PLANT
TISSUE STRUCTURE
As stated
earlier, an examination of any animal or plant shows that it is composed of a
single cell or many cells. But when one examines the cellular nature of any
higher animal or plant, he is at once impressed with the fact that not all of
the cells are alike there are many kinds of cells. In development of any higher
animal or plant from a single cell,the early mitosis result in a mass of cells
that are essentially alike.But as the process of development goes on,cells in
different regions of the developing mass gradually assume different shapes.We
say that cells differentiation takes places.These differentiated cells are
unlike in structure and function and they constitute the different
tissues.Tissues differentiation in multicellular organisms results in a
division of labor among the cells. A simple tissue is a group of like cells
that are structurally modified to perform a particular function. Plant cells
are formed at meristems, and then develop into cell types which are grouped
into tissues. Plants have only three tissue types: 1) Dermal; 2) Ground; and 3)
Vascular. Dermal tissue covers the outer surface of herbaceous plants. Dermal
tissue is composed of epidermal cells, closely packed cells that secrete a waxy
cuticle that aids in the prevention of water loss. The ground tissue comprises
the bulk of the primary plant body. Parenchyma, collenchyma, and sclerenchyma
cells are common in the ground tissue. Vascular tissue transports food, water,
hormones and minerals within the plant. Vascular tissue includes xylem, phloem,
parenchyma, and cambium cells.
All tissues of the plant body can be placed
into two categories: the meristems and the permanent tissues. The
meristematic ones are those composed of cells that are capable of undergoing division.
These are conspicuous where growth in size is taking place, at the tips of
stems and roots, and laterally just outside the wood, as in the woody stem or
root. These cells remain in definitely as young and undifferentiated cells, and
are physiologically embryonic, as are the cells of the developing embryo. The
cells of this kind of tissues may become inactive at times, but when conditions
are favorable, they function directly or indirectly in building up the various
parts of the plant body.
As they become
mature, all the tissues derived from the meritematic tissues are considered
permanent. This means that although individual cells may undergo minor changes
as they age, their basic makeup remains the same. There simple permanent
tissues can be recognized: parenchyma, collenchyma, and sclerenchyma.
Plant tissue is
formed from plant cells that undergoing division, magnification, and
differentiation. Based on its ability to split, plant tissue is grouped into,
those are meristematic tissue and permanent tissue.
1.
Meristematic tissue
Meristematic
tissue is often called embryonic tissue or basic tissue. It is called embryonic
tissue because its cell always make fision to multiply theirself. Meanwhile it
is called basic tissue because after mature, this tissue will form another
tissues.
Meristematic
tissues has several characteristics those are : its cells have thin wall, its
shape and size of cell are equal, its relatively rich of protoplasm, the
content of its cell does not contain crystal and food reservation, commonly it
has very small cell cavity.
Based on its
origin, meristematic tissue is separated into two those are: primary and
secondary meristem
a. Primary
Meristem
Primary meristem
is a meristem that its cell are direct development of embryonic cells so the
advance of embryonic vessel. Its example is in stem tip bud and the tip of
root.
Meristem found
in the tip of stem and the tip of root is called also apical meristem. The
activity of this meristem causes stem and root grow enlengthen. Growth caused by
the activity of primary meristem is called primary growth.
b. Secondary
Meristem
Secondary
meristem is a meristem that comes from adult tissue that has made
differentiation, such as cambium and cork cambium that happens from parenchyma
and collenchyma.
Cambium in root
and stem of dicotyledon plant is found in the bundle of transport vascular
called vascular cambium. Besides there is also cambium found between two
bundles of transport vascular called intervascular cambium.
Cambium will
produce transport tissue. Meanwhile the cork tissue will produce cork. The
activity of secondary meristem causes plant´s body becomes big. Growth caused
by the activity of secondary meristem it is called secondary growth.
2.
Permanent tissue
Permanent
tissue is a tissue that has undergone differentiation. This tissue has specific
characteristics, those are : its cell wall has undergone thickening, the shape
of its cells are relatively permanent, commonly it does not make fission
anymore, it has big cell cavity.
