Lecture #5

1. Lecture #5 Plant Diversity I: Non-vascular plants & Seedless Vascular plants

2. 1.2 billion years ago (BYA) – appearance of cyanobacteria on land • 500 million years ago (MYA) – appearance of plants, fungi and animals • more than 290,000 known plant species today • plants inhabit all but the harshest environments • such as some mountaintops, deserts areas and polar regions • many plants have returned to their aquatic “roots” • e.g. some species of sea grasses • most present-day plants are terrestrial • presence of plants has enabled other life forms to survive on land • through their production of O2

3. Plants and Algae Archaeplastida Unikonta Fungi Animalia Plantae Chlorophyta Charophyta Rhodophyta (Opisthokonta) (Viridiplantae) • evolution of plants proposed from algae • closest relatives are located with the clade Charaophycea • these share a common ancestor with the clade Chlorophyta – include the green algae • similarities with algae: • multicellular • photosynthetic autotrophs • cell walls with cellulose • chlorophylls a and b Choanoflagellates Charophyceans Plants Fungi Metazoans Red algae Chlorophytes Ancestral eukaryote

4. 4 key traits of plants • four key traits of plants (and charophyceans) • provided by not only morphologic evidence but genetic evidence • 1. rose-shaped complexes for cellulose synthesis – both charophyceans and land plants have rosette cellulose-synthesizing complexes • 2. peroxisome enzymes – peroxisomes have enzymes that help minimize the loss of organic production as a result of photorespiration Rosettes

5. 4 key traits of plants • four key traits of plants (and charophyceans) • 3. flagellated sperm structure – similar to the charophyceans • 4. formation of a phragmoplast= group of microtubules that forms between the daughter nuclei of the dividing plant cell during mitosis

6. Adaptations by Land plants • advantages of a terrestrial life: • stronger exposure to sunlight for photosynthesis • atmosphere offered more CO2 for photosynthesis • soil rich in nutrients • initially relatively few herbivores • movement onto land would require protection of the zygote from drying out • development of layer of durable polymer called sporopellenin– prevents exposed zygote from dessication • movement onto land resulted in the development of specific adaptations– facilitated survival and reproduction on land • e.g. development of a structural system to withstand the forces of gravity • e.g. changes adapting to the relative scarcity of water • these adaptations have defined the plant kingdom

7. Adaptations by Land plants • what adaptations are unique to plants? • depends on how you draw the boundary separating plants from algae • some traits are related to terrestrial life • for the earliest land plants – mycorrhizal associations with fungi for nutrient absorption • epidermis with a waxy covering called a cuticle • production of secondary compounds that are products of secondary metabolic pathways • primary metabolic paths produce lipids, carbohydrates, amino acids – not unique to plants • secondary paths produce compounds such as: • tannins, terpenes and alkaloids (defense against herbivores and parasites) • phenolics (flavonoids – absorb UV radiation, deter attacks by pathogenic microbes)

8. Kingdom Plantae contains the plants called embryophytes – plants the develop from embryos • however, current debate advises some changes – 2 options: • Kingdom Streptophytae – Embryophytes (land plates) + Charophyceans OR • Kingdom Viridiplantae – Embryophytes + Charophyceans + Chlorophytes Viridiplantae Streptophyta Plantae Charophyceans Red algae Embryophytes Chlorophytes Ancestral alga

9. Hey guys! How about confusing the issue? • botanists do not use the term phyla when classifying the plant kingdom – use divisions • currently accepted organization: development of two lineages or divisions: non-vascular and vascular (390 MYA) • called the Bryophyta (non-vascular) and Tracheophyta (vascular) • ** plants can be divided into 2 • major categories • non-vascular • vascular – subdivided into 2 • more categories: • seedless • seed

10. KISS: Keep it simple stupid • ** plants can be divided into 2 major categories • non-vascular • vascular – subdivided into 2 more categories: • seedless • seed

11. Land plants: 4 characteristics • 4 key derived traits found in plants: • 1. alternation of generations & multicellular, dependent embryos • 2. walled spores produced in sporangia • 3. multicellular gametangia • 4. apical meristems

12. Haploid multicellular organism (gametophyte) Mitosis Mitosis Gametes Spores MEIOSIS FERTILIZATION Zygote Mitosis Diploid multicellular organism (sporophyte) Land plants: 4 characteristics • 1. alternation of generations: alternation between multicellular haploid and diploid stages in a life cycle • seen also in some chlorophytans (algae) – but not in the charophyceans • these generations must be multicellular!! • haploid stage = gametophyte (haploid) • diploid stage = sporophyte (diploid) • the sporophyte is the mature plant produces haploid spores via meiosis • mitotic division of the haploid spore produces a multicellular gametophyte which is still haploid!!

