PHYTOCHROME CONTROL OF GIBBERELLIN RESPONSE IN ARABIDOPSIS SEEDS: CHANGES IN CYTOKININS LEVELS AND ROLE OF CKH ALLELES

ARANA, MV; MUGRABI DE KUPPLER, AL; FERNANDEZ, H; MENENDEZ, V; SANCHEZ, RA

Olsztyn

Conferencia; 9th Insternational Conference on Seed Biology; 2008

Gibberellins (GA) are an important link between light signals perceived by the seeds through the phytochromes (PHY) and the processes controlling germination.  In Arabidopsis, promotion of germination by red light (R) involves increases in seed GA content and sensitivity.  Hereby it is showed that the overexpression of the 5-isopentyl adenine transferase gene in the IPT161 transgenic line of Arabidopsis promoted the response to GA in FR-treated seeds, indicating that CK enhance the responsiveness of the seed to GA.  In addition, the ckh1-1 and ckh2-1 mutants, which exhibit a cytokinin-hypersensitive phenotype for cell division and chloroplast development, showed an enhanced response to both GA and light, when compared with their wild type.  The contents of CK were larger in R than in FR treated wild type seeds, showing that activation of PHY provokes an increment in the CK content in a way consistent with its action on GA response.  In summary, our results support the idea that in Arabidopsis PHY-mediated enhancement of the germination response to GA involves an increase of the content of CK in the seed, and that CKH1-1 and CKH2-1 alleles participate in both the perception of GA and the modulation of the response to light.