Plant Growth And Development

Question 1

Auxin literaly means

Answer 1

from Greek ‘auxein’ : to grow

Question 2

Auxin first isolated from?

Answer 2

human urine

Question 3

Discovered Auxin

Answer 3

F.W. Went

Auxin was isolated by F.W. Went from
tips of coleoptiles of oat seedlings(avena).

1. Avena shows bending upon illumination.
2. Mr. Went cut the tip of avena which now shows no bending
3. Mr. Went then put agar on the cut side of the avena shoot tip.
4. He places the agar on the decapitated avena which shows bending because Auxin tranfered to agar from the shoot tip which then tranfered to the decapitated avena resulting in bending of light.

Question 4

Physiological Effects of Auxin
(all 11)

Answer 4

🔴 initiate rooting in stem cuttings(used for plant propagation)
🔴promote flowering e.g. in pineapples
🔴 prevent fruit and leaf drop at early stages
🔴promote the abscission of older mature leaves and fruits(due to decrease in auxin)
🔴induce parthenocarpy, e.g., in
tomatoes
🔴used as herbicides - 2, 4-D used to kill dicotyledonous weeds, does not affect mature monocotyledonous plants.
🔴controls xylem differentiation (protoxylem & metaxylem)
🔴helps in cell division.
🔴helps in cell elongation
🔴helps in phototropism
🔴results in apical dominance - the growing apical bud inhibits the growth of the lateral (axillary) buds, a phenomenon called apical dominance.
Removal of shoot tips (decapitation) usually results in the growth of lateral buds. Widely used in tea plantations and hedge making.

Question 5

Physiological effects of Gibberellin

Answer 5

🟠 Stem/internode elongation
1. increase length of grape stalk
2. Improve the length and shape of apple
3. Increase length of sugarcane stems which increases yield by 20 tonnes/acre
4. Bolting in beet and cabbage - internodal elongation just prior to flowering in plants with rossette habit
🟠 Speeds up malting process in brewing industry
🟠 Spraying GA on juvenile confiers hastens the maturity period ->producing seeds early
🟠 GA delay senescence - allowing fruit to stay longer on tress to increase their Market value
🟠 GA can break seed dormancy and promote seed germination

Question 6

Who first observed Auxin

Answer 6

Charles Darwin and his son Francis Darwin

They illuminated coleoptiles of canary grass and observed:
1. They bend upon illumination
2. Decapitated canary grass shows no bending
3. Aluminium foil on the tip of decapitated canary grass shows no bending
4. Transparent sheet on the tip of canary grass shows bending

Conclusion: tip of coleoptiles was the site of transmittable influence that caused bending of entire coleoptiles

Question 7

Physiological effects of Cytokinin

Answer 7

🟡cell division
🟡produces new leaves
🟡 produces chloroplast in leaves
🟡 mobilizing nutrient to leaves
🟡 delays leaf senescence
🟡CK overcomes apical dominance - produces lateral shoots (antagonist to auxin)
🟡CK produces adventitious shoots (synergetic to auxin but there it forms adventitious roots)

Question 8

Physiological effects of Abscissic acid

Answer 8

🟢Promotes seed dormancy
🟢Inhibits seed germination (anti Gibberellin)
🟢In water stress ABA stimulate closure of stomata to not lose water(anti transpirant)
🟢 promotes abscission
🟢 promotes senescence

Question 9

Physiological effects of Ethylene/ethene/C2H4

Answer 9

🔵 Ripening hormone
🔵When plant part ripens it’s rate of respiration increase or has reached its respiratory climactic
🔵 Produces triple response in dicot seedlings - horizontal growth, swelling of main axis, apical hook formation (protects from damage in early stages of life)
🔵 Breaks seed and bud dormancy - initiate germination in penut seed and initiate sprouting in potato
🔵 Promote Stem elongation in deep water rice plants
🔵 Promote root growth and root hair formation increasing the surface area for absorption
🔵 Promotes flowering and fruit setting (synchronise)in pineapple
🔵 Promotes flowering in Mango

Aqueous solution of ethylene = Ethephon
🩵 Hastens Ripening of tomato and apple
🩵 Accelerates abscission of flowers and fruits - thinning of cotton, cherry, walnut
🩵 Promotes female flowers in cucumber increasing their yeild

Question 10

Physiological effects of Ethylene/ethene/C2H4

Answer 10

🔵 Ripening hormone
🔵When plant part ripens it’s rate of respiration increase or has reached its respiratory climactic
🔵 Produces triple response in dicot seedlings - horizontal growth, swelling of main axis, apical hook formation (protects from damage in early stages of life)
🔵 Breaks seed and bud dormancy - initiate germination in penut seed and initiate sprouting in potato
🔵 Promote Stem elongation in deep water rice plants
🔵 Promote root growth and root hair formation increasing the surface area for absorption
🔵 Promotes flowering and fruit setting (synchronise)in pineapple
🔵 Promotes flowering in Mango

Aqueous solution of ethylene = Ethephon
🩵 Hastens Ripening of tomato and apple
🩵 Accelerates abscission of flowers and fruits - thinning of cotton, cherry, walnut
🩵 Promotes female flowers in cucumber increasing their yeild