Roots Stems and Leaves

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Chapter 4

• Roots Stems and Leaves
• The Primary Plant Body

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Roots

• Main function is to anchor and absorb and conduct
  water and minerals to stems and leaves
• Roots also receive organic molecules from stems
  and leaves
• Produce hormones and compounds that regulate
  plants development and structure

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Taproot system which has a large Main root that
taps deep sources of water May develop branch
roots called lateral roots
Fibrous roots have shallow root systems, the main
root originating from stem tissue called
adventitious roots Mostly in monocots and
seedless Vascular plants
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Root development

• Cells divide in the apical meristem near the root
  tip
• The initials divide in a small area of the
  meristem known as the quiescent center
• Through mitosis cells divide into either an
  initial or a derivative that furthur
  differentiates and grows

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Apical meristems give rise to primary
meristems and differentiate to eventually become
primary tissues

• Root apical meristems give rise to these three
  primary meristems (primary plant body)
• protoderm procambium ground
  meristem

Epidermis or dermal tissue primary xylem
ground tissues
primary phloem
parenchyma, collenchyma

and
sclerenchyma
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Three overlapping regions or Zones

• Zone of cell division
• area of root apical meristem and the
  
• three primary meristems
• Zone of cell elongation
• area where cells do not divide and
• grow in length
• Zone of maturation
• area where cells begin specializing
  in
• structure and function

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Root apical meristem Produces the cells of the
root and the rootcap
Above the root apical Meristem lies the
protoderm, procambium and ground meristem,
regions of increased Cell division
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Roots have a solid central cylinder of vascular
tissue called the protostele
stele in monocots The the vascular tissues
(xylem and phloem) are surrounded by one or more
layers of pericycle and next by one layer of
endodermis
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Morphological adaptations in Roots Aerial root
and epiphytes Adventitious roots that arise from
stems
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Vanilla orchid
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Pneumatophores spongy, aerial roots of marsh or
swamps, such as in mangal (mangroves), where
roots are present in waterlogged soils
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Strangling roots
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Banyan tree in the Ficus familyShowing aerial
roots
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Climbing aerial root, adventitious root, of a
Boston ivy, anchors plant to the wall
A rapidly growing plant of maize (Zea mays,
Family Poaceae) develops adventitious roots from
the nodes. These are termed prop roots, but they
are also nodal roots.
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Buttress root
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Storage root of parsley
Cassava the most important root crop In the
tropics, where potatoes will not grow
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Mutualistic associations of roots and fungi
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STEMS

• Nodes, internodes and axillary buds are basic
  features that distinguish stems from roots and
  leaves.
• Stems do not only grow longitudinal but also
  produce leaves and axillary buds
• A stem lengthens simultaneously in several
  internodes below the shoot apical meristem

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Apical meristem Slowly dividing cells
Leaf primordia eventually Becomes the leaf
Axillary bud
Below and beyond the Apical meristem arises
the Protoderm, procambium, And ground meristem,
regions of increase cell division
Stem lengthening At several internodes
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The axillary bud is a miniature shoot with a
dormant apical Meristem and several young leaves
It is either a vegetative bud if it will grow
into a branch or a floral bud if it will Grow
into a flower
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Arrangement of leaves on a stem

• Phyllotaxy is advantageous depending on leaf size
  and shape
• Maximum sunlight positioning
• one leaf at each node is alternate
• two leaves per node is opposite
• three or more leaves per node is whorled

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Three most general types of leaf phyllotaxy
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Other phyllotaxy

• Distichous phyllotaxy
• corn
• Decussate phyllotaxy
• Crassula sp.
• There may be more!

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Stems have simple arrangements of nodes and
internodes

• Vines have long internodes
• adaptive to exploring such as stolons,
  
• runners, and tendrils
• Lettuce, cabbage, and onions internodes are short
  and leaves are tightly packed
• not suitable for photosynthesis

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Stolons

• Airplane plant also known as the spider plant,
  spreads runners in nature, the stolons droop down
  and form new plants at the tips.
• The new plants have already produced roots.

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Runners, Stolons are really horizontal stems
above ground to help the plant reproduce asexually
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Onions are bulbs Short stem with Fleshy leaves
attached Starch accumulates in these short
thick leaves attached to the Stem
Allium cepa by botanists. Allium meaning garlic
and cepa meaning onion in Latin.
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Corms

• Vertical thick stems that have thin,papery leaves
  such as gladiolus

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The bulblike Corm of autumn crocus (Colchicum
autumnale), a member of the lily family
(Liliaceae)
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Sweet potato tuber
Stems growing underground composed of Parenchyma
cells filled with starch eyes of the potato
are the axillary buds Leaves are microscopic
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Rhizomes

• Rhizomes are fleshy horizontal stems that allow a
  plant to spread underground, such as bamboo,
  irises, canna lilies

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Underground horizontal stem of an Iris plant
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Advantages of modified stems

• Being subterranean- more advantageous than being
  exposed in surface locations
• Mostly perrenial plants, need a dormant period to
  survive stress of winter or heat of summer
• Protection of nutrient reserves
• Protection from most herbivores

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Division of Labor

• Modifications that increase a stems ability to
  survive spread or store nutrients decrease its
  efficiency at other tasks
• False Solomons seal consists of subterranean
  rhizomes and aerial shoots for photosynthesis and
  flowering
• Some rhizomes, form colonies, like Solomons
  seal's, store food underground.

