Novel mode of resistance to Fusarium infection by a mild dose pre-exposure of cadmium in wheat

Exposure of healthy wheat seeds (Triticum aestivum var Sonalika) to mild dose of cadmium (Cd2+) given as 50 muM CdCl2 for 48 h and then washed off Cd2+ offered resistance to the subsequent infection by Fusarium oxysporum inoculum. Seven days old seedlings having two primary leaves were aseptically inoculated with fungus, F. oxysporum (1 x 10(6)) spores. The seedlings pre-exposed to low level of Cd2+ survived the Fusarium infection, while plantlets without Cd2+ stress wilted and then perished due to Fusarium infection. The stress associated proteins induced by Cd2+ (50 muM), F. oxysporum and by the co-stress (50 muM Cd2+ and then with F. oxysporum) treatments were observed to be of same molecular weight (51 kDa). Antibody was raised against the purified Cd2+-stress associated protein (CSAP). Immuno-gold labeling of wheat seedling root tissue showed the presence of this CSAP in Cd2+ pre-exposed and in co-stressed tissues and to be located predominantly on the inner linings of the cell membranes. We also observed that the anti-CSAP-antibody also labeled the root tissue of only Fusarium inoculated seedlings and the gold labeling was intensely located on the membrane. This cross-reaction of anti-CSAP suggests that Fusarium-induced stress protein (FISP) possibly has close homology to CSAP. We thus show for the first time the over expression of a high molecular mass protein by mild dose of Cd2+ pre-exposure to wheat seeds which subsequently provided protection against Fusarium infection. This mode of resistance developed by an abiotic stress-causing agent against pathogen infection is novel. (C) 2004 Elsevier SAS. All rights reserved.