short notes on auxin (4marks)
Answers
Auxin Definition
An auxin is a plant hormone derived from the amino acid tryptophan. An auxin may be one of many molecules, but all auxin molecules are involved in some sort of cellular regulation. Auxin molecules are one of five major types of plant hormone. The other major groups are the gibberellins, cytokinins, ethylene, and abscisic acid. Auxin was the first of these groups to be identified, and was chemically isolated in the 1930’s.
The most widespread auxin is indoleacetic acid, or simply IAA. IAA is an auxin which is very important in the growth and development of plant tissues. In studying auxin molecules, scientist have been able to recreate similar structures, called synthetic growth regulators. These “fake” auxins also stimulate growth in plants and have been used in many agricultural and commercial applications.
Auxin function
The auxin group of hormones has a wide range of uses in a plant. Auxin molecules are found in all tissues in a plant. However, they tend to be concentrated in the meristems, growth centers which are at the forefront of growth. These centers release auxin molecules, which are then distributed towards the roots. In this way, the plant can coordinate its size, and the growth and development of different tissues based on the gradient of the auxin concentration.
Auxin affects many different cellular processes. At the molecular level, auxin molecules can affect cytoplasmic streaming, the movement of fluids within a cell, and even the activity of various enzymes. This gives auxin direct control over the growth, development, and proliferation of individual cells within the plant. The auxin gradient directly affects processes such as flower initiation, fruit development, and even tuber and bulb formation. Even on a daily basis, auxin levels affect processes such as phototropism, which allows the plant to follow the sun and gain the most energy. The auxin controls this process by concentrating in the side of the plant away from the sun. This causes changes in the cells, which bend the plant toward the light.
Answer:
Auxins are a powerful growth hormone produced naturally by plants. They are found in shoot and root tips and promote cell division, stem and root growth. They can also drastically affect plant orientation by promoting cell division to one side of the plant in response to sunlight and gravity.
1) Five naturally occurring (endogenous) auxins in plants include indole-3-acetic acid, 4-chloroindole-3-acetic acid, phenylacetic acid, indole-3-butyric acid, and indole-3-propionic acid. ...
2) Synthetic auxin analogs include 1-naphthaleneacetic acid, 2,4-dichlorophenoxyacetic acid (2,4-D), and many others.
Native auxin molecules are normally derived from the amino acid tryptophan. This amino acid has a six-sided carbon ring, attached to a 5-sided ring containing carbon. This 5-sided ring has a group attached. The only difference between most auxin molecules and tryptophan is what is attached to this ring.(this para is all about structure of auxin)
Role of auxin
Auxin is a key regulator of plant growth and development, orchestrating cell division, elongation and differentiation, embryonic development, root and stem tropisms, apical dominance, and transition to flowering.
Several closely related hormones are known collectively as auxin or auxins. The chemical structure of the most common plant auxin, indole-3-acetic acid (IAA), was determined in the 1930s.