1. Review of Seed Germination and Control of Flowering
Topic 9.3

2. Seed dispersal
Way seeds are carried away from vicinity of parent plant
Seeds are dispersed in various manners:
Wind
Water
Animals
The structure of seeds indicates their dispersal type

3. From: http://theseedsite.co.uk/seedparts.html
Dicot seed structure
The seed contains the embryo of the new plant, with a supply of food for the embryo until it has formed sufficient roots and leaves to obtain its own food. The food, endosperm, may be in the seed leaves or it may be outside the seed leaves and be absorbed when the seed germinates. To start germination, the seed leaves absorb water and swell, and the radicle emerges, followed by the plumule.
From:

4. Germination of Seeds Conditions required: Moisture Temperature Oxygen
Needed so that metabolic action can take place and overcome dormacy
Temperature
Optimum range for enzyme action involved in mobilization of stored food reserves
Oxygen
Sustain aerobic cell respiration
A period of dormancy
Some conditions differ depending on seed and its environment

5. Germination of a dicot seed
Water is absorbed by the seed, kickstarting the formation of the hormone gibberellin
Gibberellin forms here
Water enters

6. Germination of a dicot seed
Gibberellin stimulates production of the enzyme amylase, which digests the starch in the seed into maltose
Gibberellin
Stimulates production of
Amylase

7. Metabolic events of germination
The maltose provides energy for the developing embryo to grow and develop.

8. Photoperiodism Response of plants to changing length of day
Plants use light to determine when to flower, germinate seeds, break bud dormancy

9. Control of Flowering Key Concepts
Phytochromes:
Blue-green pigments that regulate plant response to light; found in low concentrations
Large conjugated protein with a pigment molecule attached
Receptors for photoperiods is in leaves, but location in plant cells is unknown
Can be converted from one form to another with different wavelengths of light
Critical night length: the minimum amount of night time required for regulation of plant growth
Animation - Phytochrome Signaling

10. Plant Development and Phytochrome
Image from:
Pr is converted to Pfr in red light
Pfr is gradually converted to Pr in darkness
Action of Pfr promotes flowering in long-day plants (LDP) and acts as an inhibitor of short-day plants (SDP)

11. Short-day plants dark Critical night length
If light exceeds or interrupts critical night length, no flowering happens.
Phytochrome Red (Pr) is converted to Phytochrome Far Red (Pfr)
This only requires a short exposure to white or red light
At the end of the night time, Pfr is low, so low Pfr triggers flowering
light

12. Long-day plants dark Critical night length
Night can exceed critical night length or be interrupted, flowering can still happen.
During the day, Pr is converted to Pfr
During the night, the Pfr concentration does not drop significantly since the dark period is short High Pfr concentration triggers flowering
light