Plant Diversity I: Non-vascular plants

1. Plant Diversity I: Non-vascular plants • 1.2 billion years ago (BYA) – appearance of cyanobacteria on land • 500 million years ago (MYA) – appearance of plants, fungi and animals • evolution of plants from the green algae Phylum Charophyaeta • similarities: multicellular, photosynthetic autotrophs, cell walls with cellulose, chlorophylls a and b • four key traits of plants and charophyceans • 1. rose-shaped complexes for cellulose synthesis – both charophyceans and land plants have rosette cellulose-synthesizing complexes - arrays of proteins in the plasma membrane that synthesize cellulose microfibrils • plants and charophyceans have a higher percentage of cellulose in their cell walls than the chlorophytans • 2. peroxisome enzymes – peroxisomes have enzymes that help minimize the loss of organic production as a result of photorespiration • 3. flagellated sperm • 4. formation of a phragmoplast – synthesis of a new cell plates that divides the two daughter cells during mitosis • alignment of cytoskeletal elements and golgi-derived vesicles in the midline of the dividing cell

2. Land plants • movement onto land would require protection of the zygote from drying out • layer of durable polymer called sporopellenin – prevents exposed zygote from dessication • development of adaptations as the land plants diverged from the charophyceans – facilitated survival and reproduction on land • defining the plant kingdom • origin of land plants – 430 MYA • Kingdom Plantae contains the plants called embryophytes – plants with embryos • however, current debate advises some changes • Kingdom Streptophytae – Embryophytes (land plates) + Charophyceans • Kingdom Viridiplantae – Embryophytes + Charophyceans + Chlorophytes • botanists do not use the term phyla when classifying the plant kingdom – use divisions • development of two lineages or divisions: non-vascular and vascular (390 MYA) – called the Bryophyta and Tracheophyta • vascular lineage developed into the seedless vascular and seeded vascular plants (360 MYA) • seeded vascular plants developed into the gymnosperms and angiosperms (130 MYA)

3. LE 29-4 Viridiplantae Streptophyta Plantae Charophyceans Red algae Embryophytes Chlorophytes Ancestral alga

4. Land plants: characteristics • 4 key traits in plants and algae: • 1. chloroplasts with thylakoid membranes stacked as grana and contains chlorophylls a and b • 2. starch as a storage polysaccharide in the chloroplasts • 3. cellulose in cell walls • 4. cytoplasmic division by a cell plate (phragmoplast) • in plants: diploid sporophyte (plant) produces haploid spores via meiosis which produces the gametophyte (reproductive organ) which produces haploid gametes via mitosis - these fuse to form the zygote via syngamy • sporophytes – multicellular, diploid, produce spores via meiosis • gametophytes – multicellular, haploid, produce gametes via mitosis • additional traits related to terrestrial life • 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 • secondary paths produce compounds such as tannins, terpenes and alkaloids (defense against herbivores and parasites), plus phenolics (flavonoids – absorb UV radiation, deter attacks by pathogenic microbes)

5. Apical Meristem of shoot Developing leaves Land plants: characteristics • five characteristics define a land plant (not found in the Charophyceans) • 1. apical meristems • light and CO2 available above ground, water and minerals 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 • apical meristem – localized regions of cell division located at the tips of shoots and roots Shoot Root

6. Haploid multicellular organism (gametophyte) Mitosis Mitosis Gametes Spores MEIOSIS FERTILIZATION Zygote Mitosis Diploid multicellular organism (sporophyte) • 2. alternation of generations • alternation between multicellular haploid and diploid stages • seen also in some chlorophytans – but not in the charophyceans • must be multicellular!! • alternate between the gametophyte (haploid) and sporophyte (diploid) • diploid sporophyte produces haploid spores via meiosis • mitotic division of the spore (haploid) produces a multicellular gametophyte which is still haploid • the gametophyte produces the haploid gametes by mitosis

