Morphological dormancy, embryo growth and pericarp restraint during crop and wild Apiaceae mericarp germination in response to ambient temperature

Abstract

50 wild Apiaceae species revealed that the initial relative embryo sizes of crop species are significantly larger compared to wild species. Interestingly, the critical relative embryo sizes of the phylogenetic group that contains parsnip, were smaller for the crop compared to wild species. ABA-insensitive and auxin-promoted pre-germination embryo growth was blocked by heat (thermoinhibition), while the completion of germination by radicle emergence was inhibited by ABA. The thick pericarp of parsnip decreased in thickness and mechanical tissue resistance in parallel with the pre-germination embryo growth, while the thin pericarps of celery and carrot did not change. Parsnip pericarp contained significantly higher contents of the germination-inhibiting hormones abscisic acid (ABA) and cis-(+)-12-oxo-phytodienoic acid (cis-OPDA) compared to celery pericarp. Pericarp ablation experiments revealed that it acts as a mechanical and chemical (ABA, cis-OPDA) constraint (coat component of MD), and has a key role in narrowing the permissive temperature window for germination.