DIFFERENT PATHOGENESIS-RELATED-PROTEINS ARE EXPRESSED IN SUNFLOWER (HELIANTHUS-ANNUUS L) IN RESPONSE TO PHYSICAL, CHEMICAL AND STRESS FACTORS

PR proteins are induced by a broad range of stresses experienced by plants, from pathogen attacks to abnormal concentrations of plant hormones, or the presence of pollutants such as heavy metals. We have studied the effect of different treatments on the production of PR proteins of class 1 (PR1), 2 (PR2), 3 (PR3) and 5 (PR5) in sunflower leaf disks. Auxins and ethylene applications, but not cytokinins, induced high levels of sunflower PR proteins. Oxalic acid, the major toxin of Sclerotinia sclerotiorum, as well as citric acid were found to be efficient inducers. Manganese chloride induced all PR proteins, whereas mercuric chloride slightly induced only two classes of sunflower PR proteins. UV light exposure of the leaf disks provoked a strong induction of sunflower PR3 and PR5. Phenotypic variability between batches of sunflower plants was manifest at the level of their PR protein production. Greenhouse-grown sunflower plants often presented necrotic symptoms of unknown origins, and we have shown here that they produced high levels of PR proteins of all 4 types characterized in sunflower. Plants grown in the more controlled conditions of an incubator never presented such a high level of PR protein production. However, comparison of beta-1,3-glucanase activities between individual plants of the same batch showed significant differences between plants, indicating that the small variations of growth conditions may provoke different physiological states. This may be one of the causes of the often observed variability in experiments using explants excised from whole plants.