Science Notes on Plant tissues and Hormones

Apical Meristems: 

• Found in the root and stem apex.
• Produces auxin and causes the root to increase its length.

Lateral Meristems:

• There are two types of secondary meristems which are also called lateral meristems because they surround the plant stem and cause growth laterally.

Intercalary Meristems: 

• Located at the base of the internode.
• It is capable of cell division and allows for rapid growth and regrowth of many monocots.
• Its importance is for those plants whose apex parts are eaten by vegetarian animals.
• After being eaten the apex part the plants grow with the help of intercalary meristems only. Like – grass.

(B) Permanent tissue:

•  These are made of those mature tissues that have lost their capacity for division.
• And attain a definite form for various works.

Permanent tissues are of the following types -

Type of Complex Tissues

• Xylem and phloem are complex issues that constitute the parts of the vascular bundle. They are also called vascular tissues.

Xylem:

• Xylem is a complex tissue forming part of a vascular bundle.
• Its main functions are –
  (a) Conduction of water and minerals
  (b) Provide mechanical support.

Dendrochronology- Determination of the age of the plant is done by counting the annual rings of the xylem tissue. 

Phloem: 

• It is composed of sieve elements, companion cells, parenchyma, and some fibres.
• Its main function is to conduct foods prepared by the leaves to different parts of the plant.

Plant Hormones and their functions:

Following hormones are found in plants –

Auxins:

• Discovered by Darwin in the year 1880.
• Controls the growth of plants.
• They are produced in the stem, buds, and root tips.
• Its main functions are –
  (a) Enhance stem growth and growth of lateral buds.
  (b) Auxin also plays a role in maintaining apical dominance.
  (c) Prevents the separation of the leaves.
  (d) It saves the crops from falling and destroys the straws.

Gibberellins:

• Discovered by a Japanese scientist Kurosawa in the year 1926.
• Its main functions are-
  (a) Promotes stem elongation.
  (b) Motivates the seeds to sprout.
  (c) Increases the activity of cambium in the wooden plants.
  (d) Turns the dwarf plants into long plants. And also. 
  (e) Helps in breaking the dormancy of plants.
  (f) Helps in creating flowering, Large sized fruits and flowers can be produced by its scattering.

Cytokinins:

• Discovered by Miller in the year 1955 but it was named by Lethem.
• Its main functions are-
  (a) Promotes cell division and development in the presence of auxins.
  (b) Naturally works in coordination with auxins.
  (c) Helps in breaking the dormancy of seed.
  (d) Enhance  RNA and protein synthesis.

Abscisic Acid or ABA:

• Initially discovered by Carnes and Adicote and later on by Waring.
• Abscisic acid is also produced in the roots in response to decreased soil water potential and other situations in which the plant may be under stress.
• Its main functions are-
  (a) This hormone is against growth.
  (b) Keeps the seeds & bud in a dormant condition.
  (c) Plays the main role in the separation of leaves.
  (d) Delays in the flowering of the long-day plant.

Ethylene:

• The only hormone which is found in the gaseous form.
• Its main functions are-
  (a) Helps in the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves.
  (b) It increases the number of female flowers.
  (c) Motivates separation of leaves, flowers, and fruits.

Florigens:

• Formed in leaves but helps in controlling and/or triggering or blooming of flowers in plants.
• Also called flowering hormones.

Traumatic:

• Helps in fixing the injuries of plants.

Thanks

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