<P> CLV1 has been shown to interact with several cytoplasmic proteins that are most likely involved in downstream signalling . For example, the CLV complex has been found to be associated with Rho / Rac small GTPase - related proteins . These proteins may act as an intermediate between the CLV complex and a mitogen - activated protein kinase (MAPK), which is often involved in signalling cascades . KAPP is a kinase - associated protein phosphatase that has been shown to interact with CLV1 . KAPP is thought to act as a negative regulator of CLV1 by dephosphorylating it . </P> <P> Another important gene in plant meristem maintenance is WUSCHEL (shortened to WUS), which is a target of CLV signalling . WUS is expressed in the cells below the stem cells of the meristem and its presence prevents the differentiation of the stem cells . CLV1 acts to promote cellular differentiation by repressing WUS activity outside of the central zone containing the stem cells . SHOOT MERISTEMLESS (STM) also acts to prevent the differentiation of stem cells by repressing the expression of MYB genes that are involved in cellular differentiation . </P> <P> Unlike the shoot apical meristem, the root apical meristem produces cells in two dimensions . It harbors two pools of stem cells around an organizing center called the quiescent center (QC) cells and together produce most of the cells in an adult root . At its apex, the root meristem is covered by the root cap, which protects and guides its growth trajectory . Cells are continuously sloughed off the outer surface of the root cap . The QC cells are characterized by their low mitotic activity . Evidence suggests that the QC maintains the surrounding stem cells by preventing their differentiation, via signal (s) that are yet to be discovered . This allows a constant supply of new cells in the meristem required for continuous root growth . Recent findings indicate that QC can also act as a reservoir of stem cells to replenish whatever is lost or damaged . Root apical meristem and tissue patterns become established in the embryo in the case of the primary root, and in the new lateral root primordium in the case of secondary roots . </P> <P> In angiosperms, intercalary meristems occur only in monocot (in particular, grass) stems at the base of nodes and leaf blades . Horsetails also exhibit intercalary growth . Intercalary meristems are capable of cell division, and they allow for rapid growth and regrowth of many monocots . Intercalary meristems at the nodes of bamboo allow for rapid stem elongation, while those at the base of most grass leaf blades allow damaged leaves to rapidly regrow . This leaf regrowth in grasses evolved in response to damage by grazing herbivores, but is more familiar to us in response to lawnmowers . </P>

Which meristematic tissue is found in root and shoot apex