Chapter 29 - Sadava The Evolution of Seed Plants

1. 29 Chapter 29 - SadavaThe Evolution of Seed Plants

2. Late in Devonian, some plants developed secondary growth • Thickened woody stems of xylem • The first species with secondary growth were progymnospermsseedless vascular plants, now extinct http://www.futura-sciences.com/uploads/tx_oxcsfutura/comprendre/d/images/600/fig_1213.jpg

3. Earliest seed plants from Devonian • These seed ferns were also woody • Clades of seed ferns are known only as fossils • Two of the clades are basal to surviving seed plants http://www.palaeos.com/Plants/Lists/Glossary/Images/SeedFern.jpg

4. Surviving seed plants fall into two groups: Gymnosperms: conifers and cycads Angiosperms: flowering plants

5. Gametophyte generation is reduced even further than it is in ferns Haploid gametophyte develops partly or entirely attached to sporophyte Vascular, seed plants Vascular, seedless – Ferns Nonvascular – Mosses

6. Seed plants are heterosporous Produce two types of spores One becomes female gametophyte, one becomes male gametophyte Seed plants form separate megasporangia (female) and microsporangia (male) http://bio1151.nicerweb.com/doc/class/bio1151/Locked/media/ch30/30_03OvuleToSeedA.jpg

7. The Seed Plants - Megasporangium • Megasporangium • Contains the megagametophyte • develops into an egg that is eventually fertilized  next generation (sporophyte) • Surrounded by integument made up of sporophyte structures • Megasporangium and integument together form ovule • Will become seed after fertilization http://herbarium.usu.edu/teaching/4420/seed.GIF

8. Seed Plants - Microsporangium In microsporangium, microspores divide mitotically to produce the male gametophyte, or pollen grain Walls of pollen grains contain sporopollenin, the most resistant biological compound known protects pollen grain from chemicals and dehydration

9. Pollination When pollen grain lands near a female gametophyte Pollen tubes are produced that digests way through sporophyte tissue to megagametophyte Sperm are released from the tube, and fertilization results in a diploid zygote. http://pix.botany.org/Setabot/abot-90-5_700.jpg

10. After Pollination Resulting diploid zygote divides to produce an embryonic sporophyte Growth is then suspended Embryo enters a dormant stage, with the end product being a multicellular SEED Pumpkin seeds http://nosheteria.com/uploaded_images/PumpkinSeeds.jpg

11. Seed Seed contain tissues from three generations • Seedcoat (from integument) and megasporangium develop from ovule tissues of diploid sporophyte parent • 2n outside • Within megasporangium is haploidfemale gametophytetissue, contains nutrients for next generation • 1n • Third generation, the embryo,is the new diploid sporophyte is contained in the center of seed package. • 2n inside – new generation

12. Seeds Seeds are well-protected resting stages. May remain viable for many years, germinating when conditions are favorable. Seed coat protects from drying out as well as predators. Many seeds have adaptations for dispersal.

13. Besides seeds, secondary growth also contributes to success of seed plants Wood: proliferated xylem, gives support and allows plants to grow above their competitors for sunlight http://cache.eb.com/eb/image?id=72251&rendTypeId=35 http://mayhem-chaos.net/photoblog/images/pine_tree_med.jpg

14. EmbryophytesVascular PlantsEuphyllophytes (“True Leaves”)Seed PlantsGymnosperms Gymnosperm “naked-seeded” ovules and seeds are not protected by ovary or fruit tissue Pinus longaeva, Bristlecone pine, cone and needles http://www.conifers.org/pi/pin/lambertiana5.jpg

15. Four major groups of living gymnosperms: Cycads:Cycadophyta EmbryophytesVascular PlantsEuphyllophytes (“True Leaves”)Seed PlantsGymnosperms http://www.biologyreference.com/images/biol_02_img0213.jpg

16. Four major groups of living gymnosperms: Ginkgos:Ginkgophyta—one living species, Ginkgo biloba EmbryophytesVascular PlantsEuphyllophytes (“True Leaves”)Seed PlantsGymnosperms Branch of male Ginkgo biloba with clusters of pollen-producing microsporophylls Branch of female Ginkgo biloba with leaves and ovules

