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Plant tissues. The vascular plant sporophyte is usually composed of three kinds of vegetative organs: roots stems leaves These organs are constructed by some types of plant tissues.
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The vascular plant sporophyte is usually composed of three kinds of vegetative organs: • roots • stems • leaves These organs are constructed by some types of plant tissues. • Plant tissue - is a group of cells that are structurally and/or functionally distinct, and perform a common function.
Meristematic tissues I. According to their origin: • primary • secondary • Primary meristems - set extension of the plants organs - apical & intercalary meristems - determine the primary growth of plants • Secondary meristems - determine the thickening – lateral meristems - define the secondary growth II. According to their position in the plant: • Apical - situated at the growing tip of the stems & roots and form shoot apex & root apex . In the leaves it forms the leaves apices. • lateral - define the increasing of root and stem diameter : vascular cambium (cambium ) & cork cambium (phellogen) • Intercalary – define elongation of nodal regions
Primary meristems - (germinal) - all the cells of the embryo are meristems. The cells of primary meristems retain the ability to divide throughout life and in the cases when plant organs are damaged by predators, they resume the ability to divide and differentiate into permanent tissues. Cell division and cell elongation in the primary meristem are defined as primary growth and its result is elongation of plant organs and their differentiation. Importance - to reproduce asexually - to regenerate damaged parts of the plant body - a basic role in normal plant growth - give rise to other types of permanent tissues - formation of new organs and their correct placement Cell characteristics: - spherical,oval,polygonal or rectangular in shape, • compactly arranged & without any intercellular space • with dense or abundant cytoplasm • hold a single large nucleus
Examples for primary meristems – protoderma, procambium and ground meristem • Protoderm: lies around the outside of the stem and develops into the epidermis • Procambium: • lies inside of the protoderm and develops into primary xylem and primary phloem. • produces the vascular cambium and cork cambium - secondary meristems. 3. Ground meristem: develops into the cortex and the pith.Composedof parencyma, collenchyma and sclerenchyma cells.
Relationships between apical meristems, primary meristems and primary grouth (stem apex (tip)
Secondary meristems - determine the secondary growth (thickening) of the plant parts. The secondary growthis characterized for Dicots and it is not found in Monocots. Examples: lateral meristems vascular cambium and cork cambium
Cork cambium (= bark cambium, pericambium and phellogen): • a tissue found in many vascular plants • As a part of the periderm • lateral meristem, responsible for secondary growth • replaces epidermis in roots and stems • found in woody and many herbaceous dicots , gymnosperms and some monocots • acts in two directions: outside forms phellem (cork) – dead at maturity; inward phelloderm - composed of living parenchyma cells Result – in this way the stem and root gradually thicken towards the bark.
outwards - secondary phloem • inwards - secondary xylem The vascular cambium (plural cambia) – acts in the central cylinder Result – the stem and root gradually thicken towards the central cylinder.
Intercallary meristem - a type of primary meristem, exactly the remnant of the apical meristem. It is common of the nodal regions – especially at the base of the leaves. They occur only in Monocots (particularly grass). The main function : • elongation of nodal regions • rapid growth and regrowthof leaf and stems (afterdamage due to herbivores, heavy rains, storms, and lawnmowers).
Permanent plant tissues – they consist of cells that lost their ability to divide and perform certain functions – roof, conductive, protective. Permanent tissue types: • Simple • Complex • Special (secretory)
Simple permanent tissues - A group of cells which are similar in origin, in structure and in function Simple permanent tissues – types: • Parenchyma • collenchyma • Sclerenchyma
1. Parenchyma: Parenchyma - the most common tissue which is unspecialized. Living tissue, that fills the internal volume of the plant bodies and placed between other types of tissues. Parenchyma cells are spread everywhere in the plant body - in epidermis, cortex, pericycle, pith etc. They are responsible for photosynthesis, storage of food, secretion etc. Due to the diverse functions it performs, parenchyma is divided into 4 types: • Assimilatory parenchyma - contains chlorophyll and performs photosynthesis; • Storage parenchyma – for food storage • Aerenchyma – characterized by the aquatic plants, with large air cavities , for support to floating • Water storage parenchyma – cacti, stone crop, sedum etc. – with succulent stems and leaves Observation of parenchyma cells in apple (Malus domestica), carrot (Daucus carota) , potato (Solanum tuberosum).
