VIEW ARTICLE

Physiology and Biochemistry

Physiological and Structural Changes in Tobacco Leaves Treated with Cryptogein, a Proteinaceous Elicitor from Phytophthora cryptogea. Marie- Louise Milat, Unité des Médiateurs Chimiques INRA B.V. 1540, F-21034 Dijon Cedex; Jean-Marc Ducruet(2), Pierre Ricci(3), Francis Marty(4), and Jean-Pierre Blein(5). (2)DBCM/SBE, INRA/CEA Saclay, F-91191 Gif-sur-Yvette Cedex; (3)Station de Botanique et Pathologie Végétale INRA Villa Thuret, BP 2078, F-06606 Antibes Cedex; (4)Laboratoire de Phyto-Biologie cellulaire, Université de Bourgogne, BP 138, F-21004 Dijon Cedex; (5)Unité des Médiateurs Chimiques INRA B.V. 1540, F-21034 Dijon Cedex. Phytopathology 81:1364-1368. Accepted for publication 19 June 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1364.

Cryptogein was applied on the petiole section of excised tobacco leaves. It elicited necroses that can be correlated with histological alterations, such as rapid chloroplast breakdown and a collapse of cells leading to disorganization of the parenchyma tissue. In addition, it induced ethylene production and accumulation of capsidiol. In order to detect an early response, we analyzed the kinetics of chlorophyll fluorescence induction. When tobacco leaves were treated with cryptogein (more than 1 ?g per leaf), the level P of fluorescence (F_p) lowered progressively, indicating a decrease in the variable fluorescence. In order to rule out variations due to optical heterogeneity between leaves, the value of F_p was related to that of F_o (constant fluorescence, level O) and F₁ (intermediary fluorescence, level I), which remained constant throughout the experiment. These ratios could thus be used as a nondestructive test to detect the induced stress resulting from elicitation before necrotic areas were visible. On the basis of these results, cryptogein can be considered an elicitor of defense mechanisms.