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Monday, March 29, 2010

Plant:Meristematic and Permanent tissue

Monday, March 29, 2010
Plant:Meristematic and Permanent tissue
TISSUE:
A tissue is defined as group of similar or dissimilar cells which perform or help to perform a particular functions and have a common origin.
TYPES OF TISSUE:
Broadly,plant tissues are categorized into two categories:
1)MERISTEMATIC TISSUE:
The tissue which is composed of immature and undifferentiated cells which are either in a continuous state of division or retain the power of division is known as meristematic tissue.The cells produced by meristem later transform into permanent cells.
CHARACTERS OF MERISTEMATIC TISSUE:
1)Meristematic tissue are composed of immature,undifferentiated cells which are in the state of division and growth.
2)Usually the intercellular spaces are absent.
3)All cells are living and thin walled.
4)Cells may be round,oval or hexagonal in shape.
5)Cells don't posses reserve food vaculoes and if present are very small in size.
6)Cytoplasm is quite abundant and one or more nuclei may be present.
7)Plastids are in the form of proplastid.
TYPES OF MERISTEMATIC TISSUE:
On the basis of origin and development,meristematic tissue is of following type:
1)PRIMARY MERISTEM:
The meristematic tissue which is primary in origin and is present in the plant right from the beginning is called primary meristem.The pro meristem is always the initial stage of primary meristem.The cells of primary meristem undergo continuous division and transform into primary permanent tissue which make up the basic part of plant primary body.
The intrafascicular cambium of dicot stem though primary in origin give rise to secondary permanent tissue.
2)SECONDARY MERISTEMATIC TISSUE:
The tissue which is secondary in origin i.e it develops at the later stage of development of plant body usually at the time of secondary growth is knowm as secondary meristematic tissue.In specific areas of plants origin some of the primary plant cells acquire the power of division and become meristematic.Thus it is called secondary meristem.
The interfasicular cambium of dicot stem and cork cambium of dicot stem along with root are best example of secondary growth.

On the basis of position in the plant,Meristematic tissue is of following type:
1)APICAL MERISTEMATIC TISSUE:
The meristematic tissue which is found at the tip of root or shoot i.e apical position is known as APical meristematic tissue.The apical meristematic tissue transforms into primary permanent tissue and heip in the increase length of plant body. 2)INTERCALARY MERISTEM:
The meristematic tissue which is intercalated between permanent tissue is known as intercalary meristem.Their position is either at the base of the leaf,at the base of node or after base of internode.This type of meristem produce primary permanent tissue and help in the increment of plant.
3)LATERAL MERISTEM:
The meristematic tissue which is lateral in the position of root and stem is called lateral meristematic tissue.It is actually the secondary meristem which give rise to secondary permanent tissue.It helps to increase the diameter of plant.

SHOOT APEX:
The terminal part of shoot that lies just above the youngest leaf primodium and develop from the plumule part of embryo is called shoot apex.Nodes and internodes are formed along with leaf appendages.Usually the shoot apex is cone or dome shaped in vascular plant.

ROOT APEX:
The Apical meristem of root which is sub terminal in origin due to presence of root cap and is derived from radical part of embryo is called root apex.Lateral appendages ,nodes and internodes are not formed.usually there is Quiscent centre at the center of root apex which funtion as reserve meristem.

