Characterisation of caffeic acid O-methyltransferase and cinnamyl alcohol dehydrogenase gene expression patterns by in situ hybridisation in Eucalyptus gunnii Hook. plantlets

The developmental tissue- and cell-specific expression pattern of two 'lignification' genes, caffeic acid O-methyltransferase (C-OMT) and cinnamyl alcohol dehydrogenase (CAD), was analysed by in situ hybridisation in leaf and stem samples of Eucalyptus plantlets. Both genes are expressed, in a coordinated, developmental fashion, in the same cell types-especially developing vessels-of differentiating stem xylem tissue confirming their role in lignification and demonstrating that this process is under strict developmental control. C-OMT, but not CAD, transcripts were also localised to developing xylem vessels in the midribs of leaves. Histochemical analyses revealed that, in stem xylem tissues, C-OMT and CAD are expressed in cells poor in S-type lignin (primary xylem vessels and immature secondary xylem cells) and also in cells that later become rich in S-type lignin (mature secondary xylem cells). (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.