Poster: Late and Moved Abstracts

Abs # 1383: The cellular location of prosystemin: a functional role for phloem parenchyma in systemin signaling

Presenter:	Narvaez-Vasquez, Javier , jnarvaez@mail.wsu.edu
Authors	Narvaez-Vasquez, Javier  (A)   Ryan, Clarence A (A)
Affiliations:	(A): Institute of Biological Chemistry - Washington State University

The localization of the systemin precursor, prosystemin, has been shown to be sequestered in vascular bundles of tomato plants (Jacinto et al., 1997), but its subcellular compartmentalization and association with a specific cell type has not been established. We present in situ hybridization and immunocytochemical evidence at the light, confocal, and transmission electron microscopy levels that wound-induced and methyl jasmonate-induced prosystemin mRNA and protein are exclusively found in vascular phloem parenchyma cells of minor veins and mid ribs of leaves, and in the bicollateral phloem bundles of petioles and stems. Prosystemin protein was also found constitutively in parenchyma cells of various floral organs, including sepals, petals and anthers. At the subcellular level, prosystemin was found compartmentalized in the cytosol and the nucleus of vascular parenchyma cells, and closely associated with the endoplasmic reticulum, Golgi apparatus, vesicles, and the plasma membrane. The cumulative data indicate that vascular phloem parenchyma cells, which had not previously been associated with any specific function in plants, are the sites for the synthesis and processing of prosystemin as a first line of defense signaling in response to herbivore attacks.