THEORIES REGARDING ROOT APEX AND SHOOT APEX:
1)APICAL MERISTEM THEORY:
This theory was profounded by Naseli 1858.According to this theory the shoot apex and root apex consists of single prominent cell known as apical cap.The entire plant develops by the activity of single apical cell.This theory though true for thallophyte,bryophyte and most pteridophyte but not in gymnosperm and angiousperm.
2)HISTOGEN THEORY:
This theory was profounded by Hanstein in 1870.According to this theory,the shoot apex and root apex consists of central mass of meristematic cell known as plerome.Again,it is enveloped by two layer of meristematic cell called periblem and dermatogen.These three layers were termed as histogen.About the differentiation the dermatogen give rise to epidermis,the periblem to cortex and plerome gives rise to the tisses of stelar region.
DRAWBACKS:
a)The histogen layers are not same in all angiospermic plants.
b)It is not possible to assign in all cases histogen as the origin of various plant tissue.
c)In phanarogams at shoot apex,plerome and peristem are not distinct.
3)TUNICA CORPUS THEORY:
This theory is in reference to shoot apex.It was profounded by Schimidt in 1924.
This theory states that the shoot apex is differentiation of two layers:Outer one the tunica and inner layer corpus.Tunica consists of one or more peripheral layers of cells which are smaller in size and division mainly anticlinally increasing the surface area of plant body.The corpus consists of centre mass of cells enclosed by tunica.The cells of corpus are somewhat bigger in size and divide in many planes.Thus the tunica and corpus layer are different on the basis of their position as well as size and mode od division.About the differentiation of shoot apex,the epidermis develops from outer layer of tunica where as the rests of tissue may arise either from corpus or from tunica or from both.This theory is most accepted for differentiation of shoot apex for the seed plants(gymnosperms and spermatophyte)
FUNCTION OF MERISTEMATIC TISSUE:
1)The apical meristem and intercalary meristem help to increase the length of the plant.
2)The lateral meristem increases the diameter of the plant.
3)The protoderm give rise to epidermis which is protective in function.
4)The procambium produce primary vascular tissue i.e xylem,phloem.
5)Ground meristem gives rise to cortex and stellar region.
PERMANENT TISSUE:
The tissue which is composed of mature and differentiated cell that has already undergone definite growth and has assume definite size,shape and function is known as permanent tissue.The cell of permanent tissue have lost the power of division temporarily or permanently.The cells are thin walled,thick walled ,living or dead.Thin walled are usually living whereas thick walled are dead.The cell wall is composed of cellulose,hemicellulose,pectin,legnin etc.Intercellular spaces are present as well as absent.The permanent tissue develop from apical and intercalary meristem are primary permanent tissue and those developed rom lateral meristem are secondary permanent tissue.

TYPES OF PERMANENT TISSUE ON THE BASIS STRUCTURE,COMPOSITION AND FUNCTION:
1)SIMPLE PERMANENT TISSUE:
Simple permanent tissue is the collection of similar cells performing similar function.It is further divided into three different types on the nature of cell:
a)PARENCHYMA:
The most common type of simple permanent tissue present in all the plants which are isodiametric i.e expanded equally and vary greatly in morphology along with physiology is known as parenchyma.It is composed of thin wall living cell and cell wall is made of cellulose.Intercellular space is present and cytoplasm is vacuolated.
In transverse section,parenchyma cell appear circular,oval,rectangular or polygonal in shape.Parenchyma tissue present in almost all plant organs specially in non woody region.It forms the bulk of ground tissue iPlant:Meristematic and Permanent tissuen all plant organs.Beside ground tissue,parenchyma cells are present in epidermis and vascular tissue.
When parenchyma cell contain chlorophyll,they are said chlorenchyma.Chlorenchyma present in cortex of leaf is said mesophyll tissue which is further differentiated into pallisade and spongy.
The parenchyma cells in the cortex of aquatic plant encloses large air spaces and cavities called arenchyma.
FUNCTION:
a)The main function of parenchyma cell is to store food material.
b)The chlorenchyma cells take part in photosynthesis.
c)The aerenchyma helps plant to remain floating on surface of water by providing buoyancy.
d)The parenchyma cell in the epidermis perform protective function.
e)During secondary growth parenchyma cell acquire the power of division and become secondary meristem which by producing secondary permanent tissue help in the increase of diameter of plant.

b)COLLENCHYMA:
The mechanical tissue present in the plant body especially in the primary body of dicot stem below the epidermis forming the hypodermis is called collencyma.The cells are elongated with oblique ,slightly rounded with tapering ends.It is composed of living and thick walled cells.The cells are thickened at the corner against the intercellular spaces.The thickening is due to deposition of cellulose,hemicellulose or pectin.
In transverse section they appear circular,oval or polygonal.In secondary body of dicot stem and in monocot stem collenchyma is absent.In roots also rarely present.Collenchyma stem may be present in petiole of dicot stem.
FUNCTION:
a)Due to its peculiar thickening it provides mechanical strength and elasticity to the growing organs.
b)As collenchyma cells are capable of elongation,they help in elogation of organ along with the mechanical strength.
c)Chlorenchyma cells containing chloroplast helps in photosynthesis and also mechanical strength.

