Summary of Plant Evolution and Development PDF

**Evolution and plant development** Differences between plants and animals plants animals -------------------- ------------------------------------------------------------------------------...

**Evolution and plant development** Differences between plants and animals plants animals -------------------- ------------------------------------------------------------------------------------------ ---------------------------------------------------------------- Movement (generally) Not able to move (generally) can move around freely Mode of nutrition autotrophs Heterothrops Respriration Take in CO2 release O2 Take in O2 release CO2 Respone Sophisticated systems to detect and respond to e.g. light, gravity, temperature, touch Nervous system Growth Growth is restricted to certain meristematic tissue regions but contious throughout life Growth is not restricted to particular regions and is definite Cellular structure Basic cell features + chloroplast, cell walls, vacuoles and plasmodesmata Basic cell feature Plasmodesmata= channels that connect living part of plant cells. This way cytoplasm of adjacent cells are connected and the plant cells unify into one living continuum. Water and small solutes pass freely from cell to cell (symplastic route) Symplast= continuum of cytosol connected by plasmodesmata Apoplast= continuum of cell walls and extracellular spaces Basic features of all cells - Bounded by plasma membrane - Cytosol (nl: cytoplasma) with subcellular components - Chromosomes - Ribosomes Difference prokaryotic & eukaryotic cells - Location of DNA - Membrane-bound organelles (mitochondria, nucleus, ER, golgi apparatus) First Eukaryotic - endosymbiosis theory A ancestral prokaryote the plasma membrane folds in creating the nucleus and the ER engulfs an aerobic bacterium which becomes the mitochondrion ancestral eukaryote (heterotroph) engulfs a photosynthetic bacterium which becomes the chloroplast ancestral photosynthetic eukaryote Prove endosymbiosis theory - Bounded by two membranes instead of one - Inner membrane of organelles have enzyms & transport systems homogous to those found in plasma membranes of living bacteria - Autonomous: they are capable of transcription and translation - Circular DNA **Algae** There are 4 supergroups of Eukaryotes - Excavate - SAR - Brown algae - Archaeplastida - Red algae - Green algae - plants - Unikonta Laminaria (Brown Algae) - Almost entirely marine, live on rocky shore in cooler regions of the world - 1500 species - Alternation of heteromorphic generations (=the sporophyte and gametophyte are morphologically clearly different) 1. Male gametophytes release sperm and female gametophytes produce eggs 2. Sperm finds egg Fertilization creates a diploid zygote 3. Sporophyte develops by mitosis and remains attached to the female gametophyte 4. Sporangia produces zoospores(=motile spores) by meiosis 5. Spores develop into an independent male and female gametophytes by mitosis Polysiphonia (Red Algae) - Live in tropical and warm water - 6000 species - Alternation of generations 3 multicellular life cycle phases !unique A diagram of a life cycle Description automatically generated Phycoerythrin= pigment that gives it it's red colour\ Red algae doesn't have flagellated sperm cells it is dependent on water to bring it to an egg cell Life cycle red algae 1. Fertilizaton create diploid zygote 2. Carpogonium 3. Carpogonium produces diploid carpospores 4. Carpospores germinate develop into a sporophyte 5. Sporophyte produces sporangium which produces haploid spores by meiosis 6. Germinating spore develop into gametophytes Chlamydomonas (Green Algae) - Aquatic - 7000 species They are unicellular and often used as a model organism. They can reproduce both sexually and non-sexually. They reproduce sexually when there is stress increases survival chance species  Ulva (green algae) - Live in water, common along temperate seashores - Alternation of isomorphic generations (=gametophyte and sporophyte are look morphologically the same) **Bryophytes**  Plants evolved from green algae. Evidence for this is that many key traits of plants are also found in some algae - Multicellular, eukaryotic, photosynthetic autotroph - Cell walls composed of cellulose - Chloroplasts with chlorophylls a & b - Flagellated sperm - Pigments β-carotene and xanthophylls - Enzyme glycolate oxidase (photorespiration) The closes relatives of plants are a group of green algae called Charophytes. They share some distinctive traits - Rings of cellulose-synthesizing proteins - Flagellated sperm - Eggs encased within protective tissue - Nuclear, mitochondrial, chloroplast DNA - Sporopollenin (layer around spores) When moving to land, plants faced some challenges. But , bryophytes