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

di 0
CHAPTER: 15(D)
Plant Hormones: Cytokinins


Cytokinins:
•      Cytokinins (CK) are a class of plant growth substances (phytohormones) that promote cell division, or cytokinesis, in plant roots and shoots.
•      They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and leaf senescence. 
•      There are two types of cytokinins: adenine-type cytokinins represented by kinetin, zeatin, and 6-benzylaminopurine, and phenylurea-type cytokinins like diphenylurea and thidiazuron (TDZ). 
•      Most adenine-type cytokinins are synthesized in roots Cambium and other actively dividing tissues also synthesize cytokinins.
•      No phenylurea cytokinins have been found in plants. 
•      Cytokinins participate in local and long-distance signaling, with the same transport mechanism as purines and nucleosides. 
•      Typically, cytokinins are transported in the xylem.

•      Cytokinins act in concert with auxin, another plant growth hormone.



Biosynthesis of Cytokinins:
•      Adenosine phosphate-isopentenyltransferase (IPT) catalyses the first reaction in the biosynthesis of isoprene cytokinins.
•      It may use ATP, ADP, or AMP as substrates and may use dimethylallyl diphosphate (DMAPP) or hydroxymethylbutenyldiphosphate (HMBDP) as prenyl donors. 
•      DMAPP and HMBDP used in cytokinin biosynthesis are produced by the methylerythritol phosphate pathway (MEP).
•      Cytokinins can also be produced by recycled tRNAs in plants and bacteria. The prenylation of these adenines is carried out by tRNA-isopentenyltransferase.
•      Auxin is known to regulate the biosynthesis of cytokinin.



Physiological roles of Cytokinins:
•      Accelerates cell division, cell elongation and morphogenesis.
•      Initiation in protein and nucleic acid metabolism.
•      Counteract the influence of apical dominance.
•      Helps to delay senescence.
•      Provide resistance to plant injured by high temperature and low temperature.
•      Can break seed dormancy and promotes germination.

Practical Applications of Cytokinins in Agriculture:
  1. Accelerate the induction of flowering of Short-Day plants.
  2. Accelerate the development of fruits.
  3. Accelerate tissue culture.
  4. Stimulates root initiation.
  5. Breaking the dormancy of certain light sensitive crop seeds.
  6. Delay in senescence in vegetables and keeps the cut flowers and vegetables fresh for a long period.
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)