Describe/ explain the role of hormones in growth of plants.

a)Auxins;
-They stimulate cell division and elongation (leading to primary growth;
-They stimulate tropic responses/ growth in plants;
-They stimulate growth of adventitious roots in stem cuttings;
-They induce parthenocarpy (development of fruit from ovary without fertilization);
-They inhibit growth of lateral/ side branches from lateral buds enhancing apical dominance;
-They initiate cell division and differentiation in cambium enhancing secondary growth;
-They stimulate formation of callus tissue which causes healing of wounds (in association with other hormones);
-Some synthetic auxins are used as selective weed killer/ herbicide (by inducing distorted growth of plants and excessive respiration causing death of the plant);
b)Gibberellins/ gibberellic acid;
-They stimulate rapid cell division and elongation in dwarf plants;
-They stimulate fruit formation (by inducing the growth of ovaries into fruits after fertilization);
-They promote formation of side branches from lateral buds;
-They break dormancy in buds;
-They inhibit formation/ sprouting of side branches from stem cuttings;
-They retard the formation of abscission layer hence reduce leaf fall;
-They break seed dormancy by activating enzymes involved in breakdown of food substances during germination;
c)Cytokinins/kinetins
-They promote growth when they interact with auxins;
-They stimulate cell division in the presence of auxins;
-Break dormancy in some plants;
-Promote flowering;
-Promote formation of adventitious roots;
-Promote stomatal opening hence increased gaseous exchange and transpiration;
-Stimulate lateral bud development in shoots;
-Induce cell enlargement in leaves when in high concentration;
d)Ethene/ Ethylene;
-Causes ripening of fruits;
-Stimulates formation of abscission layer leading to leaf and fruit fall;
-Stimulates lateral bud development;
-Promotes germination of certain seeds by breaking seed dormancy;
-Promotes flowering in plants, for example in pineapples;
-Inhibits plant growth and may cause plant death;
e)Abscisic acid.
-It causes seed dormancy;
-Inhibits development of lateral buds/branches;
-Retards stem elongation;
-High concentration of abscisic acid causes stomatal closure by interfering with potassium ion uptake;
-Causes formation of an abscission layer that encourages leaf and fruit fall;
f)Florigens- they promote flowering;
g)Traumatins- they cause healing of wounds in plants;