Botanik (Subject) / Morphology (Lesson)

Morphologie = Lehre von der Struktur und Form der Organismen

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• Morphology of the cormus Cormus = vielzelliger Vegetationskörper einer Pflanze, der in Sprossachse, Blatt und Wurzel gegliedert ist Comophytes (ferns, flowering plants): land plants with efficient water transport systems; are differentiated into the three organs -Leaf: flattened organs for photosynthesis; optimization of the light yield, shielded from too much water loss by epidermis; other functions e.g. reproduction (flower) -Shoot: positioning of leaves and reproductive organs, transport, storage -Root: anchoring in soil, uptake of water & nutrients, storage 
• Metamorphosis = when organs take over functions other than typical ones and develop different forms to adapt to the enviromental conditions to guarantee their survival 
• Primary shoot ->shoot as well as cotyledons and root have already been created in the embryo in the seed -root emerges first -leaf - cotyledon -shoot - hypocotyl -root - embryonic root Apical meristem is protected in buds by leaves. All shoot and leaf tissue derive (ableiten) from this. In their axils, the axillary buds are located wich remain meristematic
• As plants grow -a few cells remain meristematic in the cambium or the axillary buds  -the other cells differentiate into dermal, vascular and ground tissue
• As plants grow -a few cells remain meristematic in the cambium or the axillary buds  -the other cells differentiate into dermal, vascular and ground tissue
• Shoots -in shoots the trasport tissue is organized in vascular bundles with the xylem directed towards the center and the phloem directed towards the outside ->this arrangement is called collateral (seitlich, begleitend)
• Dicots and gymnosperms ->a meristem, the cambium, remains between xylem and pholem: collateral open 
• Monocots ->no cambium remains: collateral closed 
• Vascular bundles ->typically surrounded by a bundle sheath of parenchyma or sclerenchyma cells
• Monocots -the primary growth can be very strong, forming relatively thick and tall stems  -grasses, e.g. bamboo, usually have hollow stems (stalks) -palms have massive stems and vascular bundles scattered across the cross-section
• Monocots -the primary growth can be very strong, forming relatively thick and tall stems  -grasses, e.g. bamboo, usually have hollow stems (stalks) -palms have massive stems and vascular bundles scattered across the cross-section -without secondary thickness growth they are characterised by slender stems -the large apical meristem is soft and can sometimes be eaten (in some bamboo and palm trees = palm heart)
• Secondary shoot ->the primary developmental state of the stem axil is maintained throughout the life of many short-lived dicots and almost all monocots e.g. field-chickweed (dicot), black nightshade (dicot), yellow star of Bethlehem (monocot) -since plants compete for light, being taller brings massive advantages -however the height growth with constant shoot diameter is limited   ->vascular tissue can only supply a limited amount of leaves, roots, shoots   ->mechanical stability limits the growth especially in height Solution: secondary thickness growth -enlargement of the vascular tissue and therefore higher transport capacity -more leaves can be exposed to light and supplied -the necesarry mechanical stability from greater diameter of lignified vascular tissue -growth in height is possible Disadvantage: large investment of recourses in unproductive stem (does not directly contribute to photosynthesis or seed production) ->periderm as a secondary dermal tissue replaces the epidermis ->it is impregnated with various antimicrobial substances (tannis) to protect against pests and pathogens ->the tick cork layer also protects against water loss, extreme temperature and mechanical damage ->in most woody plants, successive periderm layers are formed in the living bark (secondary pholem)
• Wood and bark Secondary xylem = wood (heartwood / sapwood) Secondary phloem = living bark  dead bark = protective dermal tissue outside, composed of one or several cork layers and other tissue in between -the cambium mostly produces cells elongated along the axis but some cells are radially stretched for radial transport: these form the rays A stem can be cut in any way, but three main directions of the cut permit to analyse and classify wood ->cross-section: shows the width of the longitudinal cells and of the rays ->radial section: along the extension of vessels and rays ->tangential section: along the vessels, height and width of rays are visible
• Transport in plants gases (CO2, O2, H2O): intercellular spaces water: xylem inorganic nutrients: xylem organ compunds (mainly sugar, but including RNA, amino acids, hormones, nutrients in organic molecules): phloem Challenge: -water transport in xylem: transports hundreds of litres of water per day up to 100m high in thin capillaries (vessels, tracheids) with very high friction resistance -organ, molecules in phloem: need to regulate, what, when, where to transport
