Meristems and plant structure The plant body Apical

Meristems and plant structure The plant body Apical

Meristems and plant structure The plant body Apical Meristems: how the plant grows Cell walls and plasmodesmata Some basic cell types not mentioned yet

Apical meristems Indeterminate growth e.g., many tomato varieties Determinate growth e.g., wheat

Biennial and determinate plants Digitalis purpurea Foxglove is a biennial A rosette of leaves is produced close to the

ground in the first year of growth Triticum aestivum Like many grass species wheat is determinate. It produces a fixed number of

leaves and a terminal inflorescence Ricinus: Shoot apical meristem Castor bean Meristems: how tissues are produced

Coleus Longitudinal section through the apical meristem Apical meristem Transverse section through the

apical meristem and newly forming leaves ater-milfoil Scanning electron microscope picture of Myriophyllum apical meristem

Myriophyllum SEM picture The apical dome is usually convex or flat, as in this example, and its surface is

smooth. Developing leaves cover the apex Most recently budded leaves Diagram of shoot apical growth

Cell division Elongation zone Differentiation of vascular tissue

Coleus Auxiliary bud meristem The auxiliary meristem may develop into a foliated branch. 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 cellulosemicrofibrils 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 1. Parenchyma 2. Collenchyma 3. Sclerids 4. Bulliform cells

1. Parenchyma Note the nucleus and chloroplasts Young parenchyma tissue cut parallel with the epidermis of Euphorbia pulcherrima (poinsettia). Note the cell contents.

2. Collenchyma Collenchyma is the typical supporting tissue of the primary plant body. It develops from parenchyma. The cell walls are unevenly thickened.

Apium petiole, collenchyma 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. Sclerids Thickening 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.

A sclerid with the cell completely occupied by wall 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 Note the wall laminations and the Pits around 3 & 5 o'clock. Viewed with polarized light 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 Sections you need to have read 4.19, 31.1 through 31.8 Courses that deal with this topic

Botany 441 Morphology and anatomy of land plants

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