Plant Tissues and Cells PDF

Tissues of the Plant Body  Origin of Primary Tissues Primary growth- formation of primary tissues. – Primary plant body. Internal Organization of the Plant Body Tissue- a group of similar cells organized into a structural and functional unit. Tissue System- a tissue or group...

Tissues of the Plant Body  Origin of Primary Tissues Primary growth- formation of primary tissues. – Primary plant body. Internal Organization of the Plant Body Tissue- a group of similar cells organized into a structural and functional unit. Tissue System- a tissue or group of tissues organized into a structural and functional unit; larger units of the plant body. There are 3 Tissue Systems – Ground – Vascular – Dermal  Plant Tissues Types All plant organs (roots, stems, leaves) are composed of the same tissue types. There are three types of tissue: Ground – bulk of inner layers Dermal – outermost layer Vascular – conducting tissue, transport Cell Types and Tissues of Ground Tissue System  A. Parenchyma tissue Polyhedral to round in shape Composed mainly of parenchyma cells Cells has thin primary walls Found throughout the plant body Most common cell and tissue type Constitute soft plant parts ex. edible part of apple or potato are mainly composed of these type of tissue  A. Parenchyma tissue Alive at maturity Metabolically active Ex. photosynthesis (w/ chloroplast), storage (without chloroplast) and secretion Inexpensive to produce because little glucose is expended in constructing the walls of cellulose and hemcellulose Parenchyma  Parenchyma Cells Subtypes Chlorenchyma – has abundant chloroplasts – Light and CO2 can pass through its thin walls Glandular Cells – typically contain few chloroplast – have lots of dictyosome and ER – takes lots of sugar and minerals in and transport the product out – secrete nectar, fragrance, mucilage, resins and oils Dictyosomes - are stacks of flat, membrane-bound cavities (cisternae) that together comprise the Golgi apparatus. Within the dictyosomes, proteins are stored, modified, sorted, and packed into vesicles (which are then closed off as Golgi vesicles) for further transport.  B. Collenchyma tissue Elongate in shape. Composed of collenchyma cells Cells has unevenly thickened primary cell wall specially thick in the corner Alive at maturity Support young growing tissues. Occur beneath the epidermis in young stems. Collenchyma  B. Collenchyma tissue Often occurs as long strands near the stem surface and along leaf veins Also located near vascular bundles to make its tips stronger and more resistant to breaking There wall exhibits plasticity and retains there new shape even when tension or pressure ceases  B. Collenchyma tissue Responsible in elongating root tips and in vining plants making also it flexible Turgid parenchyma and collenchyma work together like air pressure and tire  B. Collenchyma tissue Production of collenchyma require more glucose Usually produced only in shoot tips and young petioles Not present in subterranean roots and shoots  C. Sclerenchyma tissue Long or stellate in shape. Occur throughout the plant body. Cells have both primary and secondary cell wall which is strong and hard due to extreme thickening and almost always lignified Cells are often dead Exhibits elasticity  C. Sclerenchyma tissue Support (strengthen) and storage. Specialized for structural support Develop mainly in mature organs that have stopped growing and it its proper size and shape Growing and elongating plant parts are supported by collenchyma tissue and some cells mature into a sclerenchyma once the organ is matured (ex. leaf)  C. Sclerenchyma tissue Unusable in growing shoot tips because its rigidity will prevent elongation Two types of Sclerenchyma: – Mechanical sclerenchyma – Conducting sclerenchyma  a. Mechanical sclerenchyma Sclereids, short more or less cuboidal cells common in shells of nuts (can be seen in seeds) Fibers, long tapered cells that often occurs in groups or clumps, are particularly abundant in the wood and bark of flowering plants (can be seen in bamboo)  a. Mechanical sclerenchyma Sclereids: more or less isodiametric; often dead at maturity – Brittle and inflexible – Form hard and impenetrable surface such as shells of coconuts and seeds – Flexibility would be disadvantagious Types of Sclereids  Types of Sclereids Brachysclereids - isodiametric or elongated, also called stone cells (fleshy edible part of fruits) Macrosclereids - rod-like (epidermal cells of seed