• Water potential -measure for the availability of water -water always flows from places with higher water potential to places with lower water potential Definition: pure (destilled) water has water potential -water can be transported in a tube (e.g. a straw) by applying positive pressure on one end or reducing pressure (suction - sog) at the other end -molecules dissolved in water decrease the availability of (pure) water loss -the higher concentration in the cell produces a pressure by osmosis (turgor)   ->living cells: higher concentration (very negative osmotic potential) and positive turgor    ->dead (water transporting) cells: rel. low concentration (little negative osmotic potential)         and often negative pressure (suction or tension) In case of differences: water flows from high to low potential -the potential is balanced over short distances (like neighbouring cells) -over long distances water flows along the potential gradient (Gefälle) - and can thus flow against gravity
• Water transport Transport of water and nutrient salts dissolved in it often takes place over long distance and against gravity -the driving force is water loss to the dry air: transpiration by leaves -the water loss is extracted from the xylem and creates a suction that pulls water with very high negative pressure (or tension)   ->purely physical process, does not require energy input by the plant -cohesion of water molecules ensure that the water column in the vascular tissue does not break -the process of water transport in plants is described by the cohesion-tension theory -high water flows through small tubes/conduits (Leitung) - vessels and tracheids   ->requires a high water potential gradient, so that enough water supplies the leaves -the higher the leaf transpiration (water consumption), the faster water needs to flow and the higher is the necessary potential gradient -water is transported under negative pressure (=tension)
• Water transport speed silver fir (Abies alba): only tracheids - 1 m/h common beech (Fagus sylvatica): small-diameter vessels 1-6 m/h scots elm (Ulmus glabra): large-diameter vessels - max. 44 m/h clematis (Clematis vitabla) - a lianal: very large vessels > 100 m/h
• Water can boil in wood -if tension gets too high, liquid water sudden change phase to gas -cavitation leads to the formation of embolus (gas bubbles) -these block further water transport (plant dries out) -results in a high pressure difference between gas-filled and water-filled vessels -cavitation is a sudden transition fom liquid to gas -makes the cell walls vibrate and can be heard -if one element is gas-filles (no negative pressure), the pressure difference along the membrane becomes very high  -gas bubbles can be sucked through the tiny pores, causing embolism (Gefäßverschluss) what leads to water transport failure -drought resistance depends (among other things) on embolism resistance of the xylem -pit membrane is a very thin cell wall and no biomembrane
• Bordered pits in conifers -in conifer wood, specialized pits function as "check valves" (Klappen) -the central part of the membrane is thickened  -when embolism occurs (high pressure difference) the thickened part of the membrane is sucked to one side, closing a large pore (thick cell wall) -spread of emboli is blocked
• Water transport: plant growth -too negative water potential is avoided by (partially) closing stomata -reduce the water consumption, lower flow rate   ->less negative potential   ->less danger of embolisms, but also less CO2 intake and photosynthesis This is the main reason why drought stress (water limitation) reduces plant growth
• Water transport: plant growth -too negative water potential is avoided by (partially) closing stomata -reduce the water consumption, lower flow rate   ->less negative potential   ->less danger of embolisms, but also less CO2 intake and photosynthesis This is the main reason why drought stress (water limitation) reduces plant growth -trees grow tall because of competition for light -but there are limits for height growth -the tallest trees are conifers about 100m -usually conifers grow at places with a higher humidity (low transpiration) A branch in great height can only use very little water - photosynthesis becomes minimal
• Transport in the phloem -transport of assimiltates (especially sugar) in the phloem is active and demand-driven   ->from source to sink Sources: photosynthetically active tissues (leaves) or storage Sinks: all photosynthetically inactive tissues - especially growing tissues and storage tissues
• Studying phloem transport Aphids (Blattlaus) feed on the phloem sap (Saft) ->their stylet pierces the sieve tube and cut it off, so the phloem sap can be collected -the main components are mainly socruse (transport form for energy) + amino acids, hormones, nutrients Source: Companion cells actively transport sugar into sieve tube (loading)   ->osmotic concentration increases, water is taken up by osmosis, pressure increases Sink: Companion cells takes sugar from the sieve tube (unloading)   ->osmotic concentration decreases, water flows out of sieve tube by osmosis, pressure     decreases thus cells for phloem transport need a biomembrane (selective boundary) ->they are not under negative pressure (no lignification needed) ->need energy and control by companion cells (water flows along a positive pressure gradient)
