BIOL 1306 SU23 Plants Nutrient Acquisition and Transpiration 1306SU23 PDF

6/22/23 Learning Goals 1. Identify macronutrients vs. micronutrients and explain how hydroponics aided in identifying these nutrients. 2. Explain how ions/nutrients are moved into plant cells in the root systems 3. Explain how symbiotic relationships with bacteria, archaea, and/or fungi aid in nut...

6/22/23 Learning Goals 1. Identify macronutrients vs. micronutrients and explain how hydroponics aided in identifying these nutrients. 2. Explain how ions/nutrients are moved into plant cells in the root systems 3. Explain how symbiotic relationships with bacteria, archaea, and/or fungi aid in nutrient acquisition at the root systems 4. Describe how transpiration of water occurs from absorption at the roots to evaporation at the stomata. 5. Describe the movement of sugars through the phloem after being produced via photosynthesis in a source cell Nutrient Acquisition and Transpiration in Plants BIOL 1306 Jenifer Gifford, Ph.D. Plant health depends on obtaining all of the essential inorganic nutrients Plants acquire nutrients from air, water, and soil Plants synthesize all of their own nucleic acids, amino acids, enzymes and cofactors, and chlorophylls: • To synthesize these materials, plants must harvest a wide variety of elements in the form of ions and molecules • Most of these nutrients are found at low—sometimes extremely low— concentrations in soil • The one-way flow of water carries these nutrients up the xylem CO2 • To survive and grow, a plant must obtain –carbon dioxide O2 Light H 2O Sugar –inorganic substances • Essential elements are those that a plant must obtain to –complete its life cycle of growth –have reproductive success Water and minerals move upward from roots to shoots to leaves. H 2O Minerals (inorganic ions) Sugar can flow both ways between shoots and roots. O2 CO2 • Hydroponic culture studies have helped identify 17 elements essential to plant growth and reproduction. –There are nine macronutrients that plants require in relatively large amounts. Complete solution containing –There are eight micronutrients that plants require in tiny quantities. all minerals (control) Solution lacking potassium (experimental) • Both types of nutrients have vital functions. 1 6/22/23 Plant health depends on obtaining all of the essential inorganic nutrients Macronutrients: – Almost 98% of a plant’s dry weight consists of 1. carbon (C) 2. hydrogen (H) 3. oxygen (O) 4. nitrogen (N) 5. sulfur (S) 6. phosphorus (P) – About 1.7% of a plant’s dry weight consists of 1. potassium (K+) 2. calcium (Ca+2) 3. magnesium (Mg+2) • Notice that many of the macronutrients are major building blocks for nucleic acids, proteins, and carbohydrates • Ca+2: maintains structure of cell membranes; functions in cell walls; helps regulate selective permeability Plant health depends on obtaining all of the essential inorganic nutrients The eight micronutrients function in plants mainly as cofactors (0.3% of dry weight): 1. 2. 3. 4. chlorine (Cl-) iron (Fe+2) manganese (Mn+2) boron (B) 5. 6. 7. 8. zinc (Zn+2) copper (Cu+2) nickel (Ni+2) molybdenum (Mo) • K+: works with enzymes; main solute for osmotic regulation (e.g. stomatal opening/closing) • Mg+2: essential component of chlorophyll Many Nutrients are Absorbed From the Soil • Process of soil building begins with solid rock that is Weathered-- Forces applied by rain, running water, and wind continually breaks down solid rock forming gravel, sand, silt, and clay • As organisms occupy soil, they add decaying organic matter called humus Many Nutrients are Absorbed From the Soil • Soil texture differs with proportions of gravel, sand, silt, and clay • Soil texture is important for several reasons: • Affects ability of roots to penetrate soil to obtain water and nutrients and to anchor and support plants • Affects soil’s ability to hold water and make it available to plants • Affects availability of oxygen for cellular respiration • Loams, best soil for plants, contain equal amounts of sand, slit, and clay along with high proportions of humus 2 6/22/23 Many Nutrients are Absorbed From the Soil • The availability of nutrients in soil affects plant growth and health. • Growers can often determine which nutrients are missing from soil by looking at plant symptoms. • Nitrogen shortage is the most common nutritional problem for plants and can stunt growth and cause low nutritional value. • Leeching: Movement of water through soil can wash away important nutrients • Soil mixtures that contain clay contain natural anions, which bind to the positively charged ions potassium (K+) calcium (Ca+2) magnesium (Mg+2) Healthy iron (Fe+2) manganese (Mn+2) zinc (Zn+2) copper (Cu+2) nickel (Ni+2) Nitrogen (N)-deficient Phosphorus (P)-deficient Potassium (K)-deficient Plants for Symbiotic Relationships at the Root to Acquire Nutrients • Symbiotic relationships between plants and fungi/bacteria are mutualistic: • Bacteria/Fungi obtain sugars and amino acids from