Kingdom Plantae: Heterospory and Seed Plants

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.

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

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

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

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

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

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

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

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.

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.

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

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)

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).

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

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

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

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

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

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).

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.

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

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

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

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

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

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

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)!.

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.

Gymnosperms get their chance to rule the land.... The Gymnosperm Revolution and the Permian Period Permian Period (290-248 million years ago) followed Carboniferous: was relatively cool and dry. Most coal swamps dried up. Carboniferous coal swamp

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

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