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Download Plant Form and Function Intro
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Simple Tissues – consisting of one cell type • Parenchyma – thin walled & alive at maturity; often multifaceted. • Collenchyma – thick walled & alive at maturity • Sclerenchyma – thick walled and dead at maturity – Sclerids or stone cells – cells as long as they are wide – Fibers – cells longer than they are wide • Epidermis – alive at maturity – Trichomes – “pubescence” or hairs on epidermis – Root Hairs – tubular extensions of epidermal cells Parenchyma • • • • • • • All other plant cells are evolved from these. Alive when functional. Thin walls. Caused to divide, usually as a result of injury. Cells that are often the site of storage, starch. Sites of photosynthesis. Involved in short distance movement of water and nutrients. • Originate from root apical meristem. Collenchyma • Alive when functional. • Derived from parenchyma. • Walls are variously thickened compared to parachyma. • Function is to support. Strands in petiole. • Elongate stems and leaves in the petiole. • Celery: strands are collenchyma. Schlerenchyma • • • • Scheloros: greek for hard. Derived from parenchyma. Alive or dead when functional. Cells compromising schlerenchyma have hard walls. • Walls made hard by deposition of lignin. • Function in support and protection. • Lignin: broken into two types. – Fiber – Schlerids Fiber • Elongated fibers which overlap each other to form bundles. • Linum • Luffa • Rope Schlerids • Also known as stone cells. • Small, often round. • Function in protection. • Peach pit, walnut. • Pear, gritty due to schlerids. • Fig Newtons. • Reduce insect ingestion. Vascular Tissue • Consists of several cell types. • Transport • Two main types – Xylem: water movement. – Phloem: Nutrient movement. Xylem • Dead when functional. • Consists of two types of transport cells. – Traceids – Vessels. Tracheids • Found in gymnosperms and angiosperms. • Elongated like a fiber, tapering with overlapping end walls. • Closed where they overlap, with communication through pits (Small holes) Vessels • Found only in angiosperms. • Short, wide cells with open end walls. • Stacked on top of one another. Phloem • Principal cell type is the sieve element. Sieve Element • Alive when functional. • Sieve elements stack on top of one another to form a sieve tube. Formation of a Sieve Element Root Structure and Development • Root functions: – Support/Anchorage – Storage of nutrients (most often starch) – Site of absorption of water and nutrients – Establish symbiotic relationships between root and soil microorganisms. Types of Roots • • • • • Prop Roots Storage Roots Pneumatophores Strangling/Aerial Roots Buttress Roots Prop Roots Storage Roots Pneumatophores Strangling/Aerial Roots Buttress Roots Development of a root • When a seedling germinates, 1st root that is formed is called primary root (Taproot) • In eudicots, taproot goes straight down and becomes elongated. • In monocots, taproot is short lived, it is replaced by roots forming on the stem. • Monocots, root system is a shallow fibrous network of fibers. • Allows roots to hold top of soil together. (Very Important Function) Root system vs Shoot system • In seedlings, the root system is much larger that the shoot system. As it grows it comes to a ratio close to 1:1 of vegetative mass of root and shoot. Root Cap • Functions to protect meristem as it grows through soil. – Secretes a lubricant (slime) which allows it to move through the soil easier – Site of perception of gravity. Dicot vs Monocot • Dicot (like trees, etc) - broad leaves, has a tap root (like the root of a carrot), conspicuous (obvious) flowers and a network of leaf veins. • Monocot (Grasses) – narrow leaves, a network of very fine roots, not obvious flowers, parallel veins. Dicot Root vs Monocot Root Statocytes • Amyloplasts • Aid in perception for change in direction. • Similar to a statocyst. • As it moves the statocytes shift due to gravity. Shoot System/Primary Structure • • • • • Comprised of the stem, leaf, flower, and fruit. Stem: Comprised of nodes and internodes. Leaf: Comprised of blade and petiole. Flower: Reproductive Structure. Fruit: Part of the flowering plant