have a series of adaptation that enable them to overcome these challenges - Maintaining moisture: how would they withstand desiccation with a scarcity of water Cuticle(=waxy layer) to protect against desiccation, UV radiation, microbial attack and mechanical damage. The cuticle has stomata (or in Marchantia case pores) to still allow for gas exchange - Obtaining resource Specialized cells for water/nutrient uptake (sometimes developed). The cell walls of these cells are not lignified, therefore it isn't xylem - Gravity/ staying upright Rhizoids for anchoring on rock/soil and staying low to the ground - Reproduction: how to protect gametes and offspring from drying out and how about fertilization without water? Structures for the protection of reproductive cells - Walled spores produced in sporangia. The spore walls contain sporopollenin - Gametes protected inside multicellular gametangia (archegonia and antheridia) - Protected embryo Bryophytes are the most primitive land plants. They were important initial colonizers of bare rocks and soil surfaces. They live mostly in moist locations. They are still complete made of thallus and have no vascular system. There are 3 main types of Bryophytes - Liverworts - Mosses - Hornworts Marchantia (liverwort) - Live on land in moist locations - Alternation of heteromorphic generations The sporophyte is permanently attached to the gametophyte. Marchantia can reproduce asexually via gemmae form by the gemma cups They need water for fertilization Life cycle Marchantia  Atrichum (true Moss) - Live on land in moist locations - Alternation of heteromorphic generations Spores are located in the capsule. The capsule dries out. It tears open and releases the spores. They are then dispursed by the wind In both liverworts and Mosses the sporangium is inside a capsule which is connected to the sporophyte with a seta  **Ferns** Ferns are\ Like mosses in that they still need water for fertilization (flagellated sperm)\ Unlike mosses in that they - Have a dominant sporophyte, and a small, but independent gametophyte - Have a vascular system - Have a branched sporophyte with multiple sporangia - Have differentiated tissues/organ systems (true roots and leaves) Plasmodesmata are great for transporting water and nutrients over a short distance, but diffusion-imposed constraints make it pretty ineffective over longer distances. Emergence of Water-conducting ensheathe by Food-conducting cells (WCCs and FCCS). Phloem and xylem are FCCs and WCCs Extra advance: Because xylem has secondary, lignified walls, the vascular system also gave biomechanical support and plants could increase in height. Telome theory= all the vascular plants have evolved directly or indirectly from simple, leafless, dichotomously branched ancestor type "Rhynia" type made up of sterile (no sporangium) and fertile(sporangium) axis called telomes Telome= simple terminal partions of a dichotomously branched axis. A group of telome is called a syntelome. The place where they're still fussed is the mesome Formation of leaves according to the telome theory 1. Overtobbing= one of the two dichotomizing branches of axis becomes larger, stronger and vertically upward and the shorter dichotomy was displaced laterally weaker branch was overtopped by stronger branch 2. Planation= telomes and mesomes of a syntelome shift from 3-D pattern to a single plane 3. Syngenesis/fusion/webbing= fusion of telomes and mesomes by the development of parenchymatous tissue. It leads in the explanation of the formation of leaves with open dichotious pinnatified, reticulate venation 4. Reduction= transformation of a syntelome into a single needle-like leaf (explain evolution of microphylls) 5. Curvation - recurvation: telome bent down - Incurvation: shifting sporangia to ventral surface of leaf Zimmermann\'s telome theory of megaphyll leaf evolution: a molecular and cellular critique - ScienceDirect Two types of leaves - Microphylls - Small leaves supported by one strand of vascular tissue - lycophytes - Megaphylls - Leaves with highly branched vascular system - Almost all other vascular plants and monilophytes - Almost always larger than microphylls Sporophylls= modified leaves bearing sporangia. They often produce clusters of sporangia called sori (singular sorus). Sporophylls can curl in on itself and form cone-like structures called strobili  You can subdivide the ferns into - Lycophytes (lycopodium) - Monilophytes (selaginella, and polypodium In polypodium, the sporangium open because one side of the sporangium capsule dries out and shrinks like an accordion the sporangium pops and the spores get distributed **Gymnosperms** Gymnosperms= naked seeds. The sporophylls(leaves with spores in them) are arranged in a cone. There are 4 types of