C)SCLERENCHYMA:
The chief mechanical tissue of the plant body composed of highly thick walled cell with little or no protoplasm is called sclerenchyma.The thickening of cell wall is due to deposition of cellulose or lignin or both.Lignin deposited cells are said lignified.The sclerenchyma cells are broadly classified into two types:
i)FIBRES:
Fibres cells are long,narrow,thick walled spindle shape with tapering ends.As they look fibre like in longitudinal section,the name is fibre.The fibre cells are without intercellular spaces.They are dead and empty.In Transverse section fibre cell appear hexagonal.The cell walls are mostly lignified.It is present in different regions in most of the plants.It commonly occurs in hypodermis of monocot stem as bundle sheath around vascular bundle,around pericycle and also under xylem(wood fibre)and phloem(bast fibre).It's principal function is to give mechanical support to plant body.the fibre cell present in xylem and phloem also help i the conductive of water and minceral salt along with food.
ii)SCLERIDS:
These are highly thick walled,dead sclerenchyma cells which are developed in different parts of plant body in order to meet the local mechanical need.They are present in the epidermis,cortex as well as tip.The hard covering of stony fruit is sclerids.Sclerids may occur singly or in groups.On the basis of their structure,there are different sclerids as macro sclerids,osteo sclerids and brachy sclerids.
2)COMPLEX PERMANENT TISSUE:
Complex permanent tissue is collection of dissimilar cells which perform cell function.It forms vascular or conducting tissue in the plant.They are of two types:

a)XYLEM:
Xylem is one of the types of complex permanent tissue which form the conductive part in plant body.It conductis mineral salt and water from roots to upper region.Xylem is composed of four types of cells:

i)VESSELS:
Vessels are elongated tube like structure which are formed by series of cell plates end to end where the transverse partition wall get dissolved.So,vessels are syncytes and are similar to series of water pipes forming a pipe line.The vessel are dead,thick walled and lignified.On the basis of mode of deposition of lignin on vessel wall,the vessels are named as annular,spiral,reticular,sclariform,pitted etc.Vessels are chief conducting element of xylem in angiosperm and are absent in gymnosperm and pteridophyte.
It's main function is to take part in conduction of water and mineral salt from root to upper region and provide mechanical support.
ii)TRACHEIDS:
Tracheids are thick walled,elongated,dead tube like cells with lignified walls.The tracheids are somewhat smaller than vessels and form chief conducting element of xylem in gymnosperm and pteridophyte where vessels are absent.Tracheids are present in angiosperm in association with vessels but they are more associated in secondary xylem.Tracheids are not syncyte.
iii)WOOD FIBRE:
The sclerenchyma fibre cell present in xylem vessels and tracheids are termed as wood fibre or xylem sclerenchyma.The cell are thick walled and ligified.They are mostly abundant in secondary xylem rather than primary.
They provide mechanical strength to xylem and as a whole to plant body ,and also they help vessel and tracheids in conduction.

iv)WOOD PARENCHYMA:
The normal parenchyma cell present in xylem are termed as wood parenchyma.It is only living component of xylem.The cells are thin walled and made of cellulose.
Beside storing the food material,xylem parenchyma helps vessel and tracheids in the conduction.

b)PHLOEM:
Phloem is one of types of complex permanent tissue forming conductive or vascular system in plant body.it conducts the prepared food from leaves to storage organs and growing regions.It is composed of following four components:
i)SIEVE TUBE:
Sieve tubes are cylindrical tube like structure made up of cell place end to end forming syncyt.The transverse partition wall between two cell is perforated with pores.Hence,it look like a sieve and is named as sieve plate.The sieve cells are thin walled,living and cell wall made of cellulose.On maturity,they lose their nucleus.
The main function of seive tube is conduction of prepared food from leaves to storage organ and growing region.
ii)COMPANION CELL:
Lying closely with sieve tube are elongated living cell with dense cytoplasm and distinct nucleus known as companion cell.These are in close communication with sieve tube cell.Companion cells are absent in pteridophyte and gymnosperm but present in angiosperm.
It helps sieve tube in conducting food material and also control other function by its nucleus in mature condition.

iii)BAST FIBRE:
The sclerenchyma fibre cell associated with phloem are termed as bast fibre as these fibre are used for making ropes.It is only the dead component of phloem.The cells are thick walled and lignified.Bast fibre are more abundant in secondary phloem than primary.
Besides providing mechanical strength to phloem,it helps sieve tube in coduction of food.
iv)PHLOEM PARENCHYMA:
Normal parenchyma cells present in phloem are phloem parenchyma.The cells are living,thin walled and cell wall made up of cellulose.Phloem parenchyma is usually absent in monocots,present in gymnosperms,pteridophyte and dicot.
Beside storing food material it help sieve tube in conduction of food.

