Plant Hormones

Question 1

Auxin (growth hormone)

Answer 1

• produced in the apical meristem
• low concentration
• involved in growth (fruit development, hinders leaf abscission)
• helps in phototrophic responses (moving leaves towards light)
• used in Vietnam war “agent orange”

Question 2

Cytokinins (growth hormone)

Answer 2

• a modified form of adenine
• counter the effects of auxin
• travel upward in the xylem
• promote cell division, chloroplast development, lateral buds, inhibits leaf abscission
• high concentration promotes cell differentiation
• low concentration inhibits cell differentiation
• stimulate leaf expansion
• delays senescence

Question 3

Gibberellins (growth hormone)

Answer 3

• works together with auxin to promote growth
• produced in young leaves, roots, shoot apical meristem
• effect seed germination, cell division and elongation
• stimulates flowering during the day

Question 4

Brassinosteroids (steroidal growth hormone)

Answer 4

• similar to auxin
• promote cell elongation, division and xylem differentiation
• slows leaf abscission
• responsible for overall growth in plants, triggers growth spurts

Question 5

Abscisic Acid (stress hormone)

Answer 5

• ABA
• works in opposition to growth hormone
• travels in vascular tissue (through sap)
• closes stomata
• inhibits shoot growth and seed germination
• promotes winter seed dormancy
• synthesizes seed storage proteins
• can promote root growth in the winter

Question 6

Ethylene (stress hormone)

Answer 6

• a gas
• produced in stem nodes, aging leaves, ripening fruit
• a positive feedback loop
• involved in apoptosis
• abscission of leaves (death)
• hydrolyze cell walls
• triple response
• stimulates seed germination, root and shoot growth
• response to infection and wounds