Simple permanent tissue- Parenchyma, Collenchyma and Sclerenchyma

These are also termed as mature tissues.
Permanent tissues are mature tissues derived from meristematic tissues that have undergone complete growth and differentiation.
Not all the cells totally differ from the meristems as some cells retain the power of division and others cannot divide.
In a strict sense only those cells which have lost the power for division must be regarded as permanent tissues, but in a broad sense, cells derived from meristem that have acquired a special function like photosynthesis, secretion, storage are treated as part of matured tissue.
The cells of these tissues may be living or dead and thin or thick walled. The thin walled tissue are generally living whereas the thick walled may be dead or living.
Simple tissues are made up of similar type of cells forming a uniform system of cell.
Simple tissues are of three types based on various structural differences.
These are parenchyma, collenchyma and sclerenchyma.

1. Plant Anatomy Tissue- Simple Permanent Tissue By: Dr. Sunita Sangwan Assistant Prof. Deptt. of Botany MNSGC Bhiwani

2. Permanent Tissue

3. Introduction These are also termed as mature tissues . Permanent tissues are mature tissues derived from meristematic tissues that have undergone complete growth and differentiation. Not all the cells totally differ from the meristems as some cells retain the power of division and others cannot divide. In a strict sense only those cells which have lost the power for division must be regarded as permanent tissues, but in a broad sense, cells derived from meristem that have acquired a special function like photosynthesis, secretion, storage are treated as part of matured tissue. The cells of these tissues may be living or dead and thin or thick walled . The thin walled tissue are generally living whereas the thick walled may be dead or living.

4. Simple Tissue Simple tissues are made up of similar type of cells forming a uniform system of cell. Simple tissues are of three types based on various structural differences. These are parenchyma, collenchyma and sclerenchyma.

5. Parenchyma Parenchyma is the fundamental tissue of the plant body . It is found in every part of the plant body like pith and cortex of stem and root, mesophyll of leaves, flesh of fruits , floral parts and even in xylem and Phloem.

6. Parenchyma - Origin Parenchyma originates from primary meristem  either from apical meristem or from the lateral Meristem and form the framework of all the plant organs.   Parenchyma of primary vascular tissues arises from the Procambium but in  cortex, pith and mesophyll it arise from the ground Meristem. During secondary growth , it formed from cambium and cork cambium . 

7. Distribution It is the fundamental tissue found in almost all the parts of the plant.  It occurs in the cortex and pericycle of stem and roots, mesophyll tissue of leaf, the endosperm is of seeds etc.  It is also found in vascular tissues. It is the most primitive type of unspecialized tissue and gives rise to other tissues by further specialization. 

8. Shapes, size and arrangement of cells Parenchymatous cells are usually isodiametric but sometimes morphological variations stellate and armed forms also occur. A typical parenchyma cell is 14 sided. They are compactly arranged or separated by abundant intercellular spaces. The parenchyma in endosperm usually lake intercellular spaces. So there is more variation regarding the shapes and arrangement of parenchymatous cells.

9. Cell Content The parenchyma cells are living so it contains abundant Protoplasm and one or more number of nuclei. Cell contents changed according to the activity and functions of the cell. Cell wall is thin and connected to the adjacent cell through the plasmodesmata.

10. Types of Parenchyma Depending upon the structure shape and nature of function parenchyma is of different types as follow:

11. Prosenchyma Sometimes parenchymatous cells become thick walled, elongated and pointed at both the ends to provide mechanical support, protection and conduction. The tissue consisting of this type of parenchymatous cells is called prosenchyma. Cell wall thickening is due to deposition of cellulose not due to the lignin deposition. e.g. pericycle in some plants.

12. Aerenchyma  In some aquatic plants, parenchymatous cells constituting well-developed large intercellular air spaces, such tissue called aerenchyma. Sometime these spaces become star-like with short long arms and wide air spaces called stellate parenchyma . Examples are petioles of banana and Canna.

13. Chlorenchyma When parenchymatous cells contain an abundance of chloroplast these are termed as chlorenchyma.  Chlorenchyma has a well-developed   aerating system and performs the function of photosynthesis .

14. Storage parenchyma   Sometimes-parenchymatous tissue acts as a storage tissue to store material in the form of starch grains, fats, oils, protein etc.  These tissues called storage parenchyma. e.g. endosperm of seeds, Pulp of fruits .  In xerophytes and succulents , they are specialized to store large amounts of water. e.g.  Agave, Aloe etc. 

15. Idioblast   Parenchymatous cells sometimes store ergastic substances such as tennins, oils and crystals. These tissues known as Idioblast . These cells are secretory in function and supply various types of enzymes.

16. Functions of Parenchyma Parenchyma is the centre of various physiological activities such as photosynthesis and respiration, assimilation etc. In Xylem and phloem tissues, it also helps in upward and downward conduction of water and dissolved materials. Turgidity of parenchymatous cells provide rigidity to the plant and maintain the shape of the plant body.  Parenchymatous cells of meristems are also helpful in vegetative propagation through adventitious buds and roots .

