Poster: root biology

Abs # 272: pH dynamics in Phaseolus vulgaris root hair cells responding to Rhizobium etli Nod factors.

Presenter:	Cardenas, Luis , luisc@ibt.unam.mx
Authors	Cardenas, Luis  (A)   Gilroy, Simon  (B)   Sanchez, Federico  (A)   Quinto, Carmen  (A)
Affiliations:	(A): UNAM/Institute of Biotechnology (B): Pensylvania State University

Species of the genera Rhizobium, Synorhizobium Bradyrhizobium and Azorhizobium, are Gram-negative soil bacteria that elicit the development of root (and sometimes stem) nodules on plant hosts, which the bacteria inhabit as nitrogen fixing endosymbionts. The plant roots secrete signals, usually flavonoids that activate a set of rhizobial nod genes. These are then responsible for the synthesis of lipochitin-oligosaccharides, the Nod factors (NFs), which signal back, and activate early nodule development in the host plant. NFs alone can trigger alteration in root hair morphology, changes in plant gene expression, cortical cell dedifferentiation and mitosis, depolarization of root hair cells membrane potential, actin cytoskeleton rearrangements (Cárdenas et al., 1998) and, in some instances, the formation of mature structures resembling authentic nodules (for a review see Schultze et al., 1998). In order to study pH changes in root hairs from Phaseolus vulgaris responding to the NFs from Rhizobium etli, we have developed new conjugated dyes (Oregon Green-Cellulose binding domain) to be target to the cell wall compartment in root hair cells. Our results demonstrate that pH changes in the cell wall are some of the signals in the responding root hair cells. These pH changes are specific for the NFs and are strongly related to the age of the cells. This work was supported by grants from DGAPA/UNAM IN-200800 and CONACYT 33056-N. Schultze et al., Ann. Rev. Genet. 32:33-57 (1998). Cárdenas et al., Plant Physiol. 116:871-77 (1998)