Question:
The wavelength of light absorbed by $Pr$ form of phytochrome is
The wavelength of light absorbed by $Pr$ form of phytochrome is
Updated On: May 23, 2026
- 680 nm
- 720 nm
- 620 nm
- 640 nm.
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The Correct Option is A
Solution and Explanation
Phytochrome is the photoreceptor pigment that controls flowering. It has two forms as P and Pfr. Pr is bluish phytochrome and it absorbs light at 660 to 680 nm of wavelength. P is (far red) yellowish green and absorbs light at 730 nm of wavelength.
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Concepts Used:
Plant Growth Regulators
What is a plant growth regulator?
Plant growth regulators (PGRs) are chemicals used to modify plant growth such as increasing branching, suppressing shoot growth, increasing return bloom, removing excess fruit, or altering fruit maturity.
Types of Plant Growth:
There are the following types of plant growth.
- Primary and Secondary Growth: The growth of a plant is termed primary when the same happens through the mitotic division of the meristematic cells which are present at the root and the shoot of the plants.
Whereas, the secondary growth in a plant takes place through the division of the secondary meristem, which, in turn increases the diameter of the body of the plants.
- Primary and Secondary Plant Growth
- Unlimited Growth
- Limited Growth
- Vegetative Growth
- Reproductive Growth
The five groups of plant growth regulators used in fruit crops include:
- Auxins: Auxins are one of the most important plant hormones. The chief naturally occurring auxin is indole-3 acetic acid – IAA and other related compounds.
- Gibberellins: Gibberellins are an extensive chemical family based on the ent-gibberellane structure. The first gibberellin to be discovered was gibberellic acid. Now there are more than 100 types of gibberellins.
- Cytokinins: These are produced in the regions where cell division occurs; mostly in the roots and shoots. They help in the production of new leaves, lateral shoot growth, chloroplasts in leaves etc.
- Absicisic Acid: Absicsic acid controls the dormancy of buds and seeds, inhibits shoot growth and is involved in regulating water loss from plants.
- Ethylene: Ethylene is a simple, gaseous plant growth regulator, synthesised by most of the plant organs includes ripening fruits and ageing tissues.