Second, the occurrence of branching roots All the tough roots and secondary roots can occur branching. The difference in branching between the two shows that the former has fewer branches than the latter. Branches that occur directly from the root body are called branch roots. A branch root is the same as the root body, but it can also produce branches of the next level, that is, the second branch root, and so on. According to studies, the primary and secondary roots of wheat can produce three or even four branch roots, but the three and four branch roots generally only occur in the thicker roots.
In the primary growth of wheat roots, branching occurs continuously. After about 15 days after rooting, more branches can be produced on the root. The process has already begun in the root hair area, but it actually broke through the parental cortex and the epidermis and entered the soil in the area above the root hair area. The reason why the root differentiation formation of school campuses has the above time and space interval is because wheat has long been adapted to natural habitats, and the adaptation results in the formation of branches does not affect the formation and function of root hairs. According to another study, the location of branching roots is relatively fixed. In the roots of crops with multiple prototypical tough xylem, such as wheat, it is facing the position of native phloem. Therefore, the branching roots show a very regular longitudinal arrangement on the mother root.
The origin of branching roots and stem organs are not the same. Its differentiation occurs internally, and the branches originate from the mother's root sheath. When branching roots occur, certain holding cells in the local area of ​​the perisylvian sheath in the mother root, that is, competent cells are stimulated by high concentration of auxin or other growth regulators or rooting environment, and the cytoplasm is thickened and the vacuole becomes smaller, and Gradually restore meristem ability, followed by cell division and differentiation to produce branched root primordia. The earliest differentiation process of branch roots can be divided into two stages: the first stage is the division of one or a few cells in the periphery, the increase of the number of cell layers, and the formation of new tissue outwards; the second stage is the division of the week Simultaneously with the pericentral division, the root protuberances continue to grow (to produce a mass of cells), ie to form the root primordia of the branch roots. After the early differentiation process is completed, the branch primordium continues to divide, grow and gradually differentiate into conical bovine long and root crowns. Cells at the growing point continue to divide, grow, and differentiate, forming elongated and mature areas to promote the development of meristems and root caps at the growing point. Because the roots of the branches produce a large amount of mechanical pressure during their formation, and the root canal cell secretion dissolves the cortex and epidermal cells of the mother root, the lamellar roots can easily penetrate the cortex and cortex. The process of epidermis extends out of the mother root and into the soil. Electron microscopy observations indicated that during the penetrating process of the taping root, the cortex of the mother root was partially destroyed, and there was a certain gap between the branch root and the mother root cortex.
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