WHAT HAPPENS TO SEEDLINGS IN THE ABSENCE OF LIGHT IN AUXIN DISTRIBUTION
In the absence of light, seedlings exhibit elongated stems and closed cotyledons, a phenomenon known as etiolation. This is because light is required for the proper distribution of auxin hormone in plants.
Auxin is a growth-promoting hormone that controls cell elongation and differentiation. In the presence of light, auxin is distributed evenly throughout the seedling, causing the stem to grow straight and the cotyledons to open. However, in the absence of light, auxin accumulates on the side of the plant that is away from gravity (the top side) and inhibits cell elongation in that region. As a result, the stem bends and elongates towards the direction of gravity.
Additionally, the absence of light also affects the distribution of auxin in the cotyledons. In the presence of light, auxin is distributed uniformly in the cotyledons, promoting their opening. However, in the absence of light, auxin is concentrated at the base of the cotyledons, causing them to remain closed.
Overall, the absence of light disrupts the proper distribution of auxin in seedlings, leading to etiolation and altered growth patterns.
In the absence of light, a process known as etiolation occurs in seedlings. Etiolation is the elongation and growth of seedlings in response to a lack of light. In this state, several changes take place in the seedlings' development, including the distribution of auxin.
Here is a step-by-step breakdown of what happens to seedlings in the absence of light in auxin distribution:
1. Initial growth: When a seedling germinates in darkness, it undergoes initial growth in search of light. The stem elongates rapidly, while the cotyledons (embryonic leaves) remain small and pale.
2. Apical dominance: In the presence of light, the apical meristem (growth tip) of the seedling releases auxin, which inhibits the growth of lateral buds and promotes the growth of the stem. However, in the absence of light, the apical meristem does not release as much auxin, resulting in decreased apical dominance.
3. Lateral bud growth: With reduced auxin levels coming from the apical meristem, the lateral buds (side branches) are released from inhibition and begin to grow. This leads to a bushier growth pattern in the absence of light compared to plants growing in light.
4. Elongation of stem and leaves: As the seedling elongates, the stem becomes thin and fragile due to an increased internode length (the distance between leaves). The elongation of stem and leaves is driven by a higher concentration of gibberellin hormone, which promotes cell elongation but does not necessarily result in structurally strong tissues.
5. Pale yellow color: In the absence of light, seedlings produce less chlorophyll, resulting in a pale yellow color rather than the typical green color. Chlorophyll is responsible for capturing light energy and enabling photosynthesis, which is reduced in the absence of adequate light.
It's important to note that these changes in auxin distribution and seedling development are temporary and reversible. Once the seedlings are exposed to light, they undergo photomorphogenesis, where auxin distribution, chlorophyll production, and other developmental processes are restored to normal.