plant histology 2

8/13/2019 Plant Histology 2

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Plant Histology II


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Primary Growth


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MERISTEMATIC TISSUE

Meristems: - Permanent regions of active cell division- (undifferentiated plant tissue)

= plant stem cells

3 types of meristematic tissuesi. Apical

ii. Lateraliii. intercalary


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Apical Meristems

Found at the tips of roots and shoots. Increase in length as the apical meristems

produce new cells (primary growth).

Primary Meristems

ProtodermGround MeristemProcambium


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Lateral Meristems

Produce tissues that increase the girth ofroots and stems .

Involved in Secondary Growth

Cork Cambium - Lies outside vascularcambium just inside the outer bark


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Intercalary meristems

Develop at intervals along stemswhere they add to stem length.


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TISSUES PRODUCED BYMERISTEMS

Parenchyma Collenchyma Sclerenchyma


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Cross Section of a Stained Leaf


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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)


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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.


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COLLENCHYMA

Similar to parenchymain shape

more elongated Can also be thickened in

corners of cell wall(picture right)

Important in youngplants, leaves, and olderstems of non-woodyplants whereverflexibility and support isimportant.


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COLLENCHYMA

Contains living cytoplasm Fx = Provides flexible support for organs. NB in young plants (< cellulose) found

beneath epidermis


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Stained & unstained chollenchymacells


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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


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Scleroids

Found in nut shells

the hard part of seeds flexible floating leafblades of water plants.


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Stone cells in pear fruit


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Sclerenchyma fibres

Elongated & thick-walled withflattened ends.

E.g. Fibres from flaxand hemp are usedto make fabric andrope.

The fibres also storefood like starch forthe plant


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Sclerenchyma: Astroscleroidal & Fibre Cells


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PLANT CONDUCTING TISSUE

2 MAIN TYPES OF CELLS Xylem Phloem


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Xylem & Phloem Cells


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XYLEM

= Chief conducting tissue for water and minerals absorbed 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.


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Xylem Vessels

Xylem Tracheid Xylem Vessel Element


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Xylem Microscopy

Spiral thickenings in the secondary walls of vessels and tracheids givesthem the appearance of microscopic coils under high magnification with alight microscope.


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Vascular Conducting Cells

Conducting cells of the xylem; tracheids (left)are more primitive, while the various types ofvessels (the other three) are more advanced.


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PHLOEM

Fx = Conducts food materials produced byphotosynthesis throughout the plant.

Phloem cells as seen inlongitudinal section.Note the longitudinalview of the sieve plateinside the large sievetube cell


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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 foodshould be transported in. Narrow, tapered


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Phloem Cells


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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)


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Longitudinal View of Phloem Cells


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Microscopy: Phloem Cells


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OTHER PLANT TISSUES

Neither vascular nor meristematic

2 TYPES Epidermis Periderm


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EPIDERMIS = Outermost layer of cells. (One cell-layer thick)

* Most secrete fatty substance (cutin) on thesurface of the outer walls.Forms cuticle.

Leave epidermal cells have stomata bordered bypairs of guard cells

Root epidermal cells produce root hairs


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EPIDERMIS


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PERIDERM= Outer bark

Primarily composed of cork cells.

Lenticles: Living tissues under the cork layer(need oxygen) the periderm therefore possessesspecialized pores for gaseous exchange calledlenticles, made up of loosely packed parachymacells with large air spaces. They protrude throughthe epidermis, and allows for adequate gaseousexchange.


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PERIDERM

plant histology 2

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