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Chapter 7 Roots (Other Types of Roots and Root Modifications (Prop Roots,…

- - - - provide long-term storage
        
        for carbohydrates
        
        used to produce
        
        new shoot in spring
    - - biennial species
        
        examples
        
        beets
        
        carrots
        
        celery
      - many perennials
        
        examples
        
        daisies
  - - - become wider
      - more vascular bundles
      - capable of growing into air
    - - additional nutrients
      - water
        
        to stem
    - - massive trees meters in diameter
    - - tall, plate-like
      - brace the trunk against
        
        wind
      - upper side grows more rapidly
  - - - epiphytic
      - living attached to
        
        branches of trees
        
        spread along surface of bark
      - adapted to dry habitats
        
        but found in rainforests
    - - root epidermis in orchids
      - composed of
        
        several layers of dead cells
        
        white in apperence
      - acts as
        
        waterproof barrier
  - - - exists in which
        
        fungal hyphae
        
        penetrate between
        
        outermost root cortex cells
        
        never invade the cells themselves
    - - hyphae penetrate cortex
        
        as far as endodermis
        
        cannot Casparian strip
      - do not break plasma membrane
        
        or vacuole membrane
      - inside cell
        
        branch repeatedly
        
        create small structure
        
        called arbuscule
  - - - modified roots
        
        of parasitic plants
      - adhere to host by
        
        secreting adhesive
        
        growing around
        
        small branch or root
      - penetration occurs by
        
        forcing a shaft of cells
        
        through host's dermal system
        
        expanding haustorium radially
        
        cracks host's epidermis
      - many parasites
        
        attack xylem only
        
        do not draw
        
        sugars from host
        
        carry out own photosynthesis
      - other parasites
        
        contact both
        
        xylem and phloem
        
        little or no photosynthesis
- - - - structure
        
        to remain
        
        in place
        
        provide protection
      - growth pattern
    - - root meristem
        
        are meristematic
        
        undergo cell division with
        
        transverse walls
        
        form files of cells
        
        then are pushed forward
        
        2 more items...
    - - grow to the side
        
        and proliferate
        
        structure
        
        change dramatically
        
        endoplasmic reticulum becomes
        
        less conspicuous
        
        starch grains
        
        digested
        
        cell's dictyosomes
        
        secrete mucigel by exocytosis
        
        1 more item...
        
        metabolism
    - - regular files of cells
        
        originate in meristem
        
        extend into
        
        regions of mature root tissues
      - tritiated thymidine
        
        demonstrate central cells
        
        are not synthesizing DNA
        
        cell nuclei do not
        
        take up thymidine
        
        indicate they don't become radioactive
        
        region known as quiescent center
        
        more resistant to
        
        radiation
        
        toxic chemicals
        
        believed to act as
        
        reserve of healthy cells
        
        1 more item...
  - - - root apical meristem
    - - cells expand greatly
        
        some meristematic activity continues
        
        mostly cells enlarging
    - - subapical meristem region
    - - into visible pattern
      - no cells mature
      - outermost of cells
        
        are
        
        protoderm
        
        differentiate into epidermis
      - in center is provascular tissue
        
        develop into
        
        primary xylem
        
        primary phloem
        
        between this and protoderm
        
        ground tissue
        
        uniform parenchyma
        
        differentiates into root cortex
      - farther from root tip
        
        older, larger cells develop
        
        into
        
        metaxylem
        
        metaphloem
    - - quite permeable
      - minerals
        
        penetrate into
        
        root through apoplast
        
        diffuses along
        
        thin, fully hydrated young walls
        
        intercellular spaces
  - - - certain processes occur
        
        root hairs grow outwardly
        
        increasing absorption of
        
        water
        
        minerals
      - merges gradually with
        
        zone of elongation
      - minerals
        
        no free access to minerals
        
        because of
        
        innermost layer of cortical cells
        
        differentiates into a cylinder
        
        called endodermis
        
        2 more items...
      - Casparian strips
        
        involved in controlling
        
        types of minerals
        
        that enter
        
        xylem water stream
        
        are impermeable
        
        minerals can cross
        
        endodermis
        
        only if
        
        endodermal protoplasts absorb them from
        
        1 more item...
        
