The Seed- God’s wonder and tiny mystery

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

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 • 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 • 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. 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]

8. 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.

9. 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.

10. 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.

11. 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.

12. 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]

13. 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]

14. 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.

15. Dormancy (2) • Internally seeds can be dormant because of plant hormones such as absciscic 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]

16. 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]

17. 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.

18. 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.

19. Pollen germination • Another germination event during the life cycle of gymnosperms and flowering plants is the germination of a pollen grain after pollination. Like seeds, pollen grains are severely dehydrated before being released to facilitate their dispersal from one plant to another. They consist of a protective coat containing several cells (up to 8 in gymnosperms, 2-3 in flowering plants). One of these cells is a tube cell. Once the pollen grain lands on the stigma of a receptive flower (or a female cone in gymnosperms), it takes up water and germinates. Pollen germination is facilitated by hydration on the stigma, as well as the structure and physiology of the stigma and style.[1] Pollen can also be induced to germinate in vitro (in a petri dish or test tube).[3][4] • During germination, the tube cell elongates into a pollen tube. In the flower, the pollen tube then grows towards the ovule where it discharges the sperm produced in the pollen grain for fertilization. The germinated pollen grain with its two sperm cells is the mature male microgametophyte of these plants.[1

20. root • Root • From Wikipedia, the free encyclopedia •   (Redirected from Root (botany)) • Jump to: navigation, search • For other uses, see Root (disambiguation). • Primary and secondary roots in a cotton plant • In vascular plants, the root is the organ of a plant body that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial (that is, growing above the ground) or aerating (that is, growing up above the ground or especially above water). Furthermore, a stem normally occurring below ground is not exceptional either (see rhizome). So, it is better to define root as a part of a plant body that bears no leaves, and therefore also lacks nodes. There are also important internal structural differences between stems and roots. The two major functions of roots are 1.) absorption of water and inorganic nutrients and 2.) anchoring the plant body to the ground. Roots also function in cytokinin synthesis, which supplies some of the shoot's needs. They often function in storage of food. The roots of most vascular plant species enter into symbiosis with certain fungi to form mycorrhizas, and a large range of other organisms including bacteria also closely associate with roots.

21. Root growth • Root systems of prairie plants • Cross Section of a mango tree • Root system of a prairie grass • Early root growth is one of the functions of the apical meristem located near the tip of the root. The meristem cells more or less continuously divide, producing more meristem, root cap cells (these are sacrificed to protect the meristem), and undifferentiated root cells. The latter will become the primary tissues of the root, first undergoing elongation, a process that pushes the root tip forward in the growing medium. Gradually these cells differentiate and mature into specialized cells of the root tissues. • Roots will generally grow in any direction where the correct environment of air, mineral nutrients and water exists to meet the plant's needs. Roots will not grow in dry soil. Over time, given the right conditions, roots can crack foundations, snap water lines, and lift sidewalks. At germination, roots grow downward due to gravitropism, the growth mechanism of plants that also causes the shoot to grow upward. In some plants (such as ivy), the "root" actually clings to walls and structures. • Growth from apical meristems is known as primary growth, which encompasses all elongation. Secondary growth encompasses all growth in diameter, a major component of woody plant tissues and many nonwoody plants. For example, storage roots of sweet potato have secondary growth but are not woody. Secondary growth occurs at the lateral meristems, namely the vascular cambium and cork cambium. The former forms secondary xylem and secondary phloem, while the latter forms the periderm. • In plants with secondary growth, the vascular cambium, originating between the xylem and the phloem, forms a cylinder of tissue along the stem and root. The cambium layer forms new cells on both the inside and outside of the cambium cylinder, with those on the inside forming secondary xylem cells, and those on the outside forming secondary phloem cells. As secondary xylem accumulates, the "girth" (lateral dimensions) of the stem and root increases. As a result, tissues beyond the secondary phloem (including the epidermis and cortex, in many cases) tend to be pushed outward and are eventually "sloughed off" (shed). • At this point, the cork cambium begins to form the periderm, consisting of protective cork cells containing suberin. In roots, the cork cambium originates in the pericycle, a component of the vascular cylinder. • Stilt roots in the Amazon Rainforest support a tree in very soft, wet soil conditions • The vascular cambium produces new layers of secondary xylem annually. The xylem vessels are dead at maturity but are responsible for most water transport through the vascular tissue in stems and roots.

22. Types of roots • A true root system consists of a primary root and secondary roots (or lateral roots). • The primary root originates in the radicle of the seedling. It is the first part of the root to be originated. During its growth it rebranches to form the lateral roots. It usually grows downwards. Generally, two categories are recognized: • the taproot system: the primary root is prominent and has a single, dominant axis; there are fibrous secondary roots running outward. Usually allows for deeper roots capable of reaching low water tables. Most common in dicots. The main function of the taproot is to store food. • the diffuse root system: the primary root is not dominant; the whole root system is fibrous and branches in all directions. Most common in monocots. The main function of the fibrous root is to anchor the plant.

