Reduced embryo sensitivity to ABA in sprouting susceptible sorghum (Sorghum bicolor) variety is associated with an altered ABA signalling

GUALANO, N.; CARRARI, F.; RODRÍGUEZ, M.V.; PÉREZ-FLORES, L.; SÁNCHEZ, R.A.; IUSEM, N.D.; BENECH-ARNOLD, R.L.

SEED SCIENCE RESEARCH

Cambridge Uiversity Press

Año: 2007 vol. 17 p. 81 - 90

0960-2585

In this paper we tried to elucidate the nature of the different abscisic acid (ABA) sensitivities presented by developing embryos from sorghum [Sorghum bicolor (L.) Moench] lines with contrasting preharvest sprouting (PHS) behaviour (Redland B2, susceptible; IS 9530, resistant). We explored two different hypotheses for a possible mechanism: i) a different functionality of the ABA signaling pathway, and ii) a different rate of ABA degradation/conjugation in the apoplast of embryos from these genotypes. For assessing the first possibility, we used an ABA-responsive gene (rab17) as a reporter of changes in ABA endogenous levels artificially induced in embryos from both genotypes by means of fluridone applications immediately after anthesis and embryo incubation in presence of ABA. A defect in ABA signaling should be seen as a level of expression of rab17 that is independent of the endogenous ABA level. For testing the second possibility, at two stages of development, embryos from both lines were isolated and incubated in water for different periods. ABA concentration in embryos and incubation media was quantified through a radioimmunoassay. In contrast to our findings for the IS 9530 line, rab17 expression did not respond to changes in ABA levels in Redland B2 embryos. ABA degradation/conjugation rate in embryos and incubation media did not show clear differences between sorghum lines for any of the developmental stages analysed. These results suggest that a disruption in the ABA signal transduction pathway in Redland B2 underlies the low ABA sensitivity shown by embryos from this line.