Evolution of Plants

Evolution of Plants

• The terrestrial surface was lifeless for over 3 billion years
• Cyanobacteria and protists likely existed on land 1.2 billion years ago
• Algae are photosynthetic protists, not plants
• Small non-vascular plants, fungi, and animals became established on land ~500 million years ago
• Plants have diversified into roughly 290,000 living species since colonizing land
• Most plants today are terrestrial, some have returned to aquatic habitats
• Plants supply oxygen and are the source of most food for land animals
• Plants are the base of most food webs, capturing solar energy and converting it to a usable form
• Charophytes represent a transition towards terrestrial plants
• Plants evolved from green algae (charophyceans or chlorophytes)
• Charophycean ancestors (green algae) lived at the water's edge with access to sun, CO2, nutrient-rich soil, and fewer herbivores/pathogens
• Land presented challenges, including scarcity of water and lack of structural support
• Sporopollenin, a durable polymer, prevents exposed zygotes from drying out in charophyceans and their ancestors
• Sporopollenin adaptation allowed them to take advantage of new habitats and move onto land
• Movement onto land caused major changes to the Earth's surface and an explosion in available habitats and niches
• Plant evolution moves towards less dependence on water and a protected seed stage

Common Features & Derived Traits

• Common features between charophyceans and land plants:
  • Multicellularity
  • Eukaryotic nature
  • Photosynthetic capabilities
  • Autotrophic nutrition
  • Cellulose-containing cell walls
  • Similar biochemical details
• Derived traits of plants:
  • Alternation of generations (with multicellular, dependent embryos)
  • Walled spores in sporangia
  • Multicellular gametangia
  • Apical meristems

Alternations of Generations & Spores

• Alternation of generations involves two different free-living stages per generation
• Diploid sporophyte produces haploid spores that grow into the gametophyte
• Haploid gametophyte produces N gametes (sperm and egg), which fuse to form a diploid zygote
• Walled spores produced in sporangia: sporophytes produce walled spores (haploid) in sporangia
• Spore walls contain sporopollenin, making them resistant to harsh environments
• Multicellular gametangia: gametes are produced within gametangia
  • Female gametangia (archegonia) produce eggs and are the site of fertilization
  • Male gametangia (antheridia) are the site of sperm production and release
  • Sperm travels from antheridia to archegonia, requiring water
• Apical meristems: plants sustain continual growth in their apical meristems
• Cells from apical meristems differentiate into various tissues
• Fossil evidence indicates plants were on land at least 475 million years ago
• Fossilized spores and tissues have been extracted from 475 million-year-old rocks

Plant Diversification

• Plants diversified into two main types based on the presence/absence of vascular tissue ("pipes"):
  • Non-vascular plants ("Bryophytes" = mosses, liverworts, hornworts)
  • Vascular plants (with two important subgroups)
• Seedless plants can be divided into:
  • Lycophytes (club mosses and relatives)
  • Monilophytes (=Pterophytes - ferns and their relatives)
  • Seed plants

