ABSTRACT
I. Introduction.............................................................................................................................297 A. Chemical Signaling as Belowground Communication ....................................................298 B. Chemical Signals in the Rhizosphere...............................................................................299 C. Signal Mobility, Persistence, and Activity in the Rhizosphere .......................................300
II. Negative Root-Root Communication.....................................................................................301 A. Allelopathy........................................................................................................................301 B. Autoinhibition ...................................................................................................................305 C. Host-Parasitic Plant Interactions......................................................................................306
III. Negative Root-Microbe Communication...............................................................................309 A. Plant Antimicrobial Signals and Resistance to Soil Pathogens.......................................309 B. Microbial Signals and Induced Plant Disease Responses ...............................................312 C. Microbial Resistance to Plant Antimicrobial Signals ......................................................313
IV. Positive Root-Root Communication ......................................................................................313 A. Herbivore Resistance ........................................................................................................313 B. Root Detection and Navigation ........................................................................................314
V. Positive Root-Microbe Communication ................................................................................315 A. Extracellular Plant Growth-Promoting Rhizobacteria .....................................................316 B. Rhizobia-Legume Interactions .........................................................................................318 C. Frankia-Actinorhizal Interactions ....................................................................................319 D. Nostoc-Cycad Interactions ...............................................................................................320 E. Mycorrhizal Fungi ............................................................................................................320
VI. Concluding Remarks...............................................................................................................322 Acknowledgments ..........................................................................................................................322 References ......................................................................................................................................322
