Bio Plant Diversity

Synapomorphy of Plantae

Believed it has occurred ONCE in evolutionary history (with one exception for a single species in Rhizaria) giving rise to lineage of plants

• Cyanobacterium ingested and escapes digestion by vacuoles

• Horizontal gene transfer incorporates some cyanobacteria genes in nuclear genome

Organisms OUTSIDE the plant lineage that have chloroplasts gained them via endosymbiosis of an ancestral “plant” -> secondary of even tertiary endosymbiosis

Endosymbiosis was a long time ago - DNA has had ?

a lot of time to evolve and change

Primary Endosymbiosis

We define plants as beginning with priamry endosymbiosis - All plantae have the primary chloroplast

Plantae are defined as the Archaeplastida supergroup

Glaucophytes

• Unicellular organisms

• May resemble some of the earliest plants

• Sister group to all other Archaeplastida because of 

  • Retains residual peptidoglycan in chloroplast membranes

Vegetative cells in mother cell wall with extra-large chloroplasts

Plants

Aquatic and land plants

Algae

aquatic photosynthetic eukaryotes

• Not a phylogenetically meaningful term

• Some are plants, some are protists (brown algae..), some are prokaryotes (cyanobacteria/blue-green algae)

Phycology

the study of algae

Red Algae

• Contain a red accessory photosynthetic pigment

  • Phycoerythrin

  • Do not always necessarily appear red

• Most multicellular and marine -> attach to substrate via holdfast

  • (like brown algae)

• Absence on land may relate to large genome reduction

Chlorophyta

Chlorophytes have a wide diversity of forms

• Largest group of Green Algae

  • Unicellular to multicellular organisms

  • Volvox - unicellular but forms large colonies

Ulva ridida grows into thin, membranous sheaths a few cm across

Coleochaetophytes

One of the closest relatives to land plants

Multicellular

Retain eggs in the parental organism (like land plants) and have cells connected by plasmodesmata

Stoneworts

Closest relative of land plants

Multicellular

Retain eggs in the parental organism (like land plants) and have cells connected by plasmodesmata

First land plants appeared on land …

400-500 mya

How do environmental conditions on land differ from aquatic environments (think of different challenges that they had)

• How much rain they get

• What temperatures they can survive

• How are gamates going to connect to each other now that theyre on land? (stresser)

  • Protection needed for embryos from drying out

Adaptations of Land Plants

1. Protection from desiccation (water loss)

   1. Secrete their waxy membrane (cuticle) - Cells cannot lose the water directly from the cell

   2. Stromata (pores for gas exchange)

2. Protection of reproductive structures

   1. Gametangia (they are multicellular, they are organs, enclose the gametes)

   2. Embryos in protected structure

   3. Thick spore walls (desiccation and decay)

3. Protection from UV Radiation

   1. Leaf pigments - to help with increasing or decreasing the radiation

   2. Support to counteract gravity

   3. Acquiring and transporting nutrients

      1. Mycorrhizae

      2. Vascular tissue

Alteration of Generations

Multicellular diploid and haploid stages alternate

This includes ALL Land plants

Gametes - sperm and egg - haploid produces a zygote ->diploid

The zygote develops then into a diploid sporophyte

The sporophyte produces haploid spores by meiosis in a special process

The spores germinate and divide to form the haploid gametophyte

Gametophyte

Multicellualr haploid organism

Sporophyte

Multicellular diploid organism

Non-vascular Land Plants

Mosses, Hornworts and Liverworts

Non Vascular Land Plants qualities

1. They don't have any inner transport system - they must move via diffusion or capillary action - this results in them being short

2. Lack true leaves, stems, and roots

   1. Analogous structures are present

3. Thin cuticle, or none

   1. Thus moist habitats only

Mycorrhizae

symbiotic association between a fungus and a plant

Arbuscular mycorrhizae-like fossils

• Some nonvascular plants live on bare rock

• Arbuscular mycorrhizal mutualism

• Helped with absorption of water and minerals from the first soils

Life Cycle of a Non-Vascular Plant

• Dominant generation

• Fertilization requires water

• Gametophyte - what we see

• Archegonia and Anthoridium - Create the gamates

• Diploid - when the sperm and the egg meet and begin the Sporophyte

• Sporophytes are typically not photosynthetic

Liverworts

• Cuticle but no stomata

  • waxy membrane (cuticle) - Cells cannot lose the water directly from the cell

  • Stromata - gas vents

• Highly reduced sporophyte

Mosses

• Mosses have stamata (water and gas exchange)

