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Vascular Plant Structure, Growth, and Development

Plants’ Hierarchical Organization

  • Cell: fundamental unit of life

  • Tissue: group of cells consisting of 1+ cell types that perform a specialized function

  • Organ: consists of several type of tissues that carry out particular functions

Vascular Plant Organs

  • Vascular Plants: plants that can transport things up and down

  • Root system: underground

    • Roots rely on sugar produced by photosynthesis in the shoot system (cannot make sugar by themselves)

    • Root: organ with important functions

      • anchoring the plant

      • absorbing minerals and water

      • storing carbs (excess made in photosynthesis

        • because plants aren’t always guaranteed to have sunlight

    • Lateral roots: roots that emerge from the sides

      • Help anchor

      • Spread, help absorb nutrients

    • Primary root: first root to emerge from the seed

    • Taproot System: one main root and branches

      • Taproot: develops from primary root & anchors plant in soil

    • Fibrous root system: lots of small roots (no need for strong anchor)

    • Adventitious roots: side roots that arise from the stem & give rise to branching lateral roots

    • Root hairs: extensions of epidermal cells forming near root tip

      • Increase surface area, more absorption

    • Mycorrhizal associations: roots have fungus living in it that help them transform something they cannot use into something they can

      • ex/ Break down unusable nitrogen (symbiotic relationship)

  • Types of Roots

    • Prop roots: more anchorage

    • Storage roots: store carbs

    • Pneumatophores: some can do gas exchange (similar to leaves)

    • “Strangling” aerial roots: add further anchorage

    • Buttress roots: very tall and thin roots above ground, typically in forests and jungles (spread far and wide)

  • Shoot system: above ground

    • Shoots rely on water and minerals absorbed by the root system

    • Stem: plant organ consisting of nodes & internodes

      • Nodes: points at which leaves are attached

      • Internodes: space between nodes

    • Apical bud: causes elongation of a young shoot

      • where plant grows taller

    • Axillary bud: structure that can form a lateral branch, thorn, or flower

      • not main bud for height, additional buds for leaves, flowers, etc.

  • Leaf: main photosynthetic organ

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

      • ex/ chemical coat prevents fungus from attacking plant

    • Consist of blade and petiole

      • Blade: flat part

      • Petiole: stalk that joins leaf to node of stem

    • Chloroplasts in leaf

      • light shines & photosynthesis occurs

    • Why are leaves flat?

      • To maximize surface area and sun exposure

    • Monocot: 1 thing comes out of seed

      • Parallel veins

      • Vascular bundles are scattered throughout the ground tissue

    • Eudicot: 2+ things come out of seed

      • Branching veins

      • Vascular tissue consists of vascular bundles arranged in a ring

    • Vein: the vascular tissue of leaves

    • How do we categorize plants?

      • Determine if monocot or eudicot

      • What do the flowers look like?

      • What do the leaves look like?

    • Simple leaf: 1 leaf

    • Compound leaf: has several individual leaflets

      Evolutionary Adaptations of Leaves

    • Tendrils: help anchor it above the ground

    • Spines: defend

    • Storage leaves: store carbs

    • Reproductive leaves: leaves can reproduce

Dermal, Vascular, and Ground Tissues

  • Tissue system: interconnected leaf, stem, and root

    • Dermal tissue system

      • Nonwoody plants

        • Dermal tissue system: protection of the plant, consists of epidermis

        • Cuticle: waxy coating that helps prevent water loss from the epidermis (too hot from the sun)

        • No periderm

      • Woody plants

        • Periderm: outer layer protective tissues that replace epidermis in older regions of stems and roots

        • They have both periderm & epidermis

      • Guard cells: epidermal cells that facilitate gas exchange in shoots

        • too hot→ close

          • prevent water loss

        • cold→ open

      • Trichomes: outgrowths of the shoot epidermis that can reduce water loss and reflect light, also defend against insects

  • Vascular tissue system: facilitates transport of materials through the plant & provides mechanical support

    • Xylem: conducts water & dissolved minerals upwards from roots to shoots

    • Phloem: transports sugars from leaves (where they are made) to storage/sites of growth (down)

