Seeds and Seed Germination

Seeds and Seed GerminationSeeds and Seed GerminationSeedsObjectives of today’s lecture:• Learn about the structure and composition of seeds• Learn how seeds are used in horticulture• Learn what happens during germination of seeds and the factors that influence thisprocessSeeds• Seeds are normally the product of sexual reproductionSeeds• Some seeds are produced without pollination, called ______________. Examples includemany citrus crops, mango, Kentucky bluegrass• The plants produced from apomictic seed are genetically identical to the maternal plant -______________Seeds are for propagation• The biological function of seeds is for ______________ of the species• This is also one of the major functions of seeds in horticultural practice• What else are seeds used for?Seeds are the major source of food for the worldTop US seed Crops (2001)• Corn- 9.51 billion bushelsfile:///D|/meetings/ashs07/intro%20to%20hort/Orvis_05%20lect%2014%20notes.htm (1 of 8)6/2/2008 2:37:46 PM

Seeds and Seed Germination• Sorghum (for grain) – 515 million bushels• Rice – 213 million hundred weight• Soybeans- 2.89 billion bushels• Wheat 1.4 billion bushels• Oilseed- 80 million tonsSeeds are alive!• To function in propagation, seeds must be ______________• Seeds ______________ (slowly)• consume O 2 , produce CO 2 and H 2 O• Seeds have a ______________ lifespan• They cannot be stored indefinitelySeeds are alive!• Seeds of many tropical plants remain viable for only a short time, a few______________• Tropical plants grow in environments that do not have a winter season through which seedsmust survive before the spring growing season. There is a cost in dormancy.• Other seeds remain viable for a very long time, in some cases more than 100______________• Common feature of many weeds• Seed storage experiment at Michigan StateGeneral features of seedsfile:///D|/meetings/ashs07/intro%20to%20hort/Orvis_05%20lect%2014%20notes.htm (2 of 8)6/2/2008 2:37:46 PM

Seeds and Seed GerminationA number of structural features are common to almost all seeds• ______________ ______________• Root and shoot, in a miniature form• ______________ _____________• Allow seedling to grow before it is capable of performing photosynthesis• _______________ _____________• Provides protection from the environmentMonocots and Dicots• Flowering plants (angiosperms) are divided into 2 groups based on seed structure• Dicotyledonous plants with ______________ seed leaves• Monocotyledonous plants with ______________ seed leafMonocots and Dicots• In addition to differences in seed morphology, there are a number of other commondifferences between monocots and dicotsA typical seed of a dicotyledon• Embryonic axis (plant in miniature)• ______________ - first true leaves• ______________/______________- embryonic stem (H/E)• ______________ - embryonic rootA typical seed of a dicotyledon• Cotyledons (seed leaves for ______________ of ______________ reserves)• Proteinsfile:///D|/meetings/ashs07/intro%20to%20hort/Orvis_05%20lect%2014%20notes.htm (3 of 8)6/2/2008 2:37:46 PM

Seeds and Seed Germination• Starches, carbohydrates• Lipids, oilsA typical seed of a dicotyledonExterior structure• ______________ for protection• ______________• where seed was attached to mother plant, “botanical belly button”• ______________• where tube that carried pollen to the egg was attachedA typical seed of a monocotyledonEmbryonic axis• ______________ - first true leaves• ______________ - embryonic rootColeoptile• _______________ _____________over plumuleA typical seed of a monocotyledonScutellum• ____________________________ from endosperm to seedlingColeoptile and scutellum are equivalent to cotyledons in a dicotA typical seed of a monocotyledonEndospermfile:///D|/meetings/ashs07/intro%20to%20hort/Orvis_05%20lect%2014%20notes.htm (4 of 8)6/2/2008 2:37:46 PM

Seeds and Seed Germination• ______________ and ______________• Proteins, oils and starchesDiversity among seeds• Seeds are very diverseIn terms of size• Begonia and Impatiens seed weigh 10-20 micrograms (millionths of a gram)• Coconuts weigh more than a kilogram, seeds of related palms weigh more than15 kgsDiversity among seedsIn terms of adaptation• To ______________ various ______________ until conditions are favorable forgerminationIn terms of method of distribution• By animals, wind, waterDiversity among seedsDistribution of coconut seeds by waterSeed dormancy• Maintains seed during adverse growth conditions (cold, drought)• Lower metabolic rate• Energy cost to reverse dormancy• Maintained by hormone abscisic acid (ABA) / reversed by hormone gibberelic acid(GA)file:///D|/meetings/ashs07/intro%20to%20hort/Orvis_05%20lect%2014%20notes.htm (5 of 8)6/2/2008 2:37:46 PM

Seeds and Seed Germination• Stratification• ScarificationHow long can a seed remain dormant500 year old lotus seeds germinated!Germination of seedsA complex series of steps involving:• Uptake of water• Utilization of stored reserves• Development and expansion of the embryonic axis• Establishment of a seedling capable of sustained, independentgrowthGermination of seedsA. Uptake of water - ______________• Seeds are normally desiccated (~10% water)• Desiccation allows seed to remain dormant• Water uptake starts process of germinationGermination of SeedsOther important factors to consider at beginning:• ______________ requirement• Some seed require a minimum temperature to germinate, e.g. tomato will not germinatebelow 10˚C (50˚F)• Increased ______________file:///D|/meetings/ashs07/intro%20to%20hort/Orvis_05%20lect%2014%20notes.htm (6 of 8)6/2/2008 2:37:46 PM

Seeds and Seed Germination• More oxygen is required for metabolismGermination of seedsB. ____________________________In cotyledons or endosperm tissue• During germination, enzymes are made that convert stored reserves (large molecules)into compounds that can be used by the seedling (smaller molecules)• starches → sugars• lipids, fats → sugars• proteins → amino acidsGermination of seedsC. __________________________________________• Root radicle elongates down, hypocotyl expands up• Establishment of root system and emergence of shoot• Transport of compounds into growing seedling through vascular system• These compounds have two functions• Support respiration in the embryo• Provide a source of building blocks (carbon, nitrogen, etc.) for the seedlingGermination of SeedsD. __________________________________________- will discuss next lecture in more detailGermination of dicot seedsGermination of monocot seedsSeed germination and the conversion of starches into sugars is importantThe importance of converting starches into sugars during germinationfile:///D|/meetings/ashs07/intro%20to%20hort/Orvis_05%20lect%2014%20notes.htm (7 of 8)6/2/2008 2:37:46 PM

Seeds and Seed GerminationConclusions• Seeds are alive but dormant• Comprise an embryonic plant and stored reserves• Germination requires• Water - for imbibition• Oxygen - for respiration• Suitable temperature• Outcome of successful germination is a seedling capable of independent growthfile:///D|/meetings/ashs07/intro%20to%20hort/Orvis_05%20lect%2014%20notes.htm (8 of 8)6/2/2008 2:37:46 PM