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Lecture 9

Lecture 9 - 11 Notes

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Western University
Biology 2217B
Richard Gardiner

Lecture 9: Grasses  Grass family is of greater importance to humanity than any other family of flowering plants Grasses  Monocots: parallel-veined leaves and flower parts which occur in multiples of three  Growth cycle: mostly perennial or annual herbs, erect stems, ascending, prostrate or creeping, round, hollow or solid at nodes or internodes  Leaves: alternate, composed of an open sheath, ligule, and blade; sheath encloses the stem  Flowers: spikelets contain one or more florets; usually subtended by glumes  Evolved in Cretaceous period (about 65 million years ago)  Forests to deserts  Most widespread plant  Important for humans o 10, 000 years – fertile crescent  Majority of food crops, paper making, animal feed, lawns  The grass family – Poaceae o Genera: 600 – 650 o Species: 9000 – 10,000  Cereal crops (food and sugar)  Grazing/pasture/forage crops  Building materials  Source for matting  Ornamentals Vegetative Characteristics  Herbaceous - non-woody plant  Linear leaves o Parallel venation o Alternate arrangement  Both annual and perennial o Most cereals are annuals o Most pasture and lawn grasses are perennials  Primary root system is fibrous  Culm – hollow, jointed stem of grasses  Many also have horizontal stems – either aboveground stolons or underground rhizomes – that can propagate the plant vegetatively by giving rise to new shoots Sexual Reproduction in the Magnoliophyta  Sporophyte and gametophyte are two stages in plant life cycle  Sporophyte o Diploid plant that produces spores by meiosis  Gametophyte o Haploid plant that produces sperm and eggs  Wind pollination of haploid gamete spores The Flower  Spiked flowers in inflorescences  Small and incomplete o Small structures called lodicules take place of sepals and petals o Three stamens  Single ovule in ovary o Two styles and stigmas  Surrounding each flower are two bracts, the outer lemma and inner palea o Flower and bract make up the floret  1 – 12 florets arranged on a spikelet o Surrounded by two bracts called glumes o Bristle extending from glume or lemma is called the awn The Grain  Fruit for grass family  Dry, single-seeded  Chaff – bracts surrounding grain  Bran – outer wall of grain, consisting of fruit wall fused to seed coat  Aleurone layer o Interior to bran o High in protein o If seed is allowed to germinate, provides enzymes to break down food  Majority of seed is occupied by endosperm – stored starch for food  Cotyledon – transfers food to embryo which is surrounded by the coleoptile and coleorhiza sheaths o Embryo, with its sheaths, is often called germ  The “seed” of a grass is actually a fruit, called a caryopsis Culms  Hollow cylinders  Originates near ground level  Transverse sections at nodes  Elongation at leaf base o Clipping or grazing does not destroy  Maximum strength and economy  Some have solid stems, but mostly hollow active region  Rhizomes – underground stems  Sheath encircles stem node o Permits grass to form a sod o Protects auxiliary buds  Ligule o Some produce new plants at each node  Stolons or runners – run atop the ground o Where leaf attaches to main stem usually o Membrane or fringe of hairs o Form new plants at nodes  Leaf blade is linear  Special leaf growth Production  6 of the top 25 world crops (in tons produced) are grasses  Top 3 crops in terms of human caloric intake are all grasses o Rice, wheat, maize  These account for approximately 50% of all caloric intake worldwide Principal Grass Crops  Rice  Oats  Switch-grass, forage, hay  Wheat  Rye and silage  Corn  Sorghums and millets  Barley  Sugar-cane Corn Barley Sugarcane  Kingdom: Plantae  Kingdom: Plantae  Kingdom: Plantae  Division: Magnoliophyta  Division: Magnoliophyta  Division: Magnoliophyta  Class: Liliopsida  Class: Liliopsida  Class: Liliopsida  Order: Poales  Order: Poales  Order: Poales  Family: Poaceae  Family: Poaceae  Family: Poaceae  Genus: Zea  Genus: Hordeum  Genus: Saccharum  Species. Z. mays  Species: Vulgare Wheat  Kingdom: Plantae  Division: Magnoliophyta  Class: Liliopsida  Order: Poales  Family: Poaceae  Genus: Triticum  Historic significance o Triticum monococcum o The “staff of life”  Cultivated in Fertile Crescent not long after barley o Wild early wheat was diploid (e.g. Einkorn)  (1 grain) wheat o Early mutation suppressed shattering  Threshing o About 8000 B.P. Chromosome doubling yields tetraploid Emmer or Durum wheat  Wheat hybridized with ‘goat grass’ o Later, another hybridization with a second goat grass yielded hexaploid bread wheat  Modern bread wheat, Triticum aestivum, is a hexaploid, arising from serial hybridization between wild Einkorn what and two different “goat grasses” Gluten  Wheat, rye, and barley contain two proteins (gliadin and glutenin) that form a complex known as gluten  Bread flower becomes elastic when mixed with water and kneaded  Yeast releases CO2which is trapped as small bubbles – this makes it rise Milling  Wheat embryo is flattened and sieved through  Oils extracted, so flour will keep longer  Seed coat also sieved out after milling  Bran and germ can be sold separately Threshing  Hulled wheat o All wild species, along with einkorn, emmer and spelt o Toughened glumes and (in domesticated wheats) a semi-brittle rachis that breaks easily on threshing o Spike breaks into spikelets, and further processing is needed to obtain the grain  Free-threshing wheat o Durum and bread o Fragile glumes with tough rachis o On threshing, chaff breaks, releasing the grains  Complete grains (caryopses), with the bran remaining. Sometimes