plant while plants benefit from increased nutrient absorption • Two types of symbiotic relationships are common among plants: • Rhizobia: Symbiotic relationships with bacteria • Mycorrhizae: Symbiotic relationships with fungi Fungal filament Root Rhizobia Fertilizers can help prevent nutrient deficiencies Some Nutrient Uptake is Facilitated By Symbiotic Relationships at the Root with Fungi • Fungi and plant roots that live in physical association are called mycorrhizae. • Symbiotic relationship between plant and fungi is mutualistic: • Fungal symbionts obtain sugars from plant while plant symbionts benefit from increased nutrient and water uptake from the soil from the mycorrhizal fungi Fungal filament Root • Fungi are particularly efficient at acquiring nutrients required by plants for two reasons: 1. Networks of filamentous hyphae increase the surface area available for absorbing nutrients by up to 700% 2. Fungi can acquire nutrients from macromolecules in soil that are unavailable to non-mycorrhizal plants Mycorrhizae 3 6/22/23 Recall Carbon Fixation during Photosynthesis: Nitrogen Fixation by Bacteria is also accomplished by Symbiotic Relationships at the Root • Nitrogen gas (N2) is a macronutrient that makes up 80% of the atmosphere. However, plants and other eukaryotes cannot use nitrogen in this form because N2 is unreactive. • Plants instead absorb nitrogen in the form of as ammonium Nodules (NH4+) or nitrate ions (NO 3−). Roots • Nitrogen fixation is the process by which atmospheric nitrogen is converted to ammonia (NH 3), nitrites (NO2), or nitrates (NO3). Bacteria and Archaea can facilitate this process for plants. N2 ATMOSPHERE ATMOSPHERE SOIL Nitrogen-fixing bacteria N2 SOIL Root Structure Roots have several distinct tissue layers, from the outside in: 1. The epidermis and the root hairs 2. The cortex Amino acids, etc. NH4+ H+ NH3 NO3− NH (ammonium) Nitrifying (nitrate) bacteria Ammonifying bacteria Organic material 4+ Root Nutrient Uptake Begins at the Roots Structures Root hairs have large surface area and contain large numbers of membrane transport proteins that bring nutrients into cytosol of root cells. Minerals can be absorbed by either passive or active transport 3. The endodermis 4. The pericycle 5. The vascular tissue, which contains xylem and phloem 4 6/22/23 Nutrient Uptake Begins at the Roots Structures Root hairs have large surface area and contain large numbers of membrane proteins that bring nutrients into cytosol of root cells • Some ions are brought in via proton pumps (H+ -ATPases) which work in tandem with membrane proteins If soil is overfertilized, plants can die due to a particular imbalance at the root. Why would this be the case? *Think about the rules regarding osmosis of water and draw a diagram of the root and the soil showing where the majority of solutes are and the direction water would travel* H2O Soil Overfertilized Soil Contains Many Solutes Root TRANSPIRATION THE UPWARD MOVEMENT OF WATER FROM THE ROOTS THROUGH THE XYLEM Nutrient Absorption follows Water Absorption at the Roots • Root hairs greatly increase a root’s absorptive surface. • After water is absorbed through root hair, it travels through the root cortex toward the vascular tissues by one of three routes: 5 6/22/23 Nutrient Absorption follows Water Absorption at the Roots Once the water and solutes reach the endodermis, a continuous waxy barrier called the Casparian strip: –stops them from entering the xylem through cell walls and instead forces them to cross a plasma membrane into an endodermal cell • No solutes enter the vascular tissue unchecked. Root hair Epidermis Cortex Phloem Water Transport in Roots Key Dermal tissue system Ground tissue system Vascular tissue system Xylem Casparian strip Endodermis Extracellular route, via cell walls and spaces between cells; stopped by Casparian strip Root hair Intracellular Plasmodesmata route, via cell interiors, through Epidermis plasmodesmata Casparian strip Endodermis Cortex Root Pressure Can Cause Guttation • Movement of ions and water into root xylem responsible for root pressure: • While stomata normally close at night, minimizing water loss, roots continue to accumulate ions from soil • Influx of ions lowers water potential of xylem, drawing in water from nearby cells and creating positive pressure that forces water up xylem Xylem Vascular cylinder Stomata Regulate Gas and Water Exchange • Transpiration is the upward movement of water driven by the upward pull of evaporation at the stomata and the cohesive/adhesive properties of water in the xylem • Stomata open and close and help plants adjust their transpiration rates to changing environmental conditions. • Transpiration requires no energy expenditure by the plant • Guttation is due to root pressure can force water droplets out of leaf margins 6 6/22/23 Stomata Regulate Gas and Water Exchange • In a leaf, the epidermis is interrupted by tiny pores called stomata, which allow exchange of CO2 and O2 between the surrounding air and the photosynthetic cells inside the leaf. • Each stoma is flanked by two guard cells that regulate the opening and closing of the stoma. • CO is taken up from the atmosphere to be fixed into sugars 2 during photosynthesis • H2O can move in and out (needed for photosynthesis; but largely lost through evaporation ) • O2 produced by photosynthesis can move out CO2 H2O Guard cells Stoma H2O H2O H2O H2O H2O K+ H2O Vacuole H2O • Plants must make a tradeoff between its need for water and its need to make food by photosynthesis. Stomata Regulate Gas and Water Exchange • In general, stomata are open during the day and closed at night. • A least three factors influence guard cell activity. 