Collenchyma - cells are thin-walled, but the thickening of the cell wall begins - mostly this is done atthe corners where the cells join together. In that case the pectine substances accumulate between the celulose fibers.It is present in the leaf margin to resist tearing effect of the wind. Collenchyma functions: • provides mechanical support, elasticity, and tensile strength to the plant body – especially in the young plants with growth opportunities • arranges the cells in a compact mass, with a very little inter-cellular spaces • helps in a starch storage Observation of collenchyma cells in cucumber (Cucumis sativa)
Sclerenchyma - gives support to the plant and provides hardness and protective covering to seed and nuts. Its consists of thick-walled, dead cells with cells walls, rich of lignin. Lignin deposition is so thick that the cell walls become strong, rigid and impermeable to water. Main features: - closely packed without inter-cellular spaces Distribution: mainly occur in hypodermis, perycycle, secondary xylem and phloem. Types of sclerenchyma: • Sclereids- short cells with thick, lamellated, lignified walls, gathered in groups. Form plum and cherrypits, the shells of almond and walnut, placed in groups in the flesh of the pear & quince, named stone cells. • Fibres- elongated cells with pointed ends. They are placed in the stem of flax, hemp - textiles fibers. Observation of sclereids in quince ( Cydonia oblonga)
Ground tissue system Ground tissue system - includes the above mentioned three types of simple tissues : parenchyma, collenchyma and sclerenchyma. Main function: fills all interior spaces in plant organs and store organic products.
Complex permanent tissues Complex tissue- consists of more than one type of cells which work together as a unit. Complex tissues help in the transportation of organic material, water and minerals up and down the plants. Examples - xylem and phloem • Xylem or wood • Phloem or bast Xylem and phloem are elementsof vascular (conductive) tissue system
Xylem and phloem together form vascular bundles. • Xylem is responsible for transporting water and certain nutrients from the root to the rest of the plant - in upward direction. The second function – to provide mechanical support to the plant. • Phloem carries soluble organic material, i.e. food for the plant, which is produced in the leaves by photosynthesis to the other parts of the plant – in downward direction.
Xylem elements Xylem consists of non-living tissue at maturity • Tracheary elements: Tracheids & vessels • wood parenchyma – for storage and secretion • xylem fibres - for mechanical support • libriform fibers – for mechanical support 1.Tracheids - phylogenetically oldest conductive vessels - elongated cells with tapering ends and lignifiedwalls with pits. found in Gymnosperms & Angiosperms 2. Tracheas - long, non-living tubes, parallel to the main axis of the stem, and built by vessel members. The oblique cell walls between the adjacent vessel members becomes partially or completely perforated - this is the perforation plate. Found mainly in Angiosperms. The vessel originates from the vascular cambium.
Phloem - made of living sieve-tube elementsthat lack a nucleus, ribosomes, or vacuoles; their metabolic functions are provided by companion cells. Phloem elements: • Sieve cell - similar to tracheids – they are living, elongated cells • Sieve tube - parallel to the tracheas of the xylem (occurring only in Angiosperms) and consists of sieve-tube elements. Their transverse walls are oblique and perforated and the sieve plate is formed. Sieve plate is penetrated by pores . • Companion cell • Phloem fibers
Vascular bundels - In majority of plantsvascular elements cluster into bundles. Bundels types: • Simple bundles: xylem and phloem elements are located at separate bundles - young roots. • Compound bundles: contain both xylem and phloem - Concentric: xylem and phloem form concentric rings in cross section - ferns - Collateral: bundles containing xylem and phloem adjoining each other side by side, xylem facing to the centre of the organ, phloem facing outwards. - collateral closed bundle - procambium completely differentiated into xylem or phloem, so no dividing cell remains in the bundle. This bundle is incapable of secondary thickening (monocots). - collateral open bundles – procambium differentiation is not complete, thus a thin layer of dividing procambium remains between the xylem and the phloem. These bundles may take part in secondary thickening (dicots). - bicollateral bundles - phloem occurs on either side of the xylem(Cucurbitaceae)
Cross section of the stem: • Dicot - vascular bundles arranged in a ring. In plants with stems that live for more than one year, the individual bundles grow together and produce the characteristic growth rings. • Monocots - the vascular bundles are randomly scattered throughout the ground tissue
Helianthus stem Observation of different kinds of vascular bundles- permanent slides
Dermal tissue system - forms the outmost layer of a plant. It includes both epidermal and peridermal tissues. Function – prevents water loss and acts as a barrier to fungi and other invaders. Dermal tissue – types: I. Primary dermal tussue – epidermis II. Secondary dermal tissue – periderm III.Terthiary dermal tissue – the bark
I. Primary dermal tissue - epidermis - thin layer of cells that cover the surfaces of leaves, stems, and roots. In Monocotscover all above ground parts of the plants, and in Dicots cover only young branches and the leaves. Other function is controlling water and gases exchange. Origin – from protoderm,in woody plants - replaced by periderm. Epidermis – elements: • Pavement cells • Stomata • Trichomes
Pavement cells - tightly linked to each other and provide mechanical strength and protection
Cuticle- a thin hydrophobic layer which covers the outermost surface of epidermis cells of land plants – its functions are to reduce water loss, to protect from UV radiation, as well as from bacterial and fungal pathogens. The cuticle is synthesized by epidermal cells and its framework is provided by cutin - insoluble compound of C atoms (16 -18), epoxy fatty acids and glycerol.
