Nitric oxide as a bioactive signalling molecule in plant stress responses

Nitric oxide (NO) is an important signalling molecule with diverse physiological functions in plants. It was found to play a crucial role in plant growth and development, starting from germination to flowering, ripening of fruit and senescence of organs. Also in case of environmental stress hazard, caused by both abiotic and biotic factors, enhanced NO generation is observed in different plant species and organs. This review is focused mainly on the essential role of NO in plant signalling network, leading to the expression of defence response genes under various stress conditions. NO can provoke both beneficial and harmful effects in plant cells. This dual role probably depends on the local concentration of NO as an effect of the rate of synthesis, translocation, effectiveness of removal of this reactive nitrogen species, as well as its ability to directly interact with other molecules and signals.