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Auxin homeostasis in Brassica rapa as a mechanism of plant stress response

Auxin levels and the regulation of reversible auxin conjugation as a mechanism of auxin homeostasis has been investigated in Chinese cabagge (Brassica rapa L. ssp. pekinensis) upon biotic stress caused by Cucumber mosaic virus containing satellite RNA (CMVsat) infection and abiotic stress (salt stress, drought) as well as tretments with stress hormones (SA, JA, ABA). To detect the physiological state of plants and their ability to integrate given stress conditions, a set of biochemical markers (glutathione level, antioxidant enzymes activity, carbonyl content) were analysed. Endogenous free and total IAA, and ABA were analysed by GC-MS. The levels of auxin were significantly affected by biotic and abiotic stresses as well as treatments with stress hormones. All stress conditions caused perturbation of IAA levels with a tendency of increasing the IAA conjugate level. Among treatments with stress hormones, JA caused the most significant increase of free and conjugated IAA in comparison to others. Endogenous ABA was significantly higher under both abiotic stress conditions in comparison to the control showing a positive correlation with auxin levels. Results of gene expression experiments (qRT-PCR) showed an increased transcript level of auxin amidohydrolase BrIAR3 upon abiotic stress as well as after treatment with JA. The results implicated an important role of auxin and interactions with other stress hormones in the plant stress response.

auxin homeostasis ; abiotic and biotic stress ; Brassica rapa

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