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