    • Stele: everything except the leaves

    • In angiosperms, stele of root is central solid vascular cylinder (in the middle)

      • Angiosperms: plants that make flowers

  • Ground tissue system: tissues that are neither dermal nor vascular

    • Cells specialized for storage, photosynthesis, support, and transport (everything else)

      • Pith: ground tissue inside vascular tissue

      • Cortex: ground tissue outside vascular tissue

  • Stem cells are not differentiated

    • Structure changes depending on function

Different Meristems Generate New Cells for Primary & Secondary Growth

  • Indeterminate growth: plant grows until death

  • Determinate growth: stop growing after certain age/size

  • Meristems: unspecialized tissues made of dividing cells

    • how plants grow continuously

    • Apical Meristems: located at tips of roots and shoots (up and down)

      • Primary growth: growing vertically

    • Lateral Meristems: grow sides/in diameter/in width (secondary growth)

      • Vascular Cambium: adds layers of vascular tissue called secondary xylem (wood) and secondary phloem

      • Cork Cambium: replaces epidermis with periderm (thicker and tougher)

  • Initials: stem cells (new cells) that remain in meristem and produce more cells

    • unspecialized

    • the farther from meristem, they get specialized

Primary Meristems

  • Protoderm: produces dermal tissue

  • Ground meristem: produces ground tissue

  • Procambium: produces vascular tissue

Classification of Angiosperms

  • Annuals: complete life cycle in <=1 yr

  • Biennials: require 2 growing seasons

  • Perennials: live for many years

  • “Life cycle”- moment of sprouting→ reproduction

  • Root Cap: collection of cells that protects root apical meristem as root pushes through soil

Primary Growth of Shoots

  • Shoot apical meristem: dome-shaped mass of dividing cells at shoot tip

    • leaves of apical bud protect meristem

  • Axillary buds develop from meristematic cells left at the bases of lead primordia (collection of cells that were told to become leaves)

    • Kept dormant by chemical communication from apical bud (apical dominance)

      • If axillary bud + apical bud closer→ more inhibited

    • Released if shoot tip removed or shaded

Leaf Growth and Anatomy

  • Leaves develop from lead primordia along sides of shoot apical meristem

  • Epidermis (outer dermal tissue) in leaves interrupted by stomata (pores that allow CO2 and O2 exchange between air and photosynthetic cells)

    • Major evaporative loss of water, so located on bottom of leaf

    • Each stomatal pore has 2 guard cells to regulate opening and closing

  • Mesophyll: where photosynthesis occurs; ground tissue of leaf

    • Between upper and lower epidermis

    • 2 layers:

      • Palisade mesophyll: upper part of leaf

      • Spongy mesophyll: lower part of leaf (loose for gas exchange)

  • Veins are leaf’s vascular bundles; skeleton of leaf

    • Each vein enclosed by protective bundle sheath (xylem & phloem)

      • Why?

        • If xylem and phloem damaged, no transport can occur

Secondary Growth

  • Growth in thickness produced by lateral meristems

    • Occurs in gymnosperms (don’t make flowers) & many eudicots; RARE in monocots

  • Occurs in stems and roots of woody plants; RARELY in leaves

    • Consists of growth of tissues produced by vascular cambium and cork cambium

Growth, Morphogenesis, and Cell Differentiation Produce the Plant Body

  • Developmental plasticity: effect of environment on development

    • Plant can change form depending on environmental triggers

  • Morphogenesis: form body shapes

  • Growth is irreversible

  • Cell differentiation

    • Certain genes become accessible/inaccessible for the lifetime of the cell

Model

  • Arabidopsis

    • Why is it a model?

