Fusarium elicitor-dependent calcium influx and associated ros generation in tomato is independent of cell death

Abstract

Fusarium oxysporum f. sp. lycopersici elicitor (EFOL-2) treatment induces cytosolic influx of calcium in Fusarium-resistant tomato suspension culture. The calcium signature was found to be biphasic, which is characteristic of recognition of oligosaccharides in the elicitor preparation. Further, several lines of evidence such as, (i) attainment of saturation level of the [Ca(2+)](cyt) at a definite extra-cellular calcium concentration (ii) prominent reduction in EFOL-2-induced influx in [Ca(2+)](cyt) on treatment with the calcium channel blockers verapamil and diltiazem and (iii) establishment of a refractory stage of [Ca(2+)](cyt) level upon repeated stimulation by EFOL-2, is indicative of receptor-mediated activation of the calcium channel for cytosolic elevation. In addition, inhibition of EFOL-2-induced [Ca(2+)](cyt) increase by protein kinase inhibitor staurosporine and wortmannin indicate phosphorylation is a regulatory event of calcium influx. Additionally, monitoring of cell death on EFOL-2 treatment indicated that the degree of ROS generation is not capable of inducing cell death. Inhibition of ROS generation on two separate occasions such as, calcium-free media and on treatment with inhibitors causing calcium channel occlusion revealed ROS generation as a successive event of calcium influx.