Plants part 1

Protists

• Very diverse multi/unicellular eukaryotes that are present in all 4 supergroups (SAR, unikonta, archaeplastida, excavata.

• Most are unicellular, but some live in groups (colonies) and multicellular organisms

SAR clade

Stramenopiles, alveolates, rhizarians

massively diverse all protist clade defined by DNA similarities

Diatoms

• Stramenopile

• Cell wall is made up of silicon dioxide (glass)

• Microscopic and unicellular, major component of phytoplankton

• Fossilized cell walls compose much of the sediments known as diatomaceous earth (sand)

Golden algae

• Stramenopile

• Yellow/brown carotenoids. Small groups of unicellular organisms (colonies)

• Contain plastids (area for photosynthesis)

• Flagella present

Brown algae

• Stramenopile

• Larger and more complex multicellular structures than golden algae

• ex: kelp, giant seaweed

• Holdfast: Anchors plant to solid substrate (root)

• Stipe: support leaf like blades (stem)

• Blades: leaf like structures that reach for sunlight (leaves
  
  Leaves (blades), stem (stipe), root (holdfast) are all analogous structures between brown algae and land plants. CONVERGENT EVOLUTION

Life cycle of Brown alga Laminaria

• Alternation of multicellular haploid and diploid forms.

1. Sporophyte: A plant/algae that makes spores. Spores come from outer edge of the blades, house in the sporangia. DIPLOID

2. Spores are produced and settle to germinate into gametophytes (sperm/egg) by undergoing meiosis. HAPLOID

3. Fertilization: Gametes fuse to form a zygote. DIPLOID

4. Zygote develops into a sporophyte. DIPLOID
   
   Gametophytes are heteromorphic, as they are microscopic and the main life stage (sporophytes) are macroscopic

Heteromorphic

Generations are structurally different

Isomorphic

Generations are structurally similar

Heterogamy

Gametes have a distinct sex (female/male)

Isogamy

Gametes have no distinct sex but are considered (+/-)

Dinoflagellates

• Alveolates

• Body is made up of cellulose. Generally phytoplankton that live in shallow water and are microscopic, spherical and have flagella.

• Blooms (explosive growth) results in giant red tides. Occur in warm, shallow, and nutrient rich waters

• Toxins produced from blooms result in massive deaths of invertebrates and fish in that habitat

Archaeplastida

Red+ green algae

Unicellular: Chlamydomonas
Generally grouped together: Volvox
Multicellular: Ulva, Caelerpa

Closest relatives to land plants (land plants are within this clade)

Red algae

• Archaeplastida

• Red due to pigment called phycoerythrin

• Commonly multicellular, no flagellate structures

ex: nori in sushi (seaweed)

Green algae

• Archaeplastida

1. Cell wall: cellulose and some carbohydrates. Rigid when mature, permeable to water, gases, and minerals

2. Vacuole: regulate water content of cell. Water moving exerts outward pressure (turgor pressure) that keeps the plant upright. The vacuole swells up and pushes against the cell wall. Lack of turgor pressure results in wilting

3. Pyrenoids (only in algae, no in higher plants): Within chloroplasts, site of starch synthesis

Life cycle of unicellular Chlamydomonas

• Model system (we know a lot about it, often a reference for studies)

• Uses isogamy

• Prefers to reproduce asexually, but can reproduce sexually in unfavorable environments

1. Mature cell haploid cell uses mitosis to create gametes that are ± that come together to fertilize

2. Diploid zygote is produced that uses meiosis to create 4 daughter cells that become mature cells

3. Either new gametes are produced (sexual reproduction) or the cell creates zoospores and reproduces asexually.

Mature cells develop into gametes due to environmental stresses. Zygote is the only diploid state in the life cycle, everything else is haploid.

• No alternation of generations, not multicellular, main form is haploid
  
  Haplontic life cycle

Lichens

• Made up of a symbiotic relationship between a photosynthetic microorganism (algae/cyanobacteria) and a nutrient providing organism (fungus, sometimes yeast).
  