23. Specialized roots • Aerating roots of a mangrove • Buttress roots of Ceibapentandra • The roots, or parts of roots, of many plant species have become specialized to serve adaptive purposes besides the two primary functions described in the introduction. • Adventitious roots arise out-of-sequence from the more usual root formation of branches of a primary root, and instead originate from the stem, branches, leaves, or old woody roots. They commonly occur in monocots and pteridophytes, but also in many dicots, such as clover (Trifolium), ivy (Hedera), strawberry (Fragaria) and willow (Salix). Most aerial roots and stilt roots are adventitious. In some conifers adventitious roots can form the largest part of the root system. • Aerating roots (or pneumatophores): roots rising above the ground, especially above water such as in some mangrove genera (Avicennia, Sonneratia). In some plants like Avicennia the erect roots have a large number of breathing pores for exchange of gases. • Aerial roots: roots entirely above the ground, such as in ivy (Hedera) or in epiphyticorchids. They function as prop roots, as in maize or anchor roots or as the trunk in strangler fig. • Contractile roots: they pull bulbs or corms of monocots, such as hyacinth and lily, and some taproots, such as dandelion, deeper in the soil through expanding radially and contracting longitudinally. They have a wrinkled surface. • Coarse roots: Roots that have undergone secondary thickening and have a woody structure. These roots have some ability to absorb water and nutrients, but their main function is transport and to provide a structure to connect the smaller diameter, fine roots to the rest of the plant. • Fine roots: Primary roots usually <2 mm diameter that have the function of water and nutrient uptake. They are often heavily branched and support mycorrhizas. These roots may be short lived, but are replaced by the plant in an ongoing process of root 'turnover'. • Haustorial roots: roots of parasitic plants that can absorb water and nutrients from another plant, such as in mistletoe (Viscum album) and dodder. • Propagative roots: roots that form adventitious buds that develop into aboveground shoots, termed suckers, which form new plants, as in Canada thistle, cherry and many others. • Proteoid roots or cluster roots: dense clusters of rootlets of limited growth that develop under low phosphate or low iron conditions in Proteaceae and some plants from the following families Betulaceae, Casuarinaceae, Eleagnaceae, Moraceae, Fabaceae and Myricaceae. • Stilt roots: these are adventitious support roots, common among mangroves. They grow down from lateral branches, branching in the soil. • Storage roots: these roots are modified for storage of food or water, such as carrots and beets. They include some taproots and tuberous roots. • Structural roots: large roots that have undergone considerable secondary thickening and provide mechanical support to woody plants and trees. • Surface roots: These proliferate close below the soil surface, exploiting water and easily available nutrients. Where conditions are close to optimum in the surface layers of soil, the growth of surface roots is encouraged and they commonly become the dominant roots. • Tuberous roots: A portion of a root swells for food or water storage, e.g. sweet potato. A type of storage root distinct from taproot.

24. [edit] Rooting depths • The distribution of vascular plant roots within soil depends on plant form, the spatial and temporal availability of water and nutrients, and the physical properties of the soil. The deepest roots are generally found in deserts and temperate coniferous forests; the shallowest in tundra, boreal forest and temperate grasslands. The deepest observed living root, at least 60 m below the ground surface, was observed during the excavation of an open-pit mine in Arizona, USA. Some roots can grow as deep as the tree is high. The majority of roots on most plants are however found relatively close to the surface where nutrient availability and aeration are more favourable for growth. Rooting depth may be physically restricted by rock or compacted soil close below the surface, or by anaerobic soil conditions.

25. Root architecture • The pattern of development of a root system is termed 'root architecture', and is important in providing a plant with a secure supply of nutrients and water as well as anchorage and support. The architecture of a root system can be considered in a similar way to above-ground architecture of a plant - i.e. in terms of the size, branching and distribution of the component parts. In roots, the architecture of fine roots and coarse roots can both be described by variation in topology and distribution of biomass within and between roots. Having a balanced architecture allows fine roots to exploit soil efficiently around a plant, but the 'plastic' nature of root growth allows the plant to then concentrate its resources where nutrients and water are more easily available. A balanced coarse root architecture, with roots distributed relatively evenly around the stem base, is necessary to provide support to larger plants and trees.