Based on its
shape or function, permanent tissue is separated into:
a) Epidermis
tissue
This tissue is that
is located most outer so covers all of plant body surface. Epidermis tissue can
be found in the surface of root, stem, fruit, leaf, and flower. Epidermis
tissue has main function to protect tissue inside of it. Another function is to
protect of mechanical destruction, keep tissue temperature for not too high,
and
prevent the
excessive vaporization. Epidermis tissue is found in root has function to suck
water and mineral salts. In the several places epidermis cells of leaf make
modification to be leaf cover cell (stomata). Meanwhile stem e pidermis of
dicotyledon makes modification to be lenticel.
The
characteristics of epidermis tissues areas follows:
-
The shape of its cell is like cuboid, consist of one
layer of cell, and commonly it has no chlorophyll.
-
Commonly it is covered by wax layer or cuticle. The
presence of these wax layer and cuticle have relationship with its function to
protect tissue inside of it.
-
In several kind of plant epidermis make modification to
be scale or hair.
-
The outer part of cell wall of root epidermis that
still young will grow to form root hair that has function to absorb mineral
substances.
b) Parenchyma
tissue
This tissue is
called also basic tissue because formed from basic meristem. Parenchyma tissue
can be found mainly in the stem skin, root skin, leaf meat, fruit meat and
endosperm.
Parenchyma
tissue is composed of living cell that shape, size, or its physiological
function are different. But cells do not much undergo specialization. Ability
to split of parenchyma cell is keep owned until adult, it has purpose to do
regeneration or repairment of broken
body. The ability of parenchyma cell to make fission unti adult is enabled
because its protoplasm is very complex. Parenchim cell has various shape, some
are round of box shaped, enlegthen lumping each other, and some like star.
Commonly has intercellular spaces that is composed regularly with certain
system.Parenchyma cells some have chlorophyll, called chlorenchyma cell. The
presence of cholorophyl cause chlorenchyma has ability to make photosynthesis.
Cholorenchyma cell is many found in leaf stem cortex, andsometime pith.
Parenchyma cell also has function to
store water, synthesize, and store food reservation mainly is found in
parenchyma in root such as in potato and wood tuber. Meanwhile parenchyma cell
that has has function to store water, commonly active cell, enlarges and has
thin wall, it has many small vacuoles that contain water or mucilage, and its
cell plasma membrane is thin sticks to cell wall. Specialized parenchyma is
found in aquatic plants that require flotation for their leaves. The open,
air-filled parenchyma tissue in these leaves is called aerenchyma.
c) Supporter
or strengthener tissue
This tissue
consists of collenchyma and schelerenchyma tissue that has difference in their
thickening. If collenhyma tissue is thickened by cellulose, the schelerenchyma
tissue is thickened by wood substance (lignin). The main function of this
tissue is to support or strengthen the part of plant´s body.
1. Collenchyma Tissue
Cells that
compose this tissue are living cells with active protoplasm. Its cell wall can
undergo thickening by cellulose. Its cell contains chloroplast where the
simpler it differentiation then the more its chloroplast, even ir is like
parenchyma. Shape of parenchim cells are
be enlengthen, happen non uniform thickening of cell wall, and has
plastic property. Plastic means can be enlengthened but cannot be shortened
back.
Collencim
tissue commonly is formed under epidermis tissue, but some also separated from
epidermis by several layer of parenchyma. This tissue i s many found in
dicotyledon plant still young. Function of this tissue is to strengthen the
standing of plant.
2.
Schlerenchim Tissue
This tissue is
strengthener tissue that is thickened by lignin so this tissue is very strong.
Schlerenchim tissue is separated into two kinds, those are schlereid and fiber.
Schlereid
(stone cell) comes from parenchym tissue that its wall experiencec layered
thickening. Commonly it consists of short cell with its cell wall many has
spot, it is found in the various part of the body. Its cell can gather to be hard tissue between soft
tissue or compose all of hard building, such as seed skin. Schlereid cell often
appear clearly from cells that surround it, whether shape, size or thickness of
its cell wall. It cell wall can be separated into five kinds, those are
surrounding, like bar, like femur, like star, and branched long. Schlereid tissue
is many found in the hard fruit skin, such as in coconut fruit.
