1. 9.3 – Reproduction in Angiospermophytes

2. Flowers Flowers – reproductive structures of angiospermophytes
Flowers evolved from modified leaves and stems
Non-Reproductive Floral Structures:
Sepals – “leaves,” at base of flower – enclose the flower before it opens
Petals – brightly colored structures that aid in attracting birds and insects
Both sepals and petals are not directly involved in reproduction
9.3.1

3. Floral Structure
9.3.1

4. Reproductive Structures
Reproductive Floral Structures:
Stamen – male reproductive structure
Anther – sac where pollen in produced
Filament – stalk that supports anther
Carpel (Pistil) – female reproductive structure
Stigma – sticky area on top of carpel that receives pollen
Style – tube that connects stigma to ovary
Ovary – base of carpel that contains ovule and egg sac
9.3.1

5. Floral Structure
9.3.1

6. Control of Flowering
Photoperiodism – plant response to light involving relative lengths of day and night.
Very important factor in flowering – why?
9.3.6

7. Control of Flowering
Long-day plants – bloom when days are longest and nights are shortest (mid-summer)
Short-day plants – bloom in spring, late summer, and autumn when days are shorter and nights are longer
Day-neutral plants – day-length not important for flowering
Day length is not as critical as night length in regulation of flowering.
9.3.6

8. Control of Flowering
Control by light is due to a pigment in plants called phytochrome.
Phytochrome – blue-green pigment that controls various growth responses (including flowering) in plants
Two forms of phytochrome:
Pr – inactive form
Pfr – active form
9.3.6

9. Control of Flowering
Phytochrome is converted from inactive to active forms due to different light wavelengths:
In red light (660 nm) inactive Pr is rapidly converted to active Pfr.
Active Pfr can absorb far-red light (730 nm)
In daylight, Pfr is rapidly converted to back to Pr
In darkness, Pfr is very slowly converted back to Pr
The slow conversion of Pfr to Pr helps plants time the night length.
9.3.6

10. Control of Flowering
9.3.6

11. Control of Flowering
In long-day plants, the remaining Pfr at the end of the night stimulates flowering
Pfr remains due to slow conversion at night
In short-day plants, the remaining Pfr at the end of the night inhibits flowering
Short-day plants only flower when enough Pfr has been converted to Pr. (this only occurs during long nights)
9.3.6

12. Control of Flowering
9.3.6

13. Pollination
Process of moving pollen grains from the anther to the sticky stigma on the carpel
Plants have evolved numerous adaptations for pollination
Wind pollinated plants produce large amounts of pollen = allergies! Why do they do this?
Different colors and shapes of flowers allow plants to attract different pollinators
9.3.2

14. Pollination
What we see…
What insects see…

15. Pollination
Most plants have evolved adaptations to limit self-pollination – why is this important?
Stamens and carpels may mature at different times
Floral structure makes self pollination difficult
Flowers are self-incompatible – biochemical mechanisms block prevents pollination

16. Fertilization Process of fusing sperm and egg to produce new embryo
After pollination – the pollen grain produces a tube that extends down the style toward the ovary
Growth of the tube is directed by a chemical attractant (usually calcium produced by the ovary)
Sperm within the pollen grain fertilize the egg and produce the plant embryo
Pollination does not always lead to fertilization
9.3.2

17. Seed Structure
Seed coat (testa) – hard shell that encases and protects embryo
Radicle (hypocotyl) – embryonic root
Plumule (epicotyl) – embryonic shoot
Cotyledons – seed leaves
Dicots have two seed leaves
Monocots have one seed leaf
9.3.3

18. Seed Structure
9.3.3

19. Seed Dormancy
Evolutionary adaptation that germination (sprouting) will take place when conditions are favorable
For example:
Desert plants will only germinate after significant rainfall
Many forest species require heat from fire to germinate – how is this an advantage?
In areas with harsh winters – seed require a long “chilling,” period before germinating – why?
9.3.4

20. Germination Begins with imbibition – the absorption of water
Causes seed coat to rupture and triggers metabolic changes within embryo
The embryo begins producing a plant growth hormone – gibberellins
Gibberellins stimulate the production of amylase in the seed
Amylase begins digesting food stores of the endosperm (starch) into maltose
9.3.5

21. Germination
Maltose is transferred to the growing regions of the embryo – the embryonic root (radicle) and shoot (plumule)
Maltose is converted to glucose – where it used in aerobic respiration for energy or it is used to make cellulose and other materials needed for growth
Once the seedling breaks ground, photosynthesis can begin and the endosperm food stores are not needed
9.3.5

22. Germination

23. Factors Affecting Germination
Water – must be available for imbibition
Oxygen – required for aerobic respiration during germination
Temperature – enzyme action (amylase) can be affected by fluctuations in temperature
9.3.4