Plant Control Systems Lecture

Plant Control Systems Concepts 39.1-39.5 Campbell. Biology. 3rd ed. https://www.frontiersin.org/research-topics/7337/the-role-of-plant-hormones-in-plant-microbe-symbioses Outline • 1. Plant hormones regulate growth and development • 2. Plant responses to light • 3. Plant responses to other extern...

Plant Control Systems Concepts 39.1-39.5 Campbell. Biology. 3rd ed. https://www.frontiersin.org/research-topics/7337/the-role-of-plant-hormones-in-plant-microbe-symbioses Outline • 1. Plant hormones regulate growth and development • 2. Plant responses to light • 3. Plant responses to other external stimuli • 4. Plant responses to herbivores and pathogens 3 •1. Plant hormones regulate growth and development • Plant growth = An irreversible increase in the size of the plant. • Plant growth is defined as follows: …size increase by cell division and enlargement, including synthesis of new cellular material and organization of sub-cellular organelles. • Growth can be measured as increase in fresh or dry weight (biomass), or in volume, length, height, or surface area. STAGES OF DEVELOPMENT • Development: is the advancement in stages of maturation (life stages - earlier to later) e.g. a fertilized egg develops into a mature tree. • Seed germination and growth of vegetative organs • Initiation and maturation of reproductive organs • Fertilization, seed development and maturation • Senescence and death. https://fr.dreamstime.com/illustration-stock-usine-s-%C3%A9levant-de-la-graine-%C3% A0-l-arbre-orange-usine-de-cycle-de-vie-image87294655 PHYTOHORMONES EFFECT GROWTH AND DEVELOPMENT • Phytohormones are naturally occurring compounds that • act in minute amount • produced or synthesized in one part of plant • regulate the growth and development in another part of plant. PHYTOHORMONE TYPES • Auxin • Gibberellins • Cytokinins • Ethylene • Abscisic Acid AUXIN & CYTOKININ GIBBERELLIC ACID 100 8 ETHYLENE & ABSCISIC ACID AUXIN • Auxin, the first PGR to be discovered • Discovery prompted by observations made by Charles Darwin (The Power of Movement in Plants -1881) • Characterized 50 years later (in the 1920s) by F.W. Went. • Several synthetic auxins known. Natural auxin is Indole-3-acetic acid or IAA • Auxin is transported in the PHLOEM and is unidirectional (apex to base) Effect of auxin: Phototropism The growth of shoot towards or away from light is called phototropism Positive phototropism Results from growth of cells on the opposite side of the light source ie, cells on dark side elongate faster than cells on brighter side Experiments determined that signal coming from the tip was responsible for this effect Auxin was later determined to be this signal Barden et al., 1987 Negative phototropism Are they primary roots? http://previews.123rf.com/images/marzolino/marzolino1 208/marzolino120800029/14947626-Giant-specimen-of -ficus-magnolioides-with-long-branch-supported-by-adv entitious-roots-Stock-Photo.jpg PBT 264 http://www.revistas.unal.edu.co/index.php/agrocol/articl e/viewFile/32559/47058/220609 https://www2.mcdaniel.edu/Biology/botf 99/rootuse/cornrt.jpg http://leavingbio.net/FLOWERING%20PLANTS_fil es/image013.jpg Differentiation & Dedifferentiation • The cells derived from meristems • Root apical • Shoot apical • Cambium (vascular and cork) differentiate and mature and specialize (Cells develop different forms adapted to specific functions). This act leading to maturation is termed as differentiation. • The living differentiated cells, that have lost the capacity to divide can regain the capacity of division under certain conditions. This phenomenon is termed as dedifferentiation. Totipotency • Totipotency-The ability of an individual cell to reconstitute the entire plant part and functions http://agropedia.iitk.ac.in/content/plant-tissue-culture • Adventitious root formation is the primary regenerative process required in most cutting propagation. Adventitious root are of two types: • Preformed such as prop roots • Stress or Wound Induced roots Adventitious Root Formation from Stem Cutting Wounding Response • Necrotic plate forms from cells killed during cutting damage. Necrotic plate seals and protects against pathogens • Wound is sealed with suberin and xylem plugs with gum • Cells behind necrotic plate begin to divide and callus forms (callus is mass of undifferentiated cells) • Auxin coming from the shoot tip floods the wounded area • Cells of the vascular cambium begin to differentiate and cells in the area of the vascular cambium dedifferentiate • All of these cells will specialize and group into root tissues • Eg. Leaf tissue will not be produced, and a root cap is formed PBT 264 https://www.semanticscholar.org/paper/Propagation-Potentials-of-Genotypes-and-Different-Islam-Yaakob/e41ba9cce4e271b3b199a63ed7552a923f3a1fe9 Effect of auxin: apical dominance • Controls apical dominance • Removal of apex causes previously dormant bud to break Figure 39.8 Physiological effect of auxin • Girdling restricts downward flow of auxin • Auxillary buds below gridle begin to grow (bud break). AGRICULTURAL USES OF SYNTHETIC AUXIN • Rooting of cuttings • IBA (Indolebutyric acid) • Tissue culture • Naphthalene acetic acid (NAA) • 2,4-dichlorphenoxyacetic acid (2,4-D) • Herbicides • 2,4-D –old but still widely used • 2,4,5-T • Fruit thinning • NAA Rice Bakanae disease caused by Gibberella fujikuroi (Sawada) GIBBERELLIC ACID (GA) • Gibberellic Acid isolated in 1938 from cultures of Gibberella fujikuroi (Sawada) and Fusarium moniliforme, the causative agents for Bakanae disease (abnormal stem elongation) in rice. • Over 120 different natural gibberellins known. • GA3, GA4 + GA7, and Potassium Gibberellate, are registered as plant growth regulators in the US in Canada. 23 PHYSIOLOGICAL EFFECTS OF GA • Promotes cell enlargement • Promotes bolting (stem elongation) of biennial plants, replacing cold requirement. • Stimulate stem elongation by stimulating cell division and elongation. Overcoming dwarfness in corn by spraying with gibberellin. Left: Untreated, genetically dwarf corn plants. Center: Nondwarf corn sprayed with gibberellin. Right: Genetic dwarf corn sprayed with gibberellin. Photographs taken six weeks after spraying. Gibberellic Acid (GA) stimulates stem elongation •Gibberellins are also involved in overcoming dormancy in seeds & buds. •After water is imbibed, gibberellins are released which signals the embryo to break seed dormancy Increasing fruit size of seedless grapes CYTOKININS • Growth regulators that stimulate cytokinesis or cell division 28 Cytokinins • Promote cell division and promote differentiation • Coconut milk (CM), the liquid endosperm of a coconut, is rich in cytokinin(s) • Produced in actively growing tissues, particularly roots and travel up xylem PHYSIOLOGICAL EFFECTS OF Cytokinins • Promote shoot development and bud development ABSCISIC ACID (ABA) • Discovered in 1950s • Influences most aspects of plant growth and development to some extent • Interacts with other PGRs PHYSIOLOGICAL EFFECTS OF ABA Key factor regulating • Adaptation to drought • When plants begin to wilt, ABA accumulates in the leaves and causes stomata to close rapidly and reduces transpiration • Seed dormancy (recall primary dormancy) • Why tomato seeds germinate in the fruit. When ABA is insufficient or low we get precocious germination • Accumulation of ABA in the seed during maturation inhibits germination • Some desert plant seeds only germinate after a sufficient rain has washed out the ABA Precocious Germination ETHYLENE (H2C=CH2) • Used by Egyptians to stimulate ripening of figs • Chinese burned incense (gum, spice, or other substance that is burned for the smell) in close rooms to ripen pears • Ethylene identified in 1901 • Only PGR that exists as a gas • Produced by almost all plant tissues PHYSIOLOGICAL EFFECTS OF ETHYLENE • Initiates ripening of fruits • Bananas • Promotes degreening of fruit • Tomato • Orange • Pineapple • Mango • Ripening & senescence • Promoted by ethylene Degreening http://www.riversweet.com/degreening2.htm THE CLIMACTERIC • The period during which certain fruits, such as apples, ripen marked by a rise in the rate of respiration. • Ethylene concentration and climacteric rise has a positive relationship. • Climacteric fruits (ripen after harvest): Pear, bananas, avocado, tomato etc. • Non-climacteric fruits: Citrus, grape, eggplant, pineapple etc. 2. Plant responses to light • Irradiance (Light intensity/unit area) • Different plants have optimum light requirements • Above or below the optimum can cause injury • Deficient light intensities tend to reduce plant growth, development and yield • Photosynthesis is restricted; etiolation • If the light is too intense the heat it produces can damage the delicate plant cells, as well as increasing the transpiration rate, causing