Download 3. Meristems

*
PLANT TISSUES I.
PLANT HISTOLOGY = TISSUE SYSTEMS
OF THE PLANT
Plants = capable of constant growth – meristems
Zygote: totipotent  differentiation (special cell shapes and functions)
Tissues appear: Cormophyta (vascular plants)
TISSUE: cell groups of same origin, same function
TISSUE SYSTEM: common origin, cell groups with slightly different
function
PLANT TISSUES:
1. meristems
2. dermal tissues
3. vascular tissues
4. ground tissues
MERISTEMS
Order of appearance:
I. Promeristems
• shoot tips, root tips
• initial cells – totipotent
II. Primary meristems  Mature plant tissues
• dermal tissue forming primary meristem
• vascular tissue forming primary meristem
• ground tissue forming primary meristem
III. Secondary meristems
reembrionalisation
- dedifferentiation
- redifferentiation
MERISTEMS
Position:
•
•
•
•
Apical meristems (shoot and root tips)
Lateral meristems (e.g. cambium, cork cambium)
Intercalary meristems (grass stems – base of internodes)
Meristemoids
cross section of root tip - onion
fascicular cambium – Aristolochia clematitis
stem cross section
bean root
onion root
maize aerial root
onion root
MERISTEMS
Cytological features of meristematic cells:
- large nucleus, protoplasm
- thin cell wall
- closely packed cells, no intercellular
- little endoplasmic reticulum, few mitochondria
- many ribosomes
- small, simple vacuoles, proplastids
- shape: isodiametric, prosenchymatic
initial cells of root tip