• The organic compounds which are synthesised at particular locations in plant and work at very low concentration are called plant growth substances.
  • they stimulate or inhibit the growth of plant.
  • none of the plant growth substances are amino acids or protiens
  • five major type of growth substsnces are recognised. viz;

auxin

gibberellin

cytokinin
abcisic acid
ethene


AUXIN

plant growth substances 

The common natural auxin is IAA (indole acetic acid)

  • produced at: stem apices,young leave
  • transported through: parenchyma cells
  • functions: 1. elongarion of cells

                         2. maintenance of apical dominance
                         3.regulating tropic movements
                         4.inhibition of leaf abscission
                         5.induction of cambial activity
                         6.induction of root growth
                         7.induction of fruit growth

 

GIBBERELLIN/GIBBERELLIC ACID

  • produced at: young leave, roots, germinating seeds
  • transported through: parenchyma cells
  • functions: 1.elongation of stems

                         2.activating enzymes at seed germination

 

CYTOKININ

 Natural cytokinins are compound related to adenine

  • produced at: root apices, dividing cells of many tissues
  • transported through: xylem
  • functions: 1. promotion of shoot growth

                            2.inhibiting apical dominance
                            3.delay senescence of leaves
                            4.inducing cell division by interacting with auxin

 

ABCISIC ACID(ABA)

  • produced at: root caps, immature seeds
  • transported through: xylem
  • functions: 1.inhibition of seed germination

                            2.closure of stomata at water stress conditions
                            3.inhibition of bud growth and cambium activity in winter in plants growing in temperate countries.


ETHELENE

 plant growth substances

  • produced at: fruits , parenchyma cells
  • transported through: parenchyma, phloem
  • functions: 1.helps in stem elongation

                         2.induce ripening of fruits
                         3.induce flowering in some plants
                         4.abscission of leaves and fruits

 

 

Synthetic compounds

act similar to the natural plant growth substances

  • IBA
  • 2,4-D
  • MCPA


Uses of natural and synthetic plant growth substances in agriculture

  • IBA- induction of roots in stem cutting
  • Auxin- to induce parthenocarpy and fruit development
  • 2,4-D, MCPA- as weedicides
  • cytokinin - to extend freshness of cut leaves and flowers
  • gibberellin- to induce seed germination, elongation of stem
  • ethelene- to induce fruit ripening

 

 

Wanna memorize easily?  Let's give it a try using the photographic memory:)

   plant growth substances

 

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