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The Magnificent Seed as Seen through the Phenom Scanning Electron Microscope Portulaca Magic Carpet seed 355x [email protected] Dorothy K. Moore, PhD Chemeketa Community College Salem, Oregon dkm 4/2/11 Page 1 Portulaca Magic Carpet seed 355x [email protected] Introductory Note to the Instructor They often seem dry, lifeless, and inconsequential, but seeds are very much alive and essential to all living things. As teachers, we have the opportunity to share with our students insights about seeds and other areas of the natural world, a place that has become foreign to children who spend increasingly more time indoors. This document is meant to be an introductory source for the educator. It explains briefly the structure of the seed and how that structure contributes to its ability to sprout. It also discusses the various means of seed dispersal and lists a number of seeds that we eat directly as food. At the end I’ve included a few resources I have found helpful while researching this topic. Most of the microscopic images in this document were captured using the Phenom table top scanning electron microscope, an easy-to-use tool designed especially for teachers. If you’re interested in more information on the Phenom or think you might like to obtain one, you can visit the Phenom-World website at www.phenom-world.com. Otherwise, you may simply use this document and its images as a springboard to your own study and investigation of nature. The seed is a highly significant instrument of creation. I trust you and your students will find great satisfaction in researching and pondering its magnificence. dkm 4/2/11 Page 2 celery seed 390x [email protected] Seed defined Just what is a seed? There are basically two ways to think about a seed: We can think of a seed as the part of the plant that contains the embryo of that plant - the embryo being the undeveloped form of the adult plant - or we can think of a seed as the small embryonic plant itself. However we conceptualize it, the seed is an amazing little structure whose form and function enable it to propagate and spread across the earth. Seeds that are at rest and have not yet sprouted are considered dormant. In order for a seed to come out of dormancy to sprout or germinate, certain environmental factors must be in place: There must be the right combination of light (or darkness), oxygen (generated by rain water in the soil), and water. When in the right combination, these environmental factors cue the respiratory and metabolic functions within the seed that it is time to wake up the embryo to prepare it for growth. When the embryo inside a dormant seed “awakens” and resumes growing, we call the process “germination.” dkm 4/2/11 Page 3 Hinders to the viability of seeds In order to grow, the embryo within the seed must also be alive, but the viability of a seed can be hindered in several ways: The seed can be empty, without an embryo from which to grow; the embryo can be functionally incomplete; healthy seeds can become damaged or killed by predators and pathogens; fires and floods can destroy seeds; extreme temperatures can damage the embryonic plant; or a seed can simply die of “old age” before it has a chance to germinate and grow. Germination Germination is the sprouting or growing of a seed. In order to sprout, viable seeds of angiosperms and gymnosperms must be fertilized through the union of male and female sex cells. Once fertilized, various chemicals, hormones, and structures within the seed work together to grow the seed into a seedling. Visible seed coat of a carrot seed 390x [email protected] The seed coat or testa is the very outer membrane of the seed. The seed coat is usually hard so that it can protect the inside embryo. The protective nature of the seed coat is especially important during long periods of dormancy when the seed is at rest and in need of protection from the threat of cold, extreme weather conditions, or excessive moisture. dkm 4/2/11 Page 4 http://www.botanical-online.com/llavorangles.htm 1. radicle – emerges first and will develop into the main root of the plant 2. plumule – like an early leaf 3. hypocotlyl – space that will develop into a stem 4. cotyledon – food storage and/or achieves the function of primary leaves 5. seed coat (testa) – out layer for angiosperms; the seed coat for