9.3 Reproduction in Angiosperms

The Dicot Seed:
Cotelydon: organ that stores food, becomes first seed leaves
Plumule: embryo shoot
Hypocotyl: stem below attachment point
Radicle: stem tip developing into root
Micropyle: hole that allows water to enter before germination

Germination:
Specific conditions are needed for germination. This may vary for all plants:
oxygen: used in aerobic respiration
water: activation of cells
temperature: certain temperature needed for enzymes to function
Some plants have unique conditions/processes such as: fire, freezing, washing to remove inhibitors, erosion of seed coat, passing through digestive system of an animal

1. Water enters micropyle to activate cell
2. Synthesis of gibberelins (plant growth hormone)
3. Gibberelins cause synthesis of the enzyme amylase
4. Amylase hydrolysis stored starch into maltose
5. Maltose is absorbed by the plumule and the radicle
6. Hydrolysis of the maltose turns into glucose to be used in cell respiration. Other stored proteins or lipids will be hydrolysed (breakdown using water) to form enzymes, triglycerides and phospholipids

Photoperiodism: the response by a plant to changes in a photoperiod or the lengths of day and night (especially the continuous exposures to darkness). Some plants will flower during long days (LDP/long day plants), short days (SDP, short day plants), or neutral plants will flower regardless of day length.

Phytochrome is believed to be a blue-green leaf pigment that will sense the periods of day and night. The plant will become 'active' or 'inactive' in response to certain lights. Phytochrome is especially sensitive to red (Pr) and far red light (Pfr). When Pr (inactive form) absorbs red light it is converted to Pfr (activated form). Pfr turns to Pr when it absorbs far red light. Pfr also spontaneously changes back to Pr in the dark.

In LDP, Pfr will bind to receptors that promote transcription of genes used in flowering

In SDP, Pfr will inhibit transcription. During long nights, Pfr is converted into Pr so that by the daytime there won't be much Pfr to inhibit flowering. Flowering is then able to occur.