Nitric oxide and cyclic GMP are messengers in the IAA-induced adventitious rooting process

PAGNUSSAT GC, LANTERI ML, LAMATTINA L

PLANT PHYSIOLOGY.

American Society of Plant Biologists

Lugar: Rockville, USA; Año: 2003 vol. 132 p. 1241 - 1248

0032-0889

This report describes part of the signaling pathway and some of the molecules involved in the auxin-induced adventitious root formation in Cucumis sativus. Previous results showed that Nitric Oxide (NO) mediates the auxin response during adventitious root formation (Pagnussat et al., 2002). To determine the order of action of IAA and NO within the signal transduction pathway and to elucidate the target molecules that are downstream of NO action, cucumber hypocotyl cuttings were submitted to a pre-treatment leading to endogenous auxin depletion. The auxin-depletion treatment provoked a 3-fold reduction of the root number in comparison to the non-depleted explants. The NO-donor sodium nitroprusside (SNP) was able to promote adventitious rooting in auxin-depleted explants, while the specific NO scavenger cPTIO prevented the effect of SNP. The endogenous NO level was monitored in both control and auxin-depleted explants using a NO-specific fluorescent probe. The NO level was 3.5-fold higher in control (non-depleted) explants than in auxin-depleted ones. The exogenous application of IAA restored the NO concentration to the level found in non-depleted explants. Since NO activates the enzyme guanylate cyclase (GC), we analyzed the involvement of the messenger cGMP in the adventitious root development mediated by IAA and NO. The GC inhibitor LY83583 reduced root development induced by IAA and NO, while the cell permeable cGMP derivative 8-Br-cGMP reversed this effect. The endogenous level of cGMP is regulated by both the synthesis via GC and its degradation by the phosphodiesterase (PDE) activity. When assayed, the PDE inhibitor sildenafil citrate was able to induce adventitious rooting in both non-depleted and auxin-depleted explants. Results indicate that NO operates downstream of IAA promoting adventitious root development through the GC-catalyzed synthesis of cGMP.