Auxin

• Auxins were the first of the major plant hormones to be discovered
• These are a class of organic compounds which are mainly responsible for bringing about cell elongation in shoots
• They may be produced in plants as a result of metabolism or they may be of synthetic origin
• The principal natural auxin is indole acetic acid (IAA)
• Auxins have a cardinal role in coordination of many growth and behavioral processes in the plant’s life cycle and are essential for plant body development.
• All auxins are occurred at the meristematic apices of root, shoot, buds, leaves, cotyledons, bacteria, yeast, fungi etc
• There are several forms of auxins: IAA, IBA, NAA , 2,4-D etc

Role of Auxin

• Apical Dominance: Removal of apical bud stimulates lateral buds
• Cell Division And Elongation: Shoot and Root growth
• Xylem Differentiation: Auxins helps in establishing contact between vascular tissues of the callus and that of the bud and makes it possible for the bud to grow properly in callus. By adding auxin and sugar continued growth of callus may be obtained and new shoots and even new plant can be produced
• Nucleic Acid Activities IAA increases total RNA- synthesizes specific enzymes lead to cell enlargement
• Manifold Activities Play specific role in seed germination, growth, rooting, flowering (Reproductive phase), abscission, parthenorcarpy and tissue culture

Auxins use in Agriculture and Horticulture:

• Propagation of plants by hormone treatment of cuttings
• Prevention of pre harvest drops of plants
• Increasing parthenocarpy
• Increasing fruit set
• Inhibition of prolonged dormancy
• Control of flowering
• Defoliation of plants
• Prevention of leaf fall or abscission
• Thinning of compact fruits
• Selective weed killer