Meristems and plant structure
Dec 21, 2015
Meristems and plant structure
The plant body
Apical Meristems: how the plant grows
Some basic cell types not mentioned yet
Cell walls and plasmodesmata
Apical meristems
Indeterminate growth
e.g., many tomato varieties
Determinate growthe.g., wheat
Biennial and determinate plants
Foxglove is a biennial
A rosette of leaves is produced close to the ground in the first year of growth
Digitalis purpureaTriticum aestivum
Like many grass species wheat is determinate. It produces a fixed number of leaves and a terminal inflorescence
Castor bean
Ricinus: Shoot apical meristem
Meristems: how tissues are produced
ColeusApical meristem
Transverse section through the apical meristem and newly forming leaves
Longitudinal section through the apical meristem
Myriophyllum SEM picture
Scanning electron microscope picture of Myriophyllum apical meristem
The apical dome is usually convex or flat, as in this example, and its surface is smooth.
Most recently budded leaves
Developing leaves cover the apex
Water-milfoil
Diagram of shoot apical growth
Cell division
Elongation zone
Differentiation of vascular
tissue
Auxiliary bud meristem
The auxiliary meristem may develop into a foliated branch.
Coleus
Equisetum meristem
Equisetum shoot apex with a single apical cell
The organization of the meristem is different from Coleus
Root apical meristem
Zea mays root apex
Zea mays root apex showing the junction between root apex and the root cap
Lateral root development in Zea mays
A meristem develops from parenchyma and the lateral root grows out through the cortex
… structural carbohydrates?
Cellulose
Cell walls and plasmodesmata
Microfibers
Electron microscope picture of cellulose-microfibrils in the wall of the green alga Oozystis solitaria
Growing plant cells expand through water uptake. In a growing cell enzymes weaken cross-links between the cellulose microfibres of the cell wall allowing it to expand as water flows in by osmosis.
Plasmodesmata
Plasmodesmata
Plasmodesmata seen in Section through the cell wall: They are not simple openings but have a complex internal structure.
Some basic cell types
2. Collenchyma
3. Sclerids
4. Bulliform cells
1. Parenchyma
1. Parenchyma
Young parenchyma tissue cut parallel with the epidermis of Euphorbia pulcherrima (poinsettia). Note the cell contents.
Note the nucleus and chloroplasts
2. Collenchyma
Apium petiole, collenchyma
Collenchyma is the typical supporting tissue of the primary plant body. It develops from parenchyma.
The cell walls are unevenly thickened.
It is common in organs like stems, petioles, laminae or roots.
Apium is celery – and it is the petiole that you eat!
Fig 31.5 B and C
3. ScleridsThickening of the cell wall
Parenchyma Developing sclerid
Sclerenchyma cells are the principal supporting cells in plant parts that have ceased elongation. Sclerenchyma fibres are the source material for many fabrics, e.g., flax, hemp and jute.
Note the wall laminations and the Pits around 3 & 5 o'clock. Viewed with polarized light
Contrary to collenchyma mature sclerenchyma is composed of dead cells with extremely thick cell walls (secondary walls) that make up to 90% of the whole. Leaf of Podocarpus
A sclerid with the cell completely occupied by wall
Fig 31. D
turgor pressure?
4. Bulliform cells Transverse section of grass leaf Poa praetense.
During drought water is lost from the thin walled bulliform cells and the two sides of the leaf blade fold up toward each other so the leaf is less exposed to sunlight and is heated less.
Once adequate water is available, turgor increases, and the leaves open again.
4.19, 31.1 through 31.8
Courses that deal with this topic
Sections you need to have read
Botany 441 Morphology and anatomy of land plants