gymnosperms 1. Cycadophyte has flagellated sperm cells 2. Ginkgophyte has flagellated sperm cells 3. Gnetophyte doesn't have flagellated sperm cells 4. Coniferophyte (pine trees) doesn\'t have flagellated sperm cells Gymnosperms show further adaptations (than bryophytes and ferns ) that help to cope with conditions on land Characteristics of gymnosperms - Reduced gametophyte: the sporophyte is dominant. The gametophyte is microscopic and inside the cone - Heterospory: there are different types of spores created from different types of sporangia and sporophyll. Heterospory is necessary precondition for the evolution of seeds - Megasporangium on megasporophyll Megaspore female gametophyte eggs - Microsporangium on microsporophyll Microspore male gametophyte sperm - Pollen - Ovules - Seed Pollen are created from the microspores. Inside the pollen you find the male gametophyte. In a pollen, a sperm is carried to an egg by a pollen tube. The sperm is no longer dependent on water. The creation of pollen 1. The microsporocytes (2n) in the microsporangia undergo meiosis and form a tetrad of microspores (n) 2. The microspores undergo mitosis develop into a small gametophyte constating of 4 cells. - 2 cell bodies - 1 generative cell - 1 tube cell Ovules= megasporangium + megaspore + integument (= layer of sporophyte tissue). When the megasporocyte undergoes meiosis it creates 4 megaspores, 3 of which degenerate. The megaspore gives rise to a female gametophyte Build of the ovule: Ovulate scale (megasporophyll) ovule megasporangium 1 megasporocyte In the female gametophyte 2-3 archegonia are present, each with 1 egg cell Male gametophyte - Enclosed in a pollen grain - Develops from microspore Female gametophyte - Part of the ovule - Develops form megaspore, still within the megasporangium Seed= embryo + food supply(female gametophyte) + protective seed coat derived from integument Pollination= Transfer of pollen to part of the plant that contains the ovules 1. Ovulate scales are widely separated 2. Pollen grains settle on scales. They stick because of a pollination drop at the tip of the ovule 3. Pollen grain contacts megasporagium and the scales grow together 4. Pollen grain germinates and forms a pollen tube 5. Pollen tube digested its way through megasporagium 6. Generative cell divides about a year after pollination 1 sterile and 1 sperm 7. Sperm cell divides once more to produce 2 sperm cells. At this point the male gametophyte is mature and ready for fertilization Fertilization= the union of 2 haploid gametes to produce a diploid zygote. 8. After +- 15 months after pollination, pollen tube reaches egg cell of an archegonium 9. 1 sperm unites with egg nucleus, the other disintegrates 10. Usually the egg of all the archegonia are fertilized Embryo development 11. Fertilized eggs develop into embryos polyembryony (= multiple embryos develop). In general, only 1 embryo develops fully 12. Integument develops into seed coat The final seed consists of 2 diploid generations - Old generation - Seed coat - Remnants megasporagium - New generation - Embryo **\ ** **Angiosperms** Angiosperms= land plants with their seeds enclosed in megasporophylls(=carpels) In angiosperms the megasporangia are located at the edge of the megasporophyll. By fusion of the leaf edges, a vessel is formed which encloses a double row of megasporangia (ovules). The carpels develop into a fruit after ferritization Stamen of three modern plants show three possible stages in the evolution of that organ. The leaflike portion of the sporophyll was progressively reduced. In the last stage only the microsporangia remains Parts of a Flower --- Mathwizurd Carpel or Pistil - Carpel: composed of stigma, style and ovary - Simple pistil: a single unfused carpel (same as carpel) - Compound pistil: consists of 2 or more fused carpels - A flower can also have multiple unfused carpels A cone developed into a flower because the cone flattened out after that the organs separated and arrange in whorls into - Carpels - Stamens - Petals - Sepals There are 2 types of flowers - Eudicots: have typically 5 organs per whorl - Monocots: have typically 3 organs per whorl Lifecycle angiosperms Male gametophyte 1. The microsporangia (pollen sacs on anther) on the microsporophyll (stamen) contain microsporocytes 2. Microsporocytes undergo meiosis and produce microspores 3. Microspores develop into pollen grain with inside the male gametophyte 4. The generative cell divides and forms 2 sperm cells Female gametophyte 1. The megasporangium (inside the ovule) inside the megasporophyll (carpel) contain each 1 megasporocyte 2. Megasprorocyte undergoes meiosis and produces 4 megaspores 3. 