        many glands and secretory cavities
        
        have casparian strips
    - - much larger cells of
        
        metaxylem
        
        metaphloem
        
        become fully differentiated
        
        functional in
        
        zone of maturation
  - - - once thought to
        
        represent passageways
      - suspected to slop development now
    - - creates watertight sheath
        
        around vascular tissue
        
        functions to to keep water in
        
        absorption of minerals
        
        creates powerful absorption of water
        
        increases water pressure
        
        2 more items...
- - - - much larger than other roots
      - develops from embryonic root
        
        called radicle
    - - may produce
        
        other lateral roots
        
        results in
        
        highly ramified set of roots
        
        analogous to
        
        shoot system of most plants
    - - radicle dies
        
        root primordia at base
        
        grows out and form
        
        first stages
        
        then continued root primordia
        
        initiated in stem tissue
      - examples
        
        most monocots
        
        some eudicots
      - known as adventitious roots
        
        because
        
        do not arise from
        
        pre-existing roots
        
        they are not radicles
        
        increase
        
        absorptive capacities
        
        transport capacities
    - - cannot undergo secondary growth
      - after stem is formed
        
        number of
        
        vascular bundles
        
        tracheary elements
        
        cannot increase
        
        could not supply sugars to
        
        ever increasing taproot
        
        sieve tubes
        
        conducting capacity
      - other monocots
        
        increase in size
        
        by means of
        
        stolons
        
        horizontal shoots
        
        branch and produce adventitious roots
        
        1 more item...
        
        rhizomes
  - - - no leaves
      - no leaf scars
      - no leaf axils
      - no axillary buds
    - - region where
        
        growth in length occurs
    - - growth by discrete apical meristems
        
        only feasible type of longitudinal growth
        
        protected by
        
        thick layer of cells
      - elongate at
        
        meristematic regions
        
        also called
        
        localized growth
    - - secreted by
        
        dictyosomes of root cap cells
      - complex polysaccharide
        
        rich in
        
        carbohydrates
        
        foster rapid growth of
        
        soil bacteria around
        
        root tip
        
        amino acids
      - lubricates passage of
        
        root through soil
      - causes soil to release
        
        nutrient ions
    - - few mm long
      - where cells undergo
        
        division
        
        expansion
      - behind it is
        
        root hair zone
        
        region where
        
        narrow trichomes extend out
    - - form only in
        
        part of root
        
        not elongating
      - greatly increase
        
        root's surface area
      - can enter any crevice
        
        extract
        
        water
        
        minerals
        
        that a root cannot
      - combine with carbon dioxide
        
        forms carbonic acid
        
        helps release
        
        ions from soil matrix
- - - - in pericycle
  - - - with smaller vacuoles
        
        resume mitotic activity
        
        activity is localized
        
        creates small root primordium
        
        swells into cortex
        
        endodermis torn
        
        1 more item...
        
        or crushed
        
        may undergo cell division
- - - - anchoring plant to substrate
        
        provides stability
      - absorbing water and minerals
        
        distributed on
        
        all sides of roots
        
        high surface to volume ratio
        
        increases carbon dioxide capacity
      - producing hormones
        
        shoot growth
        
        depend on
        
        hormones
        
        cytokinin
        
        gibberellin
        
        helps
        
        control size
        
        development
    - - examples
        
        carrots
        
        beets
        
        radishes
      - main site of
        
        carbohydrate storage during winter
    - - in
        
        willows
        
        sorrel
        
        spread horizontally
        
        produce shoot buds
        
        grow and act as new plants
    - - roots grow into holdfasts
        
        cling to
        
        rocks
        
        brick
    - - modified roots
        
        attack other plants
        
        extract
        
        water
        
        minerals