13. Haploid multicellular organism (gametophyte) Mitosis Mitosis Gametes Spores MEIOSIS FERTILIZATION Zygote Mitosis Diploid multicellular organism (sporophyte) Land plants: 4 characteristics • 1. alternation of generations: alternation between multicellular haploid and diploid stages in a life cycle • the gametophyte is the reproductive part of the plant - produces haploid gametes by mitosis • gametes fuse via syngamy/fertilization to produce the zygote • zygote grows via mitosis to develop a new sporophyte • in non-vascular plants (ike ferns) – the sporophyte and gametophyte have distinct phenotypic appearances – but they are forms of the same species • in vascular plants – the gametophyte is microscopic • -sporophytes – multicellular, diploid, produce haploid spores via meiosis • -gametophytes – multicellular, haploid, produce haploid gametes via mitosis

14. 1. Alternation of generations and multicellular dependent embryos cont…. • in a life cycle with alternation of generations – the multicellular embryos develop from zygotes are retained within the female gametophyte • maternal tissue provides nutrients • plants with embryos are called embryophytes • embryo receives nutrition during development from placental transfer cells Multicellular, Dependent Embryos Embryo Maternal tissue 10 µm 2 µm Wall ingrowths Placental transfer cell (blue line)

15. Land plants: 4 characteristics • 2. walled spores in sporangia • within the diploid sporophyte are multicellular organs called sporangia (singular = sporangium) – production of haploid spores via meiosis • within a sporangium are diploid cells called sporocytes or spore mother cells – undergo meiosis to generate the haploid spores of the sporangium • the spores are protected bysporoporellin– key adaptation to terrestrial life Walled Spores Produced in Sporangia Longitudinal section of Sphagnum sporangium (LM) Spores Sporangium Sporophyte Gametophyte Sporophyte and sporangium of Sphagnum (a moss)

16. Land plants: 4 characteristics • 3. multicellular gametogangia • the haploid gametophyte undergoes production of haploid gametes within multicellular gametogania(singular = gametoganium) • the production of gametes is through mitotic division • female gametogania = archegonium- produces a single egg • male gametogania = antheridium– produces many flagellated sperm Multicellular female Gametangia Archegonium with egg Female gametophyte Multicellular Male Gametangia Antheridium with sperm Male gametophyte Archegonia and antheridia of Marchantia (a liverwort)

17. Apical Meristem of shoot Developing leaves Land plants: characteristics • 4. apical meristems • light and CO2 are available above ground, water and minerals are found mainly in the soil • must be a way of collecting these components • plants do this by growing in length – through the production of stems and roots • these grow from stem cell-like tissues in the plant called meristems Shoot Root

18. Apical Meristem of shoot Developing leaves Land plants: characteristics • 4. apical meristems • apical meristem – localized regions of cell division located at the tips of shoots and roots • e.g. shoot apical meristem – cells divide by mitosis and cytokinesis to produce progenitor cells for the rest of the stem • e.g. root apical meristem • progenitor cells from the meristem are the source for the tissues of the stem and root Shoot Root

19. Plant Diversification • plant fossils dating back to 475 MYA • one major way to distinguish groups of plants is to classify them as: vascular & non-vascular • vascular tissue – extensive system formed by cells joined into tubes • conduct water and nutrients • those without these tubes – non-vascular plants • bryophytes: term used to refer to all non-vascular plants • do not form a monophyletic group or a single clade • known popularly as the mosses, liverworts and hornworts • is a debate as to how they are related to each other • don’t possess the advanced adaptations of vascular plants (e.g. roots & leaves) • they do share many characteristic with vascular plants – see the slide on 4 plant characteristics • vascular plants: clade that includes 93% of all surviving plant species • categorized into smaller clades: • 1. lycophytes – club mosses • 2. pteryophytes – ferns • 3. gymnosperms • 4. angiosperms

