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Root Tip: the end 1 cm of a root contains young tissues that are divided into the root cap, quiescent center, and the subapical region. Root Cap: root tips are covered and protected by the root cap. The root cap cells are derived from the rootcap meristem that pushes cells forward into the cap region. Root cap cells differentiate first into columella cells. Columella cells contain amylopasts that are responsible for gravity detection. These cells can also respond to light and pressure from soil particles. Once columella cells are pushed to the periphery of the root cap, they differentiate into peripheral cells. These cells secrete mucigel, a hydrated polysaccharide formed in the dictyosomes that contains sugars, organic acids, vitamins, enzymes, and amino acids. Mucigel aids in protection of the root by preventing desiccation. In some plants the mucigel contains inhibitors that prevent the growth of roots from competing plants. Mucigel also lubricates the root so that it can easily penetrate the soil. Mucigel also aids in water and nutrient absorption by increasing soil:root contact. Mucigel can act as a chelator, freeing up ions to be absorbed by the root. Nutrients in mucigel can aid in the establishment of mycorrhizae and symbiotic bacteria. Quiescent Center: behind the root cap is the quiescent center, a region of inactive cells. They function to replace the meristematic cells of the rootcap meristem. The quiescent center is also important in organizing the patterns of primary growth in the root. Subapical Region: this region, behind the quiescent center is divided into three zones. Zone of Cell Division - this is the location of the apical meristem (~0.5 -1.5 mm behind the root tip). Cells derived from the apical meristem add to the primary growth of the root. Zone of Cellular Elongation - the cells derived from the apical meristem increase in length in this region. Elongation occurs through water uptake into the vacuoles. This elongation process shoves the root tip into the soil. Zone of Cellular Maturation - the cells begin differentiation. In this region one finds root hairs which function to increase water and nutrient absorption. In this region the xylem cells are the first of the vascular tissues to differentiate.
  • Last Modified: Saturday 16 February 2019, 08:37:10.