BIOLOGY OF THE PLANT NEMATODE RELATIONSHI P - PHYSIOLOGICAL-CHANGES AND THE DEFENSE-MECHANISM OF PLANTS

Studies of the effects of nematodes on the growth and physiology of pa rasitized plants are usually concerned with mineral nutrition in relat ion to water intake, photosynthesis, respiration and its associated bi osynthesis. Other studies at the interface between the biology of nema todes and their parasitic impact, are concerned with mechanisms of att raction by root exudates. Nitrogen absorption which relies on symbioti c associations with plants, can also be disturbed by plant parasitic n ematodes. Although the accumulated knowledge to date is sparse, and th e physiological mechanisms examined are numerous, the levels of effect s of nematodes on the biology of plants are diverse and are probably r elated. There are numerous papers on the mechanisms of defence of plan ts against parasitic nematodes but reviews are scarce. The intention o f this bibliographical review is to survey the research done in the la tter field, but also to structure the acquired knowledge in order to f ind a more general principle. This analysis describes the reactions of the hormonal metabolism, putting into place regulation mechanisms thr ough auxins, cytokinins and ethylene, and of the phenolic pathway whic h produces chemicals i) directly toxic to the nematodes (e.g. phytoale xins), ii) that regulate defence reactions (monophenols-polyphenols ba lance), iii) that modify tissue development (e.g. lignins). These two branches of metabolism are dependent on enzymatic regulation (peroxyda ses, polyphenol oxydases, ammonia-lyases) in response to penetration a nd migration of nematodes in roots; such metabolic activity defines th e degree of resistance of plants to nematodes.