Fiber. Fiber
that comes from meristematic tissue, commonly it consist of long cell. The most
make group to form ribbon, plaited materials, or dense fabric. Fiber is
commonly found in transport bundle, that is around xylem and phloem, but same
also found between parenchyma. Fiber found around the phloem of several
dicotyledone plants have high economical value because it can be used as raw
material to make clothes thread, string, and sac. In monocotyledone plant,
fiber can found in leaf, such as in the stem of banana leaf, opposite pineapple
and so on.
This tissue has role
to make transport function or substance transportation. Transportation tissue consists of xylem and
phloem. Xylem and phloem are never separate itself but together it called
transportation bundle. Xylem is located inside phloem.
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Xylem is a
term applied to woody (lignin-impregnated) walls of certain cells of plants.
Xylem cells tend to conduct water and minerals from roots to leaves. While
parenchyma cells do occur within what is commonly termed the
"xylem" the more identifiable cells, tracheids and vessel elements,
tend to stain red with Safranin-O. Tracheids are the more primitive of the
two cell types, occurring in the earliest vascular plants. Tracheids are long
and tapered, with angled end-plates that connect cell to cell. Vessel
elements are shorter, much wider, and lack end plates. They occur only in
angiosperms, the most recently evolved large group of plants
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Xylem
cells
 Tracheids,
longer, and narrower than most vessels, appear first in the fossil record.
Vessels occur later. Tracheids have obliquely-angled endwalls cut across by
bars. The evolutionary trend in vessels is for shorter cells, with no bars on
the endwalls.
Conducting
cells of the xylem; tracheids (left) are more primitive, while the various
types of vessels (the other three) are more advanced. Image from Purves et
al., Life: The Science of Biology, 4th Edition, by Sinauer Associates
and WH Freeman, used with permission.
Conductive
Vessel Element in Mountain Mahogany Wood (SEM x750). This image is copyright
Dennis Kunkel .
Phloem
Phloem cells
conduct food from leaves to rest of the plant. They are alive at maturity and
tend to stain green (with the stain fast green). Phloem cells are usually
located outside the xylem. The two most common cells in the phloem are the
companion cells and sieve cells. Companion cells retain their nucleus and
control the adjacent sieve cells. Dissolved food, as sucrose, flows through
the sieve cells.
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e) Cork
tissue
Cork tissue is
composed of cells that have waterproof property. This is adjusted with its
function that is to protect another tissue for not losing much water. In
dicotyledon plant, cork tissue is formed by phellogen or cork cambium.
The
formation of cork tissue inward is called pheloderm. Pheloderm is living cell.
Meanwhile the formation of cork tissue outward is called phellem. Phellem is
dead cell.
Cork cambium (pl.
cambia or
cambiums)
is a
tissue found in many vascular plants as part of the
periderm. The cork cambium is a lateral
meristem and is responsible for secondary growth that replaces the
epidermis in roots and stems. It is found in woody and many herbaceous
dicots,
gymnosperms and some
monocots, which usually lack secondary growth.
Cork cambium is one of the plant's meristems – the series of tissues
consisting of embryonic (incompletely differentiated) cells from which
the plant grows. It is one of the many layers of
bark, between the cork and primary
phloem. The function of cork cambium is to produce the
cork, a tough protective material.
Synonyms for cork cambium are
bark cambium,
pericambium and
phellogen.
Phellogen is defined as the meristematic cell layer responsible for the
development of the periderm. Cells that grow inwards from the phellogen
are termed
phelloderm, and cells that develop outwards are termed
phellem or cork (note similarity with vascular cambium). The periderm thus consists of three different layers:
- phelloderm – inside of cork cambium, composed of living parenchyma cells
- phellogen (cork cambium) – meristem that gives rise to periderm
- phellem (cork) – at maturity, dead, air-filled protective tissue on the outside
Growth and development of cork cambium is very variable between
different species, and also highly dependent on age, growth conditions
etc. as can be observed from the different surfaces of bark: smooth,
fissured, tesselated, scaly, flaking off, etc.
References
Raven, Peter H.; Evert, Ray F.; Curtis, Helena (1981), Biology of plants, New York, N.Y.: Worth Publishers, pp. 427–28,
http://www.britannica.com.
e.com
http://en.wikipedia.org/wiki/Cork_cambium
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