  Algae: glucose, food via photosynthesis
  Fungus: mines nutrients from nutrient poor environments, ascomycete (spore shooters) are the main visible fungal component of lichens
  
  Algae or cyanobacteria occupy an inner layer below the lichen surface. Lichens typically reproduce asexually via soredia (spore like structures that eventually disperse
  
  Millions of photosynthetic cells are held in a mass of fungal hyphae

• One of the oldest symbiotic relationships in nature

• Lichens are the first inhabitants on new rock/soil surfaces, first stage in succession process after mass destructions (ex: fires)

• Lichens may have helped the introduction and evolution land plants around 550-600 million years ago.

Bryophytes

• Come from aquatic algae

• Non-vascular plants, meaning they have no xylem/phloem (no real stem). This makes them smaller and occupy forest floors (mosses). No secondary growth (wood parts, seed plants, that allow plants to grow very tall)

• Consists of liverworts, mosses, and hornworts.

• Not a monophyletic group

Mosses

• Bryophyte

• Inhabits areas of high moisture, hostile environments (nutrient poor areas).

• Take in nutrients from soil, but they quickly die and release nutrients back to forest floor (nutrient cycling). Peat moss (Sphagnum) is dead/dying moss that later turns into coal.

• Sphagnum also acidifies the soil and is an important organic carbon reservoir

• Peatland covers 3% of earth’s surface, holds 30% of world’s soil carbon and helps stabilize carbon dioxide levels. Canada is the world’s largest producer of horticultural peat (17% of Manitoba is covered in peat).uyh7

Bryophyte 5 structures

Sporophyte: multicellular diploid form of the plant body

Gametophyte: structure that produces haploid gametes in plants

Sporangium: structure where meiosis occurs and haploid spores develop

Antheridia: structure where gametes develop in male structures of plants

Archegonia: structure where gametes develop in female structures of plants

Bryophyte 6 main traits

• Dominant gametophytic phase (1n)

• No xylem or phloem (non-vascular)

• No roots

• No leaves

• No cuticle (waxy surface on leaves/overall plant that protects plant from excess sunlight. Lack of this is why mosses can survive in light poor environments and have maximum absorption of nutrients, water, and sunlight)

• Sporophyte dependent on female gametophyte for nutrition as the stalk portion of the plant in the sporophyte, and the main “bush” portion of the plant is the gametophyte. Most of the moss one sees is mainly the gametophyte

Moss life cycle

• Alternating life cycle (distinct haploid/diploid stages in multicellular organism)

1. Diploid sporophyte produces sporangium (site of meiosis) that is a capsule that houses spores and is dispersed usually via wind

2. Sporangium (many morphological variations depending on environment) opens up due to water pressure and apoptosis of sporangium cells and releases spores. Spores either develop into female/male gametes

3. Female gametes grow into female haploid gametophytes (bush like structure) and have structures for sperm deposition (archegonia). Male gametes grow into male gametophytes and release sperm from the antheridia. Sperm swims into archegonia via water droplets and fertilization occurs

4. Diploid zygote develops into embryo and later into a sporophyte on top of the previously existing female gametophyte.

Sporophyte composition

• Foot: receives nutrients from female gametophyte

• Seta: elongated stalk (not true stem as there is no xylem or phloem). Also used for dispersal of sporangium so it must be tall to access the wind.

• Sporangium: site of meiosis. Sporocyte (2N)→ spores (1N)

Hornworts and moss sporophytes have stomata for gas exchange, LIVER WORTS DO NOT HAVE STOMATA

Liverworts (Hepatophyta)

• Bryophytes

• Liver shaped leafy gametophytes.

• Has smallest sporophytes out of all the bryophytes

• Male and female gametangia on seperate plants.