that derived from specific tissues of the flower, mainly one of more of the ovaries. • *All primary tissues are derived from apical meristem. Can be traced back to mitotic events in apical meristem. Stem Leaf Shoot Apical Meristem (SAM) • Zone at top of plant where all activities go on to activate all primary tissues. • Always elongating/growth. • (A) Apical Dome, apical meristem • (B) Leaf Primordia, beginning of new leaf. • (C) Axillary Buds, become branches. • (D) Older leaf primordia • (E) Zone of high cell division activity. Shoot Apical Meristem Longitudinal Section SAM Transverse Section Dicot • Bundles consist of xylem and phloem. • Phloem to the outside of bundle, xylem to the inside, always. • Bundles are arranged in an ordered pattern. • Center is called pith. Pith is parenchyma cells. • Cortex: region between epidermis and bundles. • • • • Monocot Bundles consist of xylem and phloem. Phloem and xylem and randomly distributed in bundles. Bundles are randomly distributed. No obvious pith. Axillary Buds • Grow into branches. • *Every branch that is growing/elongating has an axillary bud. Leaf • Come in various sizes from several yards to mm. • Function is primarily for photosynthesis, shape to capture light. • Leaf shape and size is modified by environment it grows in. • Form and function can change based on environment. • Originate from apical dome, leaf primordia. • Consists of blade and petiole. • Blade can be giant, petiole small, or vice versa. Leaf Cross Section of Leaf Leaf Vascular Tissue • Vascular tissue is made up of xylem and phloem. • Made up of midvein and mesh like veins. • Cross section of leaf. Special adaptations of Leaves • Tendrils: used for climbing, allows for growth where they typically can’t grow. • Spines: protection. • Storage of nutrients. Adaptations of plants • • • • Venus Fly Trap Pitcher Plant Black Horn Acacia Lily Pads Stove Plants Primary Growth Shoots/Secondary Structure • Primary growth helps to give height/elongation. • Secondary growth gives rise to increase in circumference. • Going from twig to tree allows trees to achieve great size, mass, age. Vascular Cambrium • Because new cells are formed not only by apical meristems, which promotes elongation, but also by a lateral meristem, we call these tissues secondary tissues. Consequences of Secondary Tissue • Xylem and pith are pushed towards center. • Primary phloem/cortex/epidermis are pushed to the outside. • New secondary cells produced inside the vascular cambium, called secondary xylem (Commonly known as wood) • To the outside of vascular cambium, new cells produced are secondary phloem, known as bark. Annual Growth Rings Annual Growth Rings Monocot Adaptations to growth Fibonacci Sequence Cork Cambium Charles and Frances Darwin • Interested in tropisms. (Plant Movement) – Specifically phototropism. – Studied grass seed (monocot) seedlings. Focused primarily of coleoptile. Coleoptile • Question that arose: Is there a region in the coleoptile that perceives light? – The tip of the coleoptile perceives light, also there was some material moved from the tip to the differentially elongated cells. Discovery of Auxin Addition of Auxin to plants Discovery of Auxin and Functions • From coleoptile agar plates, the substance was analyzed and found to be Indole 3 Acetic Acid, IAA, or Auxin. • Auxin is responsible to apical dominance. • Control of vascular cambium. • Fruit development. • Root formation • Abscission of leaves. • Plant Orientation. Apical Dominance • Auxin is found in apical meristem. • Shoot system unbranched, axillary bud growth inhibited by auxin. • If apex is destroyed, removing auxin, brances grow out. Control of Vascular Cambium • Determines the derivatives and the quantity of each. Root Formation • Stimulates the pericycle to form roots. • Ex. Rootone, synthetic auxin to put on broken plants to stimulate the roots to form. Abscission of Leaves • Auxin is able to measure the amount of daylight. • Uses the photoperiod to tell the leaves to reduce the amount of auxin when daylight lengths reduce. Plant Orientation • Allows a plant that has been knocked over, or a seed establish roots and shoot system. • Auxin has opposite effects due to the sensitivity, or threshold, of auxin in those types of