Warm Up 1/31

List the steps for germination of a starchy seed. (outline)
1. Imbibition - absorption of water due to low water potential in the dry seed, which rehydrates living cells in the seed and allows the cells to become metabolically active; embryo increases respiration
2. Formation of gibberellin - gibberellic acid is released
3. GA stimulates amylase, a digestive enzyme that breaks down starch, to be produced
4. Digestion of starch into maltose in the food stores of the seed
5. Maltose is transported from food stores to the growth regions of the seedlings, including the embryo root and the shoot tissue.
6. Maltose is converted to glucose, which is used in aerobic cell respiration as a source of energy, or is used to synthesize cellulose or other substances needed for growth.

2. Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.

• Flowering is controlled by phytochrome, which is affected by light (photoperiodicity)
• Phytochrome exists in two forms:
  •  A red (P_r) form absorbs red light (~660 nm) and is converted into a far red form (P_fr)
  • A far red (P_fr) form absorbs far red light (~730 nm) and is converted into a red form (P_r)
• The P_fr form is the active form of phytochrome, while the P_r form is the inactive form of phytochrome
• Sunlight contains more red light, so the P_fr form is predominant during the day, with the gradual reversion to the P_r form occurring at night
• In long day plants, the active P_fr form is a promoter of flowering and so flowering is induced when the night period is less than a critical length and P_fr levels are high
• In short day plants, the active P_fr form is an inhibitor of flowering and so flowering is induced when the night period is greater than a critical length and P_fr levels are low