7. Walled Spores Produced in Sporangia Multicellular Gametangia Multicellular, Dependent Embryos Archegonium with egg Longitudinal section of Sphagnum sporangium (LM) Female gametophyte Spores Embryo Maternal tissue Sporangium 10 µm 2 µm Sporophyte Antheridium with sperm Male gametophyte Gametophyte Wall ingrowths Placental transfer cell Archegonia and antheridia of Marchantia (a liverwort) Sporophyte and sporangium of Sphagnum (a moss) Land plants: characteristics • 3. walled spores in sporangia • within the sporophyte is the sporangia – production of haploid spores • the spores are protected by sporoporellin – key adaptation to terrestrial life • 4. multicellular gametogangia • production of gametes within a multicellular gametogania • female gametogania = archegonia (egg) • male gametogania = antheridia (flagellated sperm) • 5. multicellular, dependent embryos = embryophytes • fertilization of the egg within the archegonia followed by embryonic development • developing embryo is dependent upon the female parent • embryo receives nutrition during development from placental transfer cells • form elaborate ingrowths into the plasma membrane and cell wall of the embryo

8. Non-vascular plants: Bryophytes • non-vascular plants • three phyla – liverworts (phylum Hepatophyta), hornworts (phylum Anthocerophyta) and mosses (phylum Bryophyta) • 1. Phylum Hepatophyta • gametophytes are flattened into a thalloid or a leafy shape • 2. Phylum Anthocerophyta – e.g. Anthoceros • sporophyte can grow quite tall – sporangium along the length • 3. Phylum Bryophyta – e.g. Polytrichium • not to be confused with the vascular mosses – lycophytes • in the bryophyte - life cycle is dominated by the gametophyte stage • gamete forming stage • gametophyte is only a few cells thick • anchored to the ground by rhizoids – long tubular single cells (liverworts and hornworts) or filaments of multiple cells (mosses) • NOT roots – not composed of tissues (cells only), lack specialized conducting cells and are not responsible for water and mineral absorption • some mosses are mosses at all – Irish moss (red seaweed), reindeer moss (lichen), club mosses (seedless vascular plant)

9. 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

10. Bryophyte life cycle • production of spores by the sporangium on the sporophyte generation • if the conditions are favorable (moistness, nutrition), the spore will develop into a threadlike protonema – large surface area for absorption or water and minerals • each protonema produces a bud with an apical meristem • the AM generates the gamete producing structure known as the gametophore • the protonema and gametophore = gametophyte • at the tip of the gametophyte develops reproductive structures = gametogania • multiple gametogania on each plant • some bryophyte gametogania are bisexual – both antheridium and archegonium on the same gametophyte • most mosses have gametogania for the production of either female or male gametes – called antheridium and archegonium • are located on separate gametophytes – male and female gametophytes • production of the gametes by mitosis since the gametophyte is haploid already • fertilization is followed by development of the embryo within the archegonium • the growth of the embryo produces a small sporophyte • the sporophyte remains attached to the female gametophyte via a foot – absorption of nutrients • grows in length upward produces a seta (stalk) through a protective structure called a calyptra – at the tip of the calyptra the sporophyte forms a sporogonium surrounded by a capsule • the seta and capsule emerge through the larger gametophyte – aids in spore dispersal • in most mosses the upper part of the capsule forms a peristome – for gradual spore discharge • hornwort and moss sporophytes also have specialized pores = stomata • support photosynthesis by allowing the exchange of CO2 and O2 • also allow for the evaporation of water

12. Gametophore of female gametophyte 500 µm Foot Seta Sporangium Marchantia polymorpha, a “thalloid” liverwort Marchantia sporophyte (LM) Hepatophyta: Marchantia • thalloid-type gametophyte • damp rock and soil • actual plant is the haploid gametophyte stage • stalked uprisings are the gametogonia • some uprisings are called gemmae cups – contain asexual gemmae – discs of green tissue that when dispersed generate new gametophytes • develop by mitosis • upper epidermis overlies a diamond-shaped pattern of air chambers • hair-like rhizoids on the lower surface of the thallus – adaptations for anchorage

