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Auxin concentration level, together with other local factors, contributes to cell differentiation and specification of the cell fate. Depending on the specific tissue, auxin may promote axial elongation (as in shoots), lateral expansion (as in root swelling), or iso-diametric expansion (as in fruit growth).
Most debates have concerned the signalling role of auxin and the molecular nature of cell wall modification. The current version holds that auxin activates small auxin-up RNA (SAUR) proteins, which in turn regulate protein phosphatases that modulate proton-pump activity. Acid growth is responsible for short-term (seconds to minutes) variation ...
The auxin indole-3-acetic acid (IAA) regulates concentration of GA 1 in elongating internodes in peas. [37] Removal of IAA by removal of the apical bud, the auxin source, reduces the concentration of GA 1, and reintroduction of IAA reverses these effects to increase the concentration of GA 1. [37] This has also been observed in tobacco plants. [38]
Auxins were the first class of growth regulators discovered. A Dutch Biologist Frits Warmolt Went first described auxins. [23] They affect cell elongation by altering cell wall plasticity. They stimulate cambium, a subtype of meristem cells, to divide, and in stems cause secondary xylem to differentiate.
Acid growth refers to the ability of plant cells and plant cell walls to elongate or expand quickly at low (acidic) pH. The cell wall needs to be modified in order to maintain the turgor pressure. This modification is controlled by plant hormones like auxin. Auxin also controls the expression of some cell wall genes. [1]
When cytokinin and auxin are both added together, the cells expand and differentiate. When cytokinin and auxin are present in equal levels, the parenchyma cells form an undifferentiated callus. A higher ratio of cytokinin induces growth of shoot buds, while a higher ratio of auxin induces root formation. [2]
These stages can also be defined by the hormones that are regulating the process which are as follows: Stage I, cytokinin promoted, causing the lateral bud to form since cytokinin plays a role in cell division; Stage II, auxin is promoted, resulting in apical dominance ("imposition of inhibition"); Stage III, cytokinin released resulting in ...
On exposure to sunlight, auxin in the banana migrates from the sunlight side to the shaded side. Since auxin is a powerful plant growth hormone, the increased concentration promotes cell division and causes the plant cells on the shaded side to grow. [13] This asymmetrical distribution of auxin is responsible for the upward curvature of the banana.