Nonvascular & Seedless Plants

• Bryophyte life cycles are dominated by the gametophyte stage in nonvascular plants
• Three phyla of small herbaceous (nonwoody) plants: liverworts, hornworts, and mosses
• Mosses are most closely related to vascular plants
• Bryophytes: gametophytes are the dominant stage
  • Sporophytes are typically present only part of the time, attached to the gametophyte
  • A spore germinates into a gametophyte of protonema and gamete-producing gametophore
  • Rhizoids (not roots) anchor gametophytes to the substrate
  • The height of gametophytes is constrained by lack of vascular tissues
  • Mature gametophytes produce flagellated sperm in antheridia and an egg in archegonia
  • Sperm swim through a film of water to reach and fertilize the egg
• Bryophyte sporophytes grow out of archegonia and are the simplest sporophytes of all plant groups
• A sporophyte consists of a foot, seta (stalk), and sporangium (capsule), which discharges spores
• Hornwort and moss sporophytes have stomata for gas exchange, but liverworts do not
• Bryophyte life cycles have the gametophyte as the dominant generation
• Seedless vascular plants: ferns and other seedless vascular plants were the first plants to grow tall
  • These plants evolved vascular tissues called xylem and phloem
  • Vascular tissues provide structural support
  • Seedless vascular plants have flagellated sperm and are usually restricted to moist environments
  • Life cycles feature dominant diploid sporophytes
• Vascular tissues provide transport and structure:
  • Xylem: conducts water and minerals; includes dead cells called tracheids strengthened by lignin
  • Phloem: consists of living cells and distributes sugars, amino acids, and organic products
• Roots are organs that anchor vascular plants and enable absorption of water and nutrients
  • Roots may have evolved from subterranean stems
• Bryophytes don't have roots, they have rhizoids with no "tissues" or vascular units
• Leaves increase the surface area of vascular plants for photosynthesis
• Leaves are categorized by:
  • Microphylls: leaves with a single vein
  • Megaphylls: leaves with a branched vascular system
• Two phyla of seedless vascular plants:
  • Phylum Lycophyta: club mosses, spike mosses, and quillworts
    • Giant lycophytes thrived for millions of years in moist swamps
    • Surviving species are small herbaceous plants
    • Club mosses and spike mosses have vascular tissues and are not true mosses
  • Phylum Monilophyta = Pteridophyta: ferns, horsetails, and whisk ferns
    • Ferns are the most diverse seedless vascular plants, with more than 12,000 species
    • They are diverse in the tropics and also in temperate forests
    • Horsetails were diverse during the carboniferous period
    • Whisk ferns resemble ancestral vascular plants but are closely related to modern ferns
• The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Devonian and Carboniferous periods, forming the first forests
• Increased photosynthesis helped produce global cooling
• Decaying plants of the carboniferous forests eventually became coal

Seed Plant Evolution

• The evolution of the true seed enabled its bearers to become the dominant producers in most terrestrial ecosystems
• Seeds and pollen grains are key adaptations, allowing plants to inhabit many terrestrial ecosystems
• A seed consists of an embryo and nutrients surrounded by a protective coat
• Common characteristics among the seed plants
  • Heterospory
    • The ancestors of seed plants were likely homosporous, in contrast to seed plants
    • Seed plants produce two different spore sizes: microspores that turn into male gametophytes and megaspores that turn into female gametophytes.
    • Megasporangia (2N) produce megaspores (N) and microsporangia (2N) produce microspores (N)
  • Reduced gametophytes (virtually microscopic)
    • Provides protection as the gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte
  • Ovules (integument + megasporangium + megaspore or egg)
    • Gymnosperm megasporangia have one integument
    • Angiosperm megasporangia usually have two integuments
  • Pollen:
    • Microspores develop within pollen grains, which contain the male gametophytes
    • Pollination is the transfer of pollen to the part of a seed plant containing the ovules
    • Pollen eliminates the need for a film of water; they can be dispersed great distances by air or animals
    • If a pollen grain germinates, it gives rise to a pollen tube that discharges two sperm into the female gametophyte within the ovule
• Evolutionary advantages of seeds:
  • A seed develops from the whole ovule
  • A seed contains the sporophyte embryo and its food supply, packaged in a protective coat
  • Seeds provide several evolutionary advantages over spores:
    • They may remain dormant for days to years, until conditions are favorable for germination
    • They may be transported long distances by wind or animals