gymnosperms 6. micropyle – hole through which water enters When all of the environmental conditions are right and the seed is ready for germination, water will enter the seed through the micropyle, a small hole in the seed coat. As water enters through the micropyle, the metabolic pathways necessary for inner growth become activated. fennel seed 2820x [email protected] dkm 4/2/11 Page 5 Beneath the seed coat is the endosperm, the fleshy area of the seed that provides food for the embryo. Sometimes the endosperm is included within the cotyledon, the structure that will develop into the first leaves of the seedling. Seeds possessing only one cotyledon such as those found in grasses and palms, are called monocots; those with two cotyledons are called dicots. Broad-leaved plants and most fruit and nut species are dicots. www.biologie.uni-hamburg.de/b-online/ The epicotyl contains the initial shoots of the seedling. In addition to becoming the first leaves of the new seedling, the epicotyl also contains three embryonic leaves which help absorb nutrients inside the seed. The radicle is the main embryonic root which points towards the micropyle and absorbs water into the embryo. As the embryo grows, secondary roots will join themselves to the main root so that more water from the soil can be absorbed into the seed. The first stem tip of the embryo is called the plumule. As water fills the embryo, the embryo swells up until it eventually bursts out of its own coat. http://theseedsite.co.uk/seedparts.html dkm 4/2/11 Page 6 http://www.youtube.com/watch?v=d26AhcKeEbE&feature=related Dormancy Seeds germinate when they have the right amount of water, oxygen, and sunlight. But even when all environmental conditions are perfect for growth, some seeds will remain dormant for an extended period of time. This situation, known as “true dormancy”, is caused by special conditions within the seed which prolong germination in order to protect the species. For example, when a volcanic eruption destroys nearby wildlife – including newly-germinated seeds – new seedlings will take the place of those that were destroyed as soon as the environment becomes conducive for germination again. The original seedlings may have perished in the volcano, but the species will lives on by that process. Other forms of dormancy include “physiological dormancy,” caused by conditions within the embryo, and “physical dormancy,” caused by conditions outside the embryo such as when the shell of a seed is too thick for water to pass through. “Induced dormancy” occurs when the environmental conditions are not yet optimal for germination and the seed must wait to germinate. “Combinational dormancy” occurs when more than one of the above factors hinders germination. dkm 4/2/11 Page 7 dandelion seed 365x [email protected] dandelion seed 8800x [email protected] Seed dispersal Because plants do not physically move across the land as do animals, nature as provided them with other ways for getting their seeds to areas of land favorable for growth. Seed dispersal occurs in one of several ways: www.clipart.com Gravity: When fruit is ripe, it falls downward from the plant or tree. Examples include apples, coconuts, and passion fruit. dkm 4/2/11 Page 8 www.clipart.com Wind: Seeds can float or flutter in the wind. Feathery pappus attach to milkweed, poplar, and dandelion seeds to carry them long distances. Maple and pine seeds have wings that allow them to flutter gently to the ground. Tumbleweeds blow across the desert to disperse their seeds. Some seeds are so small that the wind simply carries them away like dust. Squirting cucumber www.wikepedia.com Self-dispersal (ballistic): The fruit tissue of some plants such as touch-me-nots or squirting cucumbers, will suddenly contract and explosively discharge their seeds. Water lily www.clipart.com Water: Water lilies are examples of plants that use hydrochory for seed dispersal. The flowers produce a fruit that floats and drops to the bottom of the pond where the seed takes root and grows into a new plant. Palm trees drop their seeds (coconuts!) into the ocean. The coconut will float on strong ocean currents until reaching dry land where it germinates and grows into a new tree. dkm 4/2/11 Page 9 www.clipart.com Dispersal by animals: Plant seeds can be dispersed by animals in a variety of ways. A very few are transported externally by