Production, composition, and ecological function of sweet basil seed mucilage during hydration
Sweet basil (Ocimum basilicum L.) fruit/pericarp produces mucilage that engulfs fruit and seed within minutes of hydration. Seed mucilage is produced by plant species adapted to arid, sandy soils, though its significance in determining ecological fitness is unclear. Basil fruit/seeds were examined using light and environmental scanning electron microscopy. Basil mucilage forms columnar structures that unfold from the pericarp upon hydration. Dilute hydrochloric acid removed mucilage and decreased water content 4-fold but did not inhibit laboratory seed germination. Fourier transform mid-infrared (FTIR) spectroscopy analysis showed mucilage is composed of hemicellulose that enabled basil seeds to cling to a smooth incline board set to a 70° steeper slope than seeds without mucilage. The fully hydrated seeds approached zero water potential, so the mucilage did not prevent full hydration. Seeds with mucilage had from 12 to 28% higher germination than seeds without mucilage planted in growing media. Seeds with mucilage also had higher survival percentages after 10 days. Basil fruit/seed mucilage provides a reservoir of loosely bound water at high water potential for seed germination and early seedling development, thus improving survivability under adverse moisture conditions.