6-7: Protective Tissues and Vascular Tissues

epidermis

- Outermost layer of cells of the primary plant body
- Usu. one layer
- With cuticle (cutin and waxes)

primary plant body

body during primary growth; increase in height

• Reduce water loss
• Mechanical protection
• Gaseous exchange (stomata)

function of epidermis

• Epidermal cells (ordinary epidermal cells)
• Stoma/ta • Trichomes

cell types in the epidermis

stomata

• Openings bounded by guard cells
• Most abundant on leaves
• Rare in roots

Guard cells

- regulate the exchange of water vapor and CO2
- with neighboring cells or subsidiary cells
- Unevenly thickened walls with radially arranged cellulose microfibrils

Amphistomatic leaf

stomata occur on both surfaces

epistomatic leaf

stomata only on upper surface; common in aquatic plants that float

Hypostomatic leaf

stomata only on lower surface; common in most

trichomes

• Epidermal appendages
• Reduces transpiration rate
• Defense against insects

root hairs

extension of absorbing surface

trichomes

what are cotton fibers

periderm

replaces the epidermis in roots and stems when it cant cope w increase in diameter

• Phellem/cork cells
• Phellogen/cork cambium
• Phelloderm

periderm consists of

phellogen

• Mostly arises in the subepidermal or epidermal layer (stem); sometimes in vascular tissues (phloem)
• Arises in the pericycle (roots)
• meristematic cell layer responsible for the development of the periderm

cork (phellem)

- tissue formed on the outer side of phellogen or cork cambium
- dead, suberized

phelloderm

- parenchymatous
- bellow the phellogen
- 2ndary cortex

bark

• All tissues outside vascular cambium
• Component varies between primary and secondary state

rhytidome

outer bark

outer nonfunctional
inner living

outer vs inner bark

lenticels

- permitting entry of air
- has a loose arrangement of cells compared to the rest of the periderm.
- has more phellogen and is more active than the phellogen of the peri derm.
- numerous intercellular spaces

- tracheary elements (tracheids, vessel elements)
- xylary fibers
- xylem parenchyma

xylem axial system

xylem parenchyma

xylem radial system

primary xylem has no rays

why does xylem systema only apply to 2X

tracheary elements

Water-conducting cells in plants that, when mature, are always dead and empty of cytosol

sclerenchyma

what are tracheids and vessel elements made of

lumen

space inside trach elements

Spindle (long and tapered at both ends)

tracheids shape

Drum or barrel shaped

vessel elements shape

imperforate

tracheids perforation

yes, devoid at both end walls

vessel elements perforation

overlapping

tracheids arrangement

end on end

vessel elements arrangement

less efficient

tracheids water conduction

more efficient

vessel elements water conduction

water leaves + enters tracheids thru bordered pits
water moves w no resistance in vessel elements

why do vessel elements conduct water more efficiently than tracheids

mx and 2x

where are simple and bordered pits located in Tracheids and Vessels

annular, helical/spiral, scaliforme, reticulate

2ndary walls ng primary xylem

cavitation

• Creation of embolism
• Blocks the movement of water
• Freezing and drought

embolism

air space that prevents water from passing thru vessel element

thru bordered pit pairs

how does water take a detour pag may embolism

water column breaks when water vapor/gas is trapped within; alternation betw freezing and thawing

how does cavitation happen

xylem sap

the water and dissolved minerals in the xylem

conifers in cold climate

where is cavitation common

xylary fibers

• Long cells, tapered both ends
• With lignified secondary walls
• Wall thicker than tracheids
• strengthening and storage

fiber tracheids

xylary fibers w bordered pits and slit-like inner aperture

libriform fibers

xylary fibers w thicker walls and longer; slit like aperture (simple pit)

xylem parenchyma

• With lignified secondary walls but living (2x)
• Storage of starch or fat
• Found in axial and ray parenchyma

procambium

origin of primary xylem

protoxylem

early-formed xylem when organs r still elongating

lacuna

since the protoxylem cells are mature when the stem is elongating, they are stretched and destroyed, forming a space called what?

metaxylem

- late-formed xylem after organs stop elongation
- most of the functional xylem in the primary xylem is this
- pag may 2ndary growth, loses its function na

- sieve elements (sieve cells, sieve-tube elements)
- sclerenchyma (fibers, sclereids)
- parenchyma

axial phloem

sieve elements

• Breakdown of nucleus and tonoplast (not entire protoplast)
• Sieve areas (with pores)

sieve cells

sieve elements ng gymnosperms

sieve tube elements

sieve elements ng angiosperms

sieve plate containing sieve pores

specialised end wall of sieve tube, with holes allowing connections between one cell and the next

sieve tube elements/members

• Contain phloem protein (p-protein/slime)
• Lack ribosomes
• With companion cells

companion cells

• Related to sieve-tube element in function and development (ontogeny)
• With prominent nucleus
• Intimately connected with associate sieve-tube element
• Provides information molecules, proteins, and ATP to sieve-tube element