Abstract
Effect of quercetin, a kind of natural plant flavonoids, on auxin-induced ethylene production in barley coleoptiles was studied. Auxin-induced ethylene production was apparently stimulated by quercetin. This stimulatory effect of quercetin appeared after 4 h of incubation period. Ethylene production was stimulated 200% over the control after 8 h of incubation by $3{\times}10^{-5}\;M$ quercetin. The quercetin effect was most prominent at $10^{-4}\;M$ of IAA. Ethylene production induced by the synthetic auxin, 2,4-D and NAA, was not significantly affected by quercetin. Also ACC-based ethylene production was unaffected by the flavonoid. In an effort to elucidate mechanisms of quercetin action on auxin-induced ethylene production, the effect of quercetin on 1M metabolism was studied. Data obtained from these experiments indicate that quercetin treatment resulted in about 90% inhibition of IAA oxidase activity. IAA ($3{\times}10^{-5}\;M$) conjugation was found to be not affected by quercetin. This results suggest that the stimulatory effect of quercetin on auxin-induced ethylene production may be due to the fact that quercetin inhibits 1M oxidase activity, thus increasing the free IAA level.
Quercetin(3,5,7,3'-4'-OH-flavone)이 보리(Hordeum vulgare var. hexastichon ASCHERS.) 자엽초 조직에서 옥신유발 에틸렌 생성을 현저히 촉진시켰다. $3{\times}10^{-5}\;M$의 quercetin에서 배양한 보리 자엽초 조직에서 옥신 유발 에틸렌 생성은 4시간 이후부터 증가되기 시작하여 8시간 이후에는 200%까지 증가되었다. Quercetin은 내재옥신인 indol-3-acetic acid(IAA)에 의한 에틸렌 생성은 촉진하나 합성 옥신인 2,4-dichlorophenoxyacetic acid(2,4-D)나 naphthaleneacetic acid(NAA)에 의한 에틸렌 생성에는 아무런 영향을 주지 않았다. 또한, 에틸렌 전구체인 1-aminocyclopropen-1-carboxylic acid(ACC) 유발 에틸렌 생성에도 촉진효과가 없었다. 이러한 결과는 에틸렌 생성에 대한 quercetin의 효과는 ACC 전단계에 작용한다는 것을 의미한다. Quercetin이 IAA 대사에 어떠한 영향을 미치는지 확인한 결과 조직을 quercetin에 1시간 배양시켰을 때 조직내 IAA oxidase 효소 활성이 90% 감소되었으며, IAA conjugation에는 별 영향을 미치지 않았다. 따라서, 옥신 유발 에틸렌 생성에 대한 quercetin의 촉진작용은 quercetin이 IAA oxidase의 활성을 억제시켜 높아진 IAA 수준이 옥신 유발 에틸렌 생성을 증가시키는 것으로 생각된다.
