to the free space of the roots), and induc tion of wall-bound and symplasmic peroxidases. On the other hand, auxi ns synthesized by the fungus could weaken these different elicitor-med iated effects.