20. Land plants Vascular plants Bryophytes Seedless vascular plants Seed plants Gymno- sperms Angio- sperms Hornworts Mosses Liverworts Lycophytes Pterophytes Charophyceans Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga

21. Non-vascular plants • commonly known as the bryophytes • even though Bryophyta is one of the 3 phyla in this group • three phyla: • 1. Phylum Hepatophyta: liverworts • gametophytes are flattened into a thalloid or a leafy shape • e.g. Marchantia • 2. Phylum Anthocerophyta – hornworts • sporophyte can grow quite tall – sporangium along the length • 3. Phylum Bryophyta – mosses Plagiochiladeltoidea= liverwort Marchantiapolymorpha= liverwort

22. Non-vascular plants • mosses are not to be confused with the vascular mosses = lycophytes • moss life cycle is dominated by the gametophyte stage • gamete forming stage • anchored to the ground by rhizoids – long tubular single cells • NOT roots – not composed of tissues (cells only), lack specialized conducting cells and are not responsible for water and mineral absorption • some mosses are NOT mosses at all – Irish moss (red seaweed), reindeer moss (lichen), club mosses (seedless vascular plant)

23. Bryophyte General Life Cycle: The Gametophyte • dominant stage in all bryophytes • when a bryophyte spore land on favorable habitats – it germinates and grows into a haploid gametophyte • first the spore develops into a threadlike protonema – covers a large surface area for absorption or water and minerals • each protonema produces a bud with an apical meristem (stem-cell like tissue for growth) • the AM generates gamete-producing structures known as gametophores • the tips of the gametophore bear the male or female gametangia • the protonema + gametophore = gametophyte the gametophyte of mosses is the actual moss!!

24. General Life Cycle: The Gametophyte • located in the gametophyte are the reproductive structures = gametangia • (singular = gametangium) • multiple gametangia develop on each gametophore • some bryophyte gametangiaare bisexual – both antheridium and archegoniumon the same gametophyte = monoecious • most mosses have separate antheridiumand archegoniumlocated on separate gametophytes on separate plants - dioecious • production of the gametes by mitosis since the gametophyte is haploid already!!! antheridium archegonium

25. Gametophore of female gametophyte 500 µm Foot Seta Sporangium Marchantia polymorpha, a “thalloid” liverwort Marchantia sporophyte (LM) General Life Cycle: The Gametophyte • the gametophores of a liverwort are found at the end of stalks • they grow out of the gametophyte • the undersurface of these gametophores is where you find the antheridia and archegonia • since both of these are found on the same sporophyte plant = monoecious the gametophyte of the liverwort is the actual liverwort!!

26. General Life Cycle: The Sporophyte • the sporophyte is very small in the non-vascular plant • fertilization is followed by development of the embryo within the archegonium • the embryo develops into a small sporophyte (diploid) - remains attached to the archegonium via a foot – for absorption of nutrients • the sporophyte is comprised of: • 1. seta (stalk) • 2. sporangium surrounded by a capsule • haploid spores develop in this sporangium via meiosis moss liverwort sporophyte

27. General Life Cycle: The Sporophyte • haploid spores develop in the sporangium via meiosis • the spores are dispersed and settle onto a new substrate • from these spores comes new protonemata(singular = protonema) • hornwort and moss sporophytes tend to be large and more complicated • liverwort sporophytes are microscopic

28. Raindrop Key Male gametophyte Haploid (n) Life Cycle of a Moss Diploid (2n) Sperm “Bud” Spores develop into threadlike protonemata. A sperm swims through a film of moisture to an archegonium and fertilizes the egg. Antheridia The haploid protonemata produce “buds” that grow into gametophytes. Most mosses have separate male and female gametophytes, with antheridia and archegonia, respectively. Protonemata “Bud” Egg Gametophore Spores Female gametophyte Archegonia Meiosis occurs and haploid spores develop in the sporangium of the sporophyte. When the sporangium lid pops off, the peristome “teeth” regulate gradual release of the spores. Rhizoid Peristome The sporophyte grows a long stalk, or seta, that emerges from the archegonium. FERTILIZATION Sporangium (within archegonium) MEIOSIS Seta Calyptra Zygote Capsule (sporangium) Mature sporophytes Foot Embryo Archegonium The diploid zygote develops into a sporophyte embryo within the archegonium. http://www.sumanasinc.com/webcontent/animations/content/moss.html Young sporophyte Attached by its foot, the sporophyte remains nutritionally dependent on the gametophyte. Female gametophytes Capsule with peristome (SEM)