17. Functions of Parenchyma Parenchyma of cambial cells divide and form the secondary meristematic tissues such as cork cambium and vascular cambium.  These are also helpful in healing wounds on the plant due to their cambial activity.  In aquatic plants, they store air and provide buoyancy to float easily in or on air. Cutinized parenchyma of leaf epidermis are protective in nature that reduce the transpiration and mechanical injury is up to some extent.

18. Collenchyma

19. Collenchyma Collenchyma is a simple, living tissue composed of elongated cells. Morphologically it is a simple tissue because of having one type of cells. Cell walls are thickened due to deposition of pectin.

20. Origin Collenchyma originated from apical meristem and cortical parenchyma and procambium is derived from a common meristem. Early differentiating collenchyma of a given organ becomes highly specialized in its morphology whereas that formed later is more parenchymatous in nature. The former has arisen from pro-cambium like meristem , while the latter ones in a parenchymatous ground meristem . In the early phase of development , intercellular spaces are present but disappear in later stages due to enlargement of cells or are filled by intercellular substances.

21. Distribution Collenchyma is usually found in the primary plant body. It is present beneath the epidermis or below a few layers of parenchyma. In stems it occurs as a complete cylinder or in longitudinal strips , whereas in leaves it is present in one or both sides of veins and along the laminar margins . Collenchyma are generally absent in underground plant body organs like underground stem, roots.

22. Shape, Size and arrangement of cells Collenchyma cells show variation in shapes. The smaller collenchymatous cell looks like parenchymatous cells whereas longer ones have tapering ends showing resemblance with fibres. Collenchyma are usually polygonal in the cross section . The cell wall thickening in collenchyma is primary in nature. It is composed of cellulose, hemicellulose and pectic materials having more percentage of water. Collenchyma cells show many variations in thickening  of cell wall.

23. Based on the cell walls thickening and arrangement of cells, collenchyma is of following different types

24. Angular Collenchyma The cell thickening primarily at the corners or angles of the cells . As a result, collenchyma become compactly arranged cells without intercellular spaces . Examples are stems of Datura and Lycopersicon .

25. Annular Collenchyma Sometimes lumen of the cells become circular due to continuous thickening of cell walls and this type is also termed as angular collenchyma by some workers. The distinction between angular and annular collenchyma is often difficult, especially when massive thickening occurs, causing the lumen to lose its angular appearance.

26. Plate/ Lamellar/ Tangential collenchyma In this type of collenchyma the thickening occurs more on the tangential walls and lesser on radial walls. As a result, the arrangement of cells appears like a plate or lamellae . Examples: Raphanus and Sambucus .

27. Lacunar or tubular Collenchyma In this type of collenchyma the wall thickenings are present only on the regions of the wall bordering the air spaces. This type often occurs as an intermediate type with angular and lamellar collenchyma, in which the size of the intercellular spaces can vary from minute spaces to large cavities surrounded by collenchymatous walls . The intercellular spaces in this collenchyma are large. This type of collenchyma are found in Salvia, Malva , Althea etc.

28. Functions of Collenchyma These tissues provide mechanical strength to the growing tissues with considerable elasticity and protect the organ from the tearing effect of wind. It provides the tensile strength to the developing organs of the plant body. As these occur on both sides of bundles in leaves so provide support to the leaves. Collenchyma tissue protects the vascular bundles in leaves by forming the bundle sheath like structure. Collenchyma which have chloroplasts perform photosynthetic functions.

29. Sclerenchyma

30. Sclerenchyma Sclerenchyma are simple tissue specially for providing mechanical strength to the plant organs. The meaning of word sclerous is hard so name of tissue itself represents the its function. Cells of sclerenchyma are thick walled due to deposition of lignin and formation of secondary wall . Protoplasm is absent in sclerenchymatous cells . Due to variation in structure, origin and development these cells sclerenchymatous tissue is divided into two groups: fibres and sclereids.

31. Fibres These are more pointed and needle like tapering ends. Origin: Fibres are either originate from procambium or from fusiform cambial initials. Some fibres also arise from ground meristem, anticlinal and periclinal divisions in protodermal cell. The fibres present in bundle sheath of monocot stems differentiate partly from procambium and partly from ground meristem.

32. Distribution Fibres can be present in groups, as sheets or as cylinders in different parts of plants. In some dicot stems fibres present in the outermost part of the primary phloem and in bundle sheath in monocot stems . Fibres are also found in primary and secondary xylem and phloem tissues of roots. In gymnosperms fibres are present only in secondary phloem and absent in primary phloem.

33. Shape and size of cells fibres are narrow, elongated, thick walled and lignifies cells with tattering and rounded ends. These possess both simple and bordered pits. Fibres show great variation in size between 20-550 mm length in angiosperms and 1-12 mm in gymnosperms.

