Phytochrome modulates the response of endosperm to Gibberellins in Datura ferox

ARANA MV; DE MIGUEL LC; AUGE GA; SÁNCHEZ RA.

Brisbane

Workshop; 8th International workshop on seeds.; 2005

International Society for Seed Science

     Promotion of germination by phytochrome (PHY) involves extensive changes in the micropylar region of the endosperm (ME) including a reduction in the mechanical resistance. Many of the changes induced in the ME are the result of light perception by PHY in the embryo, where it stimulates the synthesis of gibberellins (GA). The GA move to ME and there promote weakening. Our results show that the PHY action not only increases GA supply to the ME, it also enhances the production by the embryo of a signal that promotes the responses of ME cells to GA.  Promotion by GA of B-mannanase and B-mannosidase activities and B-mannanase (Dfman) and expansin (DfExpa) mRNA accumulation is larger in ME of red-light (R)-treated seeds than in far-red (FR) controls. Embryo-ME contact is necessary for the regulation of the GA response, since light has no effect on GA sensitivity of isolated ME.  Exogenous Zeatin replaces light in the promotion of ME responses to GA suggesting that cytokinins may be components of the embryonic signal. Moreover, R promotes DfPHOR mRNA accumulation in ME and blocking GA synthesis prevents it. Exogenous GA promotes DfPHOR expression, suggesting that this effect of R is through GA. Preliminary studies show that DfSPY and DfGAmyb mRNA accumulation is not under PHY control.  These results show that the light perceived by the embryo regulates the response of ME cells to GA, and that GA action may be related with changes in DfPHOR expression.