Cellular responses to jasmonate in Arabidopsis roots

• Main Author: Chen, Hsuan-Fu
• Published: University of East Anglia 2011
• Subjects: 572.572
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551109

Higher plants respond to biotic and abiotic stress through activation of the JA pathway, which suppresses growth and activates defence. This project describes the expression and subcellualr localisation of two of the JA signalling proteins, and the mechanism of MeJA-mediated root growth inhibition. By using immunolocalisation and reporter gene expression, localisation of COIl was shown at the subcellular and tissue level. Although COIl was constitutively expressed in the root and shoot, increased expression of COIl in MeJA-treated roots suggested that the COIl gene and the COIl protein was also regulated by the JA pathway. Co-localisation of COIl and JAZ3 protein in the nucleus confirmed that the previously reported interaction between COIl and JAZ3 took place in the nucleus. To investigate the morphological basis of root growth inhibition by MeJA, time-lapse and still imaging by confocal microscopy was used to compare root growth parameters in untreated and MeJA-treated roots. MeJA inhibited root growth by reducing the number of dividing cells and rapidly-elongating cells, and causing earlier maturation of the elongating cells, so that they ceased elongating before reaching normal mature cell length. However, the rate of individual cell elongation was unaltered. The physiological basis of MeJA-mediated growth inhibition was investigated by examining the orientation of microtubules, acid efflux from the root elongation zone, and the effect of low water potential on root elongation. MeJA-treated roots had reduced acid efflux and water uptake in the elongating cells, while microtubule orientation was not required for the inhibitory effect. The crosstalk between JA, auxin, GA and ABA was studied by measuring the change of morphological growth parameters in mutants under different hormone treatment. The impaired MeJA-mediated growth inhibition in auxl indicated that MeJA reduced root growth by altering auxin transportation. However, MeJA-mediated growth inhibition was DELLA- and ABA- independent. In summary, MeJA reduced cell division by decreasing mitosis, and inhibited cell elongation by reducing acid efflux, which prevented water uptake, possibly by regulating the auxin transportation, in the Arabidopsis root.