The walls of each locule bend outward, then split and twist as the seed falls from the capsule. Initially, the capsule splits at the top, creating an opening to each of the four locules. The cylindrical nature and cellular composition of sesame fruits leads to an even more complex form of hygroscopic movement. dehisced capsules of sesame (Sesamum indicum) photo credit: wikimedia commons (Dinesh Valke) As it dries it bends and/or twists, thereby releasing its contents. In both of these examples, water is evaporating from the plant part in question. A more complex movement can be seen in the seed pods of many species in the pea family, which both bend and twist as they split open. The simplest form of hygroscopic movement is bending, which can be seen in the opening and closing of pine cone scales. That is, their movements are driven by changes in humidity. As in the seed bearing parts of many other plant species, the capsules of sesame exhibit hygroscopic movements. This research has helped us appreciate the unique way that the capsules of the sesame plant dehisce. In order to develop these new varieties, breeders have had to gain an understanding of the mechanisms behind dehiscence and the genes involved in this process. Mechanically harvested varieties of sesame exist today, and improvements in these non-shattering varieties continue to be made. Additional threshing damaged the seeds and caused the harvest to go rancid. In early trials, seed pods were too tough and passed through threshers without opening. Developing varieties with shatter-resistant seed pods, has been challenging. But in places like the United States and Australia, where mechanical harvesting is desired, it has been necessary to develop new, indehiscent varieties that can be harvested using a combine without losing all the seed in the process. When harvested this way, naturally shattering capsules may be preferred. Once dry, they are held upside down and beaten in order to collect the seeds from their dehisced capsules. The plants are cut, tied into bundles, and left to dry. Most of the world’s sesame crop is harvested by hand. In domesticated sesame, the shattering trait persists and yield losses are often high. Selecting varieties that hold on to their seed long enough to be harvested was imperative for crops like beans, peas, and grains. If fruits dehisce before they can be harvested, seeds fall to the ground and are lost. Dehiscence is also called shattering, and in many domesticated crop plants, shattering is something that humans have selected against. Compare this to indehiscent fruits like acorns, which must either rot or be chewed open by an animal in order to free the seeds. The fruits of sesame are dehiscent, which means they naturally split open upon reaching maturity. One of my favorite uses for sesame seeds is tahini, which is one of the main ingredients in hummus. The seeds are prized for their high oil content and are also used in numerous other ways, both processed and fresh. Rows of tiny, flat, teardrop shaped seeds are produced in each chamber. The fruits are deeply-grooved capsules with at least four separate chambers called locules. They come in shades of white, pink, blue, and purple and continue to open throughout the growing season as the plant grows taller, even as fruits formed earlier mature. The flowers are tubular, similar in appearance to foxglove, and are typically self-pollinated and short-lived. Its broad lance-shaped leaves are generally arranged directly across from each other on the stem. However, the best yields are achieved on farms with fertile soils and adequate moisture.ĭepending on the variety and growing conditions, sesame can reach up to 5 feet tall and can be unbranched or highly branched. It is an annual plant that is drought and heat-tolerant and can be grown in poor soils and locations where many other crops might struggle. Sesame was first domesticated in India and is now grown in many other parts of the world. It shares a genus with about 20 other species – most of which occur in sub-Saharan Africa – and belongs to the family Pedaliaceae – the sesame family. Sesamum indicum is a domesticated plant with a 5000 plus year history of cultivation. But in this instance, the process of opening those fruits is fairly unique. Sesame’s story is similar to the stories of numerous other plant species whose seeds are born in dehiscent fruits. In order for the next generation of plants to have a chance at life, the seeds must be set free. In sesame’s case, seeds are the treasure, which are kept inside a four-chambered capsule. In certain instances, “ open sesame” might be something you exclaim to magically open the door to a cave full of treasure, but for the sesame plant, open sesame is a way of life.
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