Seed germination and mucilage production in chia (Salvia hispanica)

Chia is an oil seed crop with high ω-3 fatty acid and fiber content. Chia was domesticated in pre-Columbian Mesoamerica where its seeds were used for food, medicine and oil. Upon imbibition, seeds (nutlets) exude mucilage. Mucilage begins to emerge from the ruptured pericarp within minutes of exposure to water. The tethered mucilage continues to unfold reaching its final expansion size after approximately 1.5 h. At that time, the mucilage represents 92% of the water weight gained by the seed. The mucilage can be removed following hydration with an acid wash without impacting final germination percentage. Comparing seeds with and without mucilage, seeds with the mucilage removed germinated more slowly with only 63% of the seeds germinating after 24 h compared to 97% of the seeds producing mucilage. Chia seed germination on polyethylene glycol (PEG) solutions with increasing negative water potentials was slower and germination was totally inhibited at 1.0 mol of PEG. Germination was comparable for seeds with or without mucilage even at the higher PEG concentrations. However, germination was greater in seeds imbibed in water for 1 h prior to being transferred to 0.6 or 0.8 mol of PEG solutions. For example, after 48 h germination was 29% higher in seeds imbibed for 1 h prior to being transferred to 0.6 mol of PEG compared to dry seeds directly sown into the PEG solution. These data suggest that the mucilage may aid in supplying water to the seed resulting in more rapid imbibition and early completion of germination. The mucilage may also act as a buffer to provide free water to the seed if conditions dry following initial imbibition.