      • Small size, short generation time, abundant seed production, small genome size

    • Appearance changes depending on environment (genes on/off)

    • Easily transformed with transgenes (genes from different organism)

Cell Division

  • Increases # of cells & potential for growth

  • Cell elongation: process responsible for increase in plant size

    • Prophase: nucleus dissolves

    • Metaphase: chromosomes line up in middle

    • Anaphase: chromosomes separated by microtubules

      • Microtubules: pull apart chromosomes; become concentrated into ring called preprophase band that predicts future plane of cell division

    • Telophase: cell dividing

    • Cytokinesis: pinching off middle part

  • Transverse cell division: left and right

  • Longitudinal cell division: up and down

  • Symmetry of cell division & distribution of cytoplasm affects cell fate

    • Concentration of chemicals→ different genes turn on

    • Axis of division is predetermined

  • Polarity: condition of having structural/chemical differences at opposite ends of organism

    • Asymmetrical cell divisions

      • Uneven distribution of molecules→ determine what is the root and what is the shoot

  • Plant cells grow fast by intake and storage of water in large central vacuole

    • Cellulose microfibrils in cell wall restrict direction of cell elongation (prevent from lysing)

Morphogenesis & Pattern Formation

  • Pattern formation: development of specific structures in specific locations

    • Lineage-based mechanisms: cell fate determined early in development and passed on to daughter cells (animals)

    • Position-based mechanisms: cell fate determined by final position (plants)

  • Homeotic (Hox) Genes: affect # and placement of appendages in embryos

    • MADS-box genes: position & # of plant organs

    • KNOTTED-1: development of lead morphology (3d shape)

  • Different cells have different proteins

    • Different structure→ different function

  • Gene activation/inactivation depends on cell-to-cell communication (hormones and signals)

  • Phase changes: developmental stages

    • Juvenile phase→ adult vegetative stage→ adult reproductive stage

    • Occur within shoot apical meristem

Genetic Control of Flowering

  • Flower Formation: phase change from vegetative growth→ reproductive growth

    • Triggered by environmental cues & internal signals

      • ex/ sudden increase in water

    • Associated with switching on of floral meristem identity genes

      • takes energy to flower

  • Order of primordium’s emergence determines its fate:

    • Sepal: supports flower after blooming

    • Petal: attract pollinators

    • Stamen: male reproductive part; make pollen

    • Carpel: female reproductive part

  • 3 classes of floral organ identity genes

    • ABC Hypothesis: how floral organ identity genes direct the formation of the four types of floral organs

      • A→ sepal

      • A+B→ petal

      • B+C→ stamen

      • C→ carpel

T

Vascular Plant Structure, Growth, and Development

Plants’ Hierarchical Organization

  • Cell: fundamental unit of life

  • Tissue: group of cells consisting of 1+ cell types that perform a specialized function

  • Organ: consists of several type of tissues that carry out particular functions

Vascular Plant Organs

  • Vascular Plants: plants that can transport things up and down

  • Root system: underground

    • Roots rely on sugar produced by photosynthesis in the shoot system (cannot make sugar by themselves)

    • Root: organ with important functions

      • anchoring the plant

      • absorbing minerals and water

      • storing carbs (excess made in photosynthesis

        • because plants aren’t always guaranteed to have sunlight

    • Lateral roots: roots that emerge from the sides

      • Help anchor

      • Spread, help absorb nutrients

    • Primary root: first root to emerge from the seed

    • Taproot System: one main root and branches

      • Taproot: develops from primary root & anchors plant in soil

    • Fibrous root system: lots of small roots (no need for strong anchor)

    • Adventitious roots: side roots that arise from the stem & give rise to branching lateral roots

    • Root hairs: extensions of epidermal cells forming near root tip

      • Increase surface area, more absorption

    • Mycorrhizal associations: roots have fungus living in it that help them transform something they cannot use into something they can

      • ex/ Break down unusable nitrogen (symbiotic relationship)

  • Types of Roots

    • Prop roots: more anchorage

    • Storage roots: store carbs

    • Pneumatophores: some can do gas exchange (similar to leaves)

    • “Strangling” aerial roots: add further anchorage

    • Buttress roots: very tall and thin roots above ground, typically in forests and jungles (spread far and wide)

  • Shoot system: above ground

    • Shoots rely on water and minerals absorbed by the root system

    • Stem: plant organ consisting of nodes & internodes

      • Nodes: points at which leaves are attached

      • Internodes: space between nodes

    • Apical bud: causes elongation of a young shoot

      • where plant grows taller

    • Axillary bud: structure that can form a lateral branch, thorn, or flower

      • not main bud for height, additional buds for leaves, flowers, etc.

