Detection of reactive oxygen species downstream of cyclic nucleotide signals in plants.

Cyclic nucleotides act in plant cell signal transduction cascades by activating cyclic nucleotide gated cation-conducting ion channels (CNGCs). Activation of CNGCs results in inward cation (including Ca(2+)) conductance across the plasma membrane. Elevation of cytosolic Ca(2+) is an early step in numerous plant cell signal transduction cascades, including plant immune responses to pathogens. CNGC involvement, along with cyclic nucleotides cAMP and cGMP, in pathogen defense programs is one relatively well-studied area of cyclic nucleotide signaling in plants. During plant immune responses, CNGC-dependent Ca(2+) elevations lead to a signaling cascade that results in the generation of defense molecules such as hydrogen peroxide and nitric oxide, and induction of defense gene expression. This pathogen defense response is discussed, and methods to detect some of the downstream signaling steps in the pathway are presented.