Abstract
Nitric oxide (NO), is a redox-active, endogenous signalling molecule involved in the regulation of numerous processes. It plays a crucial role in adaptation and tolerance to various abiotic and biotic stresses. In higher plants, NO is produced either by enzymatic or non-enzymatic reduction of nitrite and an oxidative pathway requiring a putative nitric oxide synthase (NOS)-like enzyme. There are several methods to measure NO production: mass spectrometry, tissue localization by DAF-FM dye. Electron paramagnetic resonance (EPR) also known as electron spin resonance (ESR) and spectrophotometric assays. The activity of NOS can be measured by L-citrulline based assay and spectroscopic method (NADPH utilization method). A major route for the transfer of NO bioactivity is S-nitrosylation, the addition of a NO moiety to a protein cysteine thiol forming an S-nitrosothiol (SNO). This experimental method describes visualization of NO using DAF-FM dye by fluorescence microscopy (Zeiss AXIOSKOP 2). The whole procedure is simplified, so it is easy to perform but has a high sensitivity for NO detection. In addition, spectrophotometry based protocols for assay of NOS, Nitrate Reductase (NR) and the content of S-nitrosothiols are also described. These spectrophotometric protocols are easy to perform, less expensive and sufficiently sensitive assays which provide adequate information on NO based regulation of physiological processes depending on the treatments of interest.