• Archegonia (female) and antheridia (male) are developed on gametangia elevated on gemetophores/stalks

• Miniature sporophytes can be seen on the undersurface of female gametangia (like little palm trees, and the spores are the “coconuts" under the sporophyte leaves)

• NO STOMATA (gas exchange)

Hornworts (Anthocerophyta)

• Bryophytes

• Horizontal gametophytes

• Long tapered sporophytes

• No seta, only sporangium

• Relatively unexplored group due to lack of research interest

Vascular plant advantage/overview

Allowed for plants to grow taller and transport things (nutrients, water) over long distances

• Seedless vascular plants have flagellated sperm. Plants are typically found in moist areas.

• Seedless vascular plants: lycophytes and monilophytes

• Seed producing vascular plants: angiosperms and gymnosperms

Monilophyta

• Ferns, horsetails (very old species, found in river beds typically), and whisk ferns

• Most diverse seedless vascular plants (over 12,000 species)

Lycophyta

• NOT MOSSES, as lycophyta have vascular tissues: club mosses, spike mosses, and quillworts

• Giant lycophyte trees (lepidodendron) thrived for millions of years in moist swamps, survivors are small herbaceous plants

Golden fern anatomy

Golden fern sporophyte and tiny, separate and independent gametophyte

Sporophyte:

• Rhizome: underground stem. Produced by the shoot apical meristem, SAM (cluster of stem cells that results in all above ground plant structures)

• Leaves: Produced by the SAM, compound leaf, leaflets.

• Roots: Produced by root apical meristem (RAM). Each root has a RAM (cluster of stem cells that produce all the below ground plant structures)

Sporophyte is the typical fern plant structure, gametophyte is a more rarely seen almost sponge/moss like structure composed of both antheridium and archegonium.

Fern Life Cycle

1. Mature sporophyte (2N) has sori on the underside of each leaf. A Sorus (plural: sori) is a cluster of sporangia.

2. Sporangium undergoes meiosis and produces haploid spores. When the plant is ready, the sporangia curl back and catapult the spores into a new environment. Annulus helps disperse spores.

3. Spores germinate into a gametophyte, which forms a small moss/sponge like green structure. It is monoecious, meaning the gametophyte holds both female and male counter parts at the same time (“bisexual”). Antheridium releases sperm and the sperm enter the archegonium to fertilize the egg.

4. Diploid zygote is produced and forms a new sporophyte out of the gametophyte

Thallus: the green tiny sponge/moss structure that houses the archegonium and antheridium. It is poorly adapted to life on land.

• Photosynthetic, adsorbs water/minerals.

• Rhizoid cells for anchorage

• Archegonia and antheridia on the same gametophyte

• Self fertilization is rare

• LACKS: leaves, cuticle, complex tissue system, roots, stems

Sporophylls and Spore variation

• Sporophylls: modified leaves with sporangia

• Strobili: cone-like structures formed from groups of sporophylls (lycophytes) Production of spores.

• Sori: clusters of sporangia on the undersides of the sporophylls (ferns). Curl back and catapult spores into environment

Evolution of three tissue system

Vascular tissue: Most inner part.

• Xylem: transport of water and minerals (usually up the plant from the roots)

• Phloem: transport of photosynthetically produced nutrients (usually down the plant from the leaves)

Ground tissue: middle part

• Parenchyma

• Collenchyma

• Sclerenchyma

Dermal tissue: most outer part

• Periderm

• Cork

• Epidermis

• Above ground structures are covered in a cuticle

• Below ground structures have no cuticle (helps with maximum water/mineral absorbtion)

Transport in xylem/phloem

Xylem: conducts most of the water and minerals and includes dead tube-shaped cells called tracheids. Cells have no nucleus, cytoplasm, etc. to remove friction in movement of bulk transport.

• Water conduction cells strengthen by lignin and provide structural suppourt.

Phloem: consists of living cells that are arranged into tubes and distributes sugars, amino acids, and other organic products. Cells are typically alive as transportation involves active transport and cell signaling.

Plants move things up ←> down and left ←> right, so tubes in xylem/phloem have little pits (channel openings) that allow to switch flow directions.

