Reduced seed longevity or storability is a major problem in seed storage and contributes to increasedcosts in crop production. Here we investigated whether seed galactinol contents could be predictive forseed storability behavior in Arabidopsis, cabbage and tomato. The analyses revealed a positive correla-tion between galactinol content and seed longevity in the three species tested, which indicates that thiscorrelation is conserved in the Brassicaceae and beyond. Quantitative trait loci (QTL) mapping in tomatorevealed a co-locating QTL for galactinol content and seed longevity on chromosome 2. A candidate for thisQTL is the GALACTINOL SYNTHASE gene (Solyc02g084980.2.1) that is located in the QTL interval. GALACTI-NOL SYNTHASE is a key enzyme of the raffinose family oligosaccharide (RFO) pathway. To investigate therole of enzymes in the RFO pathway in more detail, we applied a reverse genetics approach using T-DNAknock-out lines in genes encoding enzymes of this pathway (GALACTINOL SYNTHASE 1, GALACTINOL SYN-THASE 2, RAFFINOSE SYNTHASE, STACHYOSE SYNTHASE and ALPHA-GALACTOSIDASE) and overexpressorsof the cucumber GALACTINOL SYNTHASE 2 gene in Arabidopsis. The galactinol synthase 2 mutant and thegalactinol synthase 1 galactinol synthase 2 double mutant contained the lowest seed galactinol contentwhich coincided with lower seed longevity. These results show that galactinol content of mature dryseed can be used as a biomarker for seed longevity in Brassicaceae and tomato.