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Plant Embryo Development Establishes a Basic Body Plan.

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Presentation on theme: "Plant Embryo Development Establishes a Basic Body Plan."— Presentation transcript:

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2 Plant Embryo Development Establishes a Basic Body Plan

3  In plants, 3D shape and form arise by regulating the amount and pattern of cell division  As plant development proceeds, cells with multiple potentials are mainly restricted to meristem regions  Meristem – tissue in all plants consisting of undifferentiated cells  Many meristems have been established by the time embryogenesis ends and the seed becomes dormant  Apical meristems establish the root shoot axis  3 basic tissue systems are established: dermal, ground, and vascular  While the embryo is developing, a food supply that will support the embryo during germination is established, and ovule tissue differentiates to form a hard, protective covering around the embryo  Seed enters dormant phase, signaling the end of embryogenesis

4  The 1 st division of the zygote in a flowering plant generates cells with 2 different fates:  Daughter cell is small with dense cytoplasm and becomes an embryo  Daughter cell is larger, forms elongated structure called a suspensor – links the embryo to the nutrient tissue of the seed

5  Investigating mechanisms for establishing asymmetry in plant embryo development is difficult. One approach has been to use fucus as a model system  Genetic approaches make it possible to explore asymmetric development in angiosperms and to study mutants

6  3 tissues differentiate while the plant embryo is still in the globular stage (b)   Dermal tissue  Produces cells that protect the plant from desiccation  Formed from photoderm  Ground tissue  Function in food and water storage  Formed from a ground meristem  Vascular tissue  Responsible for water and nutrient transport  Formed from procambium

7  Root-shoot axis is established during the globular stage  Both the shoot and the root meristems are apical meristems but their formation is controlled independently

8  Globular stage gives rise to a heart-shaped embryo with 2 bulges – dicots and monocots  These bulges are cotyledons  Produced by embryonic cells  Process is called morphogenesis  The position of the cell plate determines the direction of division  Microtubules guide cellulose deposition as the cell wall forms around the outside of a new cell  Determines the cell’s final shape

9  Throughout embryogenesis, starch, lipids, and proteins are produced  The sporophyte transfers nutrient via the suspensor in angiosperms  Seeds have stored nutrients to aid in germination until the growing sporophyte can photosynthesize

10 The seed protects the dormant embryo form water loss

11  Development of the embryo is stopped soon after the meristems and cotyledons differentiate  The integuments (outer cell layers of the ovule) develop into a seed coat which ecloses the seed with its dormant embryo and stored food

12  Seeds are important adaptively in 4 ways:  Seeds maintain dormancy under unfavorable conditions and postpone development until better conditions arise  Seeds afford maximum protection to the young plant at its most vulnerable stage of development  Seeds contain stored food that permits a young plant to develop before photosynthetic activity begins  Seeds are adapted for dispersal, facilitating the migration of plant genotypes into new habitats

13 Fruit formation enhances the dispersal of seeds

14  Fruits that contain seeds are defined as mature ovaries  Fruits form in many ways and exhibit a wide array of adaptations for dispersal  3 layers of ovary wall can have distinct fates, which account for the diversity of fruit types  Fruits contain 3 genotypes in one package

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16  Fruits exhibit a wide array of specialized dispersal methods  Fruits with fleshy coverings normally are dispersed by birds or other vertebrates  Fruits with hooked spines are often disseminated by mammals  Other fruits such as maples have wings that aid in their distribution by the wind  Coconuts and other beach plants are regularly spread throughout a region either by water or African swallow

17 Germination initiates post-seed development

18  Germination – the emergence of the radicle (first root) through the seed coat  The sporophyte pushes through the seed coat, root grows down, shoot grows up  The shoot becomes photosynthetic and the postembryonic phase of growth and development begins  Germination begins when a seed absorbs water and its metabolism resumes  Many seeds will not germinate unless they have been stratified – held for periods of time at low temperatures  Germination can occur over a wide temperature range (5 to 30 degrees celcius)  In some species, a significant fraction of a season’s seeds remain dormant

19  Germination requires the utilization of metabolic reserves stored in the starch grains of amyloplasts (colorless plastids that store starch) and protein bodies  Fats and oils produce glycerol and fatty acids which yield energy through cellular respiration  Embryo produces gibberellic acid, a hormone, that signals the outer later of the endosperm called the aleurone to produce amylase  Enzyme breaks down the endospermic starch into sugars  Abscisic acid, another hormone, can inhibit starch breakdown  Emergence of the embryonic root and shoot from the seed during germination varies widely  In most plants, the root emerges before the shoot appears and anchors the young seedling in the soil

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