Growth is one of most fundamental and irreversible characteristics of a living being. Growth can be defined as “an irreversible permanent increase in size of an organ or its parts or even of an individual cell” whereas development can be defined as “a term that includes all changes that an organism goes through during its life cycle from germination of the seed to senescence”.
Plant hormones are chemicals secreted by plants. These act as growth regulators and help in the development of plants, both morphologically and physiologically. These can induce seed germination or dormancy, can promote senescence and abscission. These are secreted in quite low concentrations. They are as follows:
1. Auxin –
· Produced by growing meristems
· These help to initiate rooting in stem cuttings
· Induces floweing in pineapples
· These induce parthenocarpy in tomatoes
· These can also be used as herbicides (example – 2,4-D) to kill dicot weeds
· Promotes abscission of older leaves and fruits
· IAA (Indole-3-acetic acid) is a natural auxin
· NAA (Naphthalene acetic acid) is a synthetically produced auxin
2. Gibberellin –
· These increase length axis. Example – in grapes
· Helps apples to improve their shapes
· These delay senescence so that fruits can be left on trees for a longer time to extend its market period.
3. Cytokinins –
· These help in cell division
· These are found on parts of plants where rapid cell div occurs. Example- root apical, buds, young fruits
· These help in delaying senescence
4. Ethylene –
· It promotes senescence and abscission of leaves and flowes
· It promotes fruit ripening
· Enhances respiration
5. Abscisic acid –
· It is known as the stress hormone
· It is a growth inhibitor
· It inhibits seed germination
· Closes stomata
· It induces dormancy
Since plant hormones have a wide variety of uses, they can be produced synthetically. They have been using in propagation and development of plants.
This was the summary of plant hormones. I hope it helps.