Plants to Feed the World - Todays Biology - Lecture Slides, Slides of Biology

Download Plants to Feed the World - Todays Biology - Lecture Slides and more Slides Biology in PDF only on Docsity! Plants to feed the world Docsity.com Plants to feed the world • Hunger, starvation, and malnutrition are endemic in many parts of the world today. • Rapid increases in the world population have intensified these problems! • ALL of the food we eat comes either directly or indirectly from plants. • Can’t just grow more plants, land for cultivation has geographic limits – Also, can destroy ecosystems! Docsity.com Plants to feed the world • Disease-resistant wheat varieties with high yield potentials are now being produced for a wide range of global, environmental and cultural conditions. • The Green Revolution has had major social and ecological impacts, which have drawn intense praise and equally intense criticism. Docsity.com Plants to feed the world • The Green Revolution is sometimes misinterpreted to apply to present times. • In fact, many regions of the world peaked in food production in the period 1980 to 1995, and are presently in decline, since desertification and critical water supplies have become limiting factors in a number of world regions. Docsity.com & FEW OF THE MANY MEDICINAL PLANTS A few of the many medicinal plants. PLANT LATIN NAME COMMON NAME NAME USE Cigitals purpurea Purple fougove dightalls strengthens heart contractions Rauwotla serpentia Inda makercot reserpine lowers blood pressure Atropa baladonna Deadly nightshade atropine blocks neurotranamitters, antispasmodic beladonna blocks neurotranemittars, antispasmodic Datura SEP. Jimson weed (thom apple) scopdlamine sadative, controls nausea Papaver somnteum Opium popples codeine cough suppressant, pain killer morphing paln killer Einchon ladgeriana Cinchona tree bark quinine malaria prevention Catheranthus mseus Madagascar rose periwinkle vinblastine cancer chemotherapy vincristine cancer chemotherapy taxcl cancer chemotherapy Ca Pacific yew Docsity.com Photosynthetic Pigments • Two types in plants: • Chlorophyll- a • Chlorophyll –b • Structure almost identical, – Differ in the composition of a sidechain – In a it is -CH3, in b it is CHO • The different sidegroups 'tune' the absorption spectrum to slightly different wavelengths – light that is not significantly absorbed by chlorophyll a, will instead be captured by chlorophyll b Docsity.com Photosynthetic Pigments • Chlorophyll has a complex ring structure – The basic structure is a porphyrin ring, co-coordinated to a central atom. – This is very similar to the heme group of hemoglobin • Ring contains loosely bound electrons – It is the part of the molecule involved in electron transitions and redox reactions of photosynthesis Docsity.com the chloroPlast • Membranes contain chlophyll and it’s associated proteins – Site of photosynthesis • Have inner & outer membranes • 3rd membrane system – Thylakoids • Stack of Thylakoids = Granum • Surrounded by Stroma – Works like mitochondria • During photosynthesis, ATP from stroma provide the energy for the production of sugar molecules Docsity.com the chemical reaction of Photosynthesis is driven by light – Quantum efficiency: Measure of the fraction of absorbed photons that take part in photosynthesis. – Energy efficiency: Measure of how much energy in the absorbed photons is stored as chemical products • ¼ energy from photons stored – the rest is converted to heat Docsity.com the light reactions • Step 1 – chlorophyll in vesicle membrane capture light energy • Step 2 – this energy is used to split water into 2H and O. • Step3 – O released to atmosphere. Each H is further split into H+ ion and an electron (e-). • Step 4 – H+ ion build up in the stacked vesicle membranes. Docsity.com the light reactions • Step 5 – The e- move down a chain of electron transport proteins that are part of the vesicle membrane. • Step 6 – e- ultimately delivered to the molecule NADP+ - forming NADPH • Step 7 - Some membrane proteins pump H+ into the interior space of the vesicle – Stored energy • Step 8 – These make ATP! Docsity.com Overview of the carbon reactions • The Calvin cycle: • The cycle runs six times: – Each time incorporating a new carbon . Those six carbon dioxides are reduced to glucose: – Glucose can now serve as a building block to make: • polysaccharides • other monosaccharides • fats • amino acids • nucleotides Docsity.com Photorespiration • Occurs when the CO2 levels inside a leaf become low – This happens on hot dry days when a plant is forced to close its stomata to prevent excess water loss • If the plant continues to attempt to fix CO2 when its stomata are closed – CO2 will get used up and the O2 ratio in the leaf will increase relative to CO2 concentrations • When the CO2 levels inside the leaf drop to around 50 ppm, – Rubisco starts to combine O2 with Ribulose-1,5- bisphosphate