  • Leaf: main photosynthetic organ

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

      • ex/ chemical coat prevents fungus from attacking plant

    • Consist of blade and petiole

      • Blade: flat part

      • Petiole: stalk that joins leaf to node of stem

    • Chloroplasts in leaf

      • light shines & photosynthesis occurs

    • Why are leaves flat?

      • To maximize surface area and sun exposure

    • Monocot: 1 thing comes out of seed

      • Parallel veins

      • Vascular bundles are scattered throughout the ground tissue

    • Eudicot: 2+ things come out of seed

      • Branching veins

      • Vascular tissue consists of vascular bundles arranged in a ring

    • Vein: the vascular tissue of leaves

    • How do we categorize plants?

      • Determine if monocot or eudicot

      • What do the flowers look like?

      • What do the leaves look like?

    • Simple leaf: 1 leaf

    • Compound leaf: has several individual leaflets

      Evolutionary Adaptations of Leaves

    • Tendrils: help anchor it above the ground

    • Spines: defend

    • Storage leaves: store carbs

    • Reproductive leaves: leaves can reproduce

Dermal, Vascular, and Ground Tissues

  • Tissue system: interconnected leaf, stem, and root

    • Dermal tissue system

      • Nonwoody plants

        • Dermal tissue system: protection of the plant, consists of epidermis

        • Cuticle: waxy coating that helps prevent water loss from the epidermis (too hot from the sun)

        • No periderm

      • Woody plants

        • Periderm: outer layer protective tissues that replace epidermis in older regions of stems and roots

        • They have both periderm & epidermis

      • Guard cells: epidermal cells that facilitate gas exchange in shoots

        • too hot→ close

          • prevent water loss

        • cold→ open

      • Trichomes: outgrowths of the shoot epidermis that can reduce water loss and reflect light, also defend against insects

  • Vascular tissue system: facilitates transport of materials through the plant & provides mechanical support

    • Xylem: conducts water & dissolved minerals upwards from roots to shoots

    • Phloem: transports sugars from leaves (where they are made) to storage/sites of growth (down)

    • Stele: everything except the leaves

    • In angiosperms, stele of root is central solid vascular cylinder (in the middle)

      • Angiosperms: plants that make flowers

  • Ground tissue system: tissues that are neither dermal nor vascular

    • Cells specialized for storage, photosynthesis, support, and transport (everything else)

      • Pith: ground tissue inside vascular tissue

      • Cortex: ground tissue outside vascular tissue

  • Stem cells are not differentiated

    • Structure changes depending on function

Different Meristems Generate New Cells for Primary & Secondary Growth

  • Indeterminate growth: plant grows until death

  • Determinate growth: stop growing after certain age/size

  • Meristems: unspecialized tissues made of dividing cells

    • how plants grow continuously

    • Apical Meristems: located at tips of roots and shoots (up and down)

      • Primary growth: growing vertically

    • Lateral Meristems: grow sides/in diameter/in width (secondary growth)

      • Vascular Cambium: adds layers of vascular tissue called secondary xylem (wood) and secondary phloem

      • Cork Cambium: replaces epidermis with periderm (thicker and tougher)

  • Initials: stem cells (new cells) that remain in meristem and produce more cells

    • unspecialized

    • the farther from meristem, they get specialized

Primary Meristems

  • Protoderm: produces dermal tissue

  • Ground meristem: produces ground tissue

  • Procambium: produces vascular tissue

Classification of Angiosperms

  • Annuals: complete life cycle in <=1 yr

  • Biennials: require 2 growing seasons

  • Perennials: live for many years

  • “Life cycle”- moment of sprouting→ reproduction

  • Root Cap: collection of cells that protects root apical meristem as root pushes through soil

Primary Growth of Shoots

  • Shoot apical meristem: dome-shaped mass of dividing cells at shoot tip

    • leaves of apical bud protect meristem

  • Axillary buds develop from meristematic cells left at the bases of lead primordia (collection of cells that were told to become leaves)

    • Kept dormant by chemical communication from apical bud (apical dominance)

