The Production and Function of Mucilage by Sweet Basil (Ocimum basilicum L.) Seed
Sweet basil (Ocimum basilicumL.) seeds produce a thick layer of mucilage around the testa within minutes after hydration. Mucilage is most prevalent among plant species adapted to surviving in arid sandy soils, though its significance in determining the ecological fitness is unclear. The mucilage produced by these seeds is reported to be composed of cell-wall polysaccharides that are deposited in testa cells during development. In this study, sweet basil seeds were examined using light and environmental scanning electron microscopy. The mucilage of basil seeds is held together by columnar structures that unfolded from the pericarp and helped hold and stabilize the mucilage to the seed surface. The mucilage was removedusing diluted hydrochloric acid to compare performance of seeds with and without mucilage. Mucilage removal inhibited laboratory seed germination under ideal conditions and significantly reduced the seed water content four fold. The mucilage anchored seeds and increased their resistance to movement in the environment. Osmometry showed the water potential of fully hydrated seeds to be near zero suggesting that the mucilage provides a pool of loosely bound water to germinating seeds and seedlings in arid environments. Testing in soil with various levels of hydration confirmed intact basil seeds with mucilage germinated to higher percentages and survived longer than seed with mucilage removed.