instead of CO2 Docsity.com The C4 carbon Cycle • The C4 carbon Cycle occurs in 16 families of both monocots and dicots. – Corn – Millet – Sugarcane – Maize • There are three variations of the basic C4 carbon Cycle – Due to the different four carbon molecule used Docsity.com water across Plant membranes • There is some diffusion of water directly across the bi- lipid membrane. • Auqaporins: Integral membrane proteins that form water selective channels – allows water to diffuse faster – Facilitates water movement in plants • Alters the rate of water flow across the plant cell membrane – NOT direction Docsity.com • Xylem: – Main water-conducting tissue of vascular plants. – arise from individual cylindrical cells oriented end to end. – At maturity the end walls of these cells dissolve away and the cytoplasmic contents die. – The result is the xylem vessel, a continuous nonliving duct. – carry water and some dissolved solutes, such as inorganic ions, up the plant water transPort in Plants Docsity.com water transPort in Plants • Phloem: – The main components of phloem are • sieve elements • companion cells. – Sieve elements have no nucleus and only a sparse collection of other organelles . Companion cell provides energy – so-named because end walls are perforated - allows cytoplasmic connections between vertically-stacked cells . – conducts sugars and amino acids - from the leaves, to the rest of the plant Docsity.com Plant cell in hyPotonic solution • Flaccid cell in 0.1M sucrose solution. • Water moves from sucrose solution to cell – swells up –becomes turgid • This is a Hypotonic solution - has less solute than the cell. So higher water conc. • Pressure increases on the cell wall as cell expands to equilibrium Docsity.com Plant cell in hyPertonic solution • Turgid cell in 0.3M sucrose solution • Water movers from cell to sucrose solution • A Hypertonic solution has more solute than the cell. So lower water conc • Turgor pressure reduced and protoplast pulls away from the cell wall Docsity.com Plant cell in isotonic solution • Water is the same inside the cell and outside • An Isotonic solution has the same solute than the cell. So no osmotic flow • Turgor pressure and osmotic pressure are the same Docsity.com stomatal control • When water is abundant: • Temporal regulation of stomata is used: – OPEN during the day – CLOSED at night • At night there is no photosynthesis, so no demand for CO2 inside the leaf • Stomata closed to prevent water loss • Sunny day - demand for CO2 in leaf is high – stomata wide open • As there is plenty of water, plant trades water loss for photosynthesis products Docsity.com stomatal control • When water is limited: – Stomata will open less or even remain closed even on a sunny morning • Plant can avoid dehydration • Stomatal resistance can be controlled by opening and closing the stomatal pores. • Specialized cells – The Guard cells Docsity.com stomatal guard cells • Guard cells act as hydraulic valves • Environmental factors are sensed by guard cells – Light intensity, temperature, relative humidity, intercellular CO2 concentration • Integrated into well defined responses – Ion uptake in guard cell – Biosynthesis of organic molecules in guard cells • This alters the water potential in the guard cells • Water enders them • Swell up 40-100% Docsity.com Plants and water • Water is the essential medium of life. • Land plants faced with dehydration by water loss to the atmosphere • There is a conflict between the need for water conservation and the need for CO2 assimilation – This determines much of the structure of land plants – 1: extensive root system – to get water from soil – 2: low resistance path way to get water to leaves – xylem – 3: leaf cuticle – reduces evaporation – 4: stomata – controls water loss and CO2 uptake – 5: guard cells – control stomata. Docsity.com nitrogen in the environment • Many biochemical compounds present in plant cells contain nitrogen – Nucleoside phosphates – Amino acids • These form the building blocks of nucleic acids and protein respectively • Only carbon, hydrogen, and oxygen are nor abundant in plants than nitrogen Docsity.com nitrogen in the environment • Present in many forms • 78% of atmosphere is N2 – Most of this is NOT available to living organisms • Getting N2 for the atmosphere requires breaking the triple bond between N2 gas to produce: • Ammonia (NH3) • Nitrate (NO3-) • So, N2 has to be fixed from the atmosphere so plants can use it Docsity.com how do Plants get their nitrogen? • Some plant species are Legumes. • Legumes seedlings germinate without any association to rhizobia – Under nitrogen limiting conditions, the plant and the bacteria seek each other out by an elaborate exchange of signals • The first stage of the association is the migration of the bacteria through the soil towards the host plant Docsity.com how do Plants get their nitrogen? • Nodule formation