Seed Science - Lesson 3: Seed Formation And Development

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Seed Formation and Development

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Meristematic regions

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Part of the plant where cell division and elongation occur

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Reproductive Meristems

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Where floral organs originate and where seeds are produced

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External stimuli and having achieved enough vegetative growth

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Floral induction occurs as a result of _________

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Temperature, Day Length, nutrient status of plant

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Name 3 stimuli for floral induction

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Vernalization

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process: exposure to low temperatures for floral induction to occur

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thermoperiodism

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phenomenon:Period of low night temperatures coupled with high daytime temperatures; for floral induction to occur

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Dark Period

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Light or dark: length of this period that influences flowering

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Short-day, long-day, day neutral

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3 types categories of plants for the day length stimuli

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Inductive Photoperiod

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Obligate Plants

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Plants that will remain vegetative indefinitely without the inductive photoperiod: means by necessity

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Facultative Plants

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plants that will eventually flower without the inductive photoperiod, but can be induced to flower sooner; means having the capacity to live under more than one specific set of environmental conditions

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Auxin

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This compound, such as indoleacetic acid, will induce floral induction in plants

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Gibberellic

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Exposure to ___________ acid causes flowering to occur in long-day plants under short-day conditions

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carbon: nitrogen ratio

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The most influential nutrient factor in plants .

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carbohydrates

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Deficiencies in this nutrient can cause microspore degeneration and thus sterile pollen

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Megasporogenisis:

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The multistep development of the megaspore from the archesporial cell

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Steps of Megasporogenisis

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1) growth of the archesporial cell in the nucellus of the ovary; 2) the division of the archesporial cell to produce two cells, a mitotic division; 3) one of these cells is the parietal spore and eventually deteriorates; 4) the megaspore mother cell or megasporocyte undergoes two consecutive meiotic cell divisions to produce 4 megaspores, 3 of which will be non-functional and one will be functional

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megagametogenesis

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production of the female gametophyte or megagametophyte from the megaspore cell

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Steps in Megagametogenesis

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1) megaspore undergoes 3 free nuclear divisions;( the nucleus divides but the cell does not) to producce 8 haploid nucleui 2) 3 of the nuclei move to the end opposite the micropylar and for the antipodals with cell walls. 3) 2 nuclei move to the center of the cell and form the polar nuclei which later fuse to form the endosperm nuclei after fertilization; 4) the final 3 nuclei move to the micropylar end to form the egg apparatus ( one of these nuclei will be the egg itself with a cell wall, the other two nuclei form the synergids

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the integuments and funiculus

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the tissue surrounding the megagametophyte develops into:

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seed coat

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the integuments will become the

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attaches the ovary to the placenta

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the funiculus is the stalk that

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microsporogenesis

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the microspore mother cell from the anther undergoes this to produce microspores

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microsporogenesis process

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1) the microspore mother cell develops from certain special cells in the anther in specialized compartments called microsporangium 2) the microspore mother cells divide to produce 4 haploid microspores

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microgametogenesis

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the actual formation of the microgametophyte (pollen grain) from the microspores

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microgametogenesis process

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1) the microspore nucleus will divide to produce two nuclei with associated cells called pollen grain (each pollen grain is composed of a tube cell and a generative cell 2) the generative cell divides and produces two sperm nuclei which are the male gametes

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process of fertilization

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1) pollen lands on the surface of the stigma and germinates 2) the pollen tube grows through the style to the ovary and ovule and enters the embryo sac through the micropyle ( the direction of the development of the pollen tube is under te influence of the tube cell nucleus 3) once the tube has punctured through the uter walls of the ovule, the tube nucleus deteriorates 4) the sperm nuclui enter the embryo sac where one sperm unites with the egg to form the zygote (2n) and becomes the embryo 5) the other sperm nuclei unites with the two polar nuclei to form the endosperm nuclei (3n)

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nucellus; funiculus

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the embryo sac gets its nutrition from the ___________ via the _____________

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nutrient gradient

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in the embryo sac a _______ _______ develops in the seed from the chalazal end to the opposite micropyle creating a smaller size at the micropyle

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makes the ovule a very strong sink

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once fertilization occurs, a hormonal response occurs that

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embryogeny

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the study of embro development

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embryo development process

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1) begins: the zygote (gertilized egg) divides to form the pro-embryo with two parts. The first part are the suspensor cells, a chain of cells that push the embryo proper to the center of t he embro sac 2) the embryo proper develops into the embryo

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endosperm

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the _________ provides nutritive materials to the embryo during development and germination

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endosperm formation

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forms from the fusion of one sperm nuclei and 2 polar nuclei

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dicot endosperm

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this is going to be asorbed by developing cotyledons and is not highly developed

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monocot endosperm

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develops into a large component of the seed and is highly developed; the outer layer of the endosperm develops into the aleurone layer which contains specialized storage proteins and releases amylase to break down the endosperm

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fertilization

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development of the seed begins only after ___________

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water, nutrients and photosynthates

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immediately after fertilization cell division and elongation is supported by the rapid imporation of (3)

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seed coat to endosperm

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8 days after seed development begins in a monocot the weight shifts from the ____________ to the __________

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seed coat to the embryo

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8 days after seed development begins in a dicot the weight shifts from the ____________ to the __________

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its maximum dry weight and quality have been achieved

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the seed reaches physiological maturity once

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funiculus

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once the seed reaches physiological maturity the ________ degenerates and the seed is no longer being fed by the mother plant

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harvest maturity

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the final stage of seed development

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mechanical harvesting

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_________ _____________ is possible once further dessication of the seed ensues to 15-20%

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(nitrogen, phosphorus, potassium)

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in general plants that have the proper amount of the 3 major elements (N, P, K) will produce larger seeds

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nitrogen

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the most important element is adequate

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reduce seed size

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lack of adequate soil moisture will