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The Seed- God’s wonder and tiny mystery

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The Seed- God’s wonder and tiny mystery

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  1. The Seed- God’s wonder and tiny mystery YOSHINOBU NAMIHIRA MD ,FACG 3000 HALLS FERRY ROAD VICKSBURG , MS 39180 PH 601-638-9800,FAX 601-638-9808 E MAIL: NAMIHIRA @VICKSBURG.COM

  2. Genesis1:3-4, 1:29 • “Let there belight and there was light. • And God saw the light, and it was good; • And God divided the light from the darkness (genesis 1:1-3-4) • God said ,”See I have given you every herb that yields seedwhich is on the face of all the the earth and every tree whose fruit yields seed;to you it shall be for food • (Gen 1:29)

  3. Germination is the process whereby growth emerges from a period of dormancy. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However, the growth of a sporeling from a spore, for example the growth of hyphae from fungal spores, is also germination. In a more general sense, germination can imply anything expanding into greater being from a small existence or germ.

  4. Seed germination • Seed germination • Brassicacampestris germinating seeds • A germinated seedling (Eranthishyemalis) emerges from the ground • Germination is the growth of an embryonic plant contained within a seed, it results in the formation of the seedling. The seed of a higher plant is a small package produced in a fruit or cone after the union of male and female sex cells. Most seeds go through a period of quiescences where there is no active growth, during this time the seed can be safely transported to a new location and/or survive adverse climate conditions until it is favorable for growth. The seed contains an embryo and in most plants stored food reserves wrapped in a seed coat. Under favorable conditions, the seed begins to germinate, and the embryonic tissues resume growth, developing towards a seedling

  5. Requirements for seed germination • Requirements for seed germination • The germination of seeds is dependent on both internal and external conditions. The most important external factors include: temperature, water, oxygen and sometimes light or darkness.[1] Often different varieties of seeds require distinctive variables for successful germination; some seeds germinate while the soil is cold, while most germinate while the soil is warm. This depends on the individual seed variety and is closely linked to the ecological conditions of the plants' natural habitat.

  6. Water (1) • Water - is required for germination. Mature seeds are often extremely dry and need to take in significant amounts of water, relative to the seeds dry weight, before cellular metabolism and growth can resume. Most seeds respond best when there is enough water to moisten the seeds but not soak them.The uptake of water by seeds is called imbibition which leads to the swelling and the breaking of the seed coat.

  7. imbibition • The uptake of water by seeds is called imbibition which leads to the swelling and the breaking of the seed coat

  8. definition • Imbibition ( imbibe) • Absorption of fluid by colloid ( gel)

  9. imbibe • Imbibe (v.)= • Drink • Down • Swallow • Take in • absorb

  10. Water (2) • When seeds are formed, most plants store food, such as starch, proteins, or oils, to provide nourishment to the growing embryo inside the seed. When the seed imbibes water, hydrolytic enzymes are activated that break down these stored food resources in to metabolically useful chemicals, allowing the cells of the embryo to divide and grow, so the seedling can emerge from the seed.[1]

  11. Water (3) • Once the seedling starts growing and the food reserves are exhausted, it requires a continuous supply of water, nutrients and light for photosynthesis, which now provides the energy needed for continued growth.

  12. Water ,hydrolytic enzymes • Water • Imbibition • Hydrolytic enzymes { inactive – active form} • Stored foods into chemicals • Seed embryo • Divide and grow • Seedling • Emerge from seed shell • Photosynthesis for additional nutients

  13. oxygen • Oxygen - is required by the germinating seed for metabolism:[2] If the soil is waterlogged or the seed is buried within the soil, it might be cut off from the necessary oxygen it needs. Oxygen is used in aerobic respiration, the main source of the seedling's energy until it has leaves, which can photosynthesize its energy requirements.[1] Some seeds have impermeable seed coats that prevent oxygen from entering the seeds, causing seed dormancy. Impermeable seed coats to oxygen or water, are types of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange or water uptake between the seed and its environment.

  14. Temperature (1) • Temperature - affects cellular metabolic and growth rates. Different seeds germinate over a wide range of temperatures, with many preferring temperatures slightly higher than room-temperature while others germinate just above freezing and others responding to alternation in temperature between warm to cool. Often, seeds have a set of temperature ranges where they will germinate and will not do so above or below this range. In addition, some seeds may require exposure to cold temperature (vernalization) to break dormancy before they can germinate.

  15. Temperature (2) • As long as the seed is in its dormant state, it will not germinate even if conditions are favorable. Seeds that are dependent on temperature to end dormancy, have a type of physiological dormancy. For example, seeds requiring the cold of winter are inhibited from germinating until they experience cooler temperatures. For most seeds that require cold for germination 4C is cool enough to end dormancy, but some groups especially with in the family Ranunculaceae and others, need less than -5C. Some seeds will only germinate when temperatures reach hundreds of degrees, as during a forest fire. Without fire, they are unable to crack their seed coats, this is a type of physical dormancy.

