Cells

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Cells Tissues
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Apical Meristems

• Tips of roots and shoots
• Extension of plant body
• Initials
• One cell remains as initial maintaining
  meristem
• Other cell is derivative new body cell

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Primary Meristems

• Multiple divisions before differentiation
• Partly differentiated tissue
• Primary growth
• Extension of the plant body
• Secondary growth
• Thickening of the plant body
• Indeterminate growth
• Formation of new organs during their entire life

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Growth, Morphogenesis Differentiation

• Development sum total of events that form an
  organisms body
• Driven by genetics
• In response to environment day length, light
  quality/quantity, temperature, gravity
• Development 3 processes
• Growth
• Morphogenesis
• Differentiation

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Growth

• Combination of cell division and elongation
• Cell division alone only increases number!
• Most growth elongation enlargement

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Morphogenesis

• Primary event expansion of tissue
• Subdivided by cell division
• Cell/tissue differentiation follow morphogenesis

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Differentiation

• Often begins while cell is still enlarging
• Depends on gene expression
• Ultimate fate positional
• Not dependant on cell lineage
• Determination
• Commitment to specific course of development
• Competency
• Ability of cell to develop in response to
  specific signal

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Differentiation
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Internal Organization

• Cells ? tissues ? tissue systems
• Tissue Systems
• Ground
• Vascular
• Dermal

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Tissue Systems

• Ground
• Parenchyma
• Collenchyma
• Sclerenchyma
• Vascular
• Xylem
• Phloem
• Dermal
• Epidermis ? periderm

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Tissue Systems

• Characteristic Distribution Patterns
• Primary difference vascular/ground tissue

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Fig 12.1
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Dicot vs Monocot
ROOT
STEM
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Tissues

• Functionally/ structurally distinct cells
• Simple tissues one type of cell
• Ground tissues
• Complex tissues more than 1 type of cell
• Vascular tissues
• Dermal tissues

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Ground Tissues -- Parenchyma

• Living at maturity
• Capable of cell division
• Some have 2º cell walls
• Adventitious roots
• Photosynthesis, storage secretion
• chlorenchyma
• Movement of water and food

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Parenchyma Transfer Cells

• Increased surface area
• Facilitates movement of solutes over short
  distances
• Intensive solute transfer
• Common
• Associated with xylem/phloem of minor veins
• Cotyledons
• Leaves in herbaceous Eudicots
• Leaf traces
• Reproductive tissues placentae, endosperm
• Glandular structures nectaries, salt glands

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Ground Tissues -- Collenchyma

• Living at maturity
• Discrete strands of elongated cells
• Continuous cylinders in stems and petioles
• Borders veins in Eudicot leaves
• Unevenly thickened, nonlignified cell walls
• Supports young growing organs

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Ground Tissues -- Sclerenchyma

• Continuous masses or small groups
• Hard, lignified cell walls
• Strengthening and supporting plant parts
• Fibers
• Long, slender cells
• strands or bundles
• Bast fibers
• Sclerids
• Variable in shape
• Seed coats, nut shells, endocarp

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Vascular Tissue

• Xylem and Phloem
• Conducts water and nutrients

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Vascular Tissues -- Xylem

• Conducts water
• Also conducts minerals
• Support
• Food storage
• 1º growth procambium
• 2º growth vascular cambium
• Dead at maturity

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Vascular Tissues -- Xylem

• Trachery elements
• Tracheids
• Vessel elements
• May have wall pits

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Xylem Vessel Elements

• Vessel elements perforation plate
• End rims

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Xylem -- Tracheids

• Less specialized
• No perforations
• Seedless vascular plants Gymnosperms
• Only water conducting cells
• Less efficient because of lack of perforations
• Safer because of pit membranes
• Stop air bubbles

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Xylem -- Tracheids

• Variety of 2º wall thickenings
• During elongation spiral or annular
• Allow for extension after differentiation
• Programmed cell death
• Only cell walls retained

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Xylem Miscellany

• Parenchyma stores stuff
• Vertical strands
• In rays -- 2º xylem
• Fibers
• Storage and support
• May be living
• Sclerids

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Vascular Tissue -- Phloem

• Principal food-conducting tissue
• Not just sugars!
• Long distance signaling molecules
• 1º or 2º growth
• Sieve elements principal conducting cells
• Sieve areas connecting adjacent sieve elements
• Sieve cells only phloem tissue in gymnosperms
• Sieve-tube elements only angiosperms

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Phloem

• Sieve Cells
• Narrow pores
• Uniform sieve areas
• Sieve-tube elements
• Sieve Plate
• Some areas ? larger pores

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Phloem

• Sieve Cells

• Sieve Tube Elements

• Narrow pores
• Uniform sieve areas

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Sieve Elements

• Living at maturity
• Differentiation
• Trachery elements complete breakdown
• Sieve elements partial breakdown
• Breakdown of nucleus, loss of ribosomes, Golgi
  cytoskeleton
• Remainder distributed along wall ? plasma
  membrane, SER, some plastids mitochondria
• P-protein except in some monocots

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Sieve Tube Elements
Arrows show P-protein bodies
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Sieve-tube Elements

• Companion Cells specialized parenchyma
• Same mother cell
• Deliver stuff to sieve-tube elements
• Hormones, proteins, ATP, etc.
• Life support system for STE
• Companion cell dies when sieve element cell dies

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Sieve-Tube Element Differentiation
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Gymnosperm Sieve Cells

• Associated with albuminous cells
• Have nucleus, etc.
• Similar function to companion cells
• Also dies when sieve element cell dies

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Dermal Tissue

• Epidermis outermost layer
• Variable functionally structurally
• Unspecialized or specialized!
• Guard cells
• Trichomes
• Protects plant
• cuticle

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Epidermis Guard Cells

• Contain chloroplasts
• Regulate stomatal opening

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Epidermis -- Trichomes

• Root hairs
• Increased reflection of radiation
• lower temps
• Lower water loss
• Absorption of water and minerals
• Secretory functions
• Protection against herbivory
• Carniverous plants

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Trichomes
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Carnivorous Plants
Nepenthes
Drosera
Dionaea
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Periderm

• 2º protective tissue
• Replaces epidermis in 2º growth
• Cork (phellem) ? nonliving
• Cork cambium (phellogen)
• Cork outer surface
• Phelloderm -- inner
• Phelloderm living parenchyma tissue

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Periderm -- Lenticels

• Loosely arranged
• Gas exchange across the cork

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