A GENE FOR BRASSICA-NAPUS EXTENSIN IS DIFFERENTIALLY EXPRESSED ON WOUNDING

We have analysed the expression of the endogenous extensin genes in Br assica napus, using northern hybridisation and dot blotting. In the un stressed plant, the extA gene is only expressed in the root, expressio n in the leaf, petiole and stem being absent. We have found that wound ing dramatically alters this normal pattern of expression. Expression in wounded leaf is seen after 36 h, in wounded petioles after 11 h and in wounded stem after 17 h. Differences in the amount of extensin mRN A accumulated are also seen: wounded petiole accumulating extensin mes sage to a level higher than the leaf or the stem. Inhibitors of ethyle ne biosynthesis greatly delay the onset of accumulation of extensin mR NA in wounded tissues. Wounding the root causes the level of extensin message to decline with time, until levels below the limit of non-spec ific hybridisation are reached 11 h after wounding. Thus, application of the wounding stimulus results in the accumulation of extensin gene transcripts to different degrees and at different times in the aerial parts of the plant, and results in a decline in the same transcripts i n the roots. Extensin transcript accumulation as a result of wounding is also dependent on the age of the tissue; high levels of message are seen in old wounded leaves, while expression in young wounded leaves is absent.