1 megaspore survives 4. The female gametophyte(embryo sac contains antipodal cells, polar nuclei in central cell, synergids and egg) develops from megaspore Pollination and fertilization 5. Pollen forms pollen tube ones it lands on the stigma 6. 2 sperms cell are discharged in each ovule 7. 1 sperm fertilizes egg the other fertilizes the central cell (3n). This will serve as food supply 8. Zygote develops into embryo in a seed Tapetum= tissue in the sporangium that provides nutrients for the growing spores Fruit is the mature ovary of a flower. There are several types of fruit - Simple fruit: fruits formed from a single carpel or several fused carpels (pistil) Eg: beans, tomato - Aggregate fruit: fruit formed from a single flower that has more than one separated carpel, each forming a small fruit Eg: raspberry - Multiple fruit: fruit develops from an inflorescence (= group of tightly clustered flowers). Walls of the many ovaries start to thicken, they fuse and become incorporated into one fruit Eg: pineapple - Accessory fruit: other floral parts contribute to the fruit Eg: apple  Pericarp= ovary wall Caryopsis= a dry one-seeded fruit in which the ovary wall (pericarp) is united with the seed coat. Typical of grasses and cereals for example maize Fruits have evolved in relation to their dispersal agents (bright colours, light, nectar) **Orchid Flowers and the ABC-Model** ABC Model of flower development= A,B and C genes work together in the development of a flower - A class: Sepal and Petal - B class: Petal and Stamen - C class: Stamen A and C are mutually antagonistic is A is mutated, C is expressed and is C is mutated, A is expressed\ B does not express individually, always A+B or B+C Mutation - A mutated: Sepal and Petal are not expressed C takes A place Stamen and Carpel are developed twice - B mutated: Petal and Stamen are not expressed sepal and carpal are developed twice - C mutated: Carpel and Stamen are not expressed A takes C place Sepal and Petal are developed twice Perianth code model= Explains genetic basis of median petal (lip) of orchids. It develop in orchids because they have a lot of copies of genes and they are the only ones that have a lip pendal The expression of two groups of genes determines if orchids have a bigger median petal - L genes: B copy3 and C copy2 - SP genes: B copy1 and C copy1  Oncidiinae model= explains the genetic basis of further orchid sepal differentiation. In orchids some median sepals look different from lateral sepals because different copy and different numbers of copies coding for the same structure are expressed. There is a shift in expression of B and C class genes. Some copies are being expressed and other are not created to understand small differences that couldn't be explained using the Perianth code model Callus(holdfast for pollinator) of a orchid on the lip used to be a stamen **Embryo development** There are two types of embryos in angiosperms - Eudicot: have 2 cotyledons that take up the entire seed - Monocots: have 1 cotyledon that doesn't take up the entire seed - Gymnosperms have more than 2 cotyledons Eudicots used to be called dicots, however dicots mean "all angiosperms other than monocots paraphyletic (having a different ancestor?)" Important! Embryogenesis=development of an embryo 1. Fertilization ovule becomes mature seed and integuments harden into a seed coat 2. Zygote divides into the basal and terminal cell (proembryo). This is a asymmetrical division, meaning that the Terminal cell is a lot smaller than the basal cell. This is because of internal polarization. One side of the zygote is mainly vacuole while the other contains more cytosol 3. Embryo develops further into a seedling - Terminal cell spherical proembryo heart-shaped embryo (formation cotyledons) torpedo-shaped embryo (hypocotyl elongation) mature embryo - Basal cell suspensor (=helps transferring nutrients to the embryo - Shoot apical meristem (SAM): develops between the cotyledons - Root apical meristem (RAM): develops at the end of the embryo axis In Angiosperms, a mature embryo fills up the entire seed coat  Different types of divisions - Longitudinal divisions: in length - Transverse divisions: in width - Periclinal division: along the axis (to make tissue thicker) - Anticlinal division: perpendicular to the axis (to make tissue wider) Divisions in embryo development 1. Asymmetric division: first step towards differentiation because it turns into the terminal and basal cell that become suspensor and embryo 2. 2 longitudinal divisions of the terminal cell 3. 