34. Types of fibres Depending on the origin and their economic use fibres are grouped into two groups:

35. Xylary fibres These fibres are present in secondary xylem so they are also termed as wood fibres. These originates from the same meristematic tissue from which other xylem elements develop. These show great variation in size, shape, thickness, number and size of pits present . Sometimes secondary wall is very thick due to more lignification so that central lumen is almost abolished.

36. Xylary fibres Depending upon thickness of wall, types of pits xylary fibres are subdivided in to libriform fibres and fibre tracheids The libriform fibres are long with very thick secondary wall and simple pits of small lumen. Fibre tracheids are short with comparatively thin walls having bordered pits with large lumen.

37. Extra Xylary fibres T hese fibres are found outside the xylem in cortex, pericycle and phloem and collectively termed a bast fibres. These fibres have spindle like shape having acute or blunt ends. The cell wall is quite thick with simple or bordered pits. Depending upon their distribution these fibres are divided into three categories: Cortical fibres , Peri -vascular fibres, Phloem fibres.

38. Functions of fibres Main function of fibres is to provide mechanical strength to plant body along with maintaining the elasticity and flexibility. Provide resistance against the gravitational tension and strains . Xylary fibres also have role in water conduction along with that of providing support.

39. Economic fibres Fibres have many economic and commercial uses to human welfare. Plants of about 44 families are used a source of commercial fibres. Commercial fibres are divided into soft fibres and hard fibres . Fibres of monocot leaf with high lignified walls are put under the hard fibre categories, e.g. Musa textiles (Manilla hemp), Yucca, Agave etc. The soft fibres are fibres obtained from phloem, e.g. Linum usitatissimum (flax), Cannabis sativa (Bhang), Corchorus capsularis (jute) etc.

40. B. Sclereids (sclerotic cells ) These cells are without pointed ends and are of different shapes and commonly known as stone cells.

41. Origin Sclereids are either arise by secondary sclerosis or sclereids primordia or parenchymatous cells. In leaves these may originate from epidermal cells, palisade or spongy parenchyma. Sclereids derived from procambial or cambial cells in vascular region.

42. Distribution These are widely distributed in the plant body as isolated cells or grouped with other types of cells. These are termed as idioblasts when present isolated. They may be present in epidermis (e.g. Allium ); in gound tissue (e.g. Hoya ) of stem and leaves and roots in Nymphaea . These are known as grit cells in fruits and seeds. Hardness of seed coat in pyrus is due to presence of abundant sclereids.

43. Cell shape and size Sclereids are dead sclerenchymatous cells having strong lignified thick walls with simple pits . The aperture is highly reduced or completely abolished. They originate from simple parenchyma cells by the deposition of secondary wall layers in lamellar arrangement. During elongation they invade intercellular spaces of neighbouring cells and become branched.

44. Brachysclereids Sclereids cells found in this group are short roughly isodiametric and are found in cortex, pith and phloem of stems and pulp of fruits, e.g. Pyrus .

45. Asterosclereids A s the name suggest these sclereids are star shaped or stellate cells found in leaves of Nymphaea and stem and leaves of Trochodendron .

46. Osteosclereids These are barrel shaped sclereids with dilated bone like ends. These are present in leaves and seed coat of many monocots.

47. Macrosclereids These are elongated rod like sclereids cells commonly found in palisade layer of epidermal layer in seed coat of leguminous seeds.

48. Trichosclereids These are hair like branched or unbranched sclereids cell found intercellular spaces present in leaves and stems of some hydrophytes.

49. Types of Sclereids Figure: A) Fruit of Prunus showing Brachysclereids B ) magnified stone cell ( sclereid ) from the juicy mesocarp of a 'Bartlett' pear C ) Maceration of bean seed coat showing macrosclereids D ) W.M. of Osteosclereids E) T.S. leaf of Nymphaea showing astrosclereids F ) Banana leaf clearing showing trichosclereids .

50. Functions of sclereids They provide tightness, stiffness and mechanical strength to the part of plants in which they are present. Provide hardness to the fruit and seed coats to protect the internal soft parts. Brachysclereids increase the compactness of the bark.

51. Characteristics Parenchyma Collenchyma Sclerenchyma Cell Shape Isodiametric cell which are oval, spherical and polygonal in shape. Circular, oval or polyhedral Fibres and sclereids variable in shape Cell Wall Thin cellulosic cell wall Uneven thickening on their cell wall. Lignified secondary cell wall present Cytoplasm Abundant Present Absent Nucleus Present (living tissue) Present (living tissue) Absent (dead tissue) Vacuoles Large vacuole Vacuolated Absent Intercellular spaces Present Absent Absent Occurrence All soft part of plant–pith, cortex, medullary rays. Dicot stems, petiole and beneath the epidermis. Absent in monocot and roots. Dicot hypodermis, bundle sheath, pericycle, seed pulp or fruits. 8. Functions Food storage and photosynthesis Provide tensile strength and mechanical support Protection from stress and strain, mechanical stress

52. Thanks