Vascular plants allowed for increased height, which provided an evolutionary advantage (more sunlight absorption = larger success rate)

Evolution of roots

Roots are organs that anchor vascular plants

• They enable vascular plants to absorb water and nutrients from the soil
  
  Types of roots:

• Primary root: originates in embryo

• Lateral root: secondary root, branches off another. Horizontal root growth, helps with stabilizing plant and accessing higher nutrient rich soil areas.

• Adventitious root: comes from stem tissue an from rhizomes, not ground. Help prop plant. Common in corn/orchids/monstera, visible roots come off of stem to stabilize plant

Evolution of leaves

Leaves are organs that increase surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis

Two leaf types:

• Microphylls: leaves with a single vein (lycophyta)

• Megaphylls: leaves with a highly branched vascular system (many veins), seen in: monilophyta, gymnosperms, and angiosperms

Seed producing plants

• Originated over 300 million years ago

• Seeds and pollen are key adaptations for life on land. (Disperse over long distances by wind/animal feces)

• Reproductive adaptations include fruits and flowers

• Reduced gametophytes (microscopic, found deep within the maternal plant, develop on very different parts of the plant)

• Heterospory: ovules, pollen grains. Different gametophytes are developed on very different parts of the plant, production of two distinct spores.

Who are the seed plants

• Gymnosperms:(naked seed) pine, spruce, fir. No development of fruit

• Angiosperms: (enclosed seed) canola, rose, corn, wheat. Development of fruit (carpel which houses the ovary (ovule → egg → development of embryo → seeds in the fruit)

Common traits of seed plants

• Reduced gametophytes: Gametophytes of seed plants develop within walls of spores that are retained in the parent plant

• Seed plants are heterosporous (develop two sex gametophytes in very different portions of the plant, while seedless plants are homosporous meaning they produce their spores together despite sex): Megasporangia produce megaspores that give rise to the female gametophytes. Microsporangia produce microspores that give rise to male gametophytes

• An ovule consists of a megasporangium, megaspore, and one or more protective integuments. Gymnosperm megaspore have one integument. Angiosperm megaspores usually have two integuments

Gametophyte-Sporophyte relationships in different plant groups

Pollen and sperm production in seed plants

Microspores (haploid) develop into pollen grains, which contain male gametophytes.

• Pollination is the transfer of pollen to part of a seed plant containing ovules (pollen nuclei entering the egg cell within the ovule/female gametophyte). Water is no longer essential for fertilization in seed plants

• If a pollen grain germinates, it gives rise to a pollen tube that discharges sperm into female gametophyte within ovule

• Pollen grain has a very tough outer covering that protects it
  
  Pollen development: pollen, commonly found in spring on the lower branches of gymnosperms. Uses wind to let spores pollinate trees nearby (hence lower branches). Spores captured by ovulate cones,

Major model plant

Arabidopsis

Gymnosperms seeds

• Seeds are exposed on sporophylls that form cones, where we see ovules that contain egg cells (surfaces of scales, not incased in an ovary). Cone bearing plants (pine cones)

• No fruit/flowers

• Has one single integument (hard outer seed covering)

• A seed develops from the whole ovule. A seed is a sporophyte embryo, along with its food supply, packaged in a protective coat

• Spore will enter the microphyte (opening in female gametophyte) and wait there for when the egg develops. Once it developed, the spore releases sperm and an embryo develops

Life cycle of pine

• Dominance of the sporophyte (diploid) generation

• Development of seed from fertilized ovules

• Transfer of sperm to ovules by pollen

• Alternation of generations (distinct haploid/diploid phase)

Ovulate cone: cone that has ovules/eggs

Pollen cone: develops all the spores that release sperm

1. Sporophyte (2N) is the pine trees, and produces sporangia in male and female cones

2. Small cones produce microspores called pollen grains, each one contains a male gametophyte (spores that house sperm)

3. The larger cones contain ovules, which produce megaspores (under go meiosis to produce eggs, female gametophytes)

4. Spore will enter the tube and stay there until the egg cell is developed and fertilized. Embryo is produced and new diploid is grown