17. Four major groups of living gymnosperms: Gnetophytes:Gnetophyta EmbryophytesVascular PlantsEuphyllophytes (“True Leaves”)Seed PlantsGymnosperms Ephedra viridis (Mormon tea or joint fir) with cones; Arizona

18. Four major groups of living gymnosperms: Conifers:Coniferophyta— the cone bearers EmbryophytesVascular PlantsEuphyllophytes (“True Leaves”)Seed PlantsGymnosperms http://www.nasa.gov/centers/goddard/images/content/156030main_Conifers_JPG.jpg

19. All living gymnosperms except gnetophytes have only tracheids for water conduction and support Gymnosperms were dominant during Mesozoic Tallest gymnosperms are California coastal redwoods over 100 m Angiosperms have vessel elements and fibers alongside of tracheids Tracheids and fiber tracheids http://www.uri.edu/cels/bio/plant_anatomy/images/47.gif

20. Gymnosperms were dominant during the Mesozoic, until about 65 Mya. Today, conifers still dominate many forests, especially at high latitudes and altitudes. The oldest living organism on Earth is a bristlecone pine that germinated about 4,800 years ago. http://media.rd.com/rd/images/rdc/family-travel/poi/CA-poi-ancient-bristlecone-pine-forest-af.jpg

21. Male and female cones contain the reproductive structures of conifers. Megastrobilus (female, seed-bearing Cone) Modified stem, bearing a tight cluster of woody scales (reduced branches) Produces seeds Microstrobilus (male, pollen-bearing cone) “Cone-like” structure Scales are modified leaves; not woody Microsporangia produces microspores  pollen grains (microgametophyte) Gymnosperms

22. Pine life cycle: Wind carries pollen grains from microstrobilus to megastrobilus Gymnosperms

23. The Gymnosperms: Naked Seeds • Pollen grains enter ovule through a small opening in the integument at tip of the ovule called the micropyle • 2 sperm enter • 1 fertilizes • 1 degenerates Pollen grains. Note the swollen bladders which helps them float in air currents. www.botany.hawaii.edu/faculty/webb/BOT201/Conifers

24. Most conifer ovules are born on the upper surfaces of the cone scales Gymnosperms Stone pine cone with pine nuts - note two nuts (seeds) that develop from the ovule under each cone scale

25. Gymnosperms Some pine cone scales (e.g., longleaf and slash pines) can only be opened by fire to release the seeds helps insure new growth after fires. Some conifers have soft, fleshy, fruit-like tissue around seeds (e.g., juniper and yew “berries”) Animals may eat these and then disperse the seeds in their feces. Not true fruits

26. EmbryophytesVascular PlantsEuphyllophytes (“True Leaves”)Seed PlantsAngiosperms Angiosperms: “enclosed seed” Oldest fossils are Jurassic, 150 my old Explosive species radiation  angiosperms became dominant during Tertiary in only 60 million years Over 250,000 species exist today http://gpc.edu/~pgore/myphotos/fossils/angiosperm-leaf.jpg

27. Extreme of evolutionary trends in vascular plants: Sporophyte generation becomes larger, gametophyte become smaller Female gametophyte even more reduced — usually only seven cells

28. Synapomorphies (shared, derived traits) in angiosperms: Double fertilization Triploid endosperm – nutritive tissue in seeds Ovules and seeds enclosed in a carpel Flowers Fruits Xylem with vessel elements and fibers Phloem with companion cells Angiosperms Phalaenopsis Orchid http://www.gallerym.com/images/work/big/schatz_howard_Botanica-%20Orchid%20Phala%20001_L.jpg

29. Double fertilization: Microgametophyte has two male gametes One nucleus combines with egg Second nucleus combines with two haploid nuclei of female gametophyte to form triploid nucleus  endosperm (3n) Endosperm nourishes developing sporophyte (embryo) Angiosperms http://www.lclark.edu/~seavey/images%20/carpel.jpg

30. Angiosperm (“enclosed seed”) Ovules and seeds are enclosed in a modified leaf called a carpel Carpels provide protection May interact with pollen to prevent self-pollination Angiosperms also produce flowers and fruits Angiosperms

31. Fiber cells: important in supporting plant body (associated with xylem) http://student.nu.ac.th/u46410387/fiber.jpeg

32. Flowers Stamens bear microsporangia Male consist of filament and anther Angiosperms

33. Flowers Carpels bear megasporangia Female One or more carpels form the pistil— stigma, style, ovary and ovule Angiosperms In this example, the pistil is a single carpel