13. An Anthroceros hornwort species Sporophyte Gametophyte Anthocerophyta: Hornworts

14. Byrophyta: Mosses • Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat • Sphagnum plays an important role in the Earth’s carbon cycle Polytrichum commune, hairy cap moss Sporophyte Gametophyte

15. Seedless Vascular Plants • characteristics: • dominant phase of the life cycle is the sporophyte • e.g. ferns – leafy portion is the sporophyte • transport of vascular tissues – xylem and phloem • xylem – conduction of water and minerals • included tracheids – dead, tube-shaped cells for the conduction of water and minerals up from the roots • vascular plants referred to as tracheophytes • water conducting cells contain a phenolic polymer – lignin • cells are said to be lignified • phloem – conduction of sugars and other nutrients • living cells • arranged into tubes for the distribution of sugars, amino acids and other organic products • presence of roots and leaves • roots – anchorage of the plant, absorption of water and nutrients • resembles the stem tissues of fossilized plants • leaves – organs for the increase of vascular surface area to capture more solar energy • either megaphylls or microphylls

16. Seedless Vascular plants • two phyla: Lycophyta and Pterophyta • have modified leaves that bear sporangia = sporophylls • sporophylls very greatly in structure • most seedless vascular plants are homosporous – one type of sporophyll producing one type of spore that develops into a bisexual gametophyte • heterosporous species have two types of sporophylls each producing only one type of spore • e.g. ferns • on fern sporophylls are clusters of sporangia called sori – usually found on the underside • megasporangia on megasporophylls produce megaspores – develop into female gametophytes • microsporangia on microsporophylls produce microspores – develop into male gametophytes • Pterophyta – ferns, horsetails and whisk ferns • the pterophytes are frequently considered separate phyla: • phylum Sphenophyta – horsetails • phylum Psilophyta – whisk ferns and relatives • phylum Pterophyta – ferns • most recent information consider these groups now to be one clade Lycophyta – club mosses, spike mosses and quillworts

18. Phylum Lycophyta • grow on tropical trees as epiphytes • they are NOT parasites • the sporophytes have upright stems with many small leaves plus ground-hugging stems that produce branching roots • in the club mosses – the sporophylls are clustered into club-shaped cones = strobili • homosporous • spike mosses and quillworts - heterosporous Isoetes gunnii, a quillwort Strobili (clusters of sporophyllis) Diphasiastrum tristachyum, a club moss

19. Phylum Pterophyta • whisk ferns • dichotomously branching stems but no roots • stems have scale-like outgrowths that lack vascular tissue • stems may have evolved as reduced leaves • homosporous with spores that give rise to bisexual gametophytes that grow underground • considered to be living fossils due to their resemblance to fossils of ancient vascular plants • horsetails • named for the brushy appearance of the stems • arthrophytes – “jointed plants” • rings of small leaves or branches can emerge from each joint • stem is the main photosynthetic organ • ferns • ferns have megaphylls • sporophylls typically have horizontal stems that give rise to large leaves called fronds divided into leaflets • frond grows as the fiddlehead • almost all species are homosporous • gametophyte shrivels and dies after the young sporophyte detaches itself • the sporangia are stalked with spring-like devices that disperse the spores

20. Key Haploid (n) Diploid (2n) Antheridium Spore Young gametophyte MEIOSIS Sporangium Sperm Archegonium Egg New sporophyte Mature sporophyte Sporangium Zygote FERTILIZATION Sorus Gametophyte Fiddlehead Fern Life Cycle • spore develops into a young gametophyte – bisexual • gametophyte develops male and female gametogania – antheridium within microsporangia and archegonium within megasporangia • production and release of sperm – swims to the egg within the archegonium – fertilization and development into a zygote • the zygote develops into the sporophyte • growth of the sporophyte produces fronds or megaphylls • fronds contain sporangia for the production of spores • heterosporous species have megasporangium and microsporangium –production of distinct spores • almost all fern species are homosporous