Takes 3 years for cone production to mature seed

Microspore: pollen (sperm)

Megaspore: ovule (egg)

Gymnosperm diversity

Cycadophyta:

• Thrived during mesozoic era, but relatively few exist today. Unlike most seed plants (have flagellated sperm). Individuals have large cones and palm like leaves
  
  Ginkgophyta:

• Living fossil, consist of a single living species (Ginkgo biloba). Like cycads has flagellated sperm. Has a high tolerance to air pollution and is a popular ornamental tree
  
  Gnetophyta (typically have a thick cuticle):

• Gnetum, Ephedra, Welwitschia. Not a lot of diversity, species vary in appearance and some are tropical/desert inhabitants
  
  Coniferophyta:

• Largest gymnosperm phyla. Emerged in the Jurassic period. Most conifers are evergreens (not all)

Angiosperms overview

• Flowers and fruits (seed plants, not naked as they are protected by a fruit/flower)

• The most widespread and diverse of all plants. Divided into monocots (one cotyledon, single embryonic leaf) and eudicots (two cotyledons, two embryonic leaves).

• Monocots: 50,000 species (lilies, orchids, grasses)

• Dicots/Eudicots: 200,000+ species (elms, willows, roses, peas, canola)

Flowers

Key reproductive adaptation of angiosperms. A flower is a specialized shoot with modified leaves.

• Sepal: enclose the flower. Green/leaf-like. Encloses other flower parts, ex: broccoli (part eaten is thousands of flower buds covered by green sepals)

• Petals: are brightly coloured and attract pollinators

• Stamens: produce pollen. Consist of a stalk (filament) with an anther where pollen is produced.

• Carpels: produce ovules:
  Ovaries (fertilization occurs here, protects ovule).
  Style (elevates stigma to make accessible to pollinators).
  Stigma (where pollen is received, lots of sugary/sticky substances at the tip)

If a flower is complete, it means that it has all four flower organs. However, not all flowers are complete. Can have radial or bilateral symmetry

ex: Holy has nonfunctional stamen and other variety has no stamens. This causes the plants to need to cross pollinate between the two variety of plants.

Fruit

• Reduced dependent gametophytes help with innovation of seed plants outcompeting ferns and other seedless plants

• A fruit is formed when the ovary wall thickens and matures (can be fleshy or dry, ex: seeds in tomato, nectarine pit, hazelnuts)

• Fruits protect seeds (and embryo) and aid in dispersal

• Fruits develop from a flower’s fertilized ovary and contain seeds, while vegetables are any other edible part of the plant, like a root, stem or leaf

• Seed dispersal in fruits: seeds can be carried by wind, water, or animals. May need physical roughing up before germination. New sporophytes are moved at a distance from the parent plant.

Angiosperm life cycle (lily)

• Sporophyte flowers are composed of both male/female structures

• Male gametophytes: contained within pollen grains produced by microsporangia of anthers

• Female gametophyte/embryo sac: develops within an ovule contained within an ovary at the base of a stigma

• Some plants self fertilize while others cross-pollinate. (genetic and biochemical factors determine whether a plant can self or cross fertilize)

• After meiosis, each microsporangium contains spore tetrads. Each spore produces pollen grains containing the male gametophyte.

• A pollen grain that lands on a stigma (sticky surface), germinates, and the pollen tube of the male gametophyte goes down to the ovary (pollen grain contains two haploid sperm nuclei: tube nucleus and generative cell).

• The ovule is accessible because small pores in the integuments called micropyle.

• Double fertilization occurs when pollen tube discharges two sperm (two nuclei) into the female gametophyte within an ovule

• One sperm fertilizes the egg and gives rise to the embryo, while the other combines with two nuclei in the central cell of the female gametophyte cell of the female gametophyte and initiates development of food storing.

• The triploid endosperm nourishes and supports the developing embryo

• Within a seed, the embryo consists of a root and two seed leaves called cotyledons.

