Nitric oxide-mediated signaling functions during the plant hypersensitive response.

Mounting evidences suggest that nitric oxide (NO) is the central molecule in several physiological fuctions, ranging from plant development and defence responses. Plants use NO as signaling molecule through pathways finely comparable to those of mammals, suggesting that there are many commonalities between NO action in plants and animals. In this chapter, first we will examine the mechanisms through which plants respond to pathogen challenge. In particular, we will describe the major NO-generating systems and their involvement in response to pathogen attack, the role of NO in the activation of the hypersensitive response (HR) and the participation in the establishment of systemic acquired resistance (SAR). Finally, we will focus on NO signaling functions in plant defence responses. Hence we will describe the evidences of the involvement of Ca2+, cyclic GMP (cGMP), cyclic ADP-ribose (cADPR) and mitogen-activated protein kinases (MAPK) in NO-mediated signal cascade, the NO role in posttransational modification of proteins and its participation in modulating gene expression.