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An Ecological Perspective (BIOL 346) Talk Six: Plants That Feed Us Plants that 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! PlantsFigure that 9.1 feed us The Earth is currently experiencing the most population increase in Human history. 2.5 billion in 1955 to 7 billion in 2012 At current rate, will double within 30 years! Fastest growing nations have growth rates at or above 4% - this will double the countries population every 17 years Plants to feed the world • At the latest count there are between 250,000 and 400,000 plant species on the earth. • But three - maize, wheat and rice - and a few close runners-up, have become the crops that feed the world. All produce starch, helping to provide energy and nutrition, and all can be stored. • Maize converts the sun’s energy into sugar faster, and potentially produces more grains, than any of the other major staples. Plant Starch (Amylose and Amylopectin) • Starch contains a mixture of amylose and amylopectin • Amylose is an unbranched polymer (forms -helix) of D-glucose molecules linked by 1,4-glycosidic bonds • Amylopectin is like amylose, but has extensive branching, with the branches using -1,6glycosidic bonds What comes from plants Popular stimulants like coffee, chocolate, tobacco, and tea. Simple derivatives of botanical natural products; for example, aspirin is based on the pain killer salicylic acid which originally came from the bark of willow trees. Most alcoholic beverages come from fermenting plants such as barley (beer), rice (sake) and grapes (wine). What comes from plants • Plants also provide us with many natural materials – hemp, cotton, wood, paper, linen, vegetable oils, some types of rope, and rubber. • The production of silk would not be possible without the cultivation of the mulberry plant. • Sugarcane, rapeseed, soy and other plants with a highly fermentable sugar or oil content have recently been put to use as sources of biofuels, which are important alternatives to fossil fuels A few of the many medicinal plants Plants to feed the world • The term Green Revolution is used to describe the transformation of agriculture in many developing nations that led to significant increases in agricultural production between the 1940s and 1960s • Scientists bred short plants that converted the sun’s energy into grain rather than stem, so preventing the mass starvation in the developing world predicted before the 1960s, at a cost of higher inputs from chemical fertilizers and irrigation. 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. Remember!! • Agriculture has changed dramatically, especially since the end of World War II. • Food and fiber productivity soared due to new technologies, mechanization, increased chemical use, specialization and government policies that favored maximizing production. • These changes allowed fewer farmers with reduced labor demands to produce the majority of the food and fiber in the U.S. Remember! • Has had major social and ecological impacts, which have drawn intense praise and equally intense criticism. • In fact, many regions of the world peaked in food production in the period 1980 to 1995 • Are presently in decline, since desertification and critical water supplies have become limiting factors in a number of world regions. Plant Basics • Roots – absorb water from the soil as well as many mineral nutrients • Xylem – transports water from the roots to the rest of the plant • Phloem – transports sugars made in the leaves via photosynthesis to the pest of the plant • Leaves – Site of gas exchange CO2 brought in and O2 out. Have structures called Stomata which also control water loss. 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. 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 Water transport in Plants • 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 and plant cells • 80-90% of a growing plant cell is water – – – – This varies between types of plant cells Carrot has 85-95% water Wood has 35-75% water Seeds have 5-15% water • Plant continuously absorb and lose water – Lost through the leaves • Called transpiration Water Water • (A) Hydrogen bonds between water molecules results in local aggregations of water molecules • (B) Theses are very short lived, break up rapidly to form more random configurations • Due to temperature variations in water Photosynthesis The (very) Basic facts Photosynthesis •Very little of the Sun’s energy gets to the ground gets absorbed by water vapor in the atmosphere •The absorbance spectra of chlorophyll. Absorbs strongly in the blue and red portion of the spectrum Green light is reflected and gives plants their color. •There are two pigments •Chlorophyll A and B General overall reaction 6 CO2 + 6 H2O Carbon dioxide Water C6H12O6 + 6 O2 Carbohydrate Oxygen Photosynthetic organisms use solar energy to synthesize carbon compounds that cannot be formed without the input of energy. More specifically, light energy drives the synthesis of carbohydrates from carbon dioxide and water with the generation of oxygen. Overall Perspective • Light reactions: – Harvest light energy – Convert light energy to chemical energy • Dark Reactions: – Expend chemical energy – Fix Carbon [convert CO2 to organic form] 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 The chemical reaction of photosynthesis is driven by light • The initial reaction of photosynthesis is: – CO2 +H2O (CH2O) + O2 – Under optimal conditions (red light at 680 nm), the photochemical yield is almost 100 % – However, the efficiency of converting light energy to chemical energy is about 27 % • Very high for an energy conversion system 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 • During photosynthesis, ATP from stroma provide the energy for the production of sugar molecules 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. 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! Summary of light reactions • Plants have two reaction centers: – PS-II • Absorbs Red light – 680mn • makes strong reductant (& weak oxidant) • oxidizes 2 H2O molecules to 4 electrons, 4 protons & 1 O2 molecule • Mostly found in Granum – PS-I • • • • Absorbs Far-Red light – 700nm strong oxidant (& weak reductant) PS-I reduces NADP to NADPH Mostly found in Stroma The Carbon reactions • The NADPH and ATP move into the liquid environment of the Stroma. • The NADPH provides H and the ATP provides energy to make glucose from CO2. • The Calvin cycle thus fixes atmospheric CO2 into plant organic material. 