      • If axillary bud + apical bud closer→ more inhibited

    • Released if shoot tip removed or shaded

Leaf Growth and Anatomy

  • Leaves develop from lead primordia along sides of shoot apical meristem

  • Epidermis (outer dermal tissue) in leaves interrupted by stomata (pores that allow CO2 and O2 exchange between air and photosynthetic cells)

    • Major evaporative loss of water, so located on bottom of leaf

    • Each stomatal pore has 2 guard cells to regulate opening and closing

  • Mesophyll: where photosynthesis occurs; ground tissue of leaf

    • Between upper and lower epidermis

    • 2 layers:

      • Palisade mesophyll: upper part of leaf

      • Spongy mesophyll: lower part of leaf (loose for gas exchange)

  • Veins are leaf’s vascular bundles; skeleton of leaf

    • Each vein enclosed by protective bundle sheath (xylem & phloem)

      • Why?

        • If xylem and phloem damaged, no transport can occur

Secondary Growth

  • Growth in thickness produced by lateral meristems

    • Occurs in gymnosperms (don’t make flowers) & many eudicots; RARE in monocots

  • Occurs in stems and roots of woody plants; RARELY in leaves

    • Consists of growth of tissues produced by vascular cambium and cork cambium

Growth, Morphogenesis, and Cell Differentiation Produce the Plant Body

  • Developmental plasticity: effect of environment on development

    • Plant can change form depending on environmental triggers

  • Morphogenesis: form body shapes

  • Growth is irreversible

  • Cell differentiation

    • Certain genes become accessible/inaccessible for the lifetime of the cell

Model

  • Arabidopsis

    • Why is it a model?

      • Small size, short generation time, abundant seed production, small genome size

    • Appearance changes depending on environment (genes on/off)

    • Easily transformed with transgenes (genes from different organism)

Cell Division

  • Increases # of cells & potential for growth

  • Cell elongation: process responsible for increase in plant size

    • Prophase: nucleus dissolves

    • Metaphase: chromosomes line up in middle

    • Anaphase: chromosomes separated by microtubules

      • Microtubules: pull apart chromosomes; become concentrated into ring called preprophase band that predicts future plane of cell division

    • Telophase: cell dividing

    • Cytokinesis: pinching off middle part

  • Transverse cell division: left and right

  • Longitudinal cell division: up and down

  • Symmetry of cell division & distribution of cytoplasm affects cell fate

    • Concentration of chemicals→ different genes turn on

    • Axis of division is predetermined

  • Polarity: condition of having structural/chemical differences at opposite ends of organism

    • Asymmetrical cell divisions

      • Uneven distribution of molecules→ determine what is the root and what is the shoot

  • Plant cells grow fast by intake and storage of water in large central vacuole

    • Cellulose microfibrils in cell wall restrict direction of cell elongation (prevent from lysing)

Morphogenesis & Pattern Formation

  • Pattern formation: development of specific structures in specific locations

    • Lineage-based mechanisms: cell fate determined early in development and passed on to daughter cells (animals)

    • Position-based mechanisms: cell fate determined by final position (plants)

  • Homeotic (Hox) Genes: affect # and placement of appendages in embryos

    • MADS-box genes: position & # of plant organs

    • KNOTTED-1: development of lead morphology (3d shape)

  • Different cells have different proteins

    • Different structure→ different function

  • Gene activation/inactivation depends on cell-to-cell communication (hormones and signals)

  • Phase changes: developmental stages

    • Juvenile phase→ adult vegetative stage→ adult reproductive stage

    • Occur within shoot apical meristem

Genetic Control of Flowering

  • Flower Formation: phase change from vegetative growth→ reproductive growth

    • Triggered by environmental cues & internal signals

      • ex/ sudden increase in water

    • Associated with switching on of floral meristem identity genes

      • takes energy to flower

  • Order of primordium’s emergence determines its fate:

    • Sepal: supports flower after blooming

    • Petal: attract pollinators

    • Stamen: male reproductive part; make pollen

    • Carpel: female reproductive part

  • 3 classes of floral organ identity genes

    • ABC Hypothesis: how floral organ identity genes direct the formation of the four types of floral organs

      • A→ sepal

      • A+B→ petal

      • B+C→ stamen

      • C→ carpel