• Morphology of a shoot -shoot consists of stems and leaves -the point where a leaf is attatched to the stem is the node -the stem between the nodes is the internode  -buds contain the apical meristem for length growth -apart from the terminal bud, buds are formed in leaf axils (axillary buds) -when they grow and form leaves, they become terminal buds (apex - Spize)
• Internode length Internodium = Teil einer Sprossachse, zwischen zwei Knoten (Nodi), der definitionsgemäß keine Blätter trägt -defines the distance between leaves, typically depending on leaf -important to avoid self-shading of leaves -in some plants there are strong variations: short shoots have shordened internodes, the leaves are densely (dicht) packed together -in plants with short shoots, shoots with normal internode length are called long shoots -in many fruit trees (cherry, apple) flowers are borne on short shoots -the meristem in buds is mostly protected by small scale-like leaves on very short internodes
• Shoot metamorphosis Stolons (Ausläufer): above ground, thin, creeping shoot with very long internodes ->for vegetative interproduction like in bugleherb, common silverweed, strawberry Rhizomes (Wurzelstock): subterranean, mostly horizontal thick shoots that serve as storage and hibernating organs Leaves are present (in contrast to roots), but strongly reduced, often scally (abblätternd) like ginger, timothy or bearded iris Tubers: the axis is thickened, internodes are short, leaves are often strongly reduced  ->mostly subterranean (as in potatoes), sometimes aboveground (some types of cabbage) Bulbs: short stems with fleshy leaves or leaf bases that serve as a storage organ (the storage is in the leaves)
• Shoot metamorphosis Stolons (Ausläufer): above ground, thin, creeping shoot with very long internodes ->for vegetative interproduction like in bugleherb, common silverweed, strawberry Rhizomes (Wurzelstock): subterranean, mostly horizontal thick shoots that serve as storage and hibernating organs Leaves are present (in contrast to roots), but strongly reduced, often scally (abblätternd) like ginger, timothy or bearded iris Tubers: the axis is thickened, internodes are short, leaves are often strongly reduced  ->mostly subterranean (as in potatoes), sometimes aboveground (some types of cabbage) Bulbs: short stems with fleshy leaves or leaf bases that serve as a storage organ (the storage is in the leaves)
• Climbing shoots Winder: the main shoot is lengthened & touchsensitiv; grows in loops around its support like hop (with climbing haris) Tendrils are lateral shoots (there are also leaf and root tendrils) with limited growth and mostly no leaves  ->they curl around it´s support as in grape vine (Rebe) ->in grape ivy (mauerkatze), tendrils have adhesive (anhaftend) disks, permitting it to climb walls
• Thorns -short lignified and pointed shoots -usually without leaves -serve for defence against herbivores e.g. blackthorn, seabuchthorn Thorns are shoots - spines are spiny leaf metamorphoses Prickles (as in roses) are not organs, they contain epidermal + ground tissue, no vascular tissue 
• Succulent Shoot -succulent organs are thick, fleshy -mostly composed of water-storing parenchyma cells -plants with succulent shoots (such as cacti) often have reduced leaves (to spines in the case of cacti) -the shoot is green and serves for photosynthesis
• Succulent Shoot - metamorphosis -succulent organs are thick, fleshy -mostly composed of water-storing parenchyma cells -plants with succulent shoots (such as cacti) often have reduced leaves (to spines in the case of cacti) -the shoot is green and serves for photosynthesis
• Flattened shoot - metamorphoses -shoot axis is flattened and green for photosynthesis, the leaves often reduced to spines or scales or missing -in Ruscus (butchers broom), they look identical to leaves, but they bear flowers, which true leaves never do -opuntia ficus-indica (prickly pear) is a cactus very common in the Mediterrenean, where it is an exotic species
• Root -usually subterranean main functions -anchoring in soil and stabilisation -water and nutrient uptake -storage ->the functions and forms are similar to the shoots (mechanical support, water transport), but in contrast to shoots, roots have -no leaves -no stomata -different (endogenous) branching -different (radial) vascular bundle During germination the organ first emerging from the seed is the root, to secure the water supply. Because the seed stores energy and nutrients, the start of photosynthesis with the first leaves can be delayed
• Primary root -after division, the cells elongate (reach their final size) and mature (cell wall thickening etc.) -the apical meristem produces the dermal, ground and vascular tissue - similar to the shoot Without leaves and in the soil, it needs to be protected in a different way: ->the root cap is produced by the apical meristem (Scheitel-Bildungsgewebe) ->the cells produce mucilage (Schleimstoff) to protect and assist the root growing into the soil ->after some time, they are seperated from the rood and die
• Primary root: maturation zone -in this zone of the young root, the cells receive their final function: the rhizodermis differentiates to absorb water and minerals from the soil solution -in contrast to the epidermis, it has no stomata and no cuticle -the rhizodermis produces single-celled root hairs that vastly increase the surface area uptake and can also penetrate fine soil pores -rhizodermis and root hairs mostly die after a few days or weeks, thus roots grow constantly to absorb water and nutrients