animals when spines, barbs, or adhesive mucus on the seed attaches to fur and feathers. Animals might also ingest and digest seeds through a process called edozoochory. Many animals depend on plants to provide seeds as food, and many plants depend on animals for the dispersal of their seed. Some seeds have appendages called elaiosomes that ants like to eat. The ants will carry the seeds back to their nests, eat the nutritious elaiosomes, but leave behind the inedible parts of the seed. The uneaten part of the seed will eventually germinate and grow into a new plant. In this case the plant depended on the ant to disperse its seed, and the ant depended on the tree to provide to provide it with food, a symbiotic relationship called mutualism. Some animals hoard and hide seeds in hidden caches. Squirrels and blue jays are seed predators who hide precious seeds for later consumption. Seeds that are buried and forgotten will germinate and grow into new plants. Seed dispersal allows seeds to be dispersed far from the parent plant, ensuring the seed’s survival. There are a number of reasons why seeds dispersed far from the parent plant are more likely to survive: 1. Predators and pathogens tend to prey on seedlings concentrated tightly together; therefore, seeds dispersed away from the crowd are often spared. 2. Seedlings that sprout further away from adult plants have far less competition for sunlight and water. 3. Seeds that are dispersed far from the parent plant are also able to reach habitats more favorable for their survival, and 4. new geographic regions and habitats are colonized when seeds are dispersed far away. www.clipart.com dkm 4/2/11 Page 10 California poppy seed 3600x [email protected] A word about spores Is a spore a seed? Like a seed, a spore is a reproductive body capable of giving rise to a new adult organism. Unlike seeds, however, spores do not contain significant food storage, and must therefore rely totally on the environment for germination. Nonetheless, the terms spore and seed are often used interchangeably. thyme seed 420x [email protected] dkm 4/2/11 Page 11 popped corn 360x [email protected] coffee bean 360x [email protected] The edibility of seeds Many seeds are edible. In fact, the majority of humans’ caloric intake comes from seeds. Cooking oils, drinks, spices, and various food additives are just a few of the many edible products that come from seeds. But seeds also can be directly consumed in the form of cereals, beans, and nuts. grassy seed 264x [email protected] Cereals Botanically speaking, cereals (grains) are crops with a grass-like structure that are harvested for their dry fruit seed. People throughout the world consume half of their calories from cereal, the seeds of which are often ground into flour. True cereals are members of the Poaceae or Grass family, whereas pseudocereals are non-grasses that are used the same way as cereals. In their whole-grain form, cereals are rich in vitamins, minerals, carbohydrates, fats, oils and protein. dkm 4/2/11 Page 12 whole wheat flour 2360x [email protected] white bread flour 1980x [email protected] yellow grain of cornmeal 405x [email protected] white grain of cornmeal 480x [email protected] Some examples of cereals include barley, maize (corn), pearl millet, oats, rice, rye, sorghum, spelt, wheat, and wild rice. dkm 4/2/11 Page 13 flax 570x [email protected] Some examples of pseudocereals include buckwheat, cattail, chia, flax, grain amaranth, quinoa, and acacia seed. chestnuts www.wikepedia.org Nuts A nut is a hard-shelled seed, the fruit of certain plants. Although not all seeds are nuts, all nuts are seeds. The fruit of a true nut is usually a semi-hard kernel surrounded by an ovary wall that hardens as it matures. The seed of a nut is indehiscent, meaning the fruit does not open to release the seed. dkm 4/2/11 Page 14 hazelnut www.ohnuts.com Examples of botanical nuts include acorn, beechnut, chestnut, hazelnut, oak Some seeds that are not nuts botanically speaking, are still called nuts in the culinary sense. walnut www.wikipedia.org Examples of culinary (not botanical) nuts include cashews, macadamia, walnuts. cherry www.clipart.com Other seeds we refer to as nuts are actually drupes, stone fruits with a hard, inner layer containing the embryo (kernel) and two hard or fleshy outer layers. Examples of drupes include