GIBBERELLIN LEVELS IN EMBRYOS OF GERMINATING SEEDS OF TWO SORGHUM LINES WITH CONTRASTING DORMANCY

PICCOLI P; RODRÍGUEZ MV; BENECH ARNOLD R; BOTTINI R

Puerto Vallarta, México

Congreso; IPGSA Conference; 2007

IPGSA

Caryopse sprouting in planta is an undesirable trait in sorghum. We have previously assessed by functional genomics that embryos of germinating seeds of a sprouting-resistant line (IS) show an increased expression of one GA2ox as compared to a non-resistant sprouting line (RB9). In order to unravel the mechanism involved in the control of dormancy of sorghum?s caryopses, the GA profile of embryos detached from caryopses of both lines along germination was assessed by GC-EIMS with stable isotopes as standards. GAs from both, the non-hydroxylative and the early-hydroxylative pathways, were searched. From the 2-hydroxy-GAs only GA51 levels were substantially higher in IS embryos after 4 days of incubation in correlation with the GA2ox expression. Nor GA29, GA8 or GA34 were detectable from the extracts. Both GA1 and GA4 levels were higher in RB9 in the first 2-3 days. The rest of the GAs assessed, i.e. GA19, GA17, GA3, GA24, GA25 and GA9 did not show appreciable differences between lines, with the exception of GA20 that increased after 4 days in RB9. Interestingly, the levels of GA1 and GA3 had values of two orders of magnitude higher respect to the other GAs. This finding suggests that in the embryos of the germinating seeds there are two different sources of GAs, one produced by the growing embryo that correlates with the gene expression previously determined, and the other coming from the endosperm and connecting tissues. It is possible that GA1/3 may be sequestered by some substances, like the polyphenolic net in which sorghum caryopses are particularly rich, and compartmentation of these GAs may account for the different sprouting behaviour of the two sorghum lines studied.