34. Flowers often have other specialized leaves that often play a role in attracting pollinators Petals – inner whorl (collectively, the corolla) Sepals – outer whorl (collectively, the calyx) Calyx protects immature flower in bud before it opens Angiosperms

35. Types of flowers: Perfect flowers have both mega- and microsporangia Imperfect flowers either mega or microsporangia, but not both Angiosperms – Perfect and Imperfect Flowers http://leon.ifas.ufl.edu/images

36. Monoecious: “one-housed” male and female flowers occur on the same plant or in perfect flowers Dioecious: “two-housed” male and female flowers on different plants separate sexes Have to have imperfect flowers

37. Perfect flowers: favors self-pollination, but usually disadvantageous many mechanisms have evolved to circumvent this problem bush monkeyflower is constructed so that two different hummingbirds must participate in pollination Mimulus aurantiacus, bush monkeyflower http://www.dkimages.com/discover/previews/931/50375608.JPG

38. Most angiosperms are animal-pollinated by insects, birds, and bats Many flowers entice pollinators with nectar and pollen Plants and their pollinators have coevolved Some relationships are very specific—e.g., one species of moth pollinates one species of yucca plant. http://bobklips.com/BOBS_WEBSITE/ILF-YUCCFILAlaying.jpg

39. Figure 29.14 The Life Cycle of an Angiosperm

40. Ovary and seeds develop into fruits Fruit protects seed and aids in dispersal, (e.g., can become attached to or eaten by animals) Angiosperms - Fruit http://www.hickerphoto.com/data/media/152/kiwi-fruit_3629.jpg

41. Types of fruits: Simple fruits develop from one carpel Plums, cherries Aggregate fruits develop from several carpels on same flower raspberries Multiple fruits form from a cluster of flowers pineapples Accessory fruits develop from parts other than carpels Apples, pears, strawberries Angiosperms - Fruit http://www.youtube.com/watch?v=bwCpQflmQG4

43. Angiosperm life cycle: Zygote develops into an embryo consists of embryonic axis (will become stem and root), and 1 or 2 cotyledons — seed leaves Cotyledons absorb and digest endosperm, some become photosynthetic Angiosperms cotyledons embryonic axis www.botany.hawaii.edu/faculty/webb/Bot201/Angiosperm/MagnoliophytaLab99

44. Most angiosperms are in two major clades: Monocots One cotyledon Grasses, cattails, orchids, palms Eudicots (dicots) Two cotyledons Majority of familiar flowering plants, most herbs, trees, shrubs Other clades include star anise and relatives, water lilies, and magnoliids EmbryophytesVascular PlantsEuphyllophytes (“True Leaves”)Seed PlantsAngiosperms

45. Monocots and Eudicots Are Not the Only Surviving Angiosperms Water lilies Amborella trichopoda Star anise Black pepper Dutchmean’s pipe Avocado Magnoliid clade

46. Monocots Lilies Wheat Date palm

47. Eudicots Prickly pear cactus Catclaw Brier Dogwood

48. How Do Plants Support Our World? Plants contribute to ecosystem services: processes by which environment maintains resources that benefit humans Plants are primary producers: photosynthesis traps energy and carbon, making them available for their own needs and for herbivores and omnivores that consume them, and for the whole food chain Plants produce O2 and remove CO2 from the atmosphere Contribute to soil formation and soil fertility Roots hold soil in place, preventing erosion Moderate local climate by increasing humidity, providing shade, and blocking wind.

49. Seed plants are our primary food source Twelve are most important: rice, coconut, wheat, corn, potato, sweet potato, cassava, sugarcane, sugar beet, soybean, common bean, banana http://3.bp.blogspot.com/_vhhw--dmXBE/SEKkOrSMjVI/AAAAAAAAAtw/E-3uz7yigtU/s400/biopact_cassava_biofuels.jpg Cassava root is an important food in Africa http://scienceafrica.com/cms/wp-content/uploads/2010/06/cassava-ethanol.jpg

50. Half the world’s population gets most of its food energy from rice (Oryza sativa) Rice been cultivated for more than 8,000 years http://www.equita.qc.ca/images/produits/gn_008.jpg