Auxin Regulation of the Response of Phaseolus vulgaris to a Fungal Elicitor

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The effect of IAA and 2,4-D on the response of Phaseolus vulgaris to limiting concentrations of cell wall elicitors of Colletotrichum lindemuthianum was investigated in attached leaves of both the susceptible, Pinto, and resistant, Kievit, cultivars. Low concentrations of the plant hormones augmented the response, as measured by changes in the activity of enzymes of the flavanoid pathway (phenylalanine ammonia-lyase (PAL) and ρ-coumaric acid coenzyme-A ligase (ρ-CL)) and phytoalexin concentration, both cultivars. This contrasts to a previous study with ethylene, where augmentation was observed in leaves of cv. Kievit only; however, in the absence of elicitor neither auxin nor ethylene have any effect. It was also observed that IAA promoted the synthesis of ethylene in the leaves of cv. Kievit; inhibition of ethylene synthesis demonstrated that the hormone could, nevertheless, act independently of ethylene to enhance phytoalexin synthesis. The effect of auxin was particularly pronounced on PAL-hitherto identified as a key regulatory enzyme on the flavanoid pathway which, it is proposed, could be under the dual regulation of both auxin and ethylene. Similarly, the mode of action of auxin was shown to resemble that of ethylene in that its effect is brought about, partially if not entirely, as a result of its regulation of the synthesis of enzymes of the flavanoid pathway.
日本植物生理学会の論文