Role of nitric oxide at the triggering of germination

JASID, SEBASTIÁN; SIMONTACCHI, M; PUNTARULO, S

Montevideo, Uruguay

Congreso; V Meeting of SFRBM, South American Group, V International Conference on Peroxynitrite and reactive Nitrogen Species; 2007

SFRBM South American Group

  It has been previously established that sorghum embryonic axes produce a sharp increase in  nitric oxide (NO) content coincidently with the triggering of germination (Plant Sci. 2004, 167, 839-847).  To analyze the role of NO on this key process, sorghum seeds were placed for 24 h in the dark, at 26oC in a medium containing sodium nitroprusside (SNP), afterwards embryonic axes were excised and employed for the measurements. Germination (96% in control seeds) was not affected by SNP exposure up to 1 mM. However, fresh and dry weight in embryonic axes significantly increased when germination was carried out in the presence of 0.1 mM SNP, as compared to control (10.0±0.4 and 6.8±0.3 mg FW axis-1, respectively; 0.88±0.06 and 1.13±0.03 mg DW axis-1, respectively). A positive correlation between SNP concentration in the milieu and NO content in axes after 24 h was found. In this regard, spin trapping EPR (MGD-Fe) was employed to assessed NO content in axes (2.4±0.2, 3.1±0.3, 4.6±0.2 nmol NO g-1FW, for control, 0.01 and 0.1 mM SNP exposed seeds, respectively). Nitration of tyrosine residues of proteins, detected by western blot analysis, raised by 27% in sorghum embryonic axes exposed to NO donor (0.1 mM SNP), as compared to axes from control seeds. Cytosol added with desferrioxamine (DF) were examined by EPR at 77K since the levels of DF-iron (III) complex is an index of labile iron pool. The content of this redox active iron increased by 40% in axes from seeds incubated in the presence of 0.1 mM SNP, as compared to control. Results presented here suggested that the higher availability of NO at the triggering of  germination of sorghum seeds lead to a wide range of changes including increase in growth, levels of protein nitration and redox active iron, suggesting a complex signaling scenario that should be further studied. This study was supported by grants from University of Buenos Aires, ANPCyT and CONICET.