pistachio, almond, pecan, avocado, cherry, peach, coconut, mango and raspberry. dkm 4/2/11 Page 15 stone pine cone and nuts www.bing.com Examples of nut-like gymnosperms include the pine nut, juniper, cycad, and single-leaf Pinion. Some nuts are actually Legumes or beans, the category of seeds we look at below. endosperm of garden bean 2800x [email protected] Beans (Legumes) Beans (Legumes) are soft seeds rich in protein. Because they are high in the essential amino acid lycine but low in the essential amino acid methionine, legumes are best paired with complimentary grains. Common pairings include beans with corn tortillas, tofu with rice, and peanut butter on whole wheat bread. dkm 4/2/11 Page 16 peanut shell 1420x Kyle Erf, University of Arkansas Examples of beans (legumes) include chickpeas, fava, lentils, lupins, peanuts, peas and soybeans. peanut [email protected] seed www.saburchill.com So there, “in a nutshell,” is an introductory overview of the magnificent seed as seen through the Phenom scanning electron microscope. Much more is waiting to be discovered about seeds online, in books, outside, or under the microscope. All we need to do is look. dkm 4/2/11 Page 17 Help Resources for More Information General Information and/or Visuals http://theseedsite.co.uk/seedparts.html good image of test, coat, shoot, root http://www.ehow.com/about_5409451_three-main-parts-seed.html three main parts of the seed. (no visuals) http://www.botanical-online.com/llavorangles.htm diagram leaves room for labeling below or to the side. http://www.botanical-online.com/english/medicinalblueberry.htm medicinal properties of Blueberries. This is a good site beyond use with the module! http://wiki.answers.com/Q/What_are_the_parts_of_the_seed simple answers to questions http://www.saburchill.com/chapters/chap0047.html diagram related to germination. http://aggie-horticulture.tamu.edu/Wildseed/info/3.1.html overview of germination http://www.ehow.com/how-does_4644403_a-seed-germinate.html germination http://www.buzzle.com/articles/seed-germination-process.html germination http://gardening.wsu.edu/library/vege004/vege004.htm gardening information from western Washington. http://www.ag.ohio-state.edu/~seedbio/seed_id/apiaceae/anethum_graveolens.html images of all kinds of seeds http://plantphys.info/seedg/seed.html info on germination. Fact sheet http://jxb.oxfordjournals.org/cgi/content/full/53/370/947 scholarly article on cereal seed storage protein dkm 4/2/11 Page 18 Lesson Plans http://quorumsensing.ifas.ufl.edu/HCS200/Seed.html has simple lesson ideas related to seed vigor. http://www.units.muohio.edu/labs/Heckman_Inquiry_Lesson.pdf high school germination lesson plan. http://www.accessexcellence.org/AE/SH/NSTA_NOR/morris_seeds.php high school experiments with radish seeds http://mypages.iit.edu/~smile/bi9417.html lesson plans for seeds. http://www.lessonplansinc.com/science.php/biology/lessonplans/C123/ links to lesson plans for seeds http://kids.britannica.com/comptons/article-200875/flower explains fertilization http://www.biologie.uni-hamburg.de/b-online/ibc99/koning/seedgerm.html for high school or college: seed germination diagram. http://www.schools.utah.gov/curr/science/core/plans/int/seed.html seed germination lesson plan. http://www.woodrow.org/teachers/esi/1998/p/effects/seedgermination.htm lesson plan for grades 7 – 12 Videos and Animation http://www.youtube.com/watch?v=d26AhcKeEbE&feature=related YouTube of radish germination. 2 minutes. No words. http://www.youtube.com/watch?v=rDN0yAFcQok&NR=1 YouTube germination. Seed and root area only. 25 seconds http://www.youtube.com/watch?v=iFCdAgeMGOA&feature=related time lapse germination - roots and leaves 36 seconds. http://www.youtube.com/watch?v=eelwEB4Z1GA germination of seeds “planted” in paper. http://www.botanical-online.com/animation4.htm this one shows an animation of germination dkm 4/2/11 Page 19 http://www.youtube.com/watch?v=To2DlJwErao&feature=related germinating seeds in paper towels Books Back, C. & Watt, B. (1984). Bean and plant. Englewood Cliffs, NJ: Silver Burdett Press. Lyle, S. (2006). Fruits and nuts: A comprehensive guide to the cultivation, uses and health benefits of over 300 food-producing plants. Portland, OR: Timber Press Toogood, A. (2002). American Horticultural Society: Growing from seed. London: DK Publishing Biologie.uni.hamburg.de dkm 4/2/11 Page 20 dkm 4/2/11 Page 21