1 transversal division of the terminal cell (8-cell embryo) 4. First periclinal division of the terminal cell (16-cell embryo) 5. First anticlinal division of the terminal cell (globular embryo)  Monocot and eudicot seed Seed - Diagram, Structure & Examples **Germination, meristem, cells and tissues** Dormancy= seeds don't immediately germinate ones the seed is matured. Some need to find a suitable environment first or need a specific cue to break their dormancy. In this time they use endosperm of cotyledons as nutrients. Resurrection genomics= reviving biological material for example germinating ancient seeds from archaeological sites to study the genomics of these individuals Epicotyle= between the plumule(=epicotyl + young leave(s) + apical meristem) and the cotyledonary node\ Hypocotyl= between the cotyledonary node and the radicle Epigeal germination= during elongation of the hypocotyl the cotyledons are brought above the ground\ Hypogeal germination= during elongation of the hypocotyl the cotyledons remain in the soil  A diagram of a plant Description automatically generated In non-dormant seeds, germination takes place as follows 1. Imbibition= a dry seed takes up water 2. Enzymes and food supplies become hydrated 3. Hydrated digestive enzymes become active 4. Enzymes digest storage material of endosperm or cotyledons. The nutrients are transferred to the embryo and produce energy for the growth process 5. The radicle (=embryonic root) develops 6. The shoot tip emergence above the soil Apical Meristem= gives rise to the primary plant body and is responsible for the extension of the roots and shoots. It remains actively dividing producing new cells for growth. There are 2 - Shoot Apical Meristem (SAM)= a structure located between the cotyledons (in an embryo) - Root Apical Meristem (RAM)= a structure located at the tip of the root The meristem contains two types of cells. - Initials= are the equivalent of stem cells in animals: Perpetually embryonic cells, not differentiated, that continuously produce new cells - Derivatives= divide and form cells for the primary meristem Apical meristem refers to the initial cells and their undifferentiated derivatives, but excludes adjacent regions that contain cells that are committed to particular developmental fates There are two ways you can picture the Apical meristem. In cytological zones (=regions with different indentities and functions) or in cell layers Cytological zones Cell layers --------------------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------- Central zone: contains a cluster of infrequently dividing initial cells (initials) Tunica (L1 & L2): mostly anticlinal division. Tissue of uniform thickness. L1 generates the epidermis Peripheral zone: flanks the cz, cells divide more frequently to produce cell that later become incorporated into lateral organs e.g. leaves Corpus (L3): more variable division planes. It's to increase in tissue volume Rib zone: lies interior to cz, generates the central tissues of the stem, pushes the meristem upwards/downwards L2 and L3 generate internal tissue  Apical meristem produces the 3 primary meristems, which develop into primary tissues Primary growth= Growth from the apical meristems. This is always growth in length; made possible by apical meristems at the tips of shoots and roots. Regions of actively dividing cells are found at the tips of plants. There are 4 developmental zones in a plant (in the root and shoot) 1. Apical meristem 2. Meristematic zone: cell division take place here 3. Elongation zone 4. Maturation zone: here the cell of primary tissues mature boundaries cannot be defined precisely  A diagram of a structure Description automatically generated Protoderm epidermis: dermal tissue system\ Ground meristem Ground tissue: parenchyma, collenchyma, and sclerenchyma\ Procambium vascular tissue: primary xylem and primary phloem Types of differentiated plant cells +-----------------------+-----------------------+-----------------------+ | Type of cell | Originates from | Characteristics and | | | | function | +=======================+=======================+=======================+ | Epidermis (rhizoderm) | protoderm | \- usually composed | | | | of one cell-layer | |  | | \- can be covered by | | | | cuticle | | | | | | | | \- cells are flat and | | | | adhering tight to one | | | | another | | | | | | | | \- transparent and no | | | | chloroplasts | | | | | | | | \- have stomata | | | | | | | | \- (in roots, root | | | | hairs form from the | | | | rhizoderm and it has | | | | a fuction in water | | | | uptake) | +-----------------------+-----------------------+-----------------------+ | Parenchyma | Ground meristem | \- most commen cell | | | | type | | | | | | | | \- found in pith and | | | | cortex | | | | | | | | \- big, round, | | | | vacuole and | | | | intercellular spaces | | | | (allow gass exchange) | | | | | | | | \- responsible for | | | | many important | | | | processes like | | | | photosynthesis, | | | | nutrient | | | | assimilation, | | | | respiration, storage | | | | and secretion | | | | | | | | \- can function as | | | | storage for starch | +-----------------------+-----------------------+-----------------------+ | Collenchyma | Ground meristem | \- least common cell | | | | type | |  | | \- unevenly thickened | | | | primary walls without | | | | lignin | | | | | | | | \- provide flexible | | | | support to young | | | | parts of the shoot | | | | without restraining | | | | growth | +-----------------------+-----------------------+-----------------------+ | Sclerenchyma | Ground meristem | \- thick secondary | | | | wall with lignin. | | Sclerenchyma \| | | Mature cells cannot | | Description, Types, & | | elongate and are | | Function \| | | mostly dead | | Britannica | | | | | | \- structural support | | | | cells. More rigid | | | | than collenchyma and | | | | occur in regions that | | | | stopped growing in | | | | length | +-----------------------+-----------------------+-----------------------+ | Xylem | Procambium | \- water-conducting | | | | cells | | | | | | | | \- tubular, | | | | elongated, lignified, | | | | dead cells | +-----------------------+-----------------------+-----------------------+ | Phloem | Procambium | -sugar-conducting | | | | cells of phloem | |  | | companion cell | | | | (parenchyma) | | | | alongside each | | | | sieve-tube that have | | | | a nucleus and | | | | ribosomes. They | | | | areconnected via | | | | plasmodesmata. They | | | | provide energy | | | | necessary for | | | | transport | +-----------------------+-----------------------+-----------------------+ There are 2 types of xylem - Tracheids: are long, thin and have tapered ends. Water moves though piths (primary wall) - Vessel elements: wide, short and less tapered. Water moves freely through perforation plates mostly in angiosperms  **Root Primary Growth** Primary function of the root - Anchorage - Absorption - Storage - Conduction There are 2 types of root systems - Taproot system - Found in eudicots - Strongly developed primary root (=taproot) with branches (=lateral roots) - Usually penetrates deep into soil - Fibrous root system - Found in monocots - Not one root more prominent than the others. You can distinguish stem-borne root(=adventitious roots) and lateral roots - Primary root is short-lived  primary root growth 1. Cells divide in RAM 2. In the meristematic zone cell become primary meristems 3. In the region of elongation cell, shockingly, elongate. This causes the root to get pushed further into the soil. After this region, there is no increase in root length 4. In the region of maturation cells of primary tissues mature forming - Primary xylem - Primary phloem - Pericycle - Endodermis with casparian strips - Cortex - Epidermis with root hairs. The roots of monocots and dicots look different A diagram of a cell Description automatically generated Tetrarch= four ridges of protoxylem found in eudicots\ Polyarch= many ridges of protoxylem found in monocots Monocots also have a pith, while eudicots don't Root hair= tubular extensions of epidermis cells that role is absorbing water and minerals. They increase absorptive surface of the root. Lateral roots= branches of the roots. They develop from the pericycle and then break through the endodermis, cortex and epidermis. They can do this because they have their own RAM at the tip symplast= continuum of cytosol connected by plasmodesmata apoplast= continuum of cell walls and extracellular spaces Transport of water and minerals from root hairs to xylem 1. Water follows a apoplastic route or a symplastic route into the plant till the endodermis - Apoplastic route= water and minerals can diffuse into the cortex along intercellular spaces and cell walls - Symplastic route= water and minerals can cross the plasma membranes of root hairs and enter thy symplast 2. The endodermis contains Casparian strips that blocks apoplastic passage of water and minerals. All substances entering/leaving the vascular cylinder must pass through protoplasts of endodermal cells this works are a filter 3. Endodermal cells and living cells within vascular cylinder discharge water and minerals into their apoplast. Xylem vessels then transport this by bulk flow into the shoot system Mycorrhizae (fungus roots)= mutualistic associations of root and fungi. The host plant provides the fungus with a steady supply or sugar. Meanwhile, the fungus - increases the surface area for water uptake - supplies the plant with phosphorus and other minerals absorbed from the soil - secretes growth factors - secretes antibiotics There are, ones again, 2 types of mycorrhizae - Ectomycorrhizae= mantle of fungal mycelium ensheathes the root. Fungal hyphae extend into the intercellular spaces of the root cortex - Endomycorrhiza (arbuscular mycorrhizae)= no mantle is formed around