Question

what are plant hormone? list and explain their functions.

Answer 1

Plant hormones called plant Growth regulators or PGRs 

These are

1) Auxin 

2) Cytokinin 

3) Gibberellin 

4) Ethylene 

5) Abscisic  acid 

Where Auxin , cytokinin , gibberellin are growth promoters 
And abscisic acid is growth inhibiter 
ANd ethylene shows both properties but mainly in growth 

Answer 2

Plant hormones or phytohormones are the organic substances which are synthesized in minute quantities in one part of the plant body and transport to another part where they influence specific physiological process.

Plant hormones include-

1-Auxins
2-Gibberellins
3-Cytokinins
4-Ethylene
5-Abscisic acid

(i)AUXINS (Gk. auxein= to grow)

The term auxin include all those chemical substances which promote the growth of stem or coleoptile sections and apex removed section, but in the same concentrations are incapable of causing plant growth.

Function of Auxins

-Cell division in cambium
-Promotes tissue culture
-Vascular tissue differentiation
-Root growth
-Apical dominance


(ii)GIBBERELLINS

The Gibberellins are plant growth hormone which enhance the longitudinal growth of stem when applied to intact plants.


Functions of Gibberellins
-Elongation of stem
-Reversal of Dawrfism
-Bolting and flowering
-Cell division in the cambium
-Parthenocarpy

(iii)CYTOKININS

The cytokinins are plant growth hormone which act primarily on cell division and have little or no effect on extension growth.


Function of Cytokinins
-Promotes cell division
-Promotes cell enlargement
-Breaking of dormancy
-Morphogenesis
-Counteraction of apical dominance

(iv) Ethylene


Ethylene is a volatile gas present in atmosphere as component of smoke. It is considered as plant growth hormone because it alters the tropic responses of roots and induces leaf abscission.

Function of Ethylene
-Helps in ripening of fruits
-Inhibitory effect on growth
-Suppression of bud growth
-Fruit growth and ripening
-Helps in flowering

(v)ABSCISIC ACID

Scientists while working on the physiological studies of the shedding of cotton balls, found that the chemical substance Abscision II (commonly known as abscisic acid) was responsible for their shedding. And hence, abscisic acid is now included in plant hormones

Function of Abscisic acid
-Promotes bud dormancy
-Inhibition of growth
-Helps in germination
-Controls geotropism
-Helps in stomatal closing