the leaves to wilt. Etiolation: plant develops white, spindly stems, elongated internodes, leaves that are not fully expanded, and a stunted root system. • Duration (daylength/ photoperiod) • Photoperiodism: reproductive responses of plants to the relative length of light and dark periods • Garner and Allard demonstrated that the dark period, not the light period, is most critical to initiation of reproductive growth • Higher plants can be classified as long day, short day or day-neutral based on effect of photoperiod on initiation of reproductive growth • Long Day – short nights; flower chiefly in the summer; Lettuce, spinach, potato • Short Day – long nights; flower chiefly in the winter; Sunnhemp, chrysanthemums, poinsettias • Day-Neutral– flowering not triggered by photoperiod • Rose – rely on other environmental or internal cues https://www.slideshare.net/mahmoudmohamed5243/flowering-physiology2-86676351 3. Plant responses to other external stimuli Temperature • Temperature affects plant propagation in many ways • Seed dormancy can be broken using warm and/or cold moist stratification Warm/moist (palms) Cold /moist (hardy hibiscus) Warm/moist --- cool/moist (holly spp.) • In grafting – heating devices are sometimes places in the graft union area to speed up process • Cuttings - Bottom heat systems can encourage rooting https://bio-protocol.org/e1362 Stratification: To be successful conditions must mimic the exact conditions found in nature (temp, moisture, substrate) Gases and Gas Exchange • Seed germination • High respiration rates • O2 consumed—CO2 produced • Hard seed coat restricts gas exchange • O2 required for germination • Scarify seeds - clip seed coat • Adventitious root formation • Cuttings stuck in highly water-saturated media with small pore spaces • Low levels of O2 • Reduced root initiation • Shipping or storing propagules • Buildup of ethylene gas can be detrimental http://inetgardens.com/kowhai-culture.htm 4. Plant responses to herbivores and pathogens • First line of defense is cuticle, epidermis and periderm • Mechanical wounding by herbivores opens up channels into tissue that allows for pathogen invasion • Can also enter through stomata • Chemical lines of defense include release of toxins that kill or inhibit growth of invading bacteria or fungi • Following that, plants next line of defense are two types of responses: • PAMP-triggered defence • Effector triggered defence Defence against Herbivores • Physical defences against herbivore attack include thorns, trichomes, spines, prickles • Production of toxins including amino acids that cause death in certain insects • Some toxins interfere with cell division in the pathogen or insect body • Other defensive plant products include mind-altering products (hallucinogenic/psychedelic) • Consequence is usually unpleasant to the animal and dissuades it from feeding on that plant again • Other volatiles released from plants in response to herbivory function as warning signals to other plants which induces defence mechanisms Defence Against Pathogens - PAMP • Dependent on the plants ability to recognize pathogen associated molecular patterns or PAMPS. Formerly known as elicitors • These are molecular sequences that are specific to certain pathogens • For example, protein or amino acid sequences present in pathogen are perceived by receptors in the plant • PAMP recognition triggers defensive mechanisms • Mechanisms are local (at site of pathogen entry) or broad spectrum antimicrobial chemicals and toughening of plant cell walls to prevent further progress of the pathogen Effector Triggered Defence Hypersensitive Response • A local defense mechanism. Occurs at or near site of infection • Effector triggered immunity • Causes local cell and tissue death • Restricts the spread of the pathogen • Plant produces enzymes and chemicals that impair the pathogens cell wall integrity, metabolism or reproduction • Formation of lignin in plant cell wall toughens the cell wall and prevents further spread of pathogen out of the plant cell • Lesions appear in localized area on leaf •Systemic Acquired Resistance • Plant wide defence mechanisms (ie not local) • Nonspecific and provides protection against a diverse set of pathogens • Involves production of chemicals and toxins that are released through the plant body • This type of response can last for days Thank you The End Questions Have a wonderful day!