vascular plants - plant tissues

primary growth

• directed by the apical meristems

• The tissues composed of these cells are the primary plant body

what type of growth do plants display

• indeterminate - continue to growth through their life

• developmental plasticity is the only way
  they can move as adults

development definition

• the sum of events that form an organism’s body

growth definition

• an irreversible increase in size

• Cell division and enlargement

morphogenesis definition

• controls the shape or form of a plant body

• The planes in which cells divide and expand

differentiation

• cells with identical genetics become different

• Controlled by gene expression, but ultimately fate is determined by
  position in the plant body

• Often viewed in terms of determination and competency

determination

the progressive course of development that
results in the loss of capacity to resume growth

competency

the ability of a cell to develop in response to a specific signal

3 primary meristems

1. protoderm

2. ground meristem

3. procambium

protoderm produces

epidermis (dermal tissue system)

ground meristem produces

ground tissue system: parenchyma, collenchyma, and sclerenchyma

procambium produces

primary xylem and phloem: vascular tissue system

tissue systems

composed of tissues linked in continuity within the plant body

parenchyma characteristics

• Vary widely in shape and size and generally occur in continuous masses

• alive at maturity = can divide

• usually only have a primary cell wall (not a secondary)

• totipotent

• keep meristematic ability

parenchyma main roles

• photosynthesis

• storage

• secretion

• wound healing/ regeneration

totipotent

Can become embryonic and give rise to new plant

where is parenchyma found

• Found in the cortex and pith of shoots and roots

• Found in the mesophyll of leaves

• Found in the flesh of fruits

• Also found as vertical strands in the primary and secondary
  vascular system and horizontal strands in the secondary vascular
  system

transfer cells

• Parenchyma with “funky” cell walls

• Ingrowths increase surface area for movement of solutes over short distances

• Occur throughout the plant body, often associated with xylem and phloem

•  Also found in reproductive tissues and glandular structures

collenchyma characteristics

• alive at maturity

• typically elongated with an unevenly thickened (non-lignified) primary cell wall

• aids in flexibility

• can develop as the plant grows

collenchyma locations

• Occur in discrete strands or continuous cylinders beneath epidermis

• Found primarily in herbaceous plants in organs than undergo no secondary
  growth

• rarely found in roots

sclerenchyma

• not alive at maturity

• Very expensive to make but important for strengthening and supporting plant
  parts that have stopped growth

• thick (lignified) secondary cell wall 

2 types of sclerenchyma

1. fibers

2. sclereids

fibers

• sclerenchyma

• Long and slender, often in strands or bundles

sclereids

• sclerenchyma

• Variable shape, short compared to fibers

sclerenchyma location

• Can be found in all parts of the primary and secondary plant body

epidermis function

• generally, Retard the loss of water with cuticle of cutin and waxes

• different types have different functions

types of epidermis

• most are undifferentiated

• guard cells

• trichomes

epidermis location

• Covers leaves, floral parts, fruits, seeds

• Also stems and roots until secondary growth

stomata

• protected by chloroplast-containing guard cells

• control the movement of gases and water vapor

• most abundant on undersides of leaves

• guard cells associated with subsidiary cells

subsidiary cells

act as water and ion reservoirs

trichomes

• Many functions

• Root hairs for example absorb water and minerals

• Increased trichome number may reduce solar radiation, temperature,
  and lower water loss

• May also secrete substances to prevent toxicity

periderm

• Replaces the epidermis in stems and roots that have secondary
  growth

• Consists of a protective cork which is non-living with heavily
  suberized walls

• The cork cambium and phelloderm are parenchyma-
  like tissues that are living

• Cork cambium forms the cork to the outside and phelloderm to
  inside

xylem

• Major role is to conduct water

• also moves minerals, provides support, and plays roles in food
  storage

• Extends throughout the plant body

• Composed of two types of tracheary elements: both are elongated cells with secondary cell wall and lack protoplast

two types of tracheary elements

• tracheids

• vessel elements

vessel elements unique traits

• contain perforations that lack primary and secondary cell walls

perforations

• found in vessel elements

• can help with unimpeded water flow

• can be dangerous because viruses can enter through them

perforation plates

the area of the wall where perforation occurs

tracheids unique traits

• less differentiated

• only type of water conducting cells in gymnosperms and seedless vascular
  plants

xylem accessories

• contain parenchyma cells to store various substances

• contain fibers which are living and act as storage and support

phloem

• Principal food-conducting tissue of vascular plants : Primarily sugars, but tons of other substances like amino acids, lipids, micronutrients, hormones

• long distance signaling

• sieve elements

• Cell walls are primary, with some pores blocked or surrounded by callose

• Phloem is living, but undergoes huge changes

two types of sieve elements

• sieve cells

• sieve-tube elements

sieve elements

• Named due to characteristic pore clusters called sieve areas

• Connects protoplast of adjacent cells

• The protoplast of sieve elements (except some monocots) are characterized by a proteinaceous substance called P-protein

• have companion cells

sieve cells

• have narrow pores, pores in sieve areas are uniform on all walls

• Most sieve areas are on the overlapping ends of sieve cells

sieve tube elements

• have sieve areas that vary in the size of their pores

• The area with larger pores is called the sieve plate

• Generally found on the end wall to form sieve tubes

  
  

changes to phloem in comparison to other living cells

• Nucleus and tonoplast breaks down

• Loss of ribosomes, Golgi apparatus, and cytoskeleton

• Remaining structures (plasma membrane, smooth ER) are moved to the wall

• Some plastids and mitochondria may remain

why are some pores phloem blocked/ surrounded by callose

occurs due to wounding to prevent spread of invaders

p-protein

thought to work with callose to plug pores, often found
surrounding sieve-plate pores

companion cells

provide substances to sieve elements since they have all organelles
intact