Simple and complex tissue (permanent tissue)

Simple and complex tissue (permanent tissue)

• 1.
  VIMAL PRIYA subramanian
• 2.
  Permanent tissue The permanenttissues may be simple or complex. A simple tissue is made up of one type of cells forming a uniform or homogeneous system of cells. The common simple tissues are parenchyma, collenchyma and sclerenchyma. A complex tissue is composed of more than one type of cells working together as a unit. The complex tissues consist of parenchymatous and sclerenchymatous cells; collenchymatous cells are not present in such tissues. The common instances are—the xylem and the phloem.
• 6.
  Parenchyma: The parenchyma tissueis made-up of living cells which are variable in their morphology and physiology, but generally having thin walls and a polyhedral shape, and concerned with vegetative activities of the plant. The individual cells are called parenchyma cells. The parenchyma includes isodiametric, thin-walled and equally expanded cells. The parenchyma cells are oval, rounded or polygonal in shape having well evolved spaces among them. The cells are not greatly elongated in any direction. The cells of this tissue are living and contain sufficient amount of cytoplasm in them. Usually each cell contains one or more nuclei.
• 7.
  Parenchyma
• 8.
  • Parenchyma makesup large parts of various organs in several plants. Pith, mesophyll of leaves, the pulp of fruits, endosperm of seeds, cortex of stems and roots, and other organs of plants consists mainly of parenchyma. The parenchyma cells also exist in xylem and phloem. • In the aquatic plants, the parenchyma cells in the cortex contain well developed air spaces (intercellular spaces) and such tissue is known as aerenchyma. Parenchyma may be specialized as water storage tissue in many succulent and xerophytic plants. • In several plants, chlorophyll-free, thin-walled and water-turgid cells are found which represent water storage tissue. When the parenchyma cells are exposed to light they develop chloroplasts in them, and this tissue is known as chlorenchyma. The chlorenchyma contains well developed aerating system. Intercellular spaces are abundant in the photosynthetic parenchyma (chlorenchyma) of stems too.
• 9.
  Cont..
• 10.
  • The turgidparenchyma cells help in giving rigidity to the plant body. • Partial conduction of water is also maintained through parenchymatous cells. The parenchyma acts as special storage tissues to store food material in the form of starch grains, proteins, fats and oils. • The parenchyma cells that possess chloroplasts in them make chlorenchyma which are responsible for photosynthesis in green plants. In water plants the aerenchyma keep up the buoyancy of the plants. • These air spaces also facilitate exchange of gases. In many succulent and xerophytic plants this tissues store water and are known as water storage tissue. • Vegetative propagation by cuttings takes place because of meristematic potentialities of the parenchyma cells which divide and evolve into buds and adventitious roots.
• 11.
  Collenchyma # Collenchyma isa living tissue made –up of somewhat elongated cells with thick primary non-lignified walls. # Important characteristics of this tissue are its early evolution and its adaptability to change in the rapidly growing organ, especially those of increases in length. # When the collenchyma becomes functional, no other strongly supporting tissues have appeared. # It gives support to the growing organs which do not evolve much woody tissue. Morphologically, collenchyma is a simple tissue, for it consists of one type of cells.
• 12.
  Collenchyma
• 13.
  Cont.. • Collenchyma isa typical supporting tissue of growing organs and of those mature herbaceous organs which are only slightly modified by secondary growth or lack this growth completely. • It is the first supporting tissue in stems, leaves and floral parts. • It is the main supporting tissue in many dicotyledonous leaves and stems of monocotyledons. • Collenchyma chiefly exists in the peripheral regions of stems and leaves. It is commonly found just beneath the epidermis. • In stems and petioles with ridges, collenchyma is particularly well developed in the ridges. In leaves it can be differentiated on one or both sides of the veins and along the margins of the leaf blade.
• 14.