1. Sunlight signals guard cells to accumulate K+ and open stomates. 2. Low CO2 concentration in leaves also signals guard cells to open stomates. 3. An internal timing mechanism—a biological clock—found in the guard cells will continue their daily rhythm of opening and closing, even in the dark. • During the day, guard cells may close stomata if the plant is losing water too fast. Adaptations Prevent Excessive Water Loss in Dry Climates: Leaves modified into spines decrease the surface area of the leaves, which decreases the number of stomata and therefore decreases the amount of water lost during the day. H2O H2O H2O Stoma opening Stoma closing The stomata of plant A are closed while those of plant B are open. Which plant will likely be able to produce more sugars through photosynthesis? Assume that both plants receive the same amount of light and that water is available. A. plant A, since it will absorb more CO2 than plant B B. plant A, since closed stomata generate more CO2 than open stomata C. D. plant B, since more oxygen will diffuse out of the stomata plant B, since CO2 will be able to diffuse into the leaf from the surrounding atmosphere Water is pulled up from the roots through xylem vessels Capillary action—movement of water up narrow tube (e.g., a xylem element) due to three forces: 7 6/22/23 Leaf Leaf Xylem sap Xylem sap Mesophyll cells Mesophyll cells Stoma Water molecule Water molecules diffuse out of stomata. This evaporation, called transpiration, Outside air creates tension on the chain of water molecules that run from the roots to the leaves. Mesophyll cells Mechanism of Transpiration Stoma Water molecule Water molecules diffuse out of stomata. This evaporation, called transpiration, Outside air creates tension on the chain of water molecules that run from the roots to the leaves. Stem Cohesion Cell wall of xylem cells Water molecule The tension pulls the chain of water molecules upward through the xylem cells. Water molecules cling to the cells by adhesion and stick to each other by cohesion. Xylem cells Root Xylem sap The tension created by transpiration pulls water and minerals upward Soil particle from the soil into the xylem cells of the roots. Root hair Water molecule Water molecules diffuse out of stomata. This evaporation, called transpiration, creates tension on the chain of water molecules that run from the roots to the leaves. Outside air Stem Cohesion Cell wall of xylem cells Adhesion Water molecule The tension pulls the chain of water molecules upward through the xylem cells. Water molecules cling to the cells by adhesion and stick to each other by cohesion. Xylem cells Evidence for Transpiration Leaf Xylem sap Adhesion Mechanism of Transpiration Mechanism of Transpiration Stoma • If the cohesion–tension theory is correct: – Water in xylem should experience a strong pulling force during transpiration • If you take a leaf that is actively transpiring and cut its petiole: – Watery fluid in xylem (xylem sap) withdraws from edge toward inside of the leaf – This is due to transpirational pull at the air–water interface in leaf cell stomata Water 8 6/22/23 Which of the following is not a route by which water travels from root hair to xylem? A. apoplastic route (water flows within porous cell walls as it travels to the xylem) B. transmembrane route (water crosses cell membranes of adjacent cells via water channels as it travels to the xylem) C. symplastic route (water flows through plasmodesmata as it travels from cell to cell on its way toward the xylem) D. epidermal route (water flows from the epidermis directly into xylem) A hot dry summer will reduce crop yields. Why? Tree A is 5 meters tall, and tree B is 10 meters tall. Which tree has to expend more energy to move water up the trunk due to cohesion– tension and transpiration? A. Tree A B. Tree B C. They expend equal energy D. Neither expends energy Transpiration A. the stomata of the plants stay open to help cool the leaves., which wastes energy. B. carbon dioxide uptake is reduced by the stomata closing to prevent excessive water loss. C. oxygen uptake is reduced by the stomata closing to prevent excessive water loss. D. carbon dioxide release is reduced by the stomata closing to prevent excessive water loss. 9 6/22/23 Transport Review Passive Transport SUGAR TRANSPORT THROUGH