Plants keep growing throughout their lives, and in mature plants many cells remain totipotent. These cells are found in meristems, regions of unspecialised cells that divide by mitosis.• Apical meristems at the tips of shoots and roots produce growth in length.
• Lateral meristems produce growth in width. The vascular cambium is a lateral meristem that divides to form new xylem and phloem.Cells produced by meristems differentiate into specialised cells such as xylem vessels, phloem sieve tube elements, palisade cells and root hair cells. As in animals, a cell specialises because it expresses only some of its genes.Because many plant cells keep their totipotency, they can develop in vitro into whole plants or plant organs when given the correct conditions. This is the basis of plant tissue culture (micropropagation):1. Small pieces of tissue (explants), often from a meristem, are cut from the parent plant and sterilised.
2. They are grown on a sterile nutrient medium containing plant growth factors, and form a mass of undifferentiated cells called a callus.
3. The callus is divided, and changing the growth factors makes cells differentiate into shoots and roots.
4. The plantlets are transferred to soil.The new plants are genetically identical clones of the parent. Tissue culture produces large numbers of plants with desirable characteristics quickly, and helps to conserve rare species. Its drawback is the lack of genetic variation: a whole crop could be wiped out by one disease.
• Lateral meristems produce growth in width. The vascular cambium is a lateral meristem that divides to form new xylem and phloem.Cells produced by meristems differentiate into specialised cells such as xylem vessels, phloem sieve tube elements, palisade cells and root hair cells. As in animals, a cell specialises because it expresses only some of its genes.Because many plant cells keep their totipotency, they can develop in vitro into whole plants or plant organs when given the correct conditions. This is the basis of plant tissue culture (micropropagation):1. Small pieces of tissue (explants), often from a meristem, are cut from the parent plant and sterilised.
2. They are grown on a sterile nutrient medium containing plant growth factors, and form a mass of undifferentiated cells called a callus.
3. The callus is divided, and changing the growth factors makes cells differentiate into shoots and roots.
4. The plantlets are transferred to soil.The new plants are genetically identical clones of the parent. Tissue culture produces large numbers of plants with desirable characteristics quickly, and helps to conserve rare species. Its drawback is the lack of genetic variation: a whole crop could be wiped out by one disease.