coats) Osteosclereids - bone like with lobed ends (seed coat of pisum)  Types of Sclereids Astrosclereids - star shaped (petiole of some plants) Trichosclereid - hard needlelike branched cells found in some species of plants that serve the purpose of protecting the plant from herbivores Filiform - long cylindrical cells (palisade and spongy parenchychyma of olive lef)  a. Mechanical sclerenchyma Fibers: long and flexible; many types are dead, other remain alive and are involved in storage – Found in the wood of most flowering plants – There strength supports the tree and its flexible characteristic allows it to sway in the wind Types of Fibers  Types of Fibers Surface fibers – found on fruit wall and seed coat (ex. coconut) Xylary fibers/wood fibers – located in xylem of plants Extraxylary fibers/bast fibers – located external to xylem – Most common are phloem fiber  Sclerenchyma SCLERIDS FIBERS Right-hand illustration modified from: Weier, Stocking & Barbour, 1974, Botany: An Introduction to Plant Biology, 5th Ed.  b. Conducting Sclerenchyma Tracheids: long and narrow with tapered ends; contain no perforations. Dead at maturity. Found in vascular plants. Vessel elements: short and wide with rather perpendicular end walls; must contain one or two perforations. Dead at maturity. Found almost exclusively in flowering plants and few ferns, horsetails and gymnosperms. b. Conducting Sclerenchyma  Ground Tissue Parenchyma – Polyhedral to round in shape. – Occur throughout the plant body. – Photosynthesis, storage, and secretion. Collenchyma – Elongate in shape. – Occur beneath the epidermis in young stems. – Support young growing tissues. Sclerenchyma- fibers and sclereids. – Long or stellate in shape. – Occur throughout the plant body. – Support (strengthen) and storage. Dermal Tissues  Functions of Epidermis protection against various chemical and physical influences, against being fed upon by animals and against infestation by parasites protection of the plant against desiccation participation in gas exchange, in secretion of metabolic compounds and in absorption of water site of receptors for light and mechanical stimuli that help to transform signals from the surrounding to the plant  Origin of Primary Tissues Primary growth- formation of primary tissues. – Primary plant body.  Plant Tissues Types All plant organs (roots, stems, leaves) are composed of the same tissue types. There are three types of tissue: Ground – bulk of inner layers Dermal – outermost layer Vascular – conducting tissue, transport  Epidermis could be: Uniseriate – single layer Multiseriate – multi layer  Epidermis main dermal tissue of primary plant organs above ground it covers the shoot, leaves, flowers, fruits, and seeds and serves several functions: – protection from: water loss against physical and chemical influences from feeding by animals – participation in gas exchange – secretion  Epidermal cells Perceptors Stomata Trichomes Papillae Glandular hairs Salt and chalk glands Nectaries  Perceptors specific receptors perceive light and mechanical stimuli Photoreceptors in plants – UVR8: UV-B light reception – Cryptochrome: blue and UV-A light reception – Phototropin: blue and UV-A light perception (to mediate phototropism and chloroplast movement) – ZeitlupeZeitlupe: blue light entrainment of the circadian clock – Phytochrome: red and far-red light reception  Stomata serve the function of transpiration and the exchange of gases used in photosynthesis and respiration stomatal complex is the unity of the guard cells and the subsidiary cells  Types of Stomatal Complex Based on Ontogeny perigenous stomata - guard cells and subsidiary cells derive from different mother cells, because guard cells are produced by the equal division of a young epidermal cell mesogenous stomata - dermatogen cell divides unequally to produce a smaller daughter cell with dense cytoplasm and a larger, highly vacuolized cell. The latter give rise to the subsidiary cell, while the other divides equally into the guard cells mesoperigenous - one stomatal meristemoid gives rise to one mesogene subsidiary cell and cell that divides symmetrically resulting two daughter guard cells – the rest of subsidiary cells are perigene and originate from cells lying around the meristemoid  Stomata shapes of the guard cells are manifold mostly bean- or kidney-shaped, but for example in grasses they resemble dumbbells contains chloroplasts cell wall is unevenly thickened: its inner region, adjacent to the stomatal