PHYSIOLOGICAL AND STRUCTURAL-CHANGES IN TOBACCO-LEAVES TREATED WITH CRYPTOGEIN, A PROTEINACEOUS ELICITOR FROM PHYTOPHTHORA-CRYPTOGEA

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-mu-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 F(I) (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.