Cross section of anther

• As anther dries down, apoptosis is present in the anther, and the pollen is released.

Female gametophyte of a typical angiosperm

Female gametophyte of a typical angiosperm contains 7 cells:

• 3 antipodal cells

• 1 central cells

• 2 synegrid cells

• 1 egg cell

Every cell is haploid expect for the central cells. Central cell is however going to be pollinated and develops into a triploid endosperm (3N)

Products from seed plants

• Most food and materials (wood, medicines) come from angiosperms

• Six crops (wheat, rice, maize, potatoes, cassava, and sweet potatoes) yield 80% of the calories consumed by humans

• Modern technologies developed from genetic engineering and breeding efforts

Plant primary growth

• Shoot apical meristem (SAM). Primary growth in the axial direction. All plant parts above ground come from this.

• Root apical meristem (RAM). Cells are protected by the root capule. All below ground structures come from this part.

• Localized regions of cell growth

• Cell divisions produce new tissues

• Populations of pluripotent stem cells

• Primary growth
  
  Plants sustain growth in apical meristems. Meristems make the plant!

Meristems

• Densely cytoplasmic (very metabolically active and dividing a lot)

• Lateral meristems add thickness to woody plants, a process called secondary growth.
  
  There are two lateral meristems:

• Vascular cambium: adds layers of vascular tissue (secondary xylem, aka wood, and secondary phloem (inner back))

• Cork cambium: replaces the epidermis with periderm. Thicker and tougher.

Shoot apical meristem (SAM):

• Primary growth

• Axial growth

• Primary tissues: ground, vascular, dermal

Root apical meristem (RAM):

• Primary growth

• Axial growth

• Primary tissues: vascular, ground, dermal

3 plant tissues

• Each plant organ has dermal, vascular, and ground tissues. Each category forms a tissue system: ground, vascular, and dermal. All tissue systems are continuous throughout the plant but organization may change.

Dermal tissue system

• In non-woody plants, the dermal tissue system consists of the epidermis

• A waxy coating called the cuticle helps prevent water loss from the epidermis

• In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots

• Trichomes (hair like) are outgrowths of shoot epidermis that help reduce water loss and with insect defense. Glandular trichomes accumulate specialized metabolites for plant defense. Trichomes are living cells with a nucleus. Other trichomes help to prevent the plant from drying out and can increase the relative humidity closer to the leaf or stem surface

• Above ground plant structures: secrete substances that form wax that then forms a cuticle to protect from sunlight and help with water absorption

• Roots do not have a cuticle: they need to absorb as much as possible.

Vascular tissue system

• Facilitates long-distance transport of materials between roots and shoots and provides mechanical support.

• Xylem: conducts water and dissolved minerals upward from roots into shoots

• Phloem: transports organic nutrients from where they are made to where they are needed

• The vascular tissue of a stem/root is collectively called the stele

• In angiosperms, the stele of the root is a solid central vascular cylinder

• The stele of stems and leaves is divided into vascular bundles, strands of xylem and phloem

Ground tissue system

• Tissues that are neither dermal nor vascular are the ground tissue system

• Ground tissue internal to the vascular system: pith

• Ground tissue external to the vascular system: cortex
  
  Ground tissue includes specialized cells used for:

• Storage

• Photosynthesis

• Support

• Transportation

Parenchyma cells

• Mature parenchyma cells: have thin and flexible primary walls. Cellulose, other sugars, and proteins

• Lack secondary walls (primary walls + lignin)

• Are the least specialized. Performs metabolic functions. Retains the ability to divide and differentiate

• Little dots within cells are chloroplasts

• Alive

Collenchyma cells

• Have thicker and uneven cell walls

• Provide flexible support without restraining growth

• Are grouped in strands and help support young parts of the plant shoot (plant can grow a bit taller)

• Alive
  
  Ex: celery: mainly made of collenchyma cells to help with growth/support. Found in strands/bundles. What makes celery crunchy

Sclerenchyma

• Thick secondary walls strengthened with lignin.

