Auxin Biosynthesis MCQ - Practice Questions with Answers

• Natural auxins are synthesized in the physiologically active parts of the plants like shoot apices, leaf primordia, developing seeds, buds, and embryos.
• The amino acid tryptophan acts as the precursor for auxin synthesis.

• In the root apices, it is synthesized in smaller amounts.
• Auxins show the polar movement. They move from the apex or tip towards the base in the stem. This type of movement is called basipetal. 
• Almost 75% of auxin shows basipetal movement.
• The movement becomes acropetal in roots when the auxins move from the root tip towards the stem.
• Almost 25% of auxin shows acropetal movement.
• Auxins show movement through diffusion from cell to cell. They do not travel through the vascular tissues.

Synthetic Auxins:

• Synthetic auxin analogues include 1-naphthaleneacetic acid, 2,4-dichlorophenoxyacetic acid (2,4-D) and many others.
• Some synthetic auxins, such as 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), are also used as herbicides.
• Broad-leaf plants (dicots), such as dandelions, are much more susceptible to auxins than narrow-leaf plants (monocots) such as grasses and cereal crops, so these synthetic auxins are useful as synthetic herbicides.

Free and Bound Auxins:

• Free auxins are the active form of auxins. 
• These can be easily extracted.
• Bound auxins cannot be extracted except with the help of organic solvents, such as IAA-aspartic acid, IBA-alanine, etc.
• Bound auxins are hormonally inactive meant for storage

Anti-auxins:

• These are the compounds that inhibit the action of auxins and compete with auxins for active sites.
• These include p-chlorophenoxy isobutyric acid (PCIB), 2,3,5-triiodobenzoic acid (TIBA), etc.