• Primary root: anatomy -the anatomy of the root differs from the shoot -there is only one radial vascular bundle, where xylem and phloem are alternating -the vascular bundle is surrounded by the pericycle and the endodermis -the endodermis is part of the root cortex (mainly storage parenchyma) -side rots develop from the pericycle (internally)
• Primary roots: Endodermis -water from the soil (+ all dissolved substances) can flow through the cell walls (apoplastic transport is uncontrolled) or through the symplast (controlled by membranes) -the plant only has direct control over the composition in spaces delimited by biomembrane (living cells) -the sum of all protoplasts (which are connected by plasmodesma): symplasts -all parts outside living cells (cell walls, intercellulars, dead xylem elements) are not filtered by membranes: apoplast -central cylinder: radial vascular bundle in the centre - phloem and xylem arranged radially and without pith rays - important difference to the shoot
• Primary root: Exodermis -consists of one / more cell layers directly below the rhizodermis  -after the death of the short-lived rhizodermis, it forms the dermal tissue in older parts of the primary root -the cell walls of the exodermis cells suberize (suberin) and reduce possible water loss from the root to the soil -a casparian strip helps to control nutrient uptake
• Secondary root -in most dicotyls and gymnosperm, secondary thickness growth also occurs in the root -cambium forms between the xylem and phloem and party of the pericycle (above the xylem branches) become meristematic -the further sequences resemble those in the secondary shoot -secondary xylem and phloem form as in the shoot with wood and bast rays (Strahlen) -pericycles form a periderm, all tissue outside of it are shed (abgeworfen) or torn apart
• Secondary root -in most dicotyls and gymnosperm, secondary thickness growth also occurs in the root -cambium forms between the xylem and phloem and party of the pericycle (above the xylem branches) become meristematic -the further sequences resemble those in the secondary shoot -secondary xylem and phloem form as in the shoot with wood and bast rays (Strahlen) -pericycles form a periderm, all tissue outside of it are shed (abgeworfen) or torn apart
• Secondary root growth -in most dicots and gymnosperm, secondary thickness growth also occurs in the root -cambium forms from the parenchyma between xylem and phloem and partly out of the pericycle -as in shoots, it produces secondary phloem (to the outside) and secondary xylem (to the inside) -the pericycle also becomes a cork cambium forming a periderm (in shoots it is the layer below the epidermis) -thus, all layers outside the periderm (cortex and rhizodermis) die and are shed
• Root crown In the lowest part of the stem, the xylem and phloem of the vascular bundles must connect from radial bundle of the root to the collateral bundles of the shoot
• Root systems -roots among species differ in growth pattern and they also always adapt to local soil conditions -plants pursue different strategies for water and nutrient intake, which makes coexistence of many species easier and helps to maintain diversity two important basic types of root systems -allorhizy (typical for dicots and gymnosperms): the seeding root remains the primary (main) root and forms side roots -homorhizy (typical for monocots): seedling root dies, is replaced by adventitious roots from the lower stem, that are similar thin
• Root systems: root sucker -are similar to shoot stolons (Ausläufer) -roots growing near the surface can form new shoots -used vor vegetative reproduction and propagation (Verbreitung) but make it difficult to eradicate (ausrotten) unwanted plants -locust tree and tree of heaven are invasive trees in Austria that produce numerous root suckers and are difficult to control
• Root metamorphosis: root tendril = Ranke similar to shoot and leaf tendrils, more common are climbing roots ->produced by the stem for anchorage like ivy 
• Root metamorphosis: root thorns ->serve as defence like other thorns, occur in above-ground roots e.g. myrmecophyte, palm tree
• Root metamorphosis: storage roots ->strong secondary thickness growth leads to formation of evenly or locally thickened (root tubers) storage organs e.g. sweet potatoe, black salsify
• Root metamorphosis: storage roots ->strong secondary thickness growth leads to formation of evenly or locally thickened (root tubers) storage organs e.g. sweet potatoe, black salsify ->in many vegetables (bete, turnip, carrot) the primary taproot is thickened and often includes parts of the lower stem
• Root metamorphosis: butress root or prop roots =Stützwurzel ->for mechanical support of the stem e.g. Ficus, Ulmus laevis
• Root metamorphosis: stilt root and respiratory root -to supply below-ground roots with oxygen -especially in plants in waterlogged soils where oxygen concentration in the soil is very low - zero -seen in many mangroves 

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