  Cont.. • The collenchymaincludes elongated cells, various in shape, with unevenly thickened walls, rectangular, oblique or tapering ends, and persistent protoplasts. • The cells overlap and interlock, forming fibre like strands. • The cell walls include cellulose and pectin and have high water content. • They are extensible, plastic and adapted to rapid growth. In the beginning the strands are of small diameter but they are added to, as growth continues, from surrounding meristematic tissue. • The border cells of the strands can be transitional in structure, passing into the parenchyma type. • The walls of collenchyma are chiefly composed of cellulose and pectic compounds and contain much water. In several plants collenchyma is a compact tissue lacking intercellular spaces.
• 15.
  Cont.. • The maturecollenchyma cells are living and contain protoplasts. Chloroplasts also exist in variable numbers. • They are found abundantly in collenchyma which approaches parenchyma in form. • Collenchyma consisting of narrow cells possesses only a few small chloroplasts or none. • Tannins can be present in collenchyma cells. • The chief primary function of the tissue is to give support to the plant body. Its supporting value is increased by its peripheral position in the parts of stems, petioles and leaf mid-ribs. When the chloroplasts are present in the tissue, they carry on photosynthesis.
• 16.
  Sclerenchyma
• 17.
  Sclerenchyma # The sclerenchyma(Greek sclerous = hard; enchyma = an infusion) includes thick-walled cells, often lignified, whose major function is mechanical. # This is a supporting tissue that withstands various strains which result from stretching and bending of plant organs without any damage to the thin- walled softer cells. #The individual cells of sclerenchyma are called sclerenchyma cells. Collectively sclerenchyma cells make sclerenchyma tissue. Sclerenchyma cells do not contain living protoplasts at maturity. #The walls of these cells are uniformly and strongly thickened. Most commonly, the sclerenchyma cells are grouped into fibres and sclereids.
• 18.
  Fibre The fibres areelongate sclarenchyma cells, generally with pointed ends. The walls of fibres are generally lignified. Sometimes their walls are so much thickened that the lumen or cell cavity is reduced very much or altogether obliterated. The pits of fibres are always small, round or slit like and often oblique. The pits on the walls can be numerous or few in number. The middle lamella is conspicuous in the fibres. In most types of fibres, however, on maturation of cells the protoplast disappears and the permanent cell becomes dead and empty. Very rarely the fibres retain protoplasts in them. The fibres are abundantly found in several plants. They may occur in patches, in continuous bands and sometimes singly among other cells. They provide strength and rigidity to the various organs of the plants to able them to withstand various strains caused by outer agencies. The average length of fibres is 1-3 mm in angiosperms.
• 19.
  Cont.. • The fibresare divided into two large groups-xylem fibres and extraxylary fibres. • The xylem fibres evolve from the same meristematic tissues as the other xylem cells and constitute an integral part of xylem. • In other word, some of the continuous cylinders in monocotyledonous stems arise in the ground tissue under the epidermis at variable distances. • They are called cortical fibres. • The fibres forming sheaths around the vascular bundles in the monocotyledonous stems arise partly from the same procambium as the vascular cells, partly from the ground tissue. • The fibres present in the peripheral region of the vascular cylinder, often close to the phloem, are called pericyclic fibres. The extraxylary fibres are sometimes combines into a group known as bast fibres.
• 20.
  Sclereids • The sclereidsare broadly distributed in the plant body. They are usually not much longer than they are broad, occurring singly or in groups. • Generally these cells are isodiametric but some are elongated too. They are commonly observed in the cortex and pith of gymnosperms and dicotyledons arranged singly or in groups. In many species of plants, the sclereids occur in the leaves. • The leaf sclereids may be few to abundant. In certain leaves the mesophyll is completely permeated by sclereids. Sclereids are also common in fruits and seeds. In fruits they are disposed in the pulp singly or in groups (viz., Pyrus). The hardness and strength of the seed coat is due to the presence of abundant sclareids. • The secondary walls of the sclereids are typically lignified and vary in thickness. In several sclerides the lumina are almost filled with massive wall deposits, and the secondary wall shows prominent pits. Commonly the pits are simple and rarely bordered pits may also exist.
