This document discusses plant hormones called auxins. It describes auxins as organic substances produced in actively growing plant tissues that influence physiological processes even at low concentrations. The document outlines the discovery of auxins in 1881 and notes they are produced in plant tissues and influence processes like cell elongation, differentiation, ethylene production, root and lateral root formation, fruit development, leaf abscission, secondary growth, and phototropism and gravitropism. It also discusses how auxins are applied to plants based on factors like plant type, age, concentration, and application method.

1. University of Salahaddin
College of Education
Environmental science department
1
Halala Rahman Qadir
4/30/2017

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Plant hormones (Phytohormones)
Are naturally occurring organic substance that can be
transported from the synthetic tissue to a specific
target tissue where, at low concentration, exert a
profound influence on physiological process.
Plant growth regulators
Plant growth regulators – include plant hormones
(natural & synthetic), but also include non-nutrient
chemicals not found naturally in plants that when
applied to plants, influence their growth and
development.

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Auxins
Auxin is a general name for a group of
hormones that are involved with growth
responses (i.e., elongate cells, stimulate cell
division in callus). the term "auxin" is
derived from the Greek word "to increase or
grow".

4. Discover of auxin
This was the first group of plant hormones discovered in
1881 by Charles and Francis Darwin, They reported
experiments on the response of growing plants to light
associated to phototrophic response.
 Occurs in very low concentrations.
 Isolated from human urine, (40mg 33 gals-1)
 In coleoptiles (1g 20,000 tons-1)
 Differential response depending on dose.
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Site
•Auxin is made in actively growing
tissue which includes young
leaves, fruits, and especially the
shoot apex.
•Made in cytosol of cells .

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Auxin Actions
1.Cellular Elongation:
Auxin can induce and amplify proton pumping.
Acidified cell walls have increased elasticity
which lead to cell elongation.
2. Cell differentiation
Auxin promotes differentiation of vascular tissue
(i.e., xylem & phloem).
3. Ethylene production
IAA apparently stimulates the production of
ethylene.

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4. Inhibition of root growth
5. Auxin Promotes the Formation of Lateral
and Adventitious Roots.
4-Auxin Promotes Fruit Development & fruit set.
5-Auxin Delays the Onset of Leaf Abscission.
6- Auxin induce secondary growth.
7- Tropic responses Such as gravitropism and
phototropism
Phototropism :is a growth movement induced by a
light stimulus.

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Gravitropism

10. Phototropism
Movement of plants toward light
Why?
Maximize amount of sun for photosynthesis to
make their food.

11. Application of auxin
Application of hormone depend upon of:
• Type of plant and age of plant.
• Doses and concentration of axuin.
• Methods used for application (like foliar , soil
application, stem injection, pretreatment seeds
with auxin.
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12. Pretreatment seeds with auxin
• The high percentage of germination of sown seeds in
the field has a bearing on the output. Pretreatment of
seeds with IAA, has been found to be very effective not
only in increased the percentage of germination but also
in the total yield of the crop plants. Suitable
concentration and combination have to be determined
for each and every crop plants.
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