Plant Anatomy
= the study of plant cell and tissue structure

Plant cell structure
“Cell” - originally coined by Robert Hooke, in 1600’s. Cell theory: 1) All life made of cells 2) Cells arise from pre-existing cells 3) Cells units of metabolism 4) Cells contain complete DNA, hereditary substance.

Cell structure

Ergastic substances = by-products of metabolism

amyloplasts - starch grains = polymer of alpha-glucose

2 forms of glucose

Ergastic substances

chromoplasts - pigmented bodies, composed of carotenoids (e.g., carotene); cause red/orange coloration.

carotene when hydrolysed, yields two vitamin A molecules: carotene ---> vitamin A + vitamin A function in plants is pigmentation, however

carotene
+ 2 H2O

2 vitamin A

Ergastic substances raphides druse

crystals - calcium oxalate (e.g., raphides/druses) or silica - waste/metabolic products or protective (deter herbivory)

Ergastic substances aleurone grains - protein (storage) tannins - phenol derivatives (deter herbivory, deter infection) fats, oils, waxes - tri-/di-glyerides (storage, secretion)

Cell structure
Cell wall Primary (1˚) cell wall Formed during growth/expansion of cells Made up mainly of cellulose = polymer of beta-glucose units Plasmodesmata Holes in 1˚ cell wall, allow for cell to cell communication

cell wall: cellulosic plasmodesmata

cellulose: beta form of glucose

Cellulosic cell wall made of cellulose microfibrils

Cell structure
Cell wall Secondary (2˚) cell wall Formed after growth/expansion of cells, inside original primary cell wall Made up mainly of lignin = polymer of phenolic units hard subtance Pits - holes in secondary cell wall

lignin - secondary cell wall

Secretory cells

laticifers - cells that secrete latex, containing isoprenes (e.g., rubber)

glandular trichomes, oil ducts secrete oils

Plant growth
Meristems - actively growing regions of plant Primary meristems Root apical meristems Shoot apical meristems Meristems - cell division - cell elongation - cell differentiation

root apical meristem

leaf primordium

apical meristem

SHOOT

cell division

cell elongation

Cell differentiation
Results in different cell and tissue types Tissue = 1 or more cell types having a common origin or function

Epidermal cell
- outer layer of all plant organs - in land plants, protected by outer cuticle
- cuticle helps to prevent dessication

cuticle - protective layer on outside - helps prevent water loss

parenchyma
• - living at maturity • - involved in metabolic reactions

parenchyma

nucleus

collenchyma
• - cells living, elongate • - cell walls unevenly thickened, rich in pectins [pectin - complex polysaccaride, mainly of galacturonic acid units]

• - functions in structural support
(while stem is still elongating)

collenchyma pectic-rich cell walls

sclerenchyma
- cells dead at maturity - thick, secondary, lignified cell walls - functions in structural support 2 cell types: fibers - very long, thin, tapered sclereids - variable in shape, mostly isodiametric

2˚ cell wall 2˚ cell wall

pits

a) fiber

b) sclereids

xylem
• -function: conduction of water and minerals • -consists of:
– parenchyma – fibers – tracheary elements (2 types: tracheids and vessels) actual conductive cells dead at maturity joined end to end, form pipe-like conduits lignified secondary cell walls with pits

vessel

perforation plate

phloem
-function: conduction of sugars -consists of: parenchyma fibers sieve elements (2 types: sieve cells or sieve tube members)
- actual sugar-conductive cells - semi-live at maturity (lose nuclei, but have cytoplasm) - primary cell-wall only - have callose-lined pores (making up a sieve plate or sieve area), through which sugar sol. passes

sieve tube member

callose-lined pore

sieve plate

Plant organs root - absorptive, anchoring, storage organ shoot = stem + associated leaves stem - conductive, supportive, storage organ leaf - photosynthetic organ bud = immature shoot, gen. arising from leaf axile; ---> lateral branch

root cap

ROOT (l.s.) 1) Protective root cap 2) Absorptive root hairs

root apical meristem

ROOT (c.s.) 3) Give rise to new roots endogenously (from within)

Casparian Strip
Function: forces fluids from outside through plasma membrane = selective absorption

SPOROPHYTIC SHOOT

STEM - has discrete vascular bundles (xylem & phloem)

eustele
STEM (of Eudicot)
-bundles in a single ring

STEM fiber “bundle” or “cap”

phloem xylem

Monocots stem with many scattered bundles (atactostele) vascular bundles ground meristem

Leaf anatomy

2 guard cells

stomate: controls gas exchange of CO2 & H2O

C3 photosynthesis: Normal type

C4 photosynthesis:
PEP (C3) + CO2 --> Malic acid (C4) [Mesophyll] Malic acid --> CO2 + PEP (C3) [B.S.C.]

Kranz anatomy (in C4 plants): enlarged Bundle Sheath Cells w/ large chloroplasts

CAM photosynthesis: CO2 fixed at night
(stomates open), released in day (stomates closed)