  16. Light or darkness (1) • Light or darkness - can be a type of environmental trigger for germination in seeds and is a type of physiological dormancy. Most seeds are not affected by light or darkness, but many seeds, including species found in forest settings will not germinate until an opening in the canopy allows them to receive sufficient light for the growing seedling.[1]

  17. Light or darkness (2) • Stratification mimics natural processes that weaken the seed coat before germination. In nature, some seeds require particular conditions to germinate, such as the heat of a fire (e.g., many Australian native plants), or soaking in a body of water for a long period of time. Others have to be passed through an animal's digestive tract to weaken the seed coat and enable germination.[1]

  18. Dormancy (1) • Dormancy • Many live seeds have dormancy, meaning they will not germinate even if they have water and it is warm enough for the seedling to grow. Dormancy factors include conditions affecting many different parts of the seed, from the embryo to the seed coat. Dormancy is broken or ended by a number of different conditions and cues both internal and external to the seed. Environmental factors like light, temperature, fire, ingestion by animals and others are conditions that can end seed dormancy.

  19. Dormancy (2) • Internally seeds can be dormant because of plant hormones such asabsciscic acid, which affects seed dormancy and prevents germination, while the production and application of the hormone gibberellin can break dormancy and induces seed germination. This effect is used in brewing where barley is treated with gibberellin to ensure uniform seed germination to produce barley malt.[1]

  20. Seed germination inhibitor = absciscic acid • Seed germination inhibitor = absciscic acid • Dormancy = absciscic acid present • Breaking dormancy = beginning germination process= Gibberellic acid (GA3)

  21. Establishment (1) • Seedling establishment • In some definitions, the appearance of the radicle marks the end of germination and the beginning of "establishment", a period that ends when the seedling has exhausted the food reserves stored in the seed. Germination and establishment as an independent organism are critical phases in the life of a plant when they are the most vulnerable to injury, disease, and water stress.[1]

  22. Establishment (2) • The germination index can be used as an indicator of phytotoxicity in soils. The mortality between dispersal of seeds and completion of establishment can be so high, that many species survive only by producing huge numbers of seeds.

  23. Germination rate • In agriculture and gardening, germination rate is the number of seeds of a particular plantspecies, variety or particular seedlot that are likely to germinate. This is usually expressed as a percentage, e.g. an 85% germination rate indicates that about 85 out of 100 seeds will probably germinate under proper conditions. Germination rate is useful in calculating seed requirements for a given area or desired number of plants.

  24. Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with peaks for violet-blue and red light. In red algae, the action spectrum overlaps with the absorption spectrum of phycobilins for blue-green light, which allows these algae to grow in deeper waters that filter out the longer wavelengths used by green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms.

  25. Seed germination (1) • Seed Germination • A seed certainly looks dead. It does not seem to move, to grow, nor do anything. In fact, even with biochemical tests for the metabolic processes we associate with life (respiration, etc.) the rate of these processes is so slow that it would be difficult to determine whether there really was anything alive in a seed.

  26. Seed germination (2) • Indeed if a seed is not allowed to germinate (sprout) within some certain length of time, the embryo inside will die. Each species of seed has a certain length of viability. Some maple species have seeds that need to sprout within two weeks of being dispersed, or they die. Some seeds of Lotus plants are known to be up to 2000 years old and still can be germinated.

  27. Seed, dormancy, germination • Seeds Lacking True Dormancy • Common vegetable garden seeds generally lack any kind of dormancy. The seeds are ready to sprout. All they need is some moisture to get their biochemistry activated, and temperature warm enough to allow the chemistry of life to proceed. Seeds taken from the wild, however, are frequently endowed with deeper forms of dormancy.

  28. Assuming the seed is still viable, the embryo inside the seed coat needs something to get its metabolism activated to start the embryo growing. The process of getting a seed to germinate can be simple or complicated, and this our present subject.

  29. Thick seed coat • Thick Seed Coat • Many kinds of seeds have very thick seed coats. These obviously keep water out of the seed, so the embryo cannot get the water needed to activate its metabolism and start growing. The lotus seeds are an example of this. An outstanding example from the northern temperate zone is the Kentucky coffee tree (Gymnocladusdioica). The seed coat is perhaps two millimeters thick! You can throw them as hard as you can against a concrete sidewalk and they just bounce! How could such a seed actually sprout?

  30. The Kentucky coffee tree holds its seed pods in the the top of the tree all winter. The inside of the pod is fleshy (lots of water). The pods are very dark in color. If you put the fickle winter and sunshine and darkness into this picture, I think you can come up with the answer. Here is a hint: you might want to recall what happens if you fill the ice cube trays in your freezer too full with water, or you might recall what happens to a container filled with soda that is then frozen.

  31. scarification • Other species might use some pounding along a river or drop seeds into seacoast surf to abrade the thick seed coat. Some of the sea beans do this. Other seeds might need an vertebrate or other animal to attack the seed coat (but give up trying to eat the seed) and thereby weaken the coat. The process of nicking the thick seed coat to initiate germination is called scarification.