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Forest advantages of upward growth of the
vertical stem or trunk vs high degree of branching

• A heavily shaded forest suppression of branching
  allows all resources to be concentrated in the
  one shoot or trunk up to the light
• With abundant light, one main trunk is not
• So advantageous,instead, a high degree of
  branching allows the rapid production of many
  leaves

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Evolution of stems

• Palm tree has a stem produced entirely by primary
  growth with a single apical meristem atop the
  stem that can grow to 200 feet. Survive hot
  tropical conditions.
• Wheat plant has stem low growing, survives drying
  conditions and damaging winds, and only live a
  year.
• Native to cold mountainous regions.

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Zone and cell layer models to describe stem growth

• shoot apical meristems give rise to the primary
  meristems the protoderm, the ground meristem, the
  procambium.
• Zone model
• Cell layer model

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Primary growth of most stemsin gymnosperms and
flowering plants

• Vascular tissue forms vascular bundles with xylem
  and phloem
• gymnosperms vascular bundles
• and dicots form a circle around
  the pith
• monocots the vascular bundles are
  scattered
• throughout the ground tissue
  (cortex and pith
• do not apply)

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LEAVES

• Leaves evolved from flattened stem systems that
  grew close together
• Stems and leaves must function together if the
  plant is to survive and reproduce
• Leaves are flat and thin for maximum absorption
  of light and CO2

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Petiole or stalk that hold the blade out into the
light

• Prevents self shading of leaf blades by those
  above them.
• Long thing flexible petioles allow blade to
  flutter in the wind , cooling the leaf, and
  bringing fresh air
• Leaf flutter makes it diffucult for insects and
  pests to land on the leaf

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If no petiole , leaves are known as Sessile
leaves and form a sheath Around the
stem Aconium grows in arid sunny regions and
the fleshy leaves are packed close together. Sun
is so intense, the leaves receive more than
enough light for photosynthesis The closeness
helps them trap water. Monocots such as
grasses, irises, lilies, yuccas have linear
leaves but still flutter and are well exposed to
light
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Leaves can be simple or compound

• Simple is single undivided blade
• Oak, poplar, castor bean

Sometimes the simple leaf can be deeply lobed
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Compound leaf

• The blade is divided into leaflets
• Palmately compound leaves the leaflets are all
  attached at the tip of the petiole, and fan out
  like a palm
• Pinnately compound leaves , the leaflets form
  rows on opposite sides of an axis like a feather

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Leaf shape

• No one leaf shape that is superior or
  disadvantageous
• Many species have different types of leaves such
  beans, with simple seedling leaves and compound
  mature leaves

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• Plants that lose all their leaves are known as
  deciduous plants
• Examples maple and sycamore are deciduous
  trees
• In deciduous plants, the areas where the leaves
  separate from the plant are abscission zones
• Usually at the node where the petiole attaches to
  the stem
• Form leaf scars

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Venation refers to the leaf veins or bundles of
vascular tissue Dicots have netted patterns or
reticulate venation Monocots have long strap
shaped leaves and veins run side by side referred
to as parallel venation
These veins distribute water from the stem into
the leaf and simultaneously collect sugars
produced by photosynthesis and carry them to the
stem for storage
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Leaf epidermis

• Protects leaf from water loss, abrasions,and
  entry of fungi and bacteria
• that cause disease
• Regulates exhange of gases such as CO2 and O2 and
  water vapor
• Single layer of cells derived from protoderm

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Located on the lower epidermis Are leaf pores
called stomata with surrounding guard cells
Guard cells are filled with chloroplasts and can
shape caused by intake of H2O
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Mesophyll in the leaves carries out photosynthesis

• Chlorenchyma ground tissue called mesophyll
  contain chloroplasts and are specialized for
  photosynthesis
• Palisade mesophyll are like picket fences
• Spongy mesophyll is loosely organized
  photosynthetic cells that lies below the palisade
  mesophyll

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Spines are a type of modified leaf not to be
confused with thorns That are actually modified
stems Prickles are projections of cells of the
epidermis or cortex
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Tendrils are slender coiling structures that
attach climbing plants to supporting
structures Type of modified leaves, such as
pea plant A Growth movement called Thigmotropi
sm where the tendril touches something and the
opposite side of the tendril grows and
curves Around that object
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Window leaves are Transparent on top And
photosynthetic cells are underground Portions
of the leaves
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Bracts are modified leaves at the base of flowers
but are not flower parts themselves Red or white
in Poinsettias