Cell biology of plant immunization against microbial infection: The potential of induced resistance in controlling plant diseases

During the course of their co-evolution, plants and pathogens have evolved an intricate relationship resulting from a continuous exchange of molecular information. Pathogens have developed an array of offensive strategies to parasitize plants and, in rum, plants have deployed a wide range of defence mechanisms similar in some respects to the immune defences produced in ani mals. The recent advances in molecular biology and plant transformation hav e provided evidence that sensitizing a plant to respond more rapidly to inf ection could confer increased protection against virulent pathogens. One im portant facet in ascertaining the significance of defence molecules in plan t disease resistance is the exact knowledge of their spatio-temporal distri bution in stressed plant: tissues. In an effort to understand the process a ssociated with the induction of plant disease resistance, the effect of mic robial and chemical elicitors on the plant cell response during attack by f ungal pathogens was investigated and the mechanisms underlying the expressi on of resistance to bacteria and nematodes studied by both histo- and cytoc hemistry. Evidence is provided that the disease-resistance response correla tes with changes in cell biochemistry and physiology that are accompanied b y structural modifications including the formation of callose-enriched wall appositions and the infiltration of phenolic compounds at sites of potenti al pathogen penetration. Activation of the phenylpropanoid pathway is a cru cial phenomenon involved in pathogen growth restriction and host cell survi val under stress conditions. Ultrastructural and cytochemical approaches ha ve the potential to significantly improve our knowledge of how plants defen d themselves and how plant disease resistance is expressed at the cell leve l. (C) 1999 Editions scientifiques et medicales Elsevier SAS.