4 - 5: Meristems and Fundamental Tissues

Promeristem

The initiating cells (initials) and their most recent derivatives in an apical meristem; the least differentiated, or determined, part of an apical meristem

Primary Meristem

- Produces tissues of the primary plant body
partly differentiated tissues such as protoderm (epidermis), procambium (vascular cambium), ground meristem (ground tissue)

meristem

actively dividing cells

1. dense cytoplasm (bc metabolically active)
2. lack large vacuoles (nucleus still in the middle)

meristem characteristics

Apical Meristem

Shoot and Root Tips; function is to produce the primary plant body for primary growth

Vascular Cambium (eudicots, gymnosperms)

Cork Cambium

Lateral Meristems for 2ndary growth - thickness

Tunica - outer layer; anticlinal plan perpendicular to surface - SQUARE CELLS
Corpus - inner layer; both anticlinal and periclinal (parallel to plane) surface - ROUND CELLS

Tunica corpus theory of the shoot apex

periclinal plane

division plane for addition of cells

anticlinal plane

division plane for increase in circumference

tunica

gives rise to leaves and buds, epidermis and most of the cortex

corpus

gives rise to vascular system; central ground system

procambial strand

gives rise to first xylem and primary phloem in the apex

root apex

where there is no tunica-corpus

calyptrogen

meristem that produces the root cap

root cap

serves as protection of the soft apical meristem from soil particles

root apex

source of regulating substances involved in positive geotropic response

root hair

tiny hair-like extensions that increase the surface of the root allowing it to absorb more water and nutrients

region of maturation/differentiation

region where root cells become more specialized (green)

region of elongation

where root cell vacuoles begin to increase in size (blue)

region of cell division

composed of apical meristem in the center of root tip (red)

exogenously

how are leaves and buds produced; coming from the outside

endogenoously (pericycle)

how lateral roots arise

derived from apical meristems

origin of primary meristems

protoderm

gives rise to epidermis

procambium

gives rise to vascular tissue

ground meristem

gives rise to the ground tissue

leaf primordia

leaf originating from shoot apex (coming from the outside)

A - leaf primordia/ procambium

B - Corpus/ground meristem

C - ground meristem

D - trichomes
E - tunica

F - younger leaf primordium

G - ground meristem

H - axillary bud

vascular tissue

label the shoot apical meristem

label the RAM

vascular cambium

cylinder of thin-walled cells that forms secondary vascular tissue

bark

tissues external to the vascular cambium; secondary phloem outward

vascular cambium - 2ndary x and p
procambium - primary x and p

constituent cells of vascular cambium vs procambium

-ray cells

-fusiform initials

vascular cambium cells

ray initials; also known as xylem rays and phloem rays.

Cambium cells that produce radial files of parenchyma cells

fusiform initials

tapered, elongated cells that divide periclinally and give rise to 2X and 2P

- initial - remains meristematic
- derivative - becomes matured cell

vascular cambium cells

multiplicative division

anticlinal; involved in increase of meristem circumference (perpendicular)

additive division

periclinal; more X and P in plant body (parallel)

phellogen

other word for cork cambium

cork cambium

one type of initials (laging meristematic)

phellem or cork cells (outer side) and phelloderm (inner side)

cork cambium divides to form which cells?

cork cells/phellem

suberized; protection (form periderm)

periderm

cork + cork cambium + phelloderm; replaces epidermis

2ndary meristems

Another name for some of the lateral meristems

primary meristems are derived from meristems
secondary from mature cells

primary vs 2ndary meristem origin

from being permanent, can reverse back to being meristematic —> dedifferentiation

what can be considered a true secondary meristem

cork cambium

true secondary meristem

parenchyma/collenchyma near the epidermis or deeper into the cortex

origin of cork cambium

vascular cambium

not a true secondary meristem

- procambium (meristem)
- interfasicular parenchyma (mature tissue)

origin of the vascular cambium

simple

one type of cell E.g. parenchyma

complex

more than one type of cell E.g. xylem

parenchyma

• Most common type
• Alive at maturity
• Least specialized
• Thin-walled
• Isodiametric

1. Space fillers
2. Basic metabolism
3. Storage

functions of parenchyma

collenchyma

• Usu. elongated
• Alive at maturity
• Uneven thickening of primary walls
• Large amount of pectins and hemicelluloses

Provide flexible (plastic) support in growing organs and mature herbaceous organs

function of collenchyma

usually in cortex, just beneath epidermis

location of collenchyma

sclerenchyma

• Have secondary walls (+lignin)
• Dead at maturity; loses protoplast, forms lumen

1. Elastic support for regions that have stopped growing in length
2. Water conducting tissues

functions of sclerenchyma

sclerenchyma fibers

• Long cells and tapered at both ends
• Less pittings
• Arise from meristematic cells
• Usually occur in groups

sclerenchyma sclereids

• Usu. cubical or spherical
• More conspicuous pittings
• Sclerosis of parenchyma cells
• Isolated or scattered