Plant Growth Hormones

#Plant Biotech #plant growth hormone #GATE #Biotechstudy #Auxin #Cytokinin #Gibberellin #Ethylene #Abscic acid

Chemicals that regulate plant growth.
Signal molecules produced within the plant, and occurs in extremely low concentration.
Chemicals messengers that affect a plant’s ability to respond to its environment.
They have wide Range effect.
Difference between plant hormone and nutrients:-

Difference between Plant hormone and Nutrients

Functions of Plant hormones

There are some plant hormones which are described below; ž

žJasmonate, Brassinosteroid are also Plant Growth hormones.

Plant Growth hormones

žAn auxin, indole‐3‐acetic acid (IAA), was the first plant Growth hormone identified.
žIt is manufactured primarily in the shoot tips, in embryos, and in parts of developing flowers and seeds. Its transport from cell to cell through the parenchyma surrounding the vascular tissues requires the expenditure of ATP energy.
IAA moves in one direction only—that is, the movement is polar and, in this case, downward. Such downward movement in shoots is said to be basipetal movement, and in roots it is acropetal.

Auxins alone or in combination with other hormones are responsible for many aspects of plant growth. IAA in particular.
Elongation of cells.
IAA induces rooting in plants
NAA, IBA, IPA induce rooting of cuttings plants
Activates the differentiation of vascular tissue in the shoot apex and in calluses; initiates division of the vascular cambium in the spring; promotes growth of vascular tissue in healing of wounds.
žActivates cellular elongation by increasing the plasticity of the cell wall.
Maintains apical dominance indirectly by stimulating the production of ethylene, which directly inhibits lateral bud growth.
Activates a gene required for making a protein necessary for growth.
Promotes initiation and growth of adventitious roots in cuttings.
žPromotes the growth of many fruits (from auxin produced by the developing seeds).
žInhibits most flowering (but promotes flowering of pineapples).
žControls aging and senescence, dormancy of seeds.
žSynthetic auxins are 2,4‐D and 2,4,5‐T.
2,4‐D and 2,4,5‐T are weed killers.
Function of Auxin
Phototropism
(bending of Plants toward Light)

žNamed because of their discovered role in cell division (cytokinesis), the cytokinins have a molecular structure similar to adenine.
Cytokinin also known as kinetin.
Cytokinin isolated first from corn ( Zea mays), is the most active of the cytokinins. Cytokinins are found in sites of active cell division in plants—for example, in root tips, seeds, fruits, and leaves.
They are transported in the xylem and work in the presence of auxin to promote cell division.
Differing cytokinin:auxin ratios change the nature of organogenesis.
If kinetin is high and auxin low, shoots are formed
If kinetin is low and auxin high, roots are formed.
ž Lateral bud development, which is retarded by auxin, is promoted by cytokinins. Cytokinins also delay the senescence of leaves and promote the expansion of cotyledons.

Break bud and seed dormancy.
Promotes the growth of the lateral bud.
Promotes cell division and apical dominance.
They are used to keep flowers fresh for a longer time.
Used in tissue culture to induce cell division in mature tissues.
Promote lateral shoot growth and adventitious shoot formation.
Promote nutrient mobilization which in turn helps delay leaf senescence.
Helps in delaying the process of ageing (senescence) in fresh leaf crops like cabbage and lettuce.
Involved in the formation of new leaves and chloroplast organelles within the plant cell.
Used to induce the development of shoot and roots along with auxin, depending on the ratio.
Function of Cytokinin

Experimentation with GA3 sprayed on genetically dwarf plants stimulates elongation of the dwarf plants to normal heights. Normal‐height plants sprayed with GA3 become giants.
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 and are mainly obtained from a variety of organisms from fungi to higher plants.
They are acidic and are denoted as follows – GA1, GA2, GA3 etc.

Delay senescence in fruits.
It Stimuluate stem elongation and leaf expansion.
It helps in Break bud and seed dormancy.
Genetically dwarf plant grows tall after Gibberellins treatment. i.e Corn, Pea.
Help fruits like apples to elongate and improve their shape.
Used by the brewing industry for increasing the speed on the malting process.
Used as the spraying agent to increase sugarcane yield by lengthening of the stem.
includes flowering in long day plants in short days.
Helps in increasing the crop yield by increasing the height in plants such as sugarcane and increase the axis length in plants such as grape stalks.
Gibberellins are acidic in nature.

Ethylene is a simple, gaseous plant growth hormone, synthesis by most of the plant organs including ripening fruits and ageing tissues. It is an unsaturated hydrocarbon having double covalent bonds between and adjacent to carbon atoms.
Ethylene is used as both plant growth promoters and plant growth inhibitors. Ethylene is synthesized by the ripening fruits and ageing tissues.

Ethylene is the most widely used plant growth regulator as it helps in regulating many physiological processes.
Induce flowering in the mango tree.
Promotes sprouting of potato tubers.
Breaks the dormancy of seeds and buds.
It helps in Ripening of fruits and Enhance respiration rate during ripening of fruits.
Applied to rubber trees to stimulate the flow of latex.
Promotes abscission and senescence of both leaves and flowers.
Used to stimulate the ripening of fruits. For example, tomatoes and citrus fruits.
Includes epinasty( the outward and often downward bending of plant parts) in leaves.
Increases root growth and root hair formation, therefore helping plants to increase their absorption surface area. Abscisic acid.

Abscisic acid (ABA) is a growth inhibitor which was discovered in the 1960s. It was initially called dormant. Later another compound abscisin-II was discovered and are commonly called as abscisic acid.
This growth inhibitor is synthesized within the stem, leaves, fruits, and seeds of the plant.
Abscisic acid mostly acts as an antagonist to Gibberellic acid.
Abscisic acid (ABA) is also known as the stress hormone as it helps by increasing the tolerance of plants to different kinds of stress.
Its principal effect is inhibition of cell growth.
If leaves experience water stress, ABA amounts increase immediately, causing the stomata to close.

Abscisic acid Stimulates closing of stomata in the epidermis.
Helps in the development and maturation of seeds.
Inhibits plant metabolism and seed germination.
It is involved in regulating abscission and dormancy or we can say that it accelerates abscission and maintain dormancy of seeds.
It is widely used as a spraying agent on trees to regulate dropping of fruits.
Induces dormancy in seeds and helps in withstanding desiccation and other unfavourable growth factors.

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