MERISTEMATIC TISSUE • Meristems: - Permanent regions of active cell division - (undifferentiated plant tissue) • = plant “stem cells” • 3 types of meristematic tissues • Apical • Lateral • intercalary
Apical Meristems Found at the tips of roots and shoots. • Increase in length as the apical meristems produce new cells (primary growth). • Primary Meristems • Protoderm • Ground Meristem • Procambium
Lateral Meristems • Produce tissues that increase the girth of roots and stems. • Involved in Secondary Growth • Cork Cambium - Lies outside vascular cambium just inside the outer bark
Intercalary meristems • Develop at intervals along stems where they add to stem length.
TISSUES PRODUCED BY MERISTEMS • · Parenchyma • · Collenchyma • · Sclerenchyma
PARENCHYMA • Main type of cell making up the cortex • All plant tissues contain parenchyma. • Found in roots, stems and leaves. • Normally they are unsepcialized • Fx = act as a packing tissue which = can later be modified. Loosely packed (Called aerenchyma)
Parenchyma • Normally alive in maturity. • In leaves: the chloroplasts are found in parenchyma tissue (called clorenchyma) • When the cells are turgid, they provide important support and shape to the plant.
Similar to parenchyma in shape more elongated Can also be thickened in corners of cell wall (picture – right) Important in young plants, leaves, and older stems of non-woody plants wherever flexibility and support is important. COLLENCHYMA
COLLENCHYMA • Contains living cytoplasm • Fx = Provides flexible support for organs. • NB in young plants (< cellulose) – found beneath epidermis
SCLENENCHYMA • Cells with thick, tough, secondary walls • Normally impregnated with lignin. • < Flexible & stronger than collenchyma • Fx = mechanical (support ) & food storage. 2 TYPES OF CELLS (based on cell-shape) • Sclerids - Stone Cells • Fibers - Contain Lumen
Found in nut shells the hard part of seeds flexible floating leaf blades of water plants. Scleroids
Elongated & thick-walled with flattened ends. E.g. Fibres from flax and hemp are used to make fabric and rope. The fibres also store food like starch for the plant Sclerenchyma fibres
PLANT CONDUCTING TISSUE • 2 MAIN TYPES OF CELLS • Xylem • Phloem
XYLEM = Chief conducting tissue forwaterand mineralsabsorbed by the roots. 3 TYPES OF XYLEM TISSUE • Vessels - Made of vessel elements. • Long tubes open at each end. • Tracheids- Tapered at the ends with pits • Allows for water to pass between cells. • Rays - Lateral conduction of water and minerals.
Xylem Tracheid Xylem Vessel Element Xylem Vessels
Xylem Microscopy • Spiral thickenings in the secondary walls of vessels and tracheids gives them the appearance of microscopic coils under high magnification with a light microscope.
Vascular Conducting Cells • Conducting cells of the xylem; tracheids (left) are more primitive, while the various types of vessels (the other three) are more advanced.
PHLOEM • Fx = Conducts food materials produced by photosynthesis throughout the plant. Phloem cells as seen in longitudinal section. Note the longitudinal view of the sieve plate inside the large sieve tube cell
4 TYPES OF PHLOEM CELLS 1. Sieve Tube Members • (makes up the sieve-tube functional unit) • Large, cylindrical • Sieve Plates - Porous region 2. Companion Cells • Provide the energy needed for the long distance transport of food. • Also help determine the direction the food should be transported in. • Narrow, tapered
3. Parenchyma Acts mainly as a storage place for food. They store many secondary metabolites such as tannins, starch, crystals, etc. 4. Sclerenchyma Fibres are very common in phloem (scleroids less common)
OTHER PLANT TISSUES • Neither vascular nor meristematic • 2 TYPES • Epidermis • Periderm
EPIDERMIS • = Outermost layer of cells. (One cell-layer thick) * Most secrete fatty substance (cutin) on the surface of the outer walls. Forms cuticle. • Leave epidermal cells have stomata bordered by pairs of guard cells • Root epidermal cells produce root hairs
PERIDERM = Outer bark • Primarily composed of cork cells. • Lenticles: Living tissues under the cork layer (need oxygen) the periderm therefore possesses specialized pores for gaseous exchange called lenticles, made up of loosely packed parachyma cells with large air spaces. They protrude through the epidermis, and allows for adequate gaseous exchange.