cells. • Shoot: Auxin promotes elongation. • Root: Auxin inhibits elongation. • This is the premise for herbicides to kill specific plants while others live. Due to the sensitivity of auxin. Gibberellin • Second PGR found by accident. • Found during the studying of a fungus, gibberella. • Fungus caused rice to elongate to high and fall from winds into water, making rice inedible. • Rice produced a substance called gibberellin, GA, gibberellic acid. • Discovered in Japan, but results were not available due to language barrier and WWII. Gibberelin continued • Gibberelin is also produced in plants. • Over a 100 types of gibberelins. • Have very distinctive effects on plants. – 1. Promote cell elongation. – 2. Affects flowering. – 3. Used commercially, can be applied to plant. • Grapes: Round vs elongated. Gibberelin continued – 4. They control the maturity of plants, juvenile vs adult. • Juvenile has high levels of gibberelin, adult has low level. Gibberelin can cause plants to alternate from juvenile to adult. Gibberelin – 5. Most important function is seed germination. • A. signal to germinate is received. • GA is produced and/or released by embryo and moves to aleurone layer. • Aleurone then stimulates an enzyme formation, alpha amylase, which converts starch to sugar. • Leads to germination. Growth Regulator Research • Scientists knew of auxin and gibberelin so they hypothesized that there may be more. • Took pith cells (Parenchyma, undifferentiated). • They were in the center of tree, away from any microbial contamination. • They are sterile or aseptic. Procedure • Ground up plant cells. • After 100’s of samples, they would add it to the culture/medium. • The result was from one of the mediums they found pith cells dividing. • When they divided, the pith cells formed a mass of undifferentiated cells called a callus. • Analyzed the callus, found substance responsible was cytokinins. Cytokinins Functions • Stimulate cell division. • Delay sonescense, slowing the death process of a cell. • In combination with other GR, (mainly auxin) they can cause the callus to yield organs. • Auxins and cytokinins were added in different ratios to callus and yielded different results. • Overcome apical dominace. – Axillary bud is inhibited by auxin, if we add cytokinins to the bud, it is released from apical dominace and branches out. Result of cytokinin • Witches broom • Tumors Growth Regulators • 1st three groups, auxin, gibberelins, cytokinins, are distributed via the vascular tissue. • 4th GR is a gas, external to plant/tree. • Discovered by gas heat, gas lamps. – When plants were in rooms with gas, pedals started to discolor and eventually fell off. – Leaves showed epinasty. – Gas caused weakening of abscission zone. PGR • This gas was analyzed in detail and found to be ethylene. • Ethylene affects and promotes fruit ripening. – It is autocatalytic, stimulates its own production. • Apples, oranges, banana ripen as a result of ethylene. Ethylene • Ethylene catalyzes more of itself in fruits. • Also formed in damaged fruits. – Green bananas are still starch, no sugar yet. Prior to being set out, they are sprayed with ethylene to stimulated ripening. Converting the starches to sugars. • One rotten apple spoils the whole barrel. Agricultural uses of ethylene • Pineapple and mangos are sprayed with ethylene to stimulate flowering. • Synchronizes harvest all at once. • Ethylene is used to harvest energy intensive crops. Walnuts and cherries. – Treat orchards with ethylene. Walnut fruits have abscission zone that is weakened by ethylene. – Tarps placed underneath. – Trees shaken with machinery. Last Group of PGR • Auxin, cytokinins, gibberlins, and ethylene. • Last group was discovered in unison from Wales and UC Davis • Wales group from UK was looking at a dormant tree, its buds were covered with scales. • The scales protected the shoot apex during winter. • If you removed scales prematurely, the bud would start to grow. • Some substance in scales inhibited growth. • Extracted and analyzed bud scales, identified Dormin, promoted dormancy. UC Davis Discovery • Problem was presented by cotton farmers. • Every June, cotton fruit, a large percentage of fruit was falling in June. (June drop) • Decreased yield and therefore profit. • Question presented to Davis was why are they falling early. • There was a compound that increased in amount just before cotton fruit dropped. • Compound identified was abscisic acid. • Important group with regard to abscission. Abscisic Acid • 1. Generally associated with stress responses to plant. – If plant is put under water stress (drought conditions), plant is going to continue to open stomata and lose water through leaves, killing shoot. – In drought conditions, the root makes abscisic acid and moves to stomata and in stomata ABA causes closure. 