THE PHLOEM Active Transport Plants produces sugars by photosynthesis 1. Chlorophyll is excited by sunlight 2. Chlorophyll donates electrons to neighboring proteins to do work 3. Proteins in the chloroplasts use the electrons to make ATP and then donate the used electrons 4. The leftover electrons are used to fix CO2 to produce glucose 5. Glucose is then transported into the Phloem • Phloem transports the products of photosynthesis from where they are made or stored to where they are needed. • Phloem sap contains inorganic ions, amino acids, hormones, sugars Translocation of Sugars Through the Phloem Translocation: The movement of sugars through plant by bulk flow from “sources” to “sinks” through the phloem • Source is a tissue where sugar enters the phloem • Sink is a tissue where sugar exits the phloem • Sugar concentrations are high in sources and low in sinks 10 6/22/23 Translocation of Sugars Through the Phloem The location of sources and sinks in a plant varies with time of year: • Early in the growing season, storage cells in roots and stems are sources while developing leaves are sinks • Later in the growing season mature leaves and stems are sources while meristems, developing leaves, flowers, seeds, and fruits, and storage cells in roots are sinks Pressure Flow Mechanism: Source to Sink • Active transport of sucrose raises the concentration of solute within the phloem and therefore draws water from the xylem into the phloem tube via osmosis. This generates high pressure at the source. • At a sugar sink, both sugar and water leave the phloem tube. This lowers the solute concentration in the phloem at the sink end of the tube. Water then leaves the phloem via osmosis and re-enters the xylem. The exit of water lowers the water pressure in the tube. Phloem Loading at the Source Sucrose enters companion cells from source tissues by secondary active transport: • Companion cells have a proton pump that uses ATP to drive transport of protons into the source cell against it’s concentration gradient • Then, a symporter uses the established proton gradient to move sucrose against its concentration gradient into the companion cells while the protons move down their concentration gradient. Leaf Cell. Companion Cell Testing the Pressure Flow Mechanism • Aphids are small insects that ingest phloem sap: • Insert a stylet, syringe-like mouthpart, into sieve-tube members • Pressure on fluid in these cells forces it through stylet, into aphid’s digestive tract, and out its anus as droplets of “honeydew” • If an aphid stylet is inserted into phloem, and the aphid is severed from it’s stylet, sap continuously flows out of the stylet, indicating that the phloem is under pressure as hypothesized by the pressure-flow model 11 6/22/23 Phloem Unloading • Phloem unloading in young, growing leaves occurs by facilitated diffusion because sucrose is rapidly used up in cells of these leaves. • Root cells have large vacuole that stores sucrose, surrounded by a membrane called the tonoplast: • Tonoplast contains two types of protein pumps that work to accumulate sucrose in vacuole • As protons diffuse back out of vacuole, proton–sucrose antiporter moves sucrose into vacuole against its concentration gradient Sucrose tends to be more concentrated in companion cells than in the photosynthetic cells where it is produced. How is this best explained? A. Sucrose diffuses into companion cells against its concentration gradient. B. Osmosis drives the movement of sucrose into the companion cells. C. Sucrose is actively transported from the companion cells to the photosynthetic cells. D. Sucrose is actively transported from the photosynthetic cells to the companion cells. Nutritional Adaptations of Plants Epiphytes are non parasitic. They grow in absence of soil, often on leaves or branches of trees Nutritional Adaptations of Plants • Plants absorb water and nutrients from rainwater, dust, and particles that collect in their tissues: • Some epiphytic bromeliads have leaves that grow in rosettes to form “tanks” that collect water and organic debris • Nutrients are actually absorbed through the leaves (exceptions to standard nutrient acquisition found in most plants) 12 6/22/23 Nutritional Adaptations of Plants • Parasites live on or in a host, obtaining water or nutrients from host and reducing host’s fitness • Some parasitic plants are heterotrophs producing structures called haustoria that can penetrate host vascular system to obtain water and nutrients • Most parasitic plants are photosynthetic and use haustoria to extract water and ions from the xylem of host plant Nutritional Adaptations of Plants Carnivorous trap insects and other animals: • These plants kill their prey and absorb the prey’s nutrients • Make their own carbohydrates via photosynthesis: • Using carnivory to supplement nitrogen available in the environment • Most are found in bogs or other habitats where nitrogen is scarce Unit Overview: Plant Nutrition 13 6/22/23 Unit Overview: Transpiration 14