Articles by "gibberellins"
Tampilkan postingan dengan label gibberellins. Tampilkan semua postingan

di 0
CHAPTER: 15(C)

Plant Hormones: Gibberellins


Gibberellins:
•      Gibberellins (GAs) are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence.
•      Gibberellin was first recognized in 1926 by a Japanese scientist, Eiichi Kurosawa, studying bakanae, the "foolish seedling" disease in rice. It was first isolated in 1935 by TeijiroYabuta and Sumuki, from fungal strains (Gibberella fujikuroi) provided by Kurosawa. Yabuta named the isolate as gibberellin.
•      They are found in several forms: GA-1, GA-2, GA-3……………………..GA-60.
•      The first gibberellins to be obtained were gibberellin GA-3. Now 52 gibberellins have been identified from different groups of plants.

Structure of Gibberellins:

The structure of gibberellins consists of diterpenoid acids. These are synthesized in plastids through terpenoid pathway. Their modification occurs in the endoplasmic reticulum & cytosol. There are two classes of gibberellins based on carbon number, one containing 19 carbons and another containing 0 carbons. In case of 19 carbon gibberellins, carbon 20 is replaced by five members Lactone Bridge. It links carbon 4 and 10 in the structure of gibberellins.



Physiological roles of Gibberellins:
1.      Induces cell elongation:
This hormone helps in the elongation of internodes. Gibberellins increase the stem of plant.

2.      Stimulates enzyme activity.
Some enzyme in plants requires gibberellins to become activated.

3.      Able to overcome dwarfism by cell elongation:
Dwarfism of plants is prevented by this hormones by elongation the internodes.

4.      Promotes Germination, leaf expansion.

5.      Induce De-Novo synthesis of enzyme.

Practical Applications of GA in Agricultural:
  1. Flowering
  1. Germination
  2. Apical Bud Dormancy
  3. Rooting
  4. Parthenocarpy
  5. Fruit Growth
  6. Increase fruit size and prevent cracking of fruits.
  7. Induce internode elongation.
  8. Prevent senescence in leaves.
  9. Increase sugar content in sugarcane and induce alpha-amylase in barley brewing



Continue reading

di 0
CHAPTER: 15(A)

Growth Regulators & Their Effects in Crop Plants


Growth Regulators & Phytohormones:
Ø  There is a complex series of events like fertilization, flowering, growing, which leads to a mature plant. These events are collectively called as development. This development is a process regulated by specific mobile chemical agents called growth regulators or growth substancs.
Ø  Sometimes, the term growth hormone (Phytohormone) is misused with growth regulator. The definition of phytohormone is “An organic substance produced naturally in plants controlling growth and other functions at a site remote from its place of production and active in minute amounts.”
Ø  According to K.V. Thiamann, whereas growth regulators include all naturally occurring as well as synthetic substance which control growth. As the above given definition indicates, all phytohormones are growth regulators but all growth regulators are not phytohormones.
Ø  Growth regulators are either growth promoters or growth inhibitors. Growth Promoters are- Auxins, Gibberellins, Cytokinins, and Growth inhibitors are- Absecisic acid & Ethylene.

What is the difference between Plant Hormones and Animal Hormones?
  1. Plant hormones are simple organic substances and animal hormones are complex organic substances.
  2. Plant hormones are transported through xylem, phloem or by diffusion and animal hormones are transported in the blood.
  3. There are no specific organs involved in the synthesis of the plant hormones, whereas animal hormones are always synthesized in endocrine glands.

The major classes of planthormones are:
1.      Auxin
2.      Cytokinins
3.      Gibberellins
4.      Abscisic Acid
5.      Ehylene


These hormones are promoters and inhibitors. Auxin, cytokinins, and gibberellins are growth promoters where as abscissic acid and ethylene are growth inhibitors. These hormones help plant for their growth, flowering, fruiting, and reproduction. Among these hormones auxin was first discovered as plant hormones. Ethylene is considered as exogenous hormones and helps in the ripening of the fruits.


Continue reading
Langganan: Postingan (Atom)