referred to as “wheat berries”the chaff (glumes, palea, lemma, etc.) are gone. Wheat (Continued)  Polyploid wheats have more gluten o Raised bread  Before free-threshing, grains were often heated to facilitate threshing. Proteins were denatured by heat, so no raised bread  Today, durum wheat is grown in areas of low rainfall o High gluten content, good for pasta  Bread wheat has thousands of cultivars, or domestic crops specific to certain farms  Wheat is very susceptible to a rust fungus (Puccinia graminis) Nutrition Information  White flour is nutritionally deficient  Whole wheat flour is nutritionally better  Nutrients are not evenly distributed in the grain – many are concentrated in the bran and germ  When wheat is refined, many of the nutrients are lost  To compensate, refined white flour is often enriched with iron and four B vitamins Lecture 10: Grasses – Grains, Canes and Cereal Meals Cereals  Grains are seeds or the seed-like fruits of plants  Cereals are edible grains produced by plants o Seed coat fused to ovary wall  Grain amaranths and buckwheat belong to the Amaranthaceae and Polygonaceae o Grains by not cereals Endosperm  Food storage tissue o Digested either before or during seed germination  Contains starch (sometimes oils and protein)  Selectively retained for white flour Aleurone Layer  Single-layered in most cereals  30% of kernel’s protein o For storage and digestion  During germination it secretes amylases to break down starch Bran  Outer hard layer of the grain o Aleurone and pericarp  Byproduct of milling o Rice, corn, wheat, oats, barley and millet  Rich in dietary fibre and contains antioxidants Germ  Different view of corn kernel  Protective sheaths – over emerging roots and emerging leaves = coleorhizae and coleoptiles Poaceae  Gramineae  A large family  About 650 genera and 10,000 species  Found on all continents, often in dry grasslands Barley  Hordeum vulgare  First domesticated cereal o Fertile crescent  Predominant grain in Europe until 4000 years ago o Overtaken by wheat in importance  Agronomic selection for more and larger seeds, and non-shattering inflorescences  Greeks used it for flatbread and in beer  Current US consumption: o 1/2 = livestock o 1/3 = beer/whiskey o 1/6 = other Malting  Purpose – to obtain sugar from seeds o A. Grain is saturated with water. 24 hours – germination signs are visible o B. Speed of germination controlled by temperature, water and aeration o C. Kiln dried with hot air o D. Malt rootlets are separated and used as animal feed o Malt is now suitable for storage and ready for brewing  To germinate the seeds under controlled conditions, amylase is secreted and starch is broken down into sugars (in this case, maltose)  During the malting process, germination is controlled by temperature and humidity  Heat is added to kill them, rootlets are then separated and broken off and maltose sugar is obtained  In the brewing industry, adding malt = adding sugar  Malt can also be used for other things in the food industry Rye  Secale cereale  Native to southwestern Asia  Hardy grain o “Poor man’s wheat” – unsuitable protein for making bread  High in lysine  Can germinate at low temperatures (1°C)  Can grow in some places where wheat cannot, as it can grow in low temperatures  Ergot poisoning – St. Anthony’s Fire - rye infected with fungus, fungus produces alkaloid and toxins, consumption of rye led to symptoms of St. Anthony’s Fire eventually leading to death Triticale  Triticosecale  Cross between wheat and rye  Human made cereal  Produces high yields in marginal grain-growing regions Oats  Avena sativa  One of the last domesticated grasses  Originally used as feed for horses  High in protein and fat o Oatmeal  Today, it is a breakfast cereal in North America  Used because of its health benefits  Oat bran may have a cholesterol-lowering effect  Bran has soluble fibre that makes oatmeal lumpy  Food companies now add this bran to many foods  Widespread growth in Ontario Rice  Oryza sativa  World’s most important crop  More wheat produced in metric tons, but more people eat rice  21% of total calories consumed by humans  Originally cultivated in Asia, up to 11, 500 years BP  Alexander the Great brought rice to Europe (about 330 BC) th  15 century Portuguese took it to W. Africa and Brazil  Indica type o Long grain rice o When cooked, grains are dry and separate easily  Japonica type o Short grained rice o When steamed or boil, becomes soft and gluey  Endosperm composed of starch granules  Walls rupture and starch gelatinizes when cooked  Grain retains its shape but is soft and chewy o Can absorb flavors  Needs large quantities of water to grow o Lots of rain (Brazil) o Paddy fields (semi-submerged)  Water rots stems after harvest  Blue green algae provide fertilizer  Weeds suppressed  Can be farmed year-round  Currently several types with different cultivation requirements grown o Upland (10%) o Deep water (15%) o Paddy rice (75%)  Specialized stem anatomy allows gas transfer under flooded conditions  Role of Azolla (an aquatic fern) o Has an endosymbiotic nitrogen-fixing cyanobacterium, Anabaena  “Polishing” white rice removes bran and vitamins but gives a longer shelf life  Beriberi – thiamine deficiency o Thiamine – involved in metabolic breakdown of carbohydrates o Symptoms of thiamine deficiency: fatigue, depression, mental confusion, cramping, enlarged heart, and eventually death from cardiac failure o Found mainly in Asia where diets were based mainly on polished or white rice rather than whole-grain brown rice  Thiamine that occurs in the outer layer of the rice is removed during polishing process  G
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