SPECIAL SECRETORY TISSUE:
There are many plants with specific tissue that are actively involved in the secretion or excretion of many products and such tissue is known as secretory tissue.These tissue may be present in certain specific part of plant body or through out the plant body.The presence of these tissue becomes the identifying character for some plants.
TYPES OF SPECIAL SECRETORY TISSUE:
1)LATICIFEROUS TISSUE:
The tissue which consists of thin walled ,living ,multinucleate branch tube like structure containing colourless,coloured or milky is known as laticiferous tissue.These tissue remain distributed irregularly in the ground tissue.The main function of laticiferous tissue is secretion and storage of organic material in the form of gum,rubber,resin,tanin etc.Also,they help in regulating water balance in plant.These are of two types:
i)LATEX VESSEL
Latex vessels are syncyte which is formed by series of elongated meristematic cell.

ii)LATEX CELLS
Latex cells are coenocyte which are highly branched and originate independently.

2)GLANDULAR TISSUE:
Glandular tissue are unicellular or multicellular in structure that secrete or excrete chemicals.

DIFFERENCES: a)PARENCHYMA AND COLLENCHYMA:

1)Parenchyma is made of living cells which are thin walled whereas collenchyma is made of living cells which are are thick walled due to deposition of cellulose and pectin.

2)Parenchyma is found in epidermis,ground tisse and vascular bundles whereas collenchyma is found below epidermis in hypodermis of dicot stem.

3)Parenchyma provide mechanical strength only when cells are turgid whereas collenchyma is living mechanical tissue.

4)Parenchyma shows several types of modification whereas collenchyma shows few modifications.

5)The cells of Parenchyma are hexagonal,polygonal or regular in shape in T.S. whereas collenchyma cells are elongated,circular,oval or polygonal in T.S.

6)Parenchyma has ability to dedifferentiate and form secondary meristem whereas in collenchyma the ability to dedifferentiate is nearly absent.


b)COLLENCHYMA AND SCLERENCHYMA:

1)Cells of collenchyma contain protoplasm and are living whereas Mature cells of sclerenchyma are empty and become dead due to deposition of impermeable secondary wall.

2)Cell wall of collenchyma is thick,non lignified and composed of cellulose and pectic whereas Cell wall of sclerenchyma is highly and often lignified.

3)The cells of collenchyma provide elasticity whereas The cells of sclerenchyma provide hardness.

4)collencyma may contain chloroplast whereas Chloroplast is absent in sclerenchyma.

5)Collencyma is composed of only one type of cell whereas sclerenchyma is omposed of two type of cells.

6)Cells of collencyma have high water absorbing capacity whereas Cells of sclerencyma have low water content.

7)Pits are simple and straight in collenchyma where as in sclerenchyma pits are simple,oblique and sometimes branched.



c)XYLEM AND PHLOEM:

1)Xylem is mainly concerned with the conduction of water or sap from root to leaf whereas phloem is mainly concerned with the conduction of food material from leaf to growing area.

2)Xylem also provides mechanical support to the plants whereas phloem has no mechanical function.

3)Xylem is generally located towards inner side of plant body whereas phloem is generally located towards the outer side of plants parts.

4)Xylem consitute the bulk of woody part whereas phloem constitute small part of vascular tissue.

5)Xylem is made of three types of dead cellsi.e tracheids,vessels and xylem fibrewhereas Phloem contains only one type of dead cell i.e bast fibre.

6)Xylem contains only one living cell,xylem parenchyma whereas Phleom contains three types ofliving cells i.e sieve tube,companion cell and phloem parenchyma.

7)The conducting cells have lignin thickening in their wall where as No lignin thickening is found in phloem.

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