• Ephemeral (meaning not always there) sporophyte

• Rhizoids (not true roots) help anchor to ground and take the function of absorbing

Archegonia

a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete

Where the egg sits waiting for a sperm

Hornworts

• Gametophytes are flat plates of cells

• Stalk-less sporophyte, basal region with indefinite cell division

• Sporophyte always green

• Internal cavities with N-fixing cyanobacteria

All of the other plants other than mosses, hornworts and liverworts have…

Vascular Tissue (Tracheophytes)

Vascular tissue allows plants to:

1. Have a greater division of labor (organs)

   1. Roots - specialized to anchor plants and to obtain water/nutrients

   2. Stems (Shoots) - specialized for light competition (suport), connect leaves and roots

   3. Leaves - specialized to photosynthesize

   4. Lignin in vascular tissue helps plants grow taller

      1. Lignin in cell walls, smaller cell in between the cells called fibers

Lignin

Helps plants grow taller - In cell walls, smaller cell in between the cells called fibers

Key Synapomorphy of Vascular Plants:

Vascular system made up of xylem and phloem

What advantage does vascular plants have over non-vascular plants?

Ability to transport water and food throughout their bodies allowed them to spread to new environements and diversify rapidly

Why is water necessary for the life cycle of nonvascular and early vascular plants?

• For non-vascular, the sperm has the flagette and needs to swim in order to reach the egg.

• For vascular, they needed water to reproduce, grow, and disperse

xylem

 Transports water and minerals from soils up to the rest of the plant

• Lignin provides structural support

Phloem

Transports sugars from photosynthesis throughout the plant

Earliest diverging group of vascular plants

Rhyniophytes - Branching nutritionally independent (photosynthetic) sporophyte

• Had central column of xylem but tracheids differ from later-diverging groups

• Increased spore production

• Lacked true leaves and roots

Critical adaptions for Tracheids (two taper ends)

• Transportation of water and minerals

• Rigid structural support (lingin)

• Allowed plants to grow taller

  • Competition for light

  • Aids in spore dispersal

    • Parents are going to compete with the children

Lycophytes

First extant group to diverge from vascular plants (400 MYA), relatively few surviving species

Possess microphylls & dichotomous branching roots and stems

Microphylls

a type of plant leaf with one single, unbranched leaf vein

Thought to have evolved from sterile sporangia

Sporangia

an enclosure in which spores are formed

Pteridophytes

Ferns and fern allies

Have a different type of leaf

Possess megaphylls - Overtopping growth & branching roots

Megaphylls

Overtopping growth & branching roots - give more light capture for the plant to use and grow

Lifecycle of Seedless Vascular Plants

(Ferns still require habitats that have a little bit of moisture because of the sperm that have the flagellates that need to swim in order to reach the egg)

Trend: Reduction of the Gametophyte

Most gametophytes nourish sporophytes

There is a size difference in the two sporophytes, but each is nutritionally independent in ferns

Where are the egg and sperm produced in seedless vascular plants vs seed plants?

Seedless:

• Egg: Archegonium

• Sperm: Antheridium

Seeds: male and female gametophytes, sperm and egg, respectively

The most ancient vascular plants had

only one spore (one gametophyte)

Homospory

The most ancient vascular plants had only one spore - Homospory

One type of gametophyte that has male and female reproductive organs

Heterospory

Multiple types of spore - Megaspore (Female) and Microspore (Male)

Megagametophytes

Produce eggs = OVULE

Microgametophytes

Produce sperm = POLLEN

Fertilized ovules become

Seeds

• Gymnosperms comes from Greed for “naked seeds”