29. The Economics of Moss • mosses have very lightweight spores • easy distribution has allowed for the establishment of mosses around the globe • very common and diverse in moist forests and wetlands • can help retain nitrogen in the soil • many species harbor cyanobacteria that increase the availability of nitrogen to the moss • many species can survive drought and rehydrate when moisture reappears

30. The Economics of Moss • one wetland moss = Sphagnum or “peat moss” • peat moss = partially decayed remnants of Sphagnum • major component of partially decayed organic material called peat • regions with thick layers of peat = peatlands (3% of Earth’s surface) • peat contains 30% of world’s soil carbon • 450 billion tons of carbon is stored as peat • Sphagnum does not decay easily – phenolic compounds in its cell walls • peat – fuel source in northern Europe rather than wood • overharvesting of Sphagnum – could alter CO2 levels globally Sphagnum moss

31. Seedless Vascular Plants • bryophytes prominent during the first 100 million years of plant evolution • but they are not very tall • rarely over 20 cm in height • those plants that could achieve heights would have better access to sunlight, better spore dispersal • height would mean the need for a transport system for water and nutrients • would also need a structural support system • ferns are example of the evolution of plants that began to develop height and a vascular system • fossils of present day vascular plants date back 425 MYA

32. Seedless Vascular Plants • 4 major characteristics of vascular plants: • 1. dominant phase in the alternation of generations life cycle is the sporophyte • the opposite case with bryophytes • e.g. ferns – the leafy plant is the sporophyte • the sporophyte becomes the larger and more complex stage of the life cycle • dramatic reduction in gametophyte stage – may be under the soil • sporophyte no longer dependent on the gametophyte for nutrition

33. Seedless Vascular Plants • 4 major characteristics of vascular plants: • 2. development of vascular tissues – xylem and phloem • xylem – conduction of water and minerals • new cell population = tracheids • so vascular plants are often referred to as tracheophytes • water conducting cells contain a phenolic polymer – lignin • phloem – conduction of sugars and other nutrients • living cells • arranged into tubes for the distribution of sugars, amino acids and other organic products

34. Seedless Vascular Plants • 4 major characteristics: • 3. development of sporophylls: modified leaves that bear sporangia • vary in structure • two types: microphyll and megaphyll • e.g. in ferns – megaphylls with clusters of sporangia called sori • e.g. in lycophytes and gymnosperms – microphylls that form cone-like strobili • most seedless vascular plants are homosporous– one type of sporangium that produces one type of spore • this spore produces a bisexual gametophyte  egg and sperm • heterosporousspecies has two types of sporangia that develop into two types of spores • megasporangium - megaspore  egg • microsporangium - microspore sperm

35. Seedless Vascular Plants • 4 major characteristics of vascular plants: • 4. development of roots and leaves • rather than rhizoids – the sporophytes of vascular plants have evolved roots • roots– organs for the anchorage of the plant & absorption of water and nutrients • leaves– organs for the increase of vascular surface area to capture more solar energy • megaphylls are larger and have a highly branched vascular system (of veins) running through them • greater photosynthetic capacity • microphyllsare spine-like • supplied by a single, unbranched vein • appeared to have evolved first

36. Evolution of Leaves • evolution of microphylls from clusters of sporangia • evolution of megaphylls from an accumulation of branches on a stem • one branch with overtopping growth • smaller branches flattened and fused to one another and to the overtop branch

37. Seedless Vascular plants • two clades: • Phylum Lycophytaand Phylum Pterophyta • both have modified leaves called sporophyllsthat bear sporangia • two types of sporophylls: microphylls and megaphylls • most seedless vascular plants are homosporous

38. Seedless Vascular plants • Phylum Pterophyta – ferns, horsetails and whisk ferns • the pterophytes are divided by some botanists into separate phyla: • phylum Sphenophyta – horsetails • phylum Psilophyta – whisk ferns and relatives • phylum Pterophyta – ferns Equisetum – horsetail fern Psilotum – whisk fern

39. Seedless Vascular plants • Phylum Lycophyta – club mosses, spike mosses and quillworts Quillwort Isoetes Club moss Selaginella