  32. Definition, scarify • Scarify = • Make scratch on the skin • Loosen soil • Scratch seeds: to break the outer cover of hard seeds to aid germination Encarta dictionary , English

  33. A final, and very common, example of a way to scarify a seed coat is observed in strawberry and raspberry. The thick seed coat is designed to be swallowed by the frugivore. The animal digests the fruit pulp, but the seed coat passes through the digestive system still protecting the viable embryo inside, but weakened enough to allow sprouting! The seed is deposited with a little organic fertilizer in the environment and can now sprout!

  34. Thin seed coat (1) • Thin Seed Coat • A thin seed coat is so thin that it is no barrier to water. Some other kind of dormancy mechanism is needed. Knowing that light can penetrate thin layers of plant tissue (leaves for example) should give you the idea that light might be a signal. That plants can absorb light and respond biochemically is a fact you know from your study of photosynthesis. All we need is a pigment molecule that can absorb light and cause a change in the behavior of the embryo.

  35. Thin seed coat (2) • The pigment is phytochrome. Like chlorophyll, it is made of a chromophore with tetrapyrole structure and is associated with proteins. This pigment is different from chlorophyll, however, in one critical way. It exists in two inter-convertible form

  36. Phytochrome ,Pfr(660nm) • One form of phytochrome, named Pfr, is the form of the phytochome found in plant cells that are exposed to red (660 nm) or common white light. This form of phytochrome is biologically very active and plays a role in all systems when a plant needs to know if the lights are "on" or "off." In lettuce (Lactuca sativa) seeds, Pfr causes the seeds to begin to germinate as we will soon see. Thus lettuce seeds germinate only when placed in white or red light. Buried in deep soil, they will not germinate. Given that lettuce has a small seed, I think you can figure out why evolution arrived at this solution.

  37. Phytochrome, Pr(730nm) • The other form of phytochrome, named Pr, is formed when phytochrome is exposed to far-red (730 nm) light. This form is biologically inactive or inhibits responses. Thus if lettuce seeds are placed in far-red light they do not germinate. • Large seeds have lots of storage material. If their seed coat is very thin, their evolution may have arrived at a completely different response. Think about pea seeds. They are large and have very thin seed coats. How would they respond to light?

  38. Insufficient development • Insufficient Development • If a seed's embryo is not completely developed, some additional maturation may be needed before the seed can sprout. This happens in seeds with little-to-no storage material invested in the seed. Examples include orchid seeds. They are the size of dust and have almost nothing but a very immature embryo on-board. Such a seed needs an association with fungi in the soil or other environments to feed the developing embryo until the embryo is mature enough to actually penetrate the seed coat. These seeds are also likely to have a very brief viability. The fungal association must be established rapidly or the embryo dies.

  39. inhibitors • Inhibitors Present • Many plant species invest chemicals in the developing seeds, and these chemicals inhibit the development of the embryos. They keep the embryos dormant. Obviously the seed must have some way to eliminate these chemicals before they can sprout.

  40. Inhibitor ,Abscisic acid • Abscisic Acid • Many temperate zone species that use inhibitors use abscisic acid. This chemical induces dormancy in the embryo. The chemical is produced in abundance in the late summer and early fall. The seeds in the fruits become dormant so, even if they are dispersed in autumn, they cannot sprout. During the winter enzymes in the seeds degrade the abscisic acid. By spring the abscisic acid is gone and the seed can sprout.

  41. Inhibitor , spring connection Inhibitor, abscisic acid level in the seed is low enough to begin germination in spring Time.

  42. Stratification, vernalization, greenhouse • We can collect seeds of these species and get them to sprout early. The seeds are put in moist soil and refrigerated for about four weeks (a process often called stratification). This is sufficient time to degrade the abscisic acid. Then the planted seeds are placed in a warm greenhouse. The seeds assume winter is over, spring has come, and they begin to sprout. This process is called vernalization. If you think of "vernal" as meaning "spring" then you understand how we got this name!

  43. Inhibitor , Phenolic compounds • Phenolic Compounds • Plants that live in deserts have a different problem. There is no cold, moist, winter to allow vernalization of abscisic acid. These plants instead use more potent toxins, phenolic compounds, to keep their seeds dormant until the proper season for germination.Phenolic compounds are freely water-soluble, the plant is living in a desert. Deserts typically have very long dry seasons and a short wet season accompanied by flash floods and so on. How do you think the phenolic compounds are lost? How would the mechanism ensure that seeds do not sprout in the dry season, but only after the seed could be sure it is in the wet season? The word leaching might give you a hint?

  44. This is a diagram of the seed of barley (Hordeumjubatum) • As any "typical" seed it has three fundamental parts: • a seed coat • a storage area (in this case the endosperm) and • a dormant embryo • The seed coat is really a fruit coat. In all grains, the seed coat (former ovule integument) is fused to the ovary wall (the true fruit wall). So in fact, the grain is technically a fruit (caryopsis) even though we often call it a seed. Barley is used primarily in beer making. Brewers use barley as a source of sugar to make the alcohol for beer. Brewers knew that sprouting the barley seeds improves the sugar yields tremendously, but they wanted even more sugar yield. The brewers came to plant physiologists to find out if anything could be done. • Study of the seed showed that the seed/fruit coat is water-resistant and thereby reduces the rate of water uptake by the seed, and water uptake is essential for seed germination and the improved sugar yields.