Question

What does one understand by growth regulators and Phytohormones.

Answer 1

Plants require light, water, oxygen, minerals, and other nutrients for his or her growth and development. aside from these external requirements, plants also depend upon certain organic compounds to signal, regulate, and control the expansion of plants.

Complete answer:
Phytohormones are organic compounds that are either synthesized in laboratories or produced naturally within the plants. They profoundly control and modify the physiological processes just like the growth, development, movement, removing excess fruit, or altering fruit maturity of plants.
Plant growth regulators are often grouped into five classes: compounds associated with auxins, gibberellins and inhibitors of gibberellin biosynthesis, cytokinins, abscisic acid, and compounds affecting the ethylene status. Products that block the biosynthesis of plant hormones also are available (Apogee, Retain).
Auxin:
It is also called as Indole ethanoic acid
The major site of auxin production is apical meristem by plants
Functions
- It promotes elongation of young shoots (Indoleacetic acid)
- Affects storage cell growth by inducing vascular cambium and secondary xylem
- Promotes fruit growth
Cytokinesis:
It stimulates cytokinesis produced in roots by plants and transported to other organs.
Functions:
- Moves in xylem sap
- Stimulates RNA and protein synthesis
- Works in conjunction with auxin
- Cytokinins and auxin are antagonistic- auxin from the terminal bud causes the shoot to elongate.
- Cytokinins from roots stimulate Axillary bud
- Slows leaf deterioration
Gibberellins:
It is produced within the meristem of apical buds and roots, young leaves, embryo.
Functions:
- Stimulates cellular division, growth of leaves
- Causes bolting- the rapid climb of floral stems
- Controlled by Gibberellins and auxin
- Grapes are sprayed to grow bigger
- Signals seeds to interrupt dormancy
Abscisic Acid:
It helps prepare plants for winter by suspending growth
Produced in leaves, stem, roots, green fruits
Functions:
- Inhibits cellular division within the vascular cambium
- The onset of seed dormancy
- Stress hormone – closes stomata
Ethylene:
Gaseous hormone- induced by high auxin inhibits the expansion
It is produced by tissues of ripening fruits, nodes of stems, aging leaves and flowers.
fruit ripening- aging cells release more ethylene.
Functions:
- Aging, fruit ripening, and leaf abscission
- Spreads from fruit to fruit
- Leaves lose pigment
- Leaf nutrients are sent to storage
- Short days and funky temperature.

Note:
Other Growth Regulators:
- Vernalin
- Caulines
- Florigen
- Morphactins
Photoperiodism is the reflex of organisms to the length of day or night. It occurs in both animals and plants and it also can be defined because of the developmental responses of plants to the relative lengths of sunshine and dark periods.
Thus, the term photoperiodism is coined to elucidate the power of plants to flower in response to changes within the relative length of day and night.