2. Stomata - most differentiated cells of the epidermis, regulates the exchange of gases and water vapors. Stoma complex - apore, guard cells (with chloroplast), accessory cells (lack chloroplasts) Situation - Typically - in dry land plants the stomata are located on the lower epidermis - floating leaves - most or all stomata are on the upper surface - Vertical leaves (grasses) - there are equal numbers of stomata on both surfaces.
Guard cells - bounded the stomata pore Mechanism of stomata opening: - in sunlight the sugars form - the concentration of potassium ions (K+) increases - this causes water potential lowering in the guard cells - water from other cells enters the guard cells by osmosis - they swell and become turgid - the swollen guard cells become curved and pull the stomata open. - At night, the sugar is used up - water leaves the guard cells - they become flaccid and the stomatal pore closes. Observation of epidermal cells and stomata in Tradescantia virginica
3. Trichomes (Plant hairs) - unicellular or multicellular • Trichomes for absorbtion - cover the plants root and are called root hairs. • Trichomes for protection – covered plant stems and leaves: Papillae - on the petals of flowers. They give the petals a soft, velvety appearance and prevent them from becoming wet. Stinging hairs - The cell walls consist of calcite and silica, the cell itself is full of complex mixture offormic acid, histamine and serotonine. In case of breakage of the hairs tip the mixture is poured and causes swellings and flushings of the skin surface - nettle Emergences - the thorns on roses
Trichomes for secretion - form some of the most important glands found in the plant kingdom. The most common glandular hairs are multicellular – a number of cells forming a stalk and a head. The secreted substances are very different – resins, gums, volatile oils, mucilage. Sometimes the oils are scented and give plants their characteristic fragrance, e.g. lavender.
Trichomes for seed dispersal - cotton seed hairs, willow and willow herb
II.Secondary delmal tissue – periderm -impermeable for water and gases - replaces the epidermis during growth in thickness of stems and roots of gymnosperms and dicots ( secondary growth). - originates from the lateral meristem cork cambium (phellogen) - periderm - includes 3 layers - the phellem (cork), phellogen (cork cambium) and phelloderm III.Tertiary dermal tissue (rhytidome) – forms from periderm, that arise at greater depths causing the accumulation of dead tissue on the surface. Contains dead tissue layers and no longer growing periderms. It is the outermost layer of the trees – the bark. * Lenticells - interruptions in the phellem through which gas exchange occurs. They form at the places of stomata, and produce a filling tissue, consisting of loosely arranged cells. Observation of lenticells and periderm in one year old stem of
Plant secretory tissue Function – includes the secretionof gums, resins, volatile oils, nectar, latex, and other substances in plants. Divided into two groups: • Laticiferous tissues • Glandular tissues The secreted substances – they are no further utilized by the plant (resins, rubber, tannins, and various crystals) - take part in the functions of the plant (enzymes and hormones) - may remain in the cell - may be excreted to the surface of the plant or into intercellular cavities or canals.
Lactiferous tissues - thin walled, greatly elongated and many-branched ducts containing a milky or yellowish colored juice known as latex.Function - act as food storage organs or as reservoir of waste products. • Latex cells - also called "non-articulate latex ducts“. These ducts are independent units which extend as branched structures for long distances in the plant body, but do not fuse together. Thus a network is not formed as in latex vessels. • Latex vessel - Also called "articulate latex ducts", these ducts or vessels are the result of anastamosing of many cells together. They form a complex network with anastamose branching. Latex vessels are commonly found in many angiospermfamilies - Papaveraceae,Compositae, Euphorbiaceae, Moraceae.
2. Glandular tissues - consist of special structures - the glands. These glands contain some secretory or excretory products. A gland may consist of isolated cells or small group cells with or without a central cavity. They are of various kinds and may be internal or external. - Internal glands are: • Oil-gland secreting essential oils - in the fruits and leaves of orange, lemon. • Mucilage secreting glands - in the betel leaf • Glands secreting gum, resin, tannin, etc. • Digestive glands secreting enzymes or digestive agents • Special water secreting glands at the tip of veins - External glands are commonly short hairs tipped by glands. They are • water-secreting hairs or glands, • Glandular hairs secreting gum like substances as in tobacco, plumbago, etc. • Glandular hairs secreting irritating, poisonous substances,as in nettles • Honey glands, as in carnivorous plants. Observation of Oil-gland secreting essential oils in orange (Citrus X sinensis)
Glands and trichomes in tomato leaf Glands in Drosera rotundifolia
