9.3: Plant Growth
Mission 1: Growth
Mission Objectives. You should be able to...
1. Explain how plants grow.
2. Describe the role of mitosis in stem extension and leaf development.
3. Define "micropropogation."
4. Explain the role of auxins in plant growth
Growth in plants is confined to regions known as meristems. Meristems are composed of undifferentiated cells that are undergoing mitosis. Apical meristems are found at the tips of stems and roots. The root apical meristem is responsible for the growth of the root and the shoot apical meristem is at the tip of the stem. Shoot growth is a tad more complicated than root growth. Details are on page 423.
Mitosis and cytokinesis in the shoot apex (tip) provide cells needed for extension of the stem and development of leaves. Cells in meristem tissue are small and go through cell division repeatedly to produce more cells via mitosis and cytokinesis. These new cells absorbed nutrients and water and therefore increase in volume and mass.
Each apical meristem can give rise to additional meristems including protoderm, procambrium and ground meristem. These give rise to different tissues. Protoderm turns into epidermis, procambrium becomes vascular tissue, and ground becomes pith (that white stuff that you peel off oranges and other citrus).
Image from brittanica.com.
Mission Objectives. You should be able to...
1. Explain how plants grow.
2. Describe the role of mitosis in stem extension and leaf development.
3. Define "micropropogation."
4. Explain the role of auxins in plant growth
Growth in plants is confined to regions known as meristems. Meristems are composed of undifferentiated cells that are undergoing mitosis. Apical meristems are found at the tips of stems and roots. The root apical meristem is responsible for the growth of the root and the shoot apical meristem is at the tip of the stem. Shoot growth is a tad more complicated than root growth. Details are on page 423.
Mitosis and cytokinesis in the shoot apex (tip) provide cells needed for extension of the stem and development of leaves. Cells in meristem tissue are small and go through cell division repeatedly to produce more cells via mitosis and cytokinesis. These new cells absorbed nutrients and water and therefore increase in volume and mass.
Each apical meristem can give rise to additional meristems including protoderm, procambrium and ground meristem. These give rise to different tissues. Protoderm turns into epidermis, procambrium becomes vascular tissue, and ground becomes pith (that white stuff that you peel off oranges and other citrus).
Image from brittanica.com.
Auxins are hormones that have a broad range of functions including initiating the growth of roots, influencing the development of fruits, and regulating leaf development. Indole-3-acetic acid (IAA) is the most common auxin. You should know the relationship between IAA concentration and plant growth.
Plants respond to the environment via phototropism and gravitropism. Phototropism is when plants turn towards the sunlight. Stems grow towards the brightest light source, causing them to bend. In the absence of sunlight, they grow upwards, against gravity. Growth in response to gravitational force is called gravitropism.
If the plant is exhibiting phototropism, then auxin is transported laterally from the side with brighter light to the side that is more shaded. Higher concentrations of auxin on the shady side of the stem causes greater growth on that side so the stem grows in a curve towards the light source. Gravitropism is also auxin-dependent. The pattern of auxin effect is opposite to what happens in the shoot. In the shoot, auxin promotes elongation but in the root, auxin inhibits elongation.
Plants respond to the environment via phototropism and gravitropism. Phototropism is when plants turn towards the sunlight. Stems grow towards the brightest light source, causing them to bend. In the absence of sunlight, they grow upwards, against gravity. Growth in response to gravitational force is called gravitropism.
If the plant is exhibiting phototropism, then auxin is transported laterally from the side with brighter light to the side that is more shaded. Higher concentrations of auxin on the shady side of the stem causes greater growth on that side so the stem grows in a curve towards the light source. Gravitropism is also auxin-dependent. The pattern of auxin effect is opposite to what happens in the shoot. In the shoot, auxin promotes elongation but in the root, auxin inhibits elongation.