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 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 The C4 carbon Cycle • The C4 carbon Cycle occurs in 16 families of both monocots and dicots. – Millet – Sugarcane – Maize • There are three variations of the basic C4 carbon Cycle – Due to the different four carbon molecule used The C4 carbon Cycle • This is a biochemical pathway that prevents photorespiration • C4 leaves have TWO chloroplast containing cells – Mesophyll cells – Bundle sheath (deep in the leaf so atmospheric oxygen cannot diffuse easily to them) • C3 plants only have Mesophyll cells • Operation of the C4 cycle requires the coordinated effort of both cell types – No mesophyll cells is more than three cells away from a bundle sheath cells • Many plasmodesmata for communication Ah, the big hitters! maize, wheat and rice Maize (Corn) • Represents the most remarkable plant breeding achievement in the history of agriculture. • The modern manifestation of this ancient plant bears very little resemblance to its original ancestor, a wild grass from southern Mexico called teosinte. Photo courtesy of Raúl Coronado Maize • Teosinte is a tall, drought-tolerant grass that produces, instead of a cob, spikes close to the ground, filled with two rows of small, triangular-shaped seeds within an enclosed husk • A hard shell around each seed protects them once they fall to the ground • This transformation from an inconspicuous grass to a diverse, highly evolved and productive food plant spans thousands of years • A story of co-evolution and interdependence between humans and corn unprecedented in nature Maize • 100 years after discovering that teosinte was edible, people began selecting spikes to plant near their homes, which were close to irrigation sources. • These selected plants continued to be developed in isolation from wild teosinte that was growing in the surrounding forests, and thus the process of developing corn had begun. • The difference between Teosinte and maize is about 5 genes. • About 5 regions of the genome (which could be single genes or groups of genes) seemed to be controlling the most-significant differences between teosinte and Maize Maize • The oldest known corncobs, distinctly different from teosinte, were found in the highlands of Oaxaca in southwestern Mexico and are estimated to be 5,400 years old. • Maize cobs uncovered by archaeologists show the evolution of modern maize over thousands of years of selective breeding. • Even the oldest archaeological samples bear an unmistakable resemblance to modern maize. • About two-thirds of the maize grown in the United States goes into livestock feed. Maize – Hogs eat almost half the corn crop. • Maize provides the base for many kinds of poultry feeds and dairy feeds. • Maize and cornstalks are also made into silage, a fermented livestock feed. • Americans eat about 45 pounds of Maize per person per year. • Many kinds of food are made from the kernels. • Maize also provides food indirectly, in the form of the meat and meat products that come from animals raised on it. Maize, in one form or another, makes up more of our diet than any other farm crop. • From: www.robinsonlibrary.com Wheat • Wheat originated in the “cradle of civilization” in the Tigris and Euphrates river valley, near what is now Iraq and the Ethiopian Highlands • The Roman goddess, Ceres, who was deemed protector of the grain, gave grains their common name today – “cereal.” • Wheat is the primary grain used in U.S. grain products — approximately three-quarters of all U.S. grain products are made from wheat flour. Six classes bring order to the thousands of varieties of wheat. They are: hard red winter (HRW), hard red spring (HRS), soft red winter (SRW), hard white (HW), soft white (SW) and durum. Wheat Genetics • Wheat genetics is more complicated than that of most other domesticated species. • Some wheat species are diploid, with two sets of chromosomes. Many are stable polyploids, with four sets of chromosomes (tetraploid) or six (hexaploid). • Genes for the 'dwarfing' trait, first used by Japanese wheat breeders to produce short-stalked wheat, have had a huge effect on wheat yields world-wide. • Dwarfing genes enable the carbon that is fixed in the plant during photosynthesis to be diverted towards seed production. Wheat • Became known as Norin 10 • This grows to just two feet tall, instead of the usual four, which made it less prone to wind damage. – Other varieties grow too high, become top-heavy, and lodge • By 1997, 81% of the developing world's wheat area was planted to semi-dwarf wheats, giving both increased yields and better response to nitrogenous fertilizer. • Norin 10 helped developing countries, such as India and Pakistan, to increase the productivity of their crops from approximately 60% during the Green Revolution. Rice • This is the seed of the monocot plants Oryza sativa (Asian rice) or Oryza glaberrima (African rice). • Rice is the most important grain with regard to human nutrition and caloric intake, providing more than one fifth of the calories consumed worldwide by humans. • Genetic evidence has shown that rice originates from a single domestication 8,200–13,500 years ago, in the Pearl River valley region of China. • Where is rice grown? • Rice is grown in eight American States • Arkansas • California • Texas • Louisiana • Minnesota • Mississippi • Missouri • Florida From the Rice knowledge Bank Rice • Rice cultivation is well-suited to countries and regions with low labor costs and high rainfall, as it is labor-intensive to cultivate and requires ample water. – Rice can be grown practically anywhere, even on a steep hill or mountain. • The traditional method for cultivating rice is flooding the fields while, or after, setting the young seedlings. • This simple method requires sound planning and servicing of the water damming and channeling, but reduces the growth of less robust weed and pest plants that have no submerged growth state, and deters vermin and many pathogens. Rice Environmental impacts • Rice cultivation on wetland rice fields is thought to be responsible for 6–21% of the annual methane emissions produced via Human interaction with the environment. – The Long-term flooding of rice fields cuts the soil off from atmospheric oxygen and causes anaerobic fermentation of organic matter in the soil. • Rice requires slightly more water to produce than other grains. • As a result of rising temperatures and decreasing solar radiation during the later years of the 20th century, the rice yield growth rate has decreased in many parts of Asia. • The reason for this falling yield is not fully understood – might involve increased respiration during warm nights, which expends energy without being able to photosynthesize The End. Any Questions?