• Only angiosperms enclosed seeds in a ovary, which becomes a fruit

Advantages Seed Plants have over non-seed plants

1. Retain spores rather than use for dispersal

   1. Fermentation conditions are always ideal

   2. Nourishment for growing gametophytes

2. Pollen as a “water-free” sperm movement mechanism -> gametes themselves protected

   1. Live in arid environments

   2. Coincide with the cooling and the drying of the air - less moisture in the air, more able to live compared to the non-seed plants

3. Seeds are mobile food sources for growing embryo/ seedling and allow dispersal

Three Major Lineages in Gymnosperm clade

Cycads, Ginkgo, and both Conifers and Gnetales

Cycads

Earliest diverging group (300 mya) of ~300 species

Many endangered, trade is regulated

Some cycads have “coralloid” roots which are symbiosis with cyanobacteria for N fixation from atmosphere

Cycad cones bear either ovules or pollen and emit odors to attract beetles/weevils when mature (convergent evolution with angiosperms)

Ginkgo

• Single relict species, popular street tree

• Individuals are either “male” or female”

• Sex chromosomes system of X and Y similar to humans

Garden plantings usually choose “male” trees

• The seeds are quite pungent (why we have males)

• Pollen is much worse for allergies

• Without “male” trees, the female trees wouldn’t set seeds

Conifers

Conifers are the most abundant group of gymnosperms - named for their seed cones (pinecones)

• Most are evergreen although some do lose their leaves (tamarack, bald cypress)

Gnetales

• Gnetales have three genera: 

  • Ephedra (Medicinal uses) (Mormon Tea)

  • Welwitschia (Only grows two leaves) (Grows only in the Namib desert)

  • Gnetum

Gymnosperm Reproduction - Conifers

Conifer spores are retained in cones

• Two spore types are produced in sporangia located in two different cone types

  • Two different cones produce different spores

Microsporangia

• Microstobili (2n) contain microsporangia in which a mother cell undergoes meiosis producing microspores (n) what develop into a multiceullar pollen grains, a strongly 

• reduced male gametophyte

Pollen grains

• Contain Sporopollenin

  • Most chemically resistant biological compound known

    • Very difficult to decompose

  • Most common way to look at fossils

  • Found in pollen and the spores of seedless vascular plants (ferns, etc.)

Female Pinecone = Megastrobilus

• Contains megagametophyte at maturity

• And eventually the developing seed with fertilized embryo

Fertilization is Internal for Pine Cones

No Water Required (although cycad/ginkgo sperm still have flagella)

Allows plants to grow in a LOT more places/habitats

Internal fertilization

Pollenation

What method do conifers use for pollination?

Wind

• All conifers are non-flowering

• Wind moves pollen from male to female cones

• Need to make a lot of pollen

Gymnosperm Seeds

• Shed in autumn, one year after fertilization

• Hold some food reserves (female gametophyte tissue)

• Competitive edge for seedlings

Integument

After fertilization, it develops into a seed coat

Four major advantages of Gymnosperms

1. The gametophyte (n) is now dependent upon the sporophyte (2n) - spores retained

2. The gametophytes are extremely reduced, and the male gametophyte serves as the dispersal agent for sperm

3. Internal fertilization via pollen delivery

4. Large food reserve for their offspring (seed)

Monocot vs Dicots

Monocots have only one cotyledon while dicots have two

Mega/Microsporangia

Megasporangia - Female sporangia that generate megasporocytes, which in turn generage megaspores

Microsporangia - Male sporangia that generate microsporocytes, which in turn generate microspores

Angiosperm Flowers

Able to use animal-facilitated pollination

• Increases the odds of successful pollination

• Lower relative resource investment for pollen

Sporophyll

A (modified) leaf that has sporangia

Sepals

Looks most like leaves, for protection

Carpels

Derived from megasporophylls and eventually become fruits

Whole plants can be monecious or dioecious

• Monecious = flowers are imperfect, but both female and male flowers appear on a plant

  • Corn

• Dioecious = complete separation of imperfect flowers

  • Individual plants will only have one type of flower

  • One will develop fruit and one will develop …?

