FRST 200 Vascular Tissue & Secondary Growth (Week 8 & 9)

Types of xylem cells?

1. Trachieds- least specialized, arose early, thin + elongated cells with pits on the side of the cell walls and these pits allow water to move passively from cell to cell and they also have rings/ helical thickenings of secondary cell wall that strengthen the cell ,allowing it to stretch

2. Vessel element- more specialized, large sections of a pipe stacked on top of each other to form a VESSEL, shorter and much wider than tracheids, like trachieds also has pits for water to flow out passively (less safe because they collapse more easily under drought stress or when air bubble but MORE EFFICIENT THAN TRACHIEDS

3. Xylarly fibers- long, very thin cells, with VERY thick cell walls, no pits,

4. Xylem parenchyma- act as storage cells, helps repair vessels and trachieds that become damaged or non functional

Types of phloem cells?

1. Sieve cells- least specialized, arose early, main one, structurally similar to trachieds, thin elongated cells with tapering ends, have sieve areas (clusters of pores) through the cell wall that connects the protoplasts of neighboring cells (creates a free-flowing transport between cells as adjacent cells share plasma membranes

2. Albuminous cells- these surround the sieve cells, unload and loading cells to add or remove sugars from the sieve cells

3. Sieve tube element- more specialized, found in angiosperms, similar to vessel elements (sections of pipes stacked on top of eachother)

-> Stack on top of eachother to form sieve tubes have areas for flow of material these SIEVE TUBES have sieve plates which can be plugged if there's damage to the cell or to prevent a pathogen/virus from moving through the system

-> These elements are surrounded by COMPANION CELLS (act as loading/unloading cells for sieve tubes

5. Phloem fibers- long, thin cells, that have thick secondary cell wall, lack pit

Purpose of vascular cambium?

used for producing secondary phloem and xylem

-> produces secondary xylem inward

-> produces secondary phloem inward

What's the formation of the vascular cambium?

1. During primary growth, each vascular bundle has a fasciular cambium between the phloem and xylem

2. Parechnyma cells between bundles receive auxin, become meristematic and forms interfassicular cambium

3. Fasculiar and interfassicular merge and form one continuous ring of cambium and can divide as a lateral meristem and creates secondary growth

-> now this vascular cambium can be used for producing secondary phloem and xylem

What type of cells make up the vascular cambium?

1. Fusiform initials- longitudinal section of vasc cambium, when divided inward = produces 2nd degree xylem when outward= 2nd degree phloem

Perclinal- adds xylem+phloem

anticlinal- expands circumference

2. Ray initial- boxed shape, smaller cells that divide inward and outward to form a continuous ray, can also act as a storage cell

What tissues are found in secondary growth of angiosperms + gymnosperms?

1. Secondary xylem (wood)

Tracheids

Vessel elements

Xylem fibers

Xylem parenchyma

2. Secondary phloem

Sieve cells

Almbunious elements

Sieve tube elements

Companion cells

Phloem fibers

3. Periderm

Cork cambium (phellogen)

Cork (phellem)

Phelloderm

What's periderm and the layers

A protective outer layer that replaces the epidermis during secondary growth

1. Cork (phellem)

2. Cork cambium (phellogen)

3. Phelloderm

What are the functions of the components of the epidermis

1. Cork (phellem)

- Outermost unit

-Made of cells filled w suberin (waxy substance making impermeable to gas and water)

-Prevents water loss

-Protects against pathogens

-Dead at maturity

2. Cork cambium (phellogen)

-Can divide sideways (anticlincial- expand circumference)-> creates replication to increase girth

-Forms more and more layers of protective cork (just bark)

-Lateral meristem

-Produces new cells, outward= phellem; inward= phelloderm

3. Phelloderm

- Storage

- Contains living parenchyma cells (most common, unspecialized cells)

Difference between earlywood and latewood?

Earlywood=

Formed early in the growing season

Large cell lumens (internal space)

Thin cellwalls

Lower cell density

angio= larger vessels

gymo= wide tracheids

Good for rapid water transport

Efficiency over strenghth

Fast growth rate

Latewood=

Formed later in the growing season

small cell lumens (internal space)

thick cellwalls

high cell density

angio= smaller vessels

gymo= narrow tracheids

What's reaction wood? What are the 2 types?

Occurs when a tree is leaning/ bent, wind stress, snowload, when a tree needs to correct its position

Difference between compression wood and tension wood?

Gymno -> compression wood (push in reference to the centere of the trunk)

Angio -> tension wood (pull in reference to the centere of the trunk)

Formation of lenticels?

Cork cambium can go through intense division that creates buildges of cork tissue below the stomata -> this pressure/ expansion causes a bulge to rip open

What are the 3 root systems?

Taproot- one deep singular one, hard to remove

flat root- spread out, but shallow

Heartroot- in between

Why does asymmetrical cambial growth occur?

Happens due to slope/ gravity stress

Root buttressing- good anchoring system, "i" beams, large flared roots at the base of the trunk