1. Kingdom Plantae: Heterospory and Seed Plants

2. Setting the stage for pollen/seeds
Most of plants discussed so far do not have specialized gametophytes
They are homosporous plants: make one kind of meiospore.

3. Setting the stage for pollen/seeds
Homosporous groups
Bryophyta
Hepaticophyta
Anthocerophyta
Psilophyta
Spenophyta

4. Setting the stage for pollen/seeds
Heterosporous plants: make 2 types of meiospores.
One becomes male gametophyte and makes sperm
One becomes female gametophyte and makes eggs
Thus, make specialized spores and specialized gametophytes.
Specialization occurs
earlier in life cycle

5. Setting the stage for pollen/seeds
Heterosporous groups:
Some Lycophyta
Some Pterophyta
All seed plant phyla (discussed later today!).

6. Setting the stage for pollen/seeds
Example of heterosporous plant life cycle: Selaginella (Lycophyta)
Seen in lab #3.

7. Setting the stage for pollen/seeds
Heterosporous plant life cycle: Selaginella (Lycophyta)
Photos of structures.

8. Heterospory Note deadbeat gametophytes
Not free-living. Dependent on sporophyte
Not (very) photosynthetic
Small: microgametophyte reduced to 1 antheridium! Megagametophyte develops mostly within megaspore.

9. Heterospory Spores specialized
Megaspore makes megagametophyte, which makes archegonia with eggs
Microspore makes microgametophyte, which makes antheridium containing sperm.

10. Heterospory Valuable ideas for life on the land:
1) Gametophytes small and protected by spore walls
2) Deadbeat gametophytes fed by big strong sporophyte (gametophytes can focus on reproduction)
3) Megaspore: keep it after fertilization and feed embryo. Embryo starts development inside megaspore and protected by its walls. Lets new embryo “eat” its mother (megagametophyte): keeps energy used to make megagametophyte from being wasted
4) Microspore: disperse it through air, instead of delicate swimming sperm.

11. Plants Nonvascular Plants Seedless Vascular Plants Seed Plants
Covered. Reproduce by spores. Gametophytes independent of sporophyte
Seedless Vascular Plants
Seed Plants
Rest of plant kingdom. Gametophytes dependent on sporophyte.

12. Seed plant features Have vascular tissue Life Cycle
Make roots, stems, leaves (megaphylls)
Some can do secondary growth in stems/roots: make new phloem and xylem and grow in diameter rather than just length
Life Cycle
Heterosporous, but spores kept by sporophyte
Gametophytes reduced, dependent on sporophyte
Male gametophyte (microgametophyte) dispersed as pollen grain (no free-swimming sperm in water)
Female gametophyte (megagametophyte) kept by sporophyte, becomes part of ovule

13. Seed plant groups
Gymnosperms (“gymno-” means naked, “sperm” means seed): do not make make seeds in sealed container (fruit)
Phylum Cycadophyta (cycads)
Phylum Coniferophyta (conifers)
Phylum Ginkgophyta (ginkgo)
Phylum Gnetophyta (gnetophytes)
Note all gymnosperms do secondary growth (form wood, are shrubs or trees)

14. Seed plant groups
Angiosperms (“angio-” means container, “sperm” means seed): make seeds in sealed container (fruit)
Phylum Anthophyta (flowering plants)
Many of these are woody, but some are herbaceous (don’t do secondary growth).

15. Pine life cycle Pine life cycle movie (for overview)
Example of gymnosperm life cycle

16. Pine life cycle Female cone: Cone scales with ovules on them Female
cone at
pollination
stage (top)
Female cone: Cone scales with ovules on them
Cone scale with ovule
Mature female cone

17. Pine life cycle
Ovule: integumented megasporangium. Megaspore mother cell does meiosis, forms meiospores, one survives & does mitosis to make female gametophyte. 1 2 3 4

18. Pine life cycle
Female gametophyte has several archegonia, each with an egg. () () 1 2 3 4

19. Pine life cycle Male cone: made up of microsporophylls
Microsporangia on sporophylls
Microsporophyll
Sporangium on underside of sporophyll

20. Pine life cycle
Sporangia on microsporophylls have microspore mother cells (2n), which do meiosis to make microspores (1n)
Each microspore does a couple mitotic divisions to form an immature male gametophyte (called pollen grain).

21. Getting male and female gametophytes together
Pollen grain flies through air (wind dispersed)
Arrives at female cone micropyle (gap between integument ends), and winds up next to female gametophyte.

22. Getting male and female gametophytes together
Now, pollen grain germinates: makes pollen tube and spermatogenous cell. Becomes mature male gametophyte.

23. Getting male and female gametophytes together
Pollen tube penetrates into female gametophyte to find archegonium, so sperm and egg can fuse to make zygote.

24. The new baby sporophyte
Zygote grows to embryo as ovule becomes seed
Integument (2n tissue from parent sporophyte) becomes hard protective seed coat
Female gametophyte serves as food for growing embryo.
Remains of seed coat
(most dissected away)
Embryo
Female gametophyte

25. Seed has wing: wind dispersed
Winged pine seed helicoptering away (most pine seeds fly this way)

26. Seed germinates and new sporophyte is on its own
Young pine seedling

27. Pine life cycle Take home lessons:
1) Pollen grain is immature male gametophyte (microgametophyte)
2) Male gametophyte matures in ovule, when pollen tube and sperm cell made. Entire male gametophyte is just a few cells.
3) Ovule contains megasporangium. Meiosis produces megagametophyte, which makes archegonia, still kept in megasporangium.
Pine pollen grain

28. Pine life cycle Take home lessons:
4) Fertilization takes place and embryo digests female gametophyte.
5) Seed is baby plant (embryo), in box (seed coat from parent sporophyte tissue), with its lunch (female gametophyte)!.

29. Pine life cycle Advantages of making seeds and pollen:
1) Male gametophyte (immature) small, protected by microspore wall, flies through air to female gametophyte
2) No swimming sperm. Male gametophyte delivers sperm to female gametophyte protected by ovule in female cone
3) Embryo nourished by megagametophyte and protected by cone of sporophyte
4) Seed has hard protective coat, supply of food (megagametophyte). Can be dispersed to new location.
5) Embryo can be dormant: allows new sporophyte to wait for good conditions to germinate.

30. Gymnosperms get their chance to rule the land....
The Gymnosperm Revolution and the Permian Period
Permian Period ( million years ago) followed Carboniferous: was relatively cool and dry. Most coal swamps dried up.
Carboniferous coal swamp

31. Gymnosperms get their chance to rule the land....
Many SVPs (especially tree species) went extinct. Gymnosperm groups prospered!
Why? Pollen and seeds adapted them to dry conditions.
Carboniferous coal swamp

32. Gymnosperms Phylum Cycadophyta (cycads)
Phylum Coniferophyta (conifers)
Phylum Ginkgophyta (gingko)
Phylum Gnetophyta (gnetophytes)