Summary: The Plant Cell, Vol. 8,1683-1698, October 1996O 1996American Society of Plant Physiologists
Bacterial Pathogens in Plants: Life up against the WalI
James R. Alfano and Alan Collmer'
Department of Plant Pathology, Cornell University, Ithaca, New York 14853-4203
Higher plants contain potentially vast sources of nutrients for
the myriad bacterial species in their environment, and most
bacteriaaresmall enoughto passthrough stomatesandother
natural openingsinto the apoplast-the anteroom for these
riches. However, surprisingly few bacteria raid the nutrient
stores of living plant cells, apparently because the metabolic
intimacy involvedin parasitismrequiresthe work of specialists.
Of thesespecialists,someinthe Rhizobiaceaeproducehyper-
trophies that are genetically engineered or developmentally
tricked into providing an undefended, nutritive niche in root
cortical tissuesand rhizospheres(seeLong, 1996;Shengand
Citovsky, 1996, in this issue), whereas others, mostly Gram-
negativebacteria in the Pseudomonadaceaeand Enterobac-
teriaceae, specialize in colonizing the apoplast.
It is the apoplastic colonizers that are the common patho-