• Can also refer to gynosperm (no flowers)

Flowers can be perfect or imperfect

• Perfect = functional mega and microsporangia -> both gametophytes within one flower

• Imperfect = one is absent or non-functiona

Angiosperms reproduction is…

heterosporous

Stamen

The pollen-producing reproducive organ of the flower

Derived from microsporophylls

Inside an anther is a captivity called the…

pollen sac

Cotyledons (Seed Leaves)

• Allows seed leaves to nourish the plant before PS is capable of supporting seedling

anther

The part of the stamen that produces and contains pollen in flowering plants

The pollen sac contains…

microspore “mother cells” that undergo meiosis once -> four haploid microspores

Each microspore divides ONCE by mitosis

Angiosperm microgametophyte has two haploid cells

• Generative cell -> will form 2 sperm upon germination

• Tube cell -> generates the pollen tube

A single style can have many ovules

Have own pollen tube that delivers a unique sperm into that egg

Angiosperm megametophyte

• The ovary contains one or more ovules

• Ovules are not enclosed in any tissues

• Ovule = macrospore “mother cell” within the protective integument - ONLY ONE IN EACH

  • Mother cell produces four megaspores via one meiosis event

    • Only ONE of the megaspores survive. Others die via apoptosis

Ovule

macrospore “mother cell” within the protective integument

The surviving haploid megaspore (the champion of the four megaspores produced from megaspore) divides…

• by mitosis THREE times

  • Megagametophyte (embryo sac) has eight nuclei in seven cells

Double Fertilization

• The microgametophyte contains TWO sperm

  • One sperm fertilizes the egg

  • One sperm fertilizes the POLAR NUCLEI

  • Forms 3n endosperm

    • Only in Angiosperms

    • Food source for embryo - remaining gametophyte tissue 

Angiosperm are the most successful group of the modern era due to:

• Animal pollination

• More efficient seed production & nutrition

• Fruits

• New conducting cell type in xylem tissue (cover later)

Shoot system

stem and leaves

Root system

just roots

What are the tissues that compose plant organs?

1. All parts of the plant body are made up of three major tissue systems

   1. Ground - center

   2. Dermal - epidermis

   3. Vascular

What affects development in plants?

1. Development in a multicellular organism is governed by four processes:

   1. Determination

      1. Certain cells are going to be part of something, like heart cell (stem cell can be anything)

   2. Differentiation

      1. Acquisition of the cell type and specialization 

   3. Morphogenesis

      1. The differentiated cells are organized into their specific places

   4. Growth

      1. Expansion of the cells

What affects development in plants?

These occur in animals and plants, but plants have unique properties that affect development

1. Apical Meristems

2. Totipotency

3. Vacuoles

4. Cell Walls

1. Apical meristems

1. Meristems = regions of undifferentiated cells

2. Location of cell division

3. Tips of roots and shoots

4. Plants grow throughout their lives

Totipotency

1.  - ability for a cell to become anything

   1. Describes cells that can differentiate into any type of cell in the body

   2. In animals, only embryonic stem cells are normally totipotent

   3. In plants, some differentiated plant cells can become totipotent

   4. Rapid repair of damage from herbivores, the environment, etc.

Vacuoles

1. May be up to 90% of the plant cells volume

2. STORAGE

3. Contains water with a high concentration of solutes (sugars from photosynthesis)

Osmosis

Water movies across a membrane from a high solute potential to low solute potential (more negative)

Turgor Pressure in plant and human cells

Hypertonic - water is moving out of the cell - dehydrated

Isotonic - equal movement of water into and out

Hypotonic - inflated cell - creating turgor in the cell walls - pressure

4. Cell Walls

1. Cell wall fixes cells in place, they cannot move as in animal development

Thus, plant morphogenesis is controlled by planes of cell division (which direction is the cell replicating)

Cells walls also affect expansion

• Cell walls resist expansion -> they must grow for cells to expand

• Proteins called expansins loosen the bonds between cellulose and other microfibrils in the walls

Primary vs. secondary cell walls

• Only primary cell walls in growing plants

• Secondary cell walls are too rigid to expand -> contain lignin

  • Too thick to have transport - will die soon