Plant Hormones

  

+First discovered plant hormone -  Auxin (By F.W. Went)

+word hormone is given by -  Starling

+word Phytohormone is given by -  Thiemann

There are 5 types of plant hormones -

1.Auxin

2.Gibberellin

3.Cytokinin

4.Abscisic Acid

5.Ethylene

1. Auxin -

                    Charles Darwin & Francis Darwin worked on canary grass for photo adoption effect and they called this matter Stimulus. Boysen & Jensen worked on Avena sativa for this effect and they called this matter Material Substance. F.W. Went worked on Avena for same effect and extracted that Auxin's odd distribution is responsible for shoot apical meristem's growth towards light, it is because of the photo reduction of Auxin.

            According to F.W. Went 27% of Auxin found in plant's light getting part, hence 57% of Auxin found in plant's dark part and 16% of Auxin get photo reduced. TIBA (Tri Iodo Benzoic Acid) is an anti-auxin.

IAA (Indole Acetic Acid) is a natural Auxin. which is found in most plants. Auxin's biosynthesis is conducted in present of Tryptophan amino acid by Zn+2 ions. IBA (Indole Butyric acid) is also a natural Auxin.

Auxin's effect on plant -

1. photo adoption

2. cell division & cell elongation

3. Stop lodging

4. Induce flowering

2. Gibberellin -

                              By Gibberella fujikuroi, rice plant gets diseased, which disease called Bakane (Foolish Seedling). Kurosawa & Swada find out this fact, that this disease caused by Gibberella fujikuroi.  Yabuta & Sumiki extracted Gibberellin from this fungus. It is biosynthesized by Mevalonic Acid Pathway.

Gibberellin's effect on plant -

1.Reduces genetic dwarfism

2.Induce flowering during LDPs

3.Bolting effect

4.Option for cold treatment for flowering

3. Cytokinin -

                          Discovered by - Miller

Letham get first natural cytokinin in coconut milk & immature seeds of Zea mays and called it Zeatin. It also biosynthesized by Mevalonic Acid Pathway, it is Adenine's derivative. Zeatin and Isopentenyl adenine are natural Cytokinin.

          BAP (Benzyl Amino Purine), Thidiazuron, Diphenyl urea are synthetic cytokinin.

Cytokinin's effect on plant -

1.Cell division

2.Morphogenesis

3.Richmand Land effect - delay in aging

4.induces flowering in SDPs

5.Induces development of plastids

4. Abscissic Acid -

                                 Addicott & Okhuma discovered Abscissin-II. Waring and Robinson discovered Dormin. Bennet, Clarck & Kefford discovered ꞵ-inhibitors from potato bud. it is biosynthesized by Mevalonic Acid Pathway by Carotene's oxidation process. This hormone is also called Stress Hormone because in lack of water it closes stomata. So it is also called Anti-vaporizing hormone.

Abscissic Acid's effect on plant -

1.Anti Auxin & anti GA

2.Induces aging process - Anti cytokinin

3.Works against cell elongation & cell division process

4.Induces abscission process

5. Ethylene -

                        Cousin discovered this plant hormone in mature oranges. It is a gas, which helps other fruit in maturing process. It is an antigrowth hormone. It is synthesized by Methionine amino acid. Roots drowned in water also synthesize this hormone.

Ethylene's effect on plant -

1.Induces aging and abscission process

2.induces flowering in pineapple

3.Three effect on stem - I. reduces stem length

                                            II. Induces stem thickness

                                            III. Induces stem's horizontal growth

4.Apinasty in leaves

*other important plant hormones -

1. Anti-GA hormones - Cyocel (CCC/chlormquet), Alar-85, AMO-1618, Phosphine-D, A-REST (ancymidol)

2. Calines - formation hormones -

                                                               Rhizocalines - root formation

                                                               Phyllocalines -  leaf formation

                                                               Caulocalines - Stem formation

3. Morphacetenes - Anti Auxin