engleski

Auxin amidohydrolases from Brassica rapa L. - a contribution to auxin homeostasis.

Auxins are signaling molecules that coordinate plant growth and differentiation in normal favorable conditions, as well as in stress conditions. Their mode of action and their accumulation at sites of physiological action are still not well established. One of the crucial factors involved in the regulation of auxin activity are enzymes auxin- amidohydrolases, which hydrolase amino acidic conjugates of auxins thereby releasing active substances (free auxins). One mechanism of growth adaptation, upon exposure of plants to stress, is a decrease in free auxin content and down-regulation of auxin signal transduction in above-ground organs. Furthermore, it was shown that changes in auxin metabolism in stress conditions or upon treatment with salicylic acid (SA), lead to the accumulation of long chain auxins IPA and IBA, in comparison to short chain IAA. We assumed these stress hormones are influencing the differences in the distribution of endogenous auxins between free and conjugated forms, so there might be a possibility they affect regulation of gene expression for the auxin-amidohydrolases in Brassica rapa L. To gain insight into the role of stress hormones (SA, JA and ABA) on auxin metabolism, their action at the physiological level was studied by the root growth inhibition assay on Chinese cabbage seedlings. Also, the effect of stress hormones on the metabolism of the endogenous auxins was investigated by GC-MS (gas chromatography- mass spectrometry), by which auxins were identified and quantified in the seedlings of Chinese cabbage. By qRT-PCR we investigated the influence of stress hormones on the expression of genes for auxin- amidohydrolases. The role of stress hormones in the regulation of auxin metabolism was discussed with regard to the obtained results.

auxin homeostasis ; stress hormones ; Brassica rapa L.

This work has been supported by doctoral fellowship to Ana Brcko granted by the Croatian Science Foundation (grant no. HRZZ-03.01/131).