Time, Seeds, Gymnosperms

• Through time, plants tend to greater complexity
  • Embryonic attachment to the mother plant
  • Cells joined in tubes for water & nutrient transport- vascular tissues
  • Seed stage- embryo packaged with food supply in a protective coat
• Gymnosperms bear “naked” seeds, typically on cones; seeds not enclosed by ovaries
• Gymnosperms consist of 4 phyla:
  • Cycadophyta (cycads)
  • Ginkgophyta (one living species: Ginkgo biloba)
  • Gnetophyta (3 genera: gnetum, ephedra, welwitschia)
  • Coniferophyta (conifers, such as pine, fir, and redwood)
• Phylum ginkgophyta has only one species, *Ginkgo biloba; Ginkgos are highly tolerant to air pollution and popular ornamental trees
• Phylum cycadophyta (cycads or sago palms) has ~200 species; thrived during the mesozoic
  • Palm-like (not palms)
  • Seeds produced in large cones
• Phylum gnetophyta is diverse, with several growth forms but few species; some are tropical and others are in deserts; includes Ephedra in N. America

Phylum Coniferophyta & Angiosperms

• Phylum coniferophyta includes conifers like pines, firs, redwoods, spruces, and cypresses, comprising about 550 species and being ecologically important
  • Needle-shaped leaves
  • Mostly evergreen
  • Largest forests on Earth are mostly conifers
  • The largest organism is the giant sequoia (Sequoiadendron gigantea)
  • The tallest organism is the coast redwood (Sequoia sempervives)
  • The oldest non-clonal organism is the bristlecone pine (Pinus longaeva)
• The life cycle of a pine (gymnosperm) features dominance of the sporophyte generation
  • Development of seeds from fertilized ovules
  • Transfer of sperm to ovules by pollen
  • The familiar pine tree is the sporophyte and produces sporangia in male and female cones
  • Small cones produce microspores within pollen grains; the microspore develops into the male gametophyte
  • The familiar larger cones contain ovules that produce megaspores that develop into female gametophytes
• Plants decreased reliance on liquid water for fertilization, increasing dominance of sporophyte generation over time
• Angiosperms (reproductive adaptations include flowers and fruits)
  • Seed plants with reproductive structures called flowers and fruits
  • The most widespread and diverse of all plants

Angiosperm Characteristics

• Single phylum: anthophyta (Greek anthos = flower)
  • The flower is a unique structure, adapted for sexual reproduction
  • Many species are animal-pollinated, while others are wind-pollinated or self-pollinating
• Flowers are specialized shoots with up to four types of modified leaves:
  • Sepals (calyx) cover immature flower bud
  • Petals (corolla) attract animals as pollinators
  • Stamens: microsporophylls; produce pollen within anthers
  • Carpels: megasporophylls make megaspores, female gametophytes, and eventually seeds
• Fruits consist of a mature ovary but can also include other flower parts
  • They protect seeds and aid in dispersal
  • Mature fruits can be either fleshy or dry
  • Various fruit or seed adaptations help disperse seeds via wind, water, or animals

Angiosperm Life Cycle & Success

• The flower of the sporophyte contains both male and female structures (not always the case)
  • Male gametophytes are contained within pollen grains produced by the microsporangia of anthers
  • The female gametophyte (embryo sac) develops within an ovule contained within an ovary at the base of a stigma
  • Most flowers have mechanisms that ensure cross-pollination, pollination between different plants of the same species
• Angiosperms have ~250,000 species, reasons for their success include: -Rapid life cycle (gymnosperms– years, angiosperms- weeks)
  • Symbioses (mutualistic partnerships: co-evolution)
    • Pollination: efficient, targeted pollen delivery is possible
    • Fruit and seed dispersal: nutritious fruits for transport
    • Mycorrhizae (interactions between soil fungi and roots)
  • More effective vascular tissues, vessel elements, sieve tube members
• The two main groups of angiosperms are monocots (one cotyledon) and eudicots (two cotyledons)

Monocots & Eudicots

• Monocots:
  • More than one-quarter of angiosperm species (65,000)
  • Single cotyledon-embryo starts with one leave
  • Leave vasculature tends to be parallel
  • Complex arrangement of vascular bundles in stems
  • Roots are fibrous
  • Flower parts (petals, etc.) in multiples of 3
  • Lilies, orchids, yuccas, palms, grasses, including all major grain crops
• Eudicots:
  • More than two-thirds of angiosperm species (165,000 species)
  • Double cotyledon
  • Leaf vasculature tends to be a network
  • Vascular bundles in stem usually arranged in a ring
  • Usually a central large taproot
  • Flower parts usually in multiples of 4 or 5
  • Legumes (pears), brad-leafed trees (oaks, maples), roses; includes most human crops

