Seed imbibition is a prerequisite for subsequent dormancy and germination control. Here, we investigated imbibition responses of Arabidopsis seeds by transcriptomic and hormone profile analyses using dormant [Cape Verde Islands (Cvi)] and non-dormant [Columbia (Col)] accessions. Once imbibed, seeds of both accessions swelled most up to 3 h, reflecting water uptake. Microarray analysis showed that in both accessions, seeds imbibed for 15 min, 30 min and 1 h were less active in gene expression than at 3 h. More than 2,000 genes were either up-regulated or down-regulated in seeds imbibed for 3 h. Some genes up-regulated at 3 h were already induced in seeds imbibed for 1 h, suggestive of genome reprogramming early after the onset of imbibition. Imbibition-induced genes in seeds imbibed for 3 h included those up-regulated in both Col and Cvi (common) or unique to either accession (accession specific). Up-regulated genes that were both common and Cvi-specific were over-represented for sugar metabolism and the pentose phosphate pathway, whereas Col-specific genes were over-represented for ribosomal protein genes. Quantification of plant hormones showed that ABA and salicylic acid (SA) contents were higher, but gibberellin A4 (GA4), N 6-(Δ2-isopentenyl)adenine (iP), jasmonic acid (JA), JAisoleucine (JA-Ile) and IAA were lower in imbibed seeds of Cvi compared with Col. In addition, changes in IAA and JA were initiated before 1 h, whereas ABA and JA-Ile declined 3 h after the onset of imbibition. An increase in GA4 and iP appeared to be correlated temporally with the initiation of secondary water uptake, which marks the completion of germination.
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