Abstract
Polyamines are mainly composed of three members, namely putrescine, spermidine and spermine (Spm) in plants. These compounds are organic cations with low molecular weight that are implicated in various physiological and developmental processes, abiotic and biotic stress responses including high osmoticum, high salinity, hypoxia, low temperature, low pH and pathogen attack. Recently, it has been reported that Spm is a salicylate-independent endogenous inducer of both acidic pathogenesis-related proteins and resistance to tobacco mosaic virus. Here, we focus on the action of Spm in plants. In this study, we demonstrate that treatment of tobacco leaves with Spm induces the activation of two mitogen-activated protein kinases, salicylic acid-induced protein kinase and wound-induced protein kinase. The activation process is calcium-dependent and blocked by antioxidants. Our results suggest that Spm is a novel signal transmitter in both disease resistance and hypersensitive cell death.
