Nitric oxide (NO) is a free radical gas formed endogenously in several biological systems, including plants, in which it perfor ms a wide range of functions. Although many aspects of the physiological role of NO in plants remain to be elucidated, evidence is emerging tha t NO plays an important regulatory role in numerous processes, including stomatal closure, root development, stem elongation, seed germinatio n, the host responses to infection, programmed cell death and senescence. In addition, it is now widely accepted that NO functions as a sig nal for hormonal responses in plants. Nonetheless, the mechanisms by which NO interacts with growth regulators is still far from clear, although considerable progress has been made during the last decade in our understanding of NO within the entire plant and in plant orga nelles. Herein, we specifically explore the role of NO and its cross talk with growth regulators in plants.