Plant structure & Roots

• Plants grow according to a genetically determined, repetitive program
• Plant development is dependent on environmental conditions, far more than in animals
• Growth in response to environmental change facilitates resource acquisition in plants
• Developmental plasticity provides ability to alter form in response to the environment
• Adaptations in morphology come from natural selection:
  • Water retention features: spines, water storage organs, shape
• The three basic plant organs: roots, stems, and leaves
• Morphology reflects their evolution as organisms that draw nutrients from below and above ground
• Parts: -Root system -Shoot system
• Roots rely on sugar produced by photosynthesis in the shoot system, and shoots rely on water and minerals absorbed by the root system
• Roots are multicellular organs with functions:
  • Anchoring the plants
  • Absorbing minerals and water
  • Storing organic nutrients
• A taproot system consists of one main vertical root that gives rise to lateral roots
• Adventitious roots arise from stems and leaves
• Seedless vascular plants and monocots have a fibrous root system, thin lateral roots with no main root
• Absorption of water and minerals occurs near the root hairs
• Vast numbers of tiny root hairs increase available surface area for water and nutrient uptake

Root Modifications & Stems

• Root modifications:
  • Prop roots: support tall, top heavy plants (corn)
  • Storage roots (carrot, beets)
  • "Air” roots= pneumatophores (mangrove)
  • Buttress roots (many rainforest trees)
  • "Strangling” roots (some figs)
• A stem consists of:
  • An alternating system of nodes, the points to which leaves are attached
  • Internodes, the stem segments between nodes
  • An axillary bud has potential to form a lateral shoot, or branch
  • An apical bud, or terminal bud, located near shoot tip; causes elongation
• Apical dominance maintains dormancy in most non-apical buds
• Types of stem modifications:
  • Rhizomes: horizontal stem just below the surface
  • Bulbs: vertical underground shoots consisting of enlarged bases of storage leaves
  • Stolons: horizontal shoots along soil surface (runners); allows asexual reproduction
  • Tubers: enlarged ends of rhizomes or stolons for food storage

Leaves & Plant Tissue

• Leaves- main photosynthetic organ
• Leaves Consist of:
  • Consist of a flattened blade and a stalk called the petiole, which joins the lead to a node of the stem
• Leaf modifications:
  • Simple leaf: single, undivided blade, sometimes deeply lobed
  • Compound leaf: multiple leaflets arising from petiole; no axillary bud at base
• Doubly compound leaf: leaflets divided again into smaller leaflets
  • Tendrils: leaves provide support
  • Spines: protection, reduced surface area, shade
  • Storage leaves: store water for food
  • Reproductive leaves: adventitious plantlets- fall and root
  • Bracts: surround flowers that attract pollinators
• Dermal, vascular and ground tissues
  • Each of these three categories forms a tissue system
    • Demal: protective ‘skin'
    • Vascular: fluid movement
    • Ground: all other functions including photosynthesis, storage, support, etc.
• The vascular tissue system carries out long distance transport of materials between roots and shoots
  • There are two main tissues:
    • Xylem: conveys water and dissolved minerals upward from roots into the shoots
    • Phloem: transports organic nutrients to roots and growth sites
• Xylem:
  • Two types of water conducting cells, tracheids and vessel elements; both dead at maturity
  • Vessel elements align end to end to form long micropipes (vessels)
• Phloem
  • Phloem tissue conducts sugars primarily
  • Sieve plates are porous end walls that allow fluid to flow between cells along the sieve tube
  • Each sieve tube element has a companion cell whose nucleus and ribosomes serve both cells