2nd Function of ABA • Plants that grow in high saline concentrations. – Salty environments in some plants, ABA increases and causes production of proteins that lessen the detrimental effects of salt. 3rd Function of ABA • Seed has the ability to go dormant in less than favorable conditions, winter or drought. • Question is how does it know when conditions are favorable. – One mechanism is ABA in seed coat. – In seed coat, they have ABA plus other inhibitors that prevent germination. – The ABA and other inhibitors are cold-labile, cold causes their break down. – Cold equals low levels of ABA, as temperature rises the ABA levels rise telling the plant to germinate. Flowering • When a plant undergoes its transition to flowering, it makes a significant change. • SAM which is comprised of undifferentiated cells which could divide forever. • When it flowers it loses these changes. What Causes the transition to flowering? • Signs that flowering transition has occurred. • SAM (transition to flowering) – 1. Apex stops producing new leaves. – 2. Apex enlarges. – 3. SAM starts to produce the organs of the flower. – 4. All of SAM becomes commited to yielding flowers. No longer undifferentiated. Works that discovered flowering • 1920’s Garner and Allard worked with tobacco. • Controls of flowering: – The length of photoperiod controls flowering. – Some plants have to have less than some specific number of hours of light to flower. – These plants are called Short Day Plants. SDP. – Others have to be more than some minimum numbers of hours. – These plants are referred to as Long Day Plants. LDP. 3rd Group • Last group has flowers irrespective of the length of the photoperiod. • These are called day neutral plants. DNP. • Examples; Easter lily, poinsettia. • We manipulate the photoperiod. An accident in the lab • Lab accident in the lab determined what we knew about photoperiod and flowering turned out to be wrong. • In a controlled experiment dealing with light dependency, someone inadvertently turned on the light switch. SDP did not flower. Too much sunlight, has to be the length of darkness that triggers flowering. • For both SDP and LDP, light is important for photosynthesis, but the length of the dark period controls flowering. • For a SDP, the length of the dark period must equal or be greater to some number of hours. • For a LDP, the length of the dark period must be shorter than some number of hours. Environmental Factors for Flowering • Temperature – some plants require both a correct photoperiod and a correct temperature. Including celery, beets, both SDP with cold temp. • Effects of cold on promoting flowers is called vernalization. • Flowers are extremely important because they are the basis for us getting our fruits, grains, and our seed crops. Where is photoperiod detected? • Photoperiod is important. • It is measured in the leaf. Experiment that determined leaf as photoperiod signal. How is flower formed • Signal to flower is formed in leaf. • Signal moves via vascular tissue to SAM. • At SAM, the signal induces transition to flowering. Research • A lot of research has been done to identify the signal, but done unsuccessfully. This ability would allow us to get plants to flower outside of their normal photoperiod. • Some observations were found during this research. Observations • GA caused flowering in LDP, but not in SDP, so GA could not be a universal signal. (Florigen) What happens when florigen arrives at apex • When signal arrives, there are groups of genes turned on. • Grouped genes into three groups, A B C. • Grouped according to when they were turned on. • If you turned on A genes = Sepals – A+B = Petals formed – B+C = Stamens – C = Carpels ABC Model