results a finely tuned interaction between the bacteria and the host plant – Involves the recognition of specific signals between the symbiotic bacteria and the host plant • The bacteria forms NH3 which can be used directly by the plant • The plant gives the bacteria organic nutrients. Docsity.com Figure 11.8 (1) how do Plants get their nitrogen? • Some plants obtain nitrogen from digesting animals (mostly insects). • The Pitcher plant has digestive enzymes at the bottom of the trap • This is a “passive trap” Insects fall in and can not get out • Pitcher plants have specialized vascular network to tame the amino acids from the digested insects to the rest of the plant Docsity.com Figure 11.13 increasing croP yields • Algal blooms - a relatively rapid increase in the population of (usually) phytoplankton algae in an aquatic system. • Causes the death of fish and disruption to the whole ecosystem of the lake. • International regulations has led to a reduction in the occurrences of these blooms. Docsity.com Figure 11.17 chemical Pest control • Each year, 30% of crops are lost to insects and other crop pests. • The insects leave larva, which damage the plants further. • Fungi damage or kill a further 25% of crop plants each year. • Any substance that kills organisms that we consider undesirable are known as a pesticide. • An ideal pesticide would:- – Kill only the target species – Have no effect on the non-target species – Avoid the development of resistance – Breakdown to harmless compounds after a short time Docsity.com Figure 11.17 chemical Pest control • DTT was first developed in the 1930s • Very expensive, toxic to both harmful and beneficial species alike. • Over 400 insect species are now DTT resistant. • As with fertilizers, there are run-off problems. • Affects the food pyramid. – Persist in the environment Docsity.com Figure 11.20 genetically modified croPs •Corn plants have been selective breed to increase oil yields or protein content for over 70 years. •Attempts to change one trait at a time can lead to the production of an inferior strain. •Breeding plants with high oil content changes inherited characteristics of a given strain Docsity.com genetically modified croPs • 1992- The first commercially grown genetically modified food crop was a tomato - was made more resistant to rotting, by adding an anti- sense gene which interfered with the production of the enzyme polygalacturonase. – The enzyme polygalacturonase breaks down part of the plant cell wall, which is what happens when fruit begins to rot. Docsity.com Figure 11.21 genetically modified croPs •So to modify a plant: •Need to know the DNA sequence of the gene of interest •Need to put an easily identifiable maker gene near or next to the gene of interest •Have to insert both of these into the plant nuclear genome •Good screen process to find successful insertion •Clone the genetically altered plant Docsity.com genetically modified croPs • Agrobacterium method – Uses the natural infection mechanism of a plant pathogen – Agrobacterium tumefaciens naturally infects the wound sites in dicotyledonous plant causing the formation of the crown gall tumors. – Capable to transfer a particular DNA segment (T-DNA) of the tumor-inducing (Ti) plasmid into the nucleus of infected cells where it is integrated fully into the host genome and transcribed, causing the crown gall disease. • So the pathogen inserts the new DNA with great success!!! Docsity.com genetically modified croPs • The vir region on the plasmid inserts DNA between the T- region into plant nuclear genome • Insert gene of interest and marker in the T-region by restriction enzymes – the pathogen will then “infect” the plant material • Works fantastically well with all dicot plant species – tomatoes, potatoes, cucumbers, etc – Does not work as well with monocot plant species - corn • As Agrobacterium tumefaciens do not naturally infect monocots Docsity.com Figure 11.21 genetically modified croPs •So to modify a plant: •Need to know the DNA sequence of the gene of interest •Need to put an easily identifiable maker gene near or next to the gene of interest •Have to insert both of these into the plant nuclear genome •Good screen process to find successful insertion •Clone the genetically altered plant Docsity.com genetically modified croPs • Issues: • Destroying ecosystems – tomatoes are now growing in the artic tundra with fish antifreeze in them! • Destroying ecosystems – will the toxin now being produced by pest-resistance stains kill “friendly” insects such as butterflies. • Altering nature – should we be swapping genes between species? Docsity.com genetically modified croPs • Issues: • Vegetarians – what about those tomatoes? • Religious dietary laws – anything from a pig? • Cross-pollination – producing a super-weed • Human health – what of the antibiotic marker gene? Docsity.com the end. any Questions? Docsity.com