Plants have developed a series of mechanisms for perception and transduction of environmental or endogenous stimuli and for integration and synchronization of physiological responses. Signal transduction, the way cells construct responses to a stimulus, is a recently defined focus in plant biology. Moreover, in addition to the accumulation of data generated by structural and functional genomic analysis, a revival of pharmacological, surgical and physiological experimental approaches assessed in the past years have led to a clear advancement in the comprehension of molecular mechanisms involved in plant physiological responses. As well as it was demonstrated in animal systems that nitric oxide (NO), cGMP and Ca²⁺ were interconnected to play a central role in vascular cell physiology, the same results are forthcoming from plant systems. Currently, the molecular basis that are responsible of transducing plant hormone messages into physiological responses are being deciphered. The auxin indole acetic acid (IAA) is the main hormone involved in determining the root architecture. Recently, we have demonstrated that NO is required in both the IAA-induced adventitious root formation (ARF) [Plant Physiol. (2002) 129: 954; (2003) 132: 1241; (2004) 135: 279] and lateral root development (LRD) [Planta (2004) 218: 900]. During ARF, the NO action is accomplished by at least two parallel mechanisms: i) the increase in cGMP level and ii) the activation of a MAPK pathway. The induction of LRD by NO is accomplished through a NO-mediated induction of cell cycle regulatory genes (cyclins and cyclin-dependent kinases) that leads to the activation of pericycle cells and their progress through G1-S phase. These and other recent findings concerning NO-related mechanisms that control root development will be presented.

Supported by Conicet, ANPCyT, UNMdP and Fundación Antorchas, Argentina.