pore is thicker and highly cutinized stomatal pore usually opens into a substomatal cavity within the ground tissue below the stoma  Stomata Guard cells open and close the stomatal pore with the aid of the surrounding cells, which movements are driven by the changing turgidity of the cells When opening, the potassium- and sugar-content of the guard cells increase, what results osmotic water uptake and so the swelling of the cells Owing to the uneven cell wall thickening, the swelling causes the opening of the stomatal pore Closure is the result of the reverse processes  Stomata Subsidiary cells also play important roles in both the opening and the closure of the pore – assist, reinforce, or protect the stomatal cells – Also plays role in water conservation  Trichomes unicellular or multicellular, branched or unbranched, living or dead derivatives of the protoderm ones are initiated by an unequal division and derive from the smaller daughter cell called trichoblast may serve a variety of functions; – they may form a pubescence on the surface or serve the function of secretion (glandular hairs).  Papillae are not individual structures, but the mere outgrowths of the epidermal cells that increasing the surface Real trichomes are protective structures against too intense transpiration, UV radiation, the chewing of herbivores etc. Their form and size are manifold. Bristle hairs are rigid structures protecting the stem against herbivores. Drought resistance is aided for instance by the squamiform hairs arranged parallel to the shoot surface, interlacing each other, or by the long candelabriform hairs giving a felted cover of the shoot. Hooked trichomes (clinging hairs) fasten the plant on their support.  Glandular hairs are epidermal secretory structures secreted material is often accumulated between the cell wall and the cuticle, and released when the cuticle ruptures glandular trichomes are composed of a stalk and a head region may be uni- or multicellular cells of the glandular hair are connected to each other via several plasmodesmata  Glandular hairs during intense secretion, the cells contain high amount of dictyosomes and ER secreted material is various (e.g. volatile oils, flavonoids etc.).  Glandular hairs unique are the glandular hairs of the carnivorous plants being responsible for both prey attraction and digestion, since they also produce proteolytic enzymes  Salt and chalk glands are typical structures of salt resistant plants (halophytes) In structure, they resemble the hydathodes. They serve the discharge of excess salt Through the hydathodes water droplets are exuded, a phenomenon called guttation. The droplets are formed on the edge of the leaves, at the termination of the vascular bundles. Actually, hydatodes are permanently open stomata. Guttated water principally contains inorganic salts.  Nectaries present usually on entomophilous species, produce a sugary solution to attract the insects principally occur in the flowers (floral nectaries), but they are also found outside of flowers (extrafloral nectaries), e.g. on the stem or the leaf nectar secreted by the nectary contains various sugars and amino acids in high concentration.  Transport in Plants Plants need a transport system so that cells deep within the plants tissues can receive the nutrients they need for cell processes The problem in plants is that roots can obtain water, but not sugar, and leaves can produce sugar, but can’t get water from the air  What substances need to be moved? The transport system in plants is called vascular tissue Xylem tissue transports water and soluble minerals Phloem tissue transports sugars  The Vascular Tissues Xylem and phloem are found together in vascular bundles, that sometimes contain other tissues that support and strengthen them  Xylem the principal water-conducting tissue of vascular plants  Adaptations of Xylem to Function Pits allow water to move sideways Lignin is strong and allows for stretching Flow of water is not impeded as: there are no end walls, no cell contents, no nucleus, lignin prevents tubes collapsing  Lignin - fills the spaces in the cell wall between cellulose, hemicellulose, and pectin components, especially in vascular and support tissues – mechanical strength to the cell wall and by extension the plant as a whole – plays a crucial part in conducting water in plant stems  Structure of Xylem also takes part in food storage, support and the conduction of minerals The principal conductive cells of