40. Strobili (clusters of sporangia) Diphasiastrum tristachyum, a club moss Phylum Lycophyta • club mosses, spike mosses and quillworts • 1200 species today • NOT true mosses since they have vascular tissue • most ancient line of vascular plants • modern lycophytes grow on tropical trees as epiphytes – BUT they are NOT parasites epiphytic ferns

41. Phylum Lycophyta • microphyllline of evolution • distinct line of evolution that came out of the first land plants • development of leaves from clusters of sporangia • earliest lycophytes formed primitive leaves = enations • enations are now called microphylls • evolution of true roots – increased the size of the sporophyte • sporangia became clustered into compact cones or strobili • many species evolved heterospory

42. Phylum Pterophyta • megaphyllline of evolution • development of leaves from a branching system of stems • seen in all seed vascular plants, ferns and arthrophytes (horsetails) • telometheory: main stem with dichotomously branching lateral stems • the lateral branches developed subdivisions – all on one plant • the last lateral branches = telomes • during evolution - tissue grew in between (webbing) • the telomes also acquired spore-forming ability • positioning of the branches became very regular and controlled telomes

43. Phylum Pterophyta alternate • development of phyllotaxy– arrangement of leaves on a stem • four basic patterns developed: • spiral phyllotaxy: lateral branches became arranged in a spiral pattern • alternating: stepwise arrangement of leaves • opposite: leaves directly opposite one another • whorled pattern: more complicated arrangement opposite whorled

44. Phylum Pterophyta • ferns • leaves are known as megaphylls • fern sporophyte is comprised of underground, horizontal stems called rhizomes • from these come vertical shoots that give rise to large leaves called fronds divided into pinna (or leaflets) • frond grows as the fiddlehead • leaf primordial cells as they grow curl inward • mature frond is called the megaphyll • megaphyll is a compound leaf with a center rachis and multiple pinna • the pinna itself may be may up of small pinnules • although some fern species – e.g. staghorn fern – have a simple leaf structure

45. Phylum Pterophyta • gametophyte is very small and shrivels and dies after the young sporophyte develops • the diploid sporophyte bears sporangia (singular = sporangium) clustered under the pinna in structures called sori (singular = sorus) • so one sorus is made up of multiple sporangia • a sporangium contains spore mother cells (2n) • the spore mother cells undergo meiosis to produce spores (n)  haploid gametophyte

46. The Annulus and spore dispersal from the Sporangium • http://www.youtube.com/watch?v=-xF83pHEx6Q • the individual sporangium is a stalked structure • at the end are spring-like devices that disperse the spores = annulus • annulus, a row of cells that bisects the sporangium like a sturdy spine. • annulus walls are permeable to water • as the sporangium dries, evaporating water is drawn out from the annulus, causing the cells to shrink – this pries the sporangium open • the presence of water within the sporangium propels the spores out like a catapult

47. Key Haploid (n) Diploid (2n) Antheridium Spore Young gametophyte MEIOSIS Sporangium Sperm Archegonium Egg New sporophyte Mature sporophyte Sporangium Zygote FERTILIZATION Sorus Gametophyte Fiddlehead • in the sporophyte – presence of multiple sporangia clustered into a sorus (sori = plural) • spores released from thesori and germination into a bisexual gametophyte • bisexual gametophyte develops male and female gametogania • male antheridium – for sperm production • female archegonium - for egg development • sperm are released and swim to the egg within the archegonium – fertilization and development into a diploid zygote Fern Life Cycle http://www.youtube.com/watch?v=9c9Zi3WFVRc

48. Key Haploid (n) Diploid (2n) Antheridium Spore Young gametophyte MEIOSIS Sporangium Sperm Archegonium Egg New sporophyte Mature sporophyte Sporangium Zygote FERTILIZATION Sorus Gametophyte Fiddlehead • the zygote develops into a new diploid sporophyte – emerges from the gametophyte • growth of the sporophyte produces fronds or megaphylls • young, developing frond is called the fiddlehead • gametophyte disappears • fronds develop sporangia for the production of spores (via meiosis) • almost all fern species are homosporous • produce one kind of spore  bisexual gametophyte Fern Life Cycle • heterosporousfern species have megasporangiumand microsporangium on the sporophyte – production of distinct spores for male and female gametophytes