RESUMO
Although considerable researches have been conducted on the physiological responses to plant iron (Fe) deficiency stress in dicotyledonous plants, much still needs to be learned about the regulation of these processes. In the present research, red clover was used to investigate the role of root phenolics accumulation in regulating Fe-deficiency induced Fe(III) chelate reductase (FCR). The root FCR activity, IAA and phenolics accumulation, and also the phenolics secretion were greatly increased by the Fe deficiency treatment. The application of TIBA (2,3,5-triiodobenoic acid) to the stem, an IAA polar transport inhibitor, which could decrease IAA accumulation in root, significantly inhibited the FCR activity, but did not effect root phenolics accumulation and secretion, suggesting that IAA itself did not involve in root phenolics accumulation and secretion. In contrast, the Fe deficiency treatment significantly decreased the root IAA-oxidase activity. Interestingly the phenolics extracted from roots inhibited IAA-oxidase activity in vitro, and this inhibition was greater with phenolics extracted from roots of Fe deficient plants than that from Fe sufficient plants, indicating that the Fe deficiency-induced IAA-oxidase inhibition probably caused by the phenolics accumulation in Fe deficient roots. Based on these observations, we propose a model where under Fe deficiency stress in dicots, an increase in root phenolics concentrations plays a role in regulating root IAA levels through an inhibition of root IAA oxidase activity. This response, leads to, or at least partially leads to an increase in root IAA levels, which in turn help induce increased root FCR activity.