the round. Fugal hyphae extend into the root **Root secondary Growth** Secondary root growth consists of the formation of - Secondary vascular tissues from vascular cambium - Periderm from cork cambium roots of monocots lack secondary growth A screenshot of a computer Description automatically generated The formation of vascular cambium is initiated by divisions of procambial cells that remain meristematic and are located between primary xylem and phloem. This happens outside the elongation zone. The formation of cork cambium is initiated by divisions of pericycle cells Diagram of a diagram of a cell Description automatically generated When vascular and cork cambium become active, primary growth has stopped in that area. Root thickens as secondary xylem/phloem and cork cells are added. Most of the primary phloem is crushed The epidermis, cortex and endodermis don't receive nutrients and water anymore because of the layer of cork and they are shed. Cork replaces the epidermis as protective layer.  Radiating line= rays, radial rows of parenchyma cells that connect the secondary and primary vascular tissues A screenshot of a computer Description automatically generated **Stem primary growth** SAM is responsible for the entire primary growth above the ground: stem, leaf, branches. When the conditions are right, the SAM is converted into a flower meristem. Shoot= stem + leaves Primary functions associated with the stem - Support - Conduction of water and nutrients Plants show indeterminate growth. They can keep growing because of the apical meristems and the secondary (lateral) meristems In the shoot, the periderm is formed from the cortex instead of the pericycle, because shoots don't have a pericycle. CLAVATA-WUSCHEL feedback signalling= pathway which coordinates stem cell proliferation with differentiation. It makes sure the shoot meristems are maintained by pluripotent stem cells.  The place of the nodes indicates the place where a SAM produced leaves and new buds. The axillary buds develop on a place where a leaf was before (a leaf scare). On the place of the bigger scars the SAM had paused the previous year. All axillary buds have their own primary meristems All along the stem axillary buds remain dormant till apical dominance is removed. Auxin induces dormancy in axillary buds. The more the plant grows, the more auxin decreases in lower axillary buds. At some point it passes a threshold axillary buds becomes active and grows out as a branch. Difference in monocots primary shoot growth - In monocots plants the SEM stays close to the ground while the leaves grow up, instead of a the top - There is no distinct cortex and pith - Vascular bundles are scattered - There is no secondary growth. In eudicots xylem and phloem are separated by the cambium residues. In monocots this is not he case **\ ** Secondary shoot growth 1. Vascular cambium forms 2. Vascular cambium froms secondary phloem toward the outside and secondary xylem towards the inside the stem thickens 3. Some cells in vascular cambium give rise to vascular rays= composed largely of parenchyma cells that connect secondary xylem and phloem. This allows for - Food substances to move from secondary phloem to xylem - Water to move from secondary xylem to phloem 4. The diameter of vascular cambium increases. Tissues external to cambium cannot keep pace because their cells no longer divide these tissues will rupture. Cork cambium develops from parenchyma cells in the cortex, just below the epidermis. Cork cambium produces cork cells that replace the epidermis 5. A year later the vascular cambium produces more secondary xylem and phloem and cork cambium produces more cork 6. Diameter of the stem increases tissues exterior to cork rupture and are sloughed off 7. Cork cambium re-forms deeper in the cortex. If no cortex is left, cambium develops from phloem parenchyma cells Bark= all tissues outside the vascular cambium\ Periderm= cork, cork cambium and phellomderm Cork cells deposit suberin, which is waxy and hydrophobic, in their walls before dying. This make the periderm impermeable for water and gases. Cork protects agains - Water loss - Physical damage - Pathogens problem: How can living cells in interior tissues of woody organs absorb oxygen and transpire? Lenticels= a pore or aggregeation of cells that penetrates the surface and through which gases are exchanged between the atmosphere and the underlying tissues Early (sping) wood secondary xylem cells with a large diameter and thin walls to maximize water delivery to the leaves\ Late (summer) wood thick-walled, less water transport but provides more support Sapwood is new wood, it's still alive and contains water and minerals.\ Heartwood is more to the centre. Its dead and contains almost no moisture