iPad 79% 4:43 PM learn.unt.edu Auxins What is meant by \"polaransport (both shoo
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iPad 79% 4:43 PM learn.unt.edu Auxins What is meant by "polaransport (both shoot and root) Describe the mechanism of the polar transport of auxin in plants Cytokinins; Give examples to show how the cytokinin/auxin ratio regulates the differentiation of cells. Ethylene Describe the effects of applied ethylene on (a) fruit ripening, (b) abscission, and (c) seedling development in the dark. Abscisic Acid List some of the effects of ABA. Use these examples to show that ABA can be classed as an inhibitor in some respects and a promoter in others Gibberellins Discuss the role of GA in stem growth using results obtained with GA-deficient mutants. Gibberellins Describe the mechanism by which gibberellins stimulate the germination of barley seeds. The Molecular Basis of Hormone Action Using barley aleurone tissues as an example, explain how hormones are able to switch genes on and off. The Molecular Basis of Hormone Action Discuss the ways in which plant hormones affect the shape of cells. The Molecular Basis of Hormone Action Explain how receptor proteins are involved in the mechanism of action of hormones. Give examples The Molecular Basis of Discuss the mechanism by which ABA regulates the opening of stomata. The Molecular Basis of Hormone Action;Explanation / Answer
Auxins)
Polar transport: The directional active movement or transport of hormones from one cell to another cell according to polarity is called polar transport. The plant hormone auxin follows the mechanism of acid trap or Polar auxin transport (PAT). In this movement, the membrane transport proteins (ABCB and PIN) act as carriers of hormone and act according to the principle of chemiosmotic model.
The alkaline environment favors the transport of auxin, whereas acidic environment inhibits it. So, in acidic conditions the auxin traps inside the cell, it is called auxin trap. The pH of inside the cell is ~7, whereas outside the cell is ~5. So, auxin inside the cell will be un-dissociated and able to cross the membrane.
Once, they reach to other cell and become anionic (pH~5) and trapped inside the cell. The PIN carriers are responsible for movement of auxin toward root and works based on gravitropic response. The auxin growth response basically depends upon both its concentration and the target tissue. It is transported unidirectional from the apex down to the shoots.
Cytokinins)
The plant hormone such as auxin may affect the cell elongation by synthesizing it in the apical root and shoot meristems or in young embryo. At low concentration, it promotes the elongation of certain organ of plants, as a result of cell expansion. Cytokinins cause the effects on the promotion of the cell division, also increases the root developments in the arid conditions.
Ethylene)
Ethylene is a plant hormone that causes fruits to ripen. It also stimulates Cellulase, an enzyme that breaks down plant cell walls and weakens that portion of the plant, causing leaves, flowers and fruits to fall off. Ethylene is in the form of a gas, and can move from one plant or fruit to another through the air. This is why one ripe fruit can cause another fruit within proximity to ripen.
Abscisic acid)
Abscisic acid is a plant hormone that causes dormancy in the seeds and buds of a plant when conditions are not favorable for growth. This plant hormone also causes the stomata to close. Because of its effects, abscisic acid is referred to as a stress hormone.
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