• Dead at maturity (thick cell wall does not allow for movement/transport across the membrane of the cell)
  
  Two types:

• Sclereids: short and irregular in shape with thick lignified secondary walls. ex: grainy texture in pears

• Fibers: long and slender and arranged in threads

Angiosperm seed

• Embryo (2N): primary dermal, ground vascular tissue. SAM, RAM, established in the embryo. Cotyledons (dictates eudicot vs. monocot)

• Endosperm (3N): stores starch, proteins and lipids. Supports embryo in organogenesis. Forms from the double fertilization, as the pollen has two nuclei, one becomes the embryo, the other becomes the endosperm.

• Seed coat (Parent 2N tissues): thickened cell walls of seed coat help to protect the seed, especially during periods of dormancy.

• The two cells that are fertilized in a typical angiosperm are: central cell (endosperm) and egg cell (embryo)

• Embryo is much more reduced in monocot seeds and a single cotyledon. They have protective sheaths called coleoptile that helps protects the young shoot.

• Endosperm is greatly reduced in eudicots.

• Gymnosperm seeds are not held in an ovary, while angiosperm seeds are.

Seed dormancy

• Seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling.

• The breaking of seed dormancy often requires environmental cues, such as moisture, temperature, or lighting changes. Environmental cues set off biochemical and genetic cascades that promote seed germination.

• Most seeds remain viable after a year or two of dormancy, but some last only days, and others can remain viable for centuries

• Germination depends on imbibition: the uptake of water due to low water potential of a dry seed. As seed expands, cell walls begin to rupture.

• The radicle (embryonic root) emerges first. The developing root system anchors the plant. Next, shoot tip breaks through soil surface.

Roots

Functions:

• Anchoring plant

• Absorbing minerals and water

• Storing carbohydrates
  
  Primary roots emerge first. Lateral roots/hairs branch from primary root. Increase in surface area of roots increases the uptake of nutrients and water. Mycorrhizas (soil fungus), forms a mutualistic association.

Root apical meristem (RAM)

• Primary root growth occurs at the RAM. The RAM produces cells in two directions: RAM produces a cap tissues called the root cap and it covers the distal tip of the root. This protects the root tip as it grows through the soil. Cells are sloughed off during this process

• RAM produces cells proximally that contribute to the root proper. Produce no lateral appendages (root hairs)

• Growth occurs just behind the root tip in three zones of the cells: Zone of cell division, zone of elongation, zone of differentiation/maturation (root hairs are developed from this zone, ideal for nutrient/water uptake).

Root cap

• The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil. It secretes polysaccharide slime, continually sloughs off and regrows, produces signals to attract beneficial microbes, and senses gravity to grow down into the soil.

• Protect the essential cells of the RAM.

Typical dicot root cross section

• In most eudicots, the xylem is starlike in appearance with phloem between the “arms”

• The ground tissue, mostly parenchyma cells, fills the cortex (massive), the region between the vascular cylinder and epidermis.

• The innermost layer of the cortex is called the endodermis

• The endodermis regulates passage of substances from soil into the vascular cylinder

• (Pink granules are stained starches in image)

• Distinct cross shape with xylem and phloem

Typical monocot root cross section

• In many monocots, the core parenchyma cells are surrounded by rings of xylem, then phloem. Endodermis is more waxy to create a physical barrier to prevent pathogenic microbes and soil particles from entering the central vascular stele.

• Distinct circle shape with xylem and phloem

Primary growth of roots

• Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder. They are in line with xylem to facilitate transport.