26. Economic importance • Roots can also protect the environment by holding the soil to prevent soil erosion • Tree roots at Cliffs of the Neuse State Park, NC • The term root crops refers to any edible underground plant structure, but many root crops are actually stems, such as potato tubers. Edible roots include cassava, sweet potato, beet, carrot, rutabaga, turnip, parsnip, radish, yam and horseradish. Spices obtained from roots include sassafras, angelica, sarsaparilla and licorice. • Sugar beet is an important source of sugar. Yam roots are a source of estrogen compounds used in birth control pills. The fish poison and insecticide rotenone is obtained from roots of Lonchocarpus spp. Important medicines from roots are ginseng, aconite, ipecac, gentian and reserpine. Several legumes that have nitrogen-fixing root nodules are used as green manure crops, which provide nitrogen fertilizer for other crops when plowed under. Specialized bald cypress roots, termed knees, are sold as souvenirs, lamp bases and carved into folk art. Native Americans used the flexible roots of white spruce for basketry. • Tree roots can heave and destroy concrete sidewalks and crush or clog buried pipes. The aerial roots of strangler fig have damaged ancient Mayantemples in Central America and the temple of Angkor Wat in Cambodia. • Vegetative propagation of plants via cuttings depends on adventitious root formation. Hundreds of millions of plants are propagated via cuttings annually including chrysanthemum, poinsettia, carnation, ornamental shrubs and many houseplants. • Roots can also protect the environment by holding the soil to prevent soil erosion.

40. Root water uptake is an important process of water circle and a component of water balance in the field, and it should be understood better and effectively. A quantitative means of describing root water uptake should be established for efficient water use

41. The objectives of this research are to develop a two-dimensional (2D) model of root water uptake for single apple trees and to validate the model with sap flow and soil water content measurements in an orchard.

42. Tube-time domain reflectometry (TDR) was used to measure soil volumetric water content, and sap flow sensors based on heat-pulse technology were used to monitor locally the rates of sap flow in the trunk of the apple tree. Also leaf area index (LAI) was measured using the Hemiview system, root density distribution was determined and soil hydraulic characteristics parameters were fitted from measurements. A 2D model of root water uptake was established, which includes root density distribution function, potential transpiration and soil water stress-modified factor.

43. The measured data were compared against the outputs of transpiration rate and soil water contents from the numerical simulation of the soil water dynamics that uses Richards' equation for 2D water flow and the established root uptake model. The results showed an excellent agreement between the measured data and the simulated outputs, which indicate that the developed root water uptake model is effective and feasible. Agricultural water management   ISSN 0378-3774   CODEN AWMADF  Source / Source • 2006, vol. 83, no1-2, pp. 119-129 [11 page(s) (article)] (29 ref.)

44. A cell wall is a tough, flexible and sometimes fairly rigid layer surrounding a cell, located external to the cell membrane, which provides the cell with structural support, protection, and acts as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing over-expansion when water enters the cell. They are found in plants, bacteria, fungi, algae, and some archaea. Animals and protozoa do not have cell walls.

45. The materials in a cell wall vary between species, and in plants and fungi also differ between cell types and developmental stages. In plants, the strongest component of the complex cell wall is a carbohydrate, the glucosepolymer called cellulose. In bacteria, peptidoglycan forms the cell wall. Archaean cell walls have various compositions, and may be formed of glycoproteinS-layers, pseudopeptidoglycan, or polysaccharides. Fungi possess cell walls of the glucosamine polymer chitin, and algae typically possess walls constructed of glycoproteins and polysaccharides. However the diatoms have a cell wall composed of silicic acid. Often, other accessory molecules are found anchored to the cell wall.

47. Rigidity • The rigidity of cell walls is often over-estimated. In most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength. The apparent rigidity of primary plant tissues is a function of hydraulic turgor pressure of the cells and not due to rigid cell walls. This flexibility is seen when plants wilt, so that the stems and leaves begin to droop, or in seaweeds that bend in water currents. The rigidity of healthy plants results from a combination of the wall construction and turgor pressure

48. As John Howland states it: • “ Think of the cell wall as a wicker basket in which a balloon has been inflated so that it exerts pressure from the inside. Such a basket is very rigid and resistant to mechanical damage. Thus does the prokaryote cell (and eukaryotic cell that possesses a cell wall) gain strength from a flexible plasma membrane pressing against a rigid cell wall.[1]

49. The rigidity of the cell wall thus results in part from inflation of the cell contained. This inflation is a result of the passive uptake of water. • In plants, a secondary cell wall is a thicker additional layer of cellulose which increases wall rigidity. Additional layers may be formed containing lignin in xylem cell walls, or containing suberin in cork cell walls. These compounds are rigid and waterproof, making the secondary wall stiff. Both wood and bark cells of trees have secondary walls. Other parts of plants such as the leaf stalk may acquire similar reinforcement to resist the strain of physical forces.

50. Certain single-cell protists and algae also produce a rigid wall. Diatoms build a frustule from silica extracted from the surrounding water; radiolarians also produce a test from minerals. Many green algae, such as the Dasycladales encase their cells in a secreted skeleton of calcium carbonate. In each case, the wall is rigid and essentially inorganic.