Describe the role of hormones in the growth and development of plants.

K.C.S.E Biology Q & A - MODEL 2002PP1QN19

Describe the role of hormones in the growth and development of plants.

answers

Indole acetic acid/IAA/ Auxins

• Promote cell division  tropic responses, ( accept cell division in cambium)
• Promote formation of absecission layers/ bring abrupt  leaf – fall
• Promote fruit formation ( parthenocarpy)
• Promotes cell differentiation ( of vascular tissue)
• Causes apical dominance/ inhabit growth and development of lateral buds
• Promote growth of adventitious roots ( on stems)
• IAA + cytokine induce formation of callus tissue ( during healing of wounds)

GIBBECETINS ( accept GA3)

• Promotes cell division  / cell  elongation in dwarf varieties
• Parthenocapy/ initiating  formation of IAA/ setting of fruits after fertilization
• Formation  of side  branches  ( of stems)  and dormancy ( in buds); inhibit growth of  adventitious roots.
• Activates ( hydrolytic) enzymes during germination/ promotes germination of seeds/ breaks seed dormancy.
• Affects  leaf expansion and shapes / retard leaf absecission

CYTOKININS’

• Accept any correct example kinetin 8 zeatin
• Breaks dormancy ( in some species); promotes flowering in some species
• Promotes cell division  ( in presence of IAA)
• Stabilizes proteins and chlorophyll
• Promotes root formation
• Low concentration encourages leaf senescence/ high concentration protein increased cell enlargement
• Promotes flowering ( in some species)
• Ethylene  / Ethene / C2114 ( reject ethane)
• Stimulate  lateral bud development
• Ripening of bananas/ fruits
• Induces thickening of stem/ inhabits stem elongation
• Promotes germination of certain seeds/ acc  promotes flowering in pineapples
• Causes abscission pf leaves/ fruits/ leaf fall abscisic acid  / ABA
• High concentration of ABA stomata closure ( by interfering with  uptake  of potassium ions
• Inhibits germination/ growth  of  embryo/ cause seed dormancy
• Causes abscission of leaves/ fruits / leaf fall
• Inhibit elongation growth, inhibit sprouting of bud/ induces  dormancy  in buds ( accept Dormin causes/ dormancy in buds/ seeds

Traumatin

• Heal wounds by callus tissue formation

Florigens

• Promote flowering