Author: ass.-prof. Shanayda M.I.

Lecture 3VASCULAR AND MECHANICAL

TISSUES OF PLANTS. VASCULAR BUNDLES

At the last lecture were stadied different types of plant

tissues – the meristem, dermal, secretory and ground.

At present we are studying the VASCULAR

and MECHANICAL tissues of plants.

VASCULAR and MECHANICAL tissues of plants

contain 90 % of wood in trees

The tissues that supportsupport plant are called mechanical tissues. Their cells have thickening of walls in different directions. They belong to simple tissues, because include only one type of cells. There are two types of mechanical tissues…

MECHANICAL TISSUES

Collenchyma tissues are mainly found under the epidermis in young stems and in the large veins of leaves. The cells are composed of living, elongated cells. Collenchyma cells have thick cellulose cell wallscellulose cell walls. The cells sometimes

contain chloroplasts.

Types of collenchyma are classifiedclassified according to the according to the arrangement of arrangement of the the cell cell wall wall thickeningsthickenings and include:

angular collenchyma: cell wall is thickest in the corners (in herbal parts of plants).

lamellar collenchyma: cell wall is thickest on two opposite sides (in the bark)

lacunar collenchyma: cell wall is thickest in

the corners, intercellular air

(in water plants)

Sclerenchyma tissues have the rigid thick secondary cell

walls with lignin. They support nonextending

regions of plants such as mature stems, and are usually dead.

Sclerenchyma also makes up the hard outer covering of seeds and

nuts. Cell walls are usually lignified.

Sclerenchyma tissues have the rigid thick secondary cell

walls with lignin. They support nonextending

regions of plants such as mature stems, and are usually dead.

Sclerenchyma also makes up the hard outer covering of seeds and

nuts. Cell walls are usually lignified.Types of sclerenchyma are clasclassifiedsified

according to cell shapeaccording to cell shape and include fibers and sclereids

1) fibers are long, straight and thin, often occurring in vascular bundles.

Usually fiber cells are much longer than they are wide and have a very tiny cavity

in the center of the cell.

2) Sclereids are variable in shape, but not like fibers. Types are classified according to shape and include the following:

brachysclereids: also called stone cells, their length and width are nearly equal.astrosclereids: star shaped, with several projecting arms.trichosclereids: hair-like, similar to a fibers, except branched.osteosclereids: bone shaped, elongated with swollen ends.macrosclereids: column shaped

Groups of brachybrachysclereidssclereids (3,4)

on cross section of the oak-treeoak-tree bark bark

The VASCULAR TISSUES are specialized for long-distance. Xylem and phloem are two the most important complex tissues in a plant, as their primary functions include the transporttransport of water, dissolved minerals and soluble food substances (photosynthate) throughout the plant.

The VASCULAR TISSUES

Xylem and phloemXylem and phloem

XYLEM conducts water and dissolved minerals from the roots to all the other parts of the plant ((xxylem is the water-ylem is the water-conducting tissue of plantsconducting tissue of plants)). .

Xylem is a complex tissue composed of xylem vessels (or tracheids), fibers and parenchyma cells:

VVessel elementessel elementss are the are the longlong tubetube with perforation plates. with perforation plates. Xylem vessels of Angiosperm

are deposited in spirals and rings and are usually perforated by pits.

Tracheids are the conducting elements that lack perforations plates (there are pits).

The xylem of Conifers contains only tracheids.

2) Libriform fibers are the cells of mechanical tissue in the xylem. They are very long and dead.

Their functions are to serve as supporting

elements of xylem. 3) Xylem parenchyma cells

are alive and have thin wall. They distinct

the intercellular spaces.

SUMMARY …SUMMARY …

PHLOEM is the photosynthate-conducting tissue of plants.

Phloem is a complex tissue composed of sieve elements, companion cells, long fiber elements and parenchyma cells. The main components of phloem are sieve elements and companion cells.

1)Sieve elements are the conducting cells in the phloem.

They are with perforation plates and without secondary wall.

Sieve elements have no nucleus and depend on the adjacent companion cells

for many functions. Companion cells are cells

in the phloem that is connectedto a sieve-tube member by

numerous plasmodesmata. They have a nuclei.

The phloem of Conifers has no companion cells.

SUMMARY …SUMMARY …

The VASCULAR BUNDLESThe VASCULAR BUNDLESThe xylem and phloem are the two most important complex tissues

in a plant and situated in organs of plants together as vascular bundles. Sometimes they contain a vascular cambium (the lateral meristem).

The VASCULAR BUNDLES are classified according to special relationships of

xylem and phloem. There are several types of vascular bundles. All these types are

typical for some taxonomical categories some taxonomical categories ((divisions, classes, families) and different different

plant organsplant organs::

Div

isi

on

o

f...

Div

isi

on

o

f...

Div

isio

n

of.

..

Dicotyledonous class

Div

isi

on

of

Gre

en

alg

ae

The Poppy Family

The Grass Family

Monocotyledonous class

Div

isi

on

o

f...

Div

isi

on

o

f...

Div

isi

on

o

f...

Div

isi

on

o

f...

KINGDOM OF PLANTS

Div

isi

on

of

An

gio

sper

m

Collateral bundles have xylem on one side and phloem on the other side. There are close and

open collateral bundles: opened collateral vascular bundle (with cambium) formed in

stems of Dicotyledon plants (1); closed collateral vascular bundle (without

cambium) formed in stems and leaves of Monocotyledon plants (3);

Bicollateral bundles have phloem on both sides of the xylem; they also have cambium

(formed in stems of pumpkin (2),

Concentric bundles are common only for rhizomes (underground shoot modifications). They are divide to:

Centerphloem amphivasal – if xylem surrounds the phloem (in Monocots – (4),

Centerxylem amphicribral – if phloem surrounds the xylem (in Ferns – (5)

Radial bundles have xylem occurs occurs in radial directions, and phloem takes placetakes place between them

(in young roots with primary structuraein young roots with primary structurae). Radial polyarch vascular bundle is typical only for roots of Monocot plants. Dicot have radial tetraarch or tryarch vascular bundle.

GLOSSARY OF TISSUES OF THE PLANT BODY

1. MERISTEMS produce all types of permanent tissues. There are general zone in which cell dividing is frequent.

2. DERMAL TISSUES cover the surface of the plant body and protect it. There are alive and

dead complex tissues.

3. GROUND TISSUES SYSTEM are simple tissues composed of alive cell. They can

accumulate of storage products, air and photosynsate.

4. SECRETORY STRUCTURES produce different solutions, can be of outer and inner forms.

5. MECHANICAL TISSUES….6. VASCULAR TISSUES …

KROK-1 test questionsThe stems microscopically analysis revealed complex tissue that

consists of sieve tubes with companion cells, fibers and parenchyma. This is... A periderm

B cork C xylem

D phloem E epidermis

The investigation found that rising transport of dissolved minerals is provide by...

A Sieve elementsB. Vessels and tracheids

C Libriform fibersD. Angular collenchyma

E. Fiber phloem elementsWhat type of vascular bundle is typical for the primary structure of root?

A RadialB Concentric

C Сollateral closed D Bikollateral

E Сollateral open