| Examination of the relationship between germination efficiency and reproductive success using a simple model of seed population dynamics reveals that for short-lived seeds, opportunistic germination is required in order to facilitate population growth. For long-lived seeds, some inhibition of germination is required in order to achieve population growth. The simulation predicts that for plants growing in restrictive environments, germination frequencies should be low. For seeds which exhibit maternally-derived seasonal germination effects, physiological characteristics that facilitate growth under "off-season" conditions should be evident in the laboratory.;The germination response of Arabidopsis thaliana accessions is consistent with the predictions made by the simulation analysis. Cvi, which was collected from a restrictive climate, showed extreme germination delay. Col-O, Ler and No-O all showed the high germination efficiency predicted for their more favorable habitat. No-O and Cvi both exhibited tolerance to high-temperature, high-humidity storage. In No-O, a positive correlation between season of seed production and germination efficiency was dependent on the maternal parent in F1 hybrids in a Cvi X No-O reciprocal cross.;QTL analysis in 160 Ler/Cvi recombinant inbred lines reveals that Cvi's delay phenotype is conferred in 12-week old seeds by a single locus on chromosome 5, called Germination Delay 1 ( GD1). In 60-week seeds, an additional novel locus on Chromosome 3 (GD2) is required for the most extreme delay phenotype. The overall lower mean 48-hour germination frequency of the 60=week old lines is the result of a single Ler-derived locus (GD3) that lies 3 cM to the left of the peak of the GD1 locus. Annotation of GD1 reveals that this locus is potentially distinct from the after-ripening gene DOG1.;The model of seed population dynamics presented here made two predictions regarding seed adaptation under limiting and intermittently catastrophic environmental conditions: (a) low germination efficiency under restrictive conditions and (b) the necessity for consistent off-season seed production for short-lived seeds. Each of these predictions is evident physiologically and genetically in a panel of four Arabidopsis thaliana accessions. |
