BIOL 1030 – TOPIC 4 LECTURE NOTESTopic 4: Plant Diversity II - Seed Plants (Chs. 30, 38)I. Seed plants A. all are heterosporous vascular plants (make two types of meiospores)B. three major reproductive adaptations1. gametophyte reduced to dependence on sporophyte; retained in moist reproductive tissue 2. seed – “baby plant in a lockbox with its lunch”; highly resistant structures that allow for a dormant phase in the life cycle to wait out poor environmental conditions3. evolution of pollen as male gametophyte – many seed plants are no longer tied to external water for fertilization C. common ancestor with seeds gave rise to all seed plants (gymnosperms and angiosperms); together, gymnosperms and angiosperms are a monophyletic groupD. fossil evidence indicates origins in progymnosperm group about 360 MYA E. gametophytes are completely dependent on parent sporophytes for nutrition and are composed of only a few cells1. male gametophytes develop from microspores- become pollen grains- entire male gametophyte moved to the female as pollen grains- cannot perform photosynthesis, depends on nutrients that came from the parent sporophyte2. female gametophytes develop from megaspores within ovules- ovule contains female gametophyte surrounded by nucellus (megasporangium)- nucellus is surrounded by 1-2 integuments (cell layers that serve as protective covers)- micropyle – opening in integuments (allows sperm to get in)- cannot perform photosynthesis, depends on nutrients from the parent sporophyte3. means of transporting sperm to egg varies, but typically uses a growing pollen tube that does not require outside water4. moving pollen to vicinity of ovule called pollination; agents include wind, animalsF. seed develops from ovule 1. seeds are highly resistant structures that allow for a dormant phase in the life cycle to wait out poor environmental conditions2. embryo protected by a seed coat, an extra layer of hardened tissue derived from sporophyte tissue in the ovule (sporophyte tissue from parent, not from embryo)- enhanced protection from drought, cold, heat- some protection from pathogens and predators- external water only needed at germination- initial food supply for germinating plant is enclosed3. seeds replace spores as means of dispersal; can enhance means of dispersalG. seeds plants together are a monophyletic groupH. divided into two “groups” based on whether or not ovule is completely enclosed by sporophyte tissue at time of pollination 1. gymnosperms – “naked seed”2. angiosperms – “covered seed” – covered in Topic 7II. gymnospermsA. long thought to be a grade, but molecular data shows that living members may actually form a cladeB. 4 phyla with living members1. essentially, all seed plants that are not angiosperms2. all lack flowers and fruits that are found in angiosperms3. ovule not completely enclosed by sporophyte tissue at time of pollination4. instead, ovule sits exposed on a scale (a modified leaf)C. 4 phyla1. Phylum Coniferophyta (the conifers)2. Phylum Cycadophyta (the cycads)3. Phylum Ginkgophyta (Ginkgo)4. Phylum Gnetophyta (the gnetophytes)III. Phylum Coniferophyta (the conifers) A. monophyletic groupB. ~600 living species; worldwide distribution, more common in cold or dry regions C. pines, spruces, firs, cedars, junipers, hemlocks, yews, larches, cypresses, redwoods D. nearly all are evergreen E. many have needle-shaped leaves adapted to dry conditions (resistant to water loss) 1. thick cuticle 1 of 8BIOL 1030 – TOPIC 4 LECTURE NOTES2. stomata in pits F. tallest plant: more than 110 m (Coastal Redwood, Sequoia sempervirens) G. oldest tree: Methuselah, estimated more than 4600 years old (Bristlecone Pine, Pinus longaeva) H. sources of timber, paper, resin, cancer drug taxol, etc. I. “soft” wood (unlike angiosperm trees, no vessels or fibers in xylem) J. pines as a representative group 1. over 100 species 2. native to Northern hemisphere 3. typically thick bark (survive fires, drought)4. secrete resin from leaves and bark - response to wounding - deters fungal and insect attacks - source of turpentine (volatile liquid, organic solvent) and solid rosin K. pine life cycle 1. pine tree is sporophyte, with sporangia located on cones 2. gametophyte generations reduced; retained within sporangia - male gametophyte is pollen grain (no antheridium) - female gametophyte produces archegonia within ovule 3. heterosporous: separate male and female cones4. male cones (pollen cones) - clusters of 30-70- usually at tips of lower branches - 1-4 cm long; papery scales in spirals or whorls - pair of microsporangia sacs within each scale - microspore mother cells in microsporangia form haploid microspores - each microspore becomes 4-celled pollen grain - pollen grain carried by wind (pair of air sacs provides buoyancy)- mature pollen grains have a “Mickey Mouse” appearance- one cluster of pollen cones can yield over 1 million pollen grains 5. female cones (ovulate cones)- typically on upper branches of same tree with pollen cones - larger than pollen cones- scales become woody (highly lignified)- pair of ovules develop at base of each scale megasporangium called nucellus embedded in each ovule nucellus is nutritive tissue surrounded by thick integument (covering) with hole (micropyle) near one end  one layer of integument later becomes seed coat - single megaspore mother cell in each megasporangium  produces 4 haploid megaspores; 3 break down  surviving megaspore develops over about one year into female gametophyte with sometimes thousands of cells - female gametophyte has 2-6 archegonia, at micropylar end - each archegonium has one large egg (visible without a microscope)- female cones take two or more seasons to mature 6. reproduction - scales of ovulate cone open - pollen lands near micropyle, caught by sticky fluid - evaporating fluid pulls pollen through micropyle into ovule - scales close (female gametophyte not mature) - pollen grain germinates, forming pollen tube that digests through nucellus (takes about 15 months to reach archegonium) - one of the four pollen grain cells (the generative cell) undergoes mitosis; one of products divides again, making twosperm cells - mature male gametophyte is germinated pollen grain with pollen tube and sperm - when archegonium is reached, one sperm fertilizes egg - zygote develops into embryo within seed; usually only one successful zygote per ovule - embryo (new sporophyte, 2N) has