the xylem are tracheary elements, of which there are two types: – Tracheids – Wood vessels Both are elongated cells with secondary cell walls that lack protoplasts at maturity  Structure of Xylem Bordered pits are typical for tracheids, while wood vessels are marked by perforated or completely dissolved final walls  a. Tracheids are the chief water-conducting elements in gymnosperms and seedless vascular plants can also be found in angiosperms elongated cells, closed at both ends 1 mm on average  Tracheids look often square in cross-section, the lignified secondary wall is relatively thin and entire cell surface is evenly coated walls are opened by numerous pits  pits occurs solitarily, statistically scattered, arranged in turns around the middle axis or grouped together (can often be found at the cell's ends) If gap-like pits lay on top of one another, a ladder- or stair-like perforation commonly called scalariform may be the result  Patterns of Secondary Thickening in Tracheids  pits often surrounded by a halo that are called bordered pits – especially common in the tracheids of some gymnosperms – Their structure can be discerned best in a cross-section through neighboring cells  bordered pits middle lamella between the cells is preserved within the pits margo - the area between torus and wall (the former middle lamella), its porosity allows the movement of water and ions from tracheid to tracheid  bordered pits Torus - their centre is made up by a disc of primary cell wall material No secondary walls exists in the pit's structure exist only in cells with secondary walls  Wood Vessels (tracheae) the water-filled tubes of the xylem Wood vessels are the chief water-conducting elements of angiosperms  Wood Vessels final walls of the single vessels are perforated or, much more so, completely perforated generally thought to be more efficient water conductors than tracheids  Wood Vessels can be as long as several meters commonly assumed that at least in some species the wood vessels are as long as the whole shoot  Wood Vessels usually round in cross-section and have a larger diameter (than the tracheids) that enhances their capacity for water-conduction Exceptionally wide-lumened elements can be seen with deciduous trees  Wood Vessels The water-loss of a fully developed birch tree with an estimated number of 200 000 leaves can be up to 400 litres per day.  Xylem Fiber provide structural support for the most important xylem cells, the tracheary elements (TE) very much elongated with tapering ends  Xylem Fiber dead cells having lignified walls with narrow lumen both in primary and secondary xylem Xylem fibres or wood fibre are two types Fibres tracheids - are intermediate forms between fibre and tracheids, possessing border pits whose borders are not fully developed Libriform fibres - are narrow, having obliterated lumen – They contain thick secondary wall with simple pits – provide additional mechanical support to the plant body  Xylem Parenchyma cells associated with the xylem are known as xylem parenchyma (only living component found in xylem tissue) cell wall is thin and made up of cellulose act as storage house of starch and fat which assist in conduction of water The Phloem  The Phloem principal food-conducting tissue of vascular plants its elements are elongated in contrast to tracheids and wood vessels, mature phloem elements contain a protoplast and sometimes even a nucleus  The Phloem The main conducting elements of the phloem are the sieve elements, of which there are two different types: – sieve cells – sieve-tube members  Sieve cells Elongated cells with steep inclined end walls Pores are narrow, quite uniform in structure and are distributed evenly on all walls (sieve areas) only type of food-conducting cells in most seedless vascular plants and gymnosperms  Sieve-tube Members only food conducting elements in angiosperm occur end-on-end in longitudinal series called sieve tubes are in contact via plasmodesmata  Sieve-tube Members End walls are inclined to transverse End walls are typically interspersed with primary pit areas (groups of plasmodesmata), that later on develop into sieve plates  Sieve-tube Members Sieve tubes in the phloem of angiosperms are flanked by one or several plasma-rich, nucleated companion cells, that do not occur in gymnosperms In Ginkgo and other gymnosperms are associated by specialized parenchyma cells called albuminous cells – Albuminous cells participate in loading and unloading of these cells.