Root systems

• Tap root system: Tall plants, result in large shoot masses (eudicots, gymnosperms

• Fibrous root system: Adventitious roots that come from the stem. Results in lots of lateral roots (monocots, aka grasses)

Stem terminology

• Nodes: where leaves attach

• Internodes: between leaves

• Axillary buds: potential to form a lateral shoot/branch (dormant meristems, that when activated, forms a new branch)

• Apical bud: Elongation of young shoot. Apical dominance helps to maintain dormancy in most axillary buds

Stem adaptations

• Rhizomes: a horizontal shoot that grows just below the surface (Irises)

• Stolon: horizontal shoots that grow along the surface. These “runners” enable a plant to reproduce asexually, as plantlets form at nodes along each runner (strawberries)

• Tubers: (potatoes). Enlarged ends of rhizomes or stolons specialized for storing food. The “eyes” of a potato are clusters of axillary buds that mark the node.

Dicot vs Monocot stem

• Eudicots: the vascular tissue consists of vascular bundles arranged in a ring

• Monocot: the vascular bundles are scattered throughout the ground tissue, rather than forming a ring. Monocot bundles are surrounded by a sheath.

Water conducting cells in xylem

• Tracheids: are found in the xylem of all vascular plants. Very slender, contain pits. (smallest opening in xylem)

• Vessel elements: common to most angiosperms and a few gymnosperms. Vessel elements align end to end to form long micropipes called vessels. Have more girth to them. Have perforation plates and pits. (Biggest opening is xylem)

Both cells are water conducting and dead at maturity. They are very closely packed and this allows for capillary action to take place

Sugar conducting cells in the phloem

• Sieve-tube elements: are alive at functional maturity, though they lack organelles. Sieve plates are the porous end walls that allow fluid to flow between cells along the sieve tube. Also prevents the movement of microbes into the phloem (fungi, other pathogens)

• Each sieve-tube element has a companion cell whose nucleus and ribosomes serve both cells.

Primary growth of the shoot

• SAM initiates new stem tissues and new leaves. Primary growth is concentrated at the shoot tip

• Primary growth is continuous and increases stem length (internode elongation, stimulated by auxin and gibberellic acid, aka plant hormones).

• Leaf development is mostly determinant

• Cells of the SAM are undifferentiated

Leaves

• Initiated by the activity of the SAM

• Main photosynthetic structures of the plant

• Leaves intercept light, exchange gases, dissipate heat, defend the plant from herbivores and pathogens

• Generally consist of a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem

• Holes in leaves (stomata) allow for gas exchange

• Leaves can reflect more light (sunscreen) by secreting waxy chemicals that form a cuticle

Leaf types:

• Simple leaf: blade not divided into leaflets (oak, maple)

• Compound leaf: blade is divided into leaflets. Pinnate leaf is the leaflets attached along the petiole (fern) . Palmate leaf is all the leaflets that connect to a central location (Cannabis).

• Needles/spines (cactus)

• Storage leaves (onion)

• Tendrils (peas, beans, that help the plant to climb things)

• Reproductive leaves (succulents)

Tissue organization of leaves

• Epidermis: interrupted by stomata, pores that allow carbon dioxide and oxygen exchange between the air and the photosynthetic cells in a leaf. Stomata are also major avenues for evaporative water loss

• Each stomatal pore is flanked by two guard cells, which regulate opening and closing

• Vast majority of stomata are found on the underside of the leaf

Mesophyll: ground tissue in leaf, sandwiched between the upper and lower epidermis.

• Eudicots: have two layers of mesophyll: palisade mesophyll in the upper part of the leaf. Spongy mesophyll in the lower part of the leaf.

• Loose arrangement with ample air spaces around cells allows for gas exchange. Vast majority of photosynthesis takes place in the mesophyll

Vascular tissues: continuous in each leaf. Veins are the leaf’s vascular bundles and function as the leaf’s skeleton. Each vein in a leaf is enclosed by a protective bundle sheath. Xylem is found in the bottom of the bundle, and the phloem is found in the upper part of the bundle.

Most monocots have parallel veins

Most eudicots have branching veins

Stomata

• Occur in pairs in the epidermis of the leaf stem. Guard cells and stomata.

• Function: gas exchange. Changes in potassium ions and plant hormones like cytokinin and abscisic acid open/close the stomata. Open during the day and closed at night.