Plant cells

• Some major types of plant cells:
  • Dermal and ground tissues:
    • Parenchyma
    • Collenchyma
    • Sclerenchyma
  • Water-conducting cells of the xylem
  • Sugar-conducting cells of the phloem
• Parenchyma cells:
  • Have thin and flexible primary walls
  • Are the initial undifferentiated cells
  • Are the least specialized
  • Retain the ability to divide and differentiate
  • examples: phloem cells, leaf photosynthetic cells, some storage tissues
• Collenchyma cells:
  • Grouped in strands and help support young parts of the plant shoot
  • Have thicker and uneven cell walls Provide flexible support without restraining growth
  • Often serve as mechanical support (especially for young or growing parts
• Sclerenchyma cells:
  • Highly specialized for mechanical rigidity
  • Thick secondary walls, often strengthened with lignin for rigidity
  • Usually elongate when mature; resistant to bending, cannot grow
  • Often dead at maturity (no active biochemistry needed to function) ; support and fluid conduction in xylem

Plant growth

• Meristems allow for Indeterminate growth
  • Apical meristems are at the tips and auxiliary buds of shoots and roots
  • Elongate shoots and roots through growth called primary growth
  • Add thickness to woody plants and called secondary growth via Lateral meristems
  • Vascular cambium and the cork cambium are the two lateral meristems
• Primary Growth
  • Roots: Vascular system is known as the stele -In angiosperms, the stele of the root is organized into a vascular cylinder - The primary growth produces the epidermis, growth tissue, and vascular tissue - The innermost layer of the cortex is called the endodermis - Lateral roots arise from within the pericycle
  • Shoots: A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip - Leaves develop leaf primordia along the sides of the apical meristem - Axillary buds develop from meristematic cells left at the bases of leaf primordia - Lateral shoots develop from axillary buds on the stem's surface
• Tissue Organization
  • Stems- vascular tissue of eudicots consists of bundles that are arranged in a ring
  • Vascular bundles are scattered in monocots
  • Epidermis reduces water loss -Stomata allow CO2 -Stomatal pores regulate openings -Ground tissue in a leaf is called mesophyll -gas exchange occurs in loosely arranged spongy mesophyll

Plant Transport

• Plants have succeeded their land environment by gathering and conserving resources
• The transport of minerals and resources integrated functioning of the whole plant
• Adaptations represent a compromise between enhancing photosynthesis and minimizing water loss
• Light capture is influenced by: canopy structure, phyllotaxy, and leaf area index
• Nutrient acquisition is determined by symbiotic associations, root structure, and proliferation in high nutrient zones
• Material is transported through short-distance diffusion/transport, and long-distance bulk flow
• permeability of substances is regulated by the plasma membrane

Plant Diffusion & Cotransport

• Diffusion
• Active Transport: pumps solutes accross a membrane, needs ATP
• Solutes pass through transport proteins embedded in the cell membrane
• Aquaporins channel water in/out of cells
• Proton pumps in plant cells are important; make H+ and harness their energy
• Proton Pumps generate membrane potential and H+ gradient
• Catiions are driven into the cell by membrane potential, causing root cells to absorb K+
• Cotransport Couples when a transport protein couples the diffusion of one solute H+ with active transport of another

Plant Diffusion & Pressure

• Requires balance between water uptake and loss
• Osmosis determines net absorption or loss of water
• Plant cells have rigid walls where the physical pressure of the cell wall pushes the expanding protoplast back
• Water potential combines the effects of solute concentration and pressure
• Water potential measures the determination and direction of movement of water
• Water flows from areas with higher potential to lower potential
• Water potential is labeled Ψ (“psi”) and pressure in units called megapascals
• Water Potential equation is Ψ = ΨS + ΨΡ
• Solute potential (ΨS) is proportional to the number of dissolved molecules
• Pressure potential (ΨP) is the physical pressure on a solution
• Turgor pressure is the pressure exerted by the plasma membrane against the cell wall, and by cell walls against the protoplast
• Water moves from higher potential to lower potential/water presence
• Water Transport is controlled by affected by uptake and loss of water