• 21.
  Sclerieds
• 24.
  Complex tissue • Acomplex plant tissue is made up of more than one type of cells. There are two types of complex plant tissues, viz. • Xylem and phloem. • Xylem: Xylem is composed of four elements, viz. Tracheids, vessels, xylem fibres and xylem parenchyma.
• 25.
  Tracheids: # These areelongated or tube-like cells. They have thick and lignified walls and tapering ends. # The tracheid cells are dead and protoplasm is absent. # Tracheids and vessels are the main conducting elements in flowering plants.
• 27.
  Vessel: • These arelong, cylindrical tube-like structures. • These are made up of many cells which are called vessel members. Each vessel member has lignified walls and a large central cavity. • Protoplasm is absent in vessel cells. • The vessel members are interconnected through perforations in their common walls. • The presence of vessels is a characteristic feature of angiosperms.
• 28.
  Xylem Fibres: Thexylem fibres have highly thickened walls and obliterated central lumens. • Septa may be present or absent in xylem fibres. Xylem Parenchyma: • The xylem parenchyma is composed of living cells which are thin- walled. • The cell wall of xylem parenchyma is made up of cellulose. Xylem parenchyma stores food in the form of starch or fat, and some other substances like tannins. • Parenchymatous cells facilitate the radial conduction of water in plants.
• 29.
  Xylem vessel andtrachids
• 30.
  • Primary xylemis of two types, viz. Protoxylem and metaxylem. Protoxylem are the first formed primary xylem elements, while the metaxylem are formed later. • Endarch: The protoxylem lies towards the pith in stem and the metaxylem lies towards the periphery. This type of primary xylem is called endarch. • Exarch: The protoxylem lies towards the periphery in roots and the metaxylem lies towards the pith. This type of primary xylem is called exarch. • Transportation of water and minerals from roots to different plant parts is the main function of xylem. Xylem also provides mechanical strength.
• 31.
  Phloem
• 32.
  • Phloem: • Thephloem; in angiosperms; is composed of four elements, viz. Sieve tube, companion cells, phloem parenchyma and phloem fibres. • In case of gymnosperms, the phloem has albuminous cells and sieve cells. • Sieve tubes and companion cells are absent in the phloem in gymnosperms.
• 33.
  Sieve Tube: • Thesieve tube elements are long, tube-like structures. • They are arranged longitudinally. • The end walls of sieve tubes are perforated to form sieve plates. • A mature sieve element has a peripheral cytoplasm and a large vacuole but no nucleus. • The nucleus of the companion cell controls the function of sieve element.
• 34.
  • Companion Cells: •These are specialized parenchymatous cells. • The companion cells are closely associated with sieve tube elements. • There is a common pit field in the common longitudinal wall between the sieve tube element and companion cell. • These piths connect both of them. • The companion cell helps in maintaining the pressure gradient in the sieve tubes.
• 35.
  • Phloem Parenchyma: •The cells of phloem parenchyma are elongated, tapering cylindrical cells. • The cells have dense cytoplasm and nucleus. • Cell wall is composed of cellulose and has pits. • Plasmodesmatal connections exist between the cells through these pits. • Phloem parenchyma stores food and other substances like resin, latex and mucilage. • Phloem parenchyma is usually absent in monocotyledonous
• 36.
  • Phloem Fibre: •These are also called bast fibres and are made up of sclerenchyma. • Phloem fibres are usually absent in primary phloem but present in secondary phloem. • The phloem fibres are much elongated, unbranched and have pointed, needle-like apices. • Phloem fibres of jute, flax and hemp are commercially used.
• 37.
  • The primaryphloem which is first formed consists of narrow sieve tubes and is called protophloem. The later formed phloem has bigger sieve tubes and is called metaphloem.