Phenylpropanoid metabolism and resistance of spruce to root disease

An elicitor preparation from mycelia of Heterobasidion annosum induced increases in PAL, detected enzymically within 24 h, when applied to the hypocotyl and root axis of Sitka spruce seedlings. In contrast, similar rapid increases in activity were not found in seedlings following treatment with H. annosum conidiospores (5 x 10(6).m(-1)), or solutions of jasmonic acid or salicylic acid at 100 and 1000 mu g.ml(-1). Compared with published results from other plants, constitutive levels of PAL activity were high in Sitka spruce seedlings.

A homologous pal probe was amplified by PCR from genomic DNA of Sitka spruce, and labelled with digoxigenin. Use of this probe in northern blotting to detect PAL transcripts in spruce following elicitor treatment or inoculation with H. annosum conidial suspensions indicated that levels of transcripts were similar in all treatments. The 0.3 kb PCR fragment was sequenced and proved to be a partial pal gene encoding a PAL enzyme.

Rapid increases in PAL activity in Sitka spruce seedlings following elicitor application indicate that this response is an important and early component of defence to fungal pathogens in this conifer. Failure to detect increases in pal transcripts using molecular techniques was probably a consequence of the presence of more than one gene encoding for PAL.