Water Pathways & Plant Transport

• Water pathways is affected by cell membranes
• Water potential is affected by water uptake and loss in plant cells
  • if a flaccid cell is placed in a high solute environment, the cell will undergo plasmolysis
  • if a flaccid cell is placed in a low solute concentrated environment, the cell gains water and becomes turgid -Turgor causes wilting and is reversed via watering
• Transport across plants are regulated through plant-cell structures and are regulated through compartments
  • Water travels through a plant by transmembrane, symplastic, and apoplastic movement techniques
  • short distances diffuse efficiently
  • move fluids to the xylem
  • transpiration will go from roots for water and minerals to shoots

Plant Uptake & Summary

• Water is uptook near roots where are water hairlines that are permeable

  • The concentration of essential minerals is greater in the roots than soil because of active transport +Soil Solution enters the roots

• Water flows through Cortex

• Caspiarn Strip endodermal blocks transfers of minerals in the cortex

Xylem & Plant Transport

• Plants that lose water from evaporation from a plants surface is called Tronsperation -Is the bulk flow of water/minerals called xylem
• Sap travels upwards and is is pushed/pulled- Xylem pushes sap: Root
• Water flows in creating root pressure (minor)
• Pulls xylem via the transportation mechanism
• Water is being pulled upwards via negative pressure
• Plant loses H2O by being gradient through stomata and transpirations
• The negative pressure pulls onto the water so they can the root’s

Cohesion, Adhesion, & Water Loss

• The transpiratonal pull is facilitated by cohesion
  • Water molecules are attracted to cellulose in the xylem
• Water loss happens with damaged and freezing caused by Cavitation
• Stomata pathways are major indicators of water loss - 95% plant water is caused by stomata - Controlled by diameter and shape - Result from changes and uptake with - ions by the guard cells = Minimize water loss

Adaptations & Loss

• Stimulate and minimize water loss
  • Stomata loss is minimzed via drought, wind, etc when stomata closes
• Stressee of drought with high leaves
• Transpiration results in wilting in Leafs + plants
• Can loose water from not getting the mineral transport and water it needs
• Resulting can cause enzyme functions which helps with preventing denaturation
• Minimizing losses of heat:
  • Adaption
  • Xerophytes which are adaated to arid temps
  • They had stomata cas exchahes and cAM to prevemt evaporative loss

Plant Transport & Nutrition

• Moving of Product via products of photosynthesis
• Moving materials by transports is by pholem and translocation methods to keep sugar
• They travel to what is called the sugar sunk + mature leaves that come from producers and mature leaves
• The product has both symphonic, aplastic and transferred methods
• Require active transport
• Researchers concluded that SAP moves through the flow of pressure
• Soil is made up for 3 parts: orizn and orizont.
• Transports protons and transports of H+

Plant Nutrition

• Soils contain organic/inorganic Components
• organic Compounds are broken done by micorbail organizsm
• plant soil solutions with H2) + roots
• H - ions cause cation changed
• The membrane potential (charge separation) and the proton gradient can drive the transport of solutes into the cell
• The membrane potential generated by proton pumps contribute to the absorption of K+ by root cells- Cotransport occurs when a transport protein couples the diffusion of one solute composed of decayingTopsoil is composed of ‘humus', organic matter plant and animal matter and feces of decomposing organisms
• 1 teaspoon of topsoil- contain 5 mill bacteria

Deficiencies & Elements

• functions impact nutritionaed soil are decaying organic
• soil is managed by rotation via soil and
• agriculture needs stable conditions
• what plants eat is noursheed by air
• all elements orignate dfrom air -Macronturients are needed in large quantites -Micrnurients are needed in small qualites
• Essential elemnts needed by plants are determined through hydrolyic means- Diagnosing nutrient deficiency
• rhizboium aids with somse
• mychorrizae aids with root form
• Arbuscular mycorrhizae