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The substrate-specific induction of wheat (Trificum aestivum 1. cv Fenman) leaf cinnamyl alcohol dehydrogenase (CAD, EC 1.1.1.195) was examined in relation to its role in regulating the composition of defensive lignin induced at wound margins. Treatment of wounds with a partially acetylated chitosan hydrolysate or spores of the nonpathogen Bofryfis cinerea elicited lignification at wound margins and invoked significant increases in phenylalanine ammonia-lyase (EC 4.3.1.5), peroxidase (EC 1.11.1.7), and CAD activities. The substrate-specific induction of CAD with time was determined in elicitor-treated leaves and in excised lignifying wounds. In whole leaf extracts no significant increases in p-coumaryl and coniferyl alcohol dehydrogenase adivities were detedable, but a significant 5-fold increase in sinapyl alcohol dehydrogenase adivity was evident 32 h after elicitor treatment. Similarly, fungal challenge resulted in elevated levels of only sinapyl alcohol dehydrogenase in whole-leaf extrads. In excised lignifying tissues p-coumaryl alcohol dehydrogenase levels were similar to those observed in healthy tissue. A small yet significant increase in coniferyl alcohol dehydrogenase was apparent, but the most dramatic increase occurred in sinapyl alcohol dehydrogenase adivity, which increased to values approximately 10 times higher than the untreated controls. Our results show for the first time that CAD induction in lignifying tissus of wheat is predominantly attributable to highly localized increases in sinapyl alcohol dehydrogenase adivity.
Mitchell et al. (Tue,) studied this question.