Plant Science L14 - Germination and Embryo Growth and Development

Germination and Embryo Growth and Development www.usask.ca Plant Growth § Begins with ______________ germination and the emergence of the seedling. Vegetative stage beginning Floral initiation * of flowering Flow...

Germination and Embryo Growth and Development www.usask.ca Plant Growth § Begins with ______________ germination and the emergence of the seedling. Vegetative stage beginning Floral initiation * of flowering Flowering Pollination and zygote formation Fruit and seed maturity Senescence * SENESCENCE DORMACY Definitions _________________ zygote the beginning of a new plant. formed by the fertilization of the ovule by the pollen. ______________ Senescence Natural process that occur as the plant deteriorates and then dies. This is not dormancy (Dormancy is when normal functions are suspended or slowed down for a period of time. This helps to conserve energy until conditions are favorable for activity to return to normal). GERMINATION Germination § Germination is the sequence of events which begins with the absorption of __________ water and leads to the growth and Friedevelopment of the seedling. gers enzymes in seed - > develops meristens What is Needed for Germination? 1) _________________ SUITABLE WATER 2) _________________ SUITABLE TEMPERATURE 3) _________________ DEQUATE OXYGEN * AMNT- 1) Water § First step in germination is the absorption of water called __________________ imbibition § Cereals require ~ 50% of weight in moisture to begin germination, beans require ~ 75%. § Imbibition causes the seed to swell and may cause the seed coat (testa) to rupture. NOT ENOUGH WATER GROWTH SLOWS = DOWN = DEATH Water § Water activates enzymes break down stored ______________ food Increases __________________ respiration - > take food to turn into activates cell division at the energy _______________ NEW CELLS = meristems seed > - adult quickly ↑ GOAL Of PLANT Activation of Enzymes and Increased Respiration § The level of physiological activity increases greatly. § Absorbed water stimulates hormones which trigger the activation and synthesis of____________. enzymes § Enzymes break down stored food into simpler compounds which are transported and used for growth. Example: Activation of Enzymes in Cereal Crops § The embryo produces a hormone (gibberellin) that surrounds triggers the enzymes in the ______________ alyerone layer > - the. crop (a layer of cells that surrounds the endosperm). § The enzyme alpha amylase in the aleurone layer converts starch to ____________that plucose is used by the embryo for growth (respiration). § In respiration heat is generated and carbon dioxide is - - - - - # released. concern : ability enzymes of. to do their job Water Imbibition is influenced: § Water imbibition is influenced by several conditions including these two factors: don't want lot § _________________ a soil firmness -> of air around seed. (so water doesn't § _________________ soil water content turn to vapour Soil Firmness § If the soil is firm, the moisture will be in close contact to the seed and easier for the seed to take up. § If there are large pockets of _________, air the soil moisture will evaporate into the air and be lost to the atmosphere instead of being taken up by the seed. Soil Water Content § Too much or too little water will inhibit germination. § If there is not sufficient water, germination may begin but not be sufficient to complete it. § Water logged soils have insufficient ______________ Oxygen for germination. Rate of Imbibition (Seed Factors) § Rate of Imbibition depends on: ______________ composition of the seed For example, proteins absorb more water than starches, therefore the embryo absorbs more than the endosperm. Seed coat Some seeds have seed coats that are initially impermeable to water. ↳ no water in Cresistant) 2) Temperature § Each plant has an optimum temperature for germination and a range which beyond, germination will not occur. § Cereal crops on the prairies will germinate just above freezing and germinate up to 37oC. The optimum temp for germination of cereals is 15oC. § ________________ warm season crops such as corn need higher temps for germination (10oC). 3) Oxygen § Oxygen is required for respiration. Respiration is the use of the stored food in order to get the first leaves to the surface for photosynthesis. § If seeds are planted too __________ deep or in water logged soils, there may be oxygen shortages and germination will not occur. § If the seeds sits too long with beginning germination, microorganisms will begin feeding on it. This is called ______________ seed decay * Other Factors that Affect Germination § Most plants will germinate in light or dark. § Some have light requirements. Only seeds that are close to the surface germinate, and those deep not exposed to light remain dormant (which is good because they would not make it to the surface anyway). want § Other plants are inhibited by light. - > darkness Too close to surface and too dry? Germination § If a seed is ____________, alive there are no impediments and acceptable environmental conditions are present, germination will occur. EMBRYO GROWTH AND DEVELOPMENT Embryo Growth and Development stem &leaves § The radicle (first) and plumule begin to grow by cell division and enlargement. cells dre getting bigger § Food is transported to the growing points. § The _____________ testa ruptures and the radicle emerges to take up moisture and nutrients. § The plumule then emerges and begin photosynthetic activity when it reaches the light. § The embryo is now called a seedling. Monocot Germination PROTECTER § Remember the cotyledon, the plumule (coleoptile) and the radicle make up the embryo of a seed. § The radicle begins to grow into the root system. § The shoot (plumule) is protected in a structure called a coleoptile. The coleoptile emerges through the soil first and then from within the coleoptile, the first true leaf emerges. § The __________________ cotyledon always remains below ground in monocots. Example of Monocot Germination https://youtu.be/BFuA0xtog6M Dicot Germination § Two types of germination depending on whether the cotyledons are lifted above ground or remain below ground: § __________________ epigeal- above § __________________ nypogeal -> below Epigeal Germination (Dicots) § In epigeal (epi=above) germination, the __________________ nypocotyl (the stem below the cotyledons) pushes the cotyledons above ground. § The cotyledons function as leaves until the true leaves emerge. § Example CANOLA : Epigeal Germination END Up DRYING + FALLING Off IN FEW DAY S > - COTYLEDONS HYPOCOT Example of Epigeal Germination https://youtu.be/iZMjBO6A7AE Hypogeal Germination (Dicot) § In hypogeal germination, the cotyledons remain ____________________ below ground § The ___________________ epicotyl (it is stem above the cotyledons) grows and raises the plumule out of the soil. § Example PeaS : Hypogeal Germination CAN TRY & GROWTo REGROW If T POINT SOMETHING MAPPENS Example of Hypogeal Germination https://youtu.be/oDBX2gCXxYw What conditions promote good germination? § Factors such as: > - viable Seed _________________(is viability the seed alive and have no impediments to germination?) Seeding __________________ depth Seedling _________________ vigor (do the seeds have enough strength and health to grow into a healthy plant?) HOW HEALTHY IS IT ? all determine health of a new crop. § Seed tests can be done prior to seeding to give an idea of how well the seed will germinate. What conditions promote good germination? § Seeding depth effects the availability of oxygen and moisture to the seed. the deeper the seed in planted the more food reserves it will need to reach the surface. Generally, it is safer to plant ____________ larger seeds deeper than _______________ smaller seeds. § Successful germination is dependent of the seedling becoming self-sustaining before the __________ food in the seed is used up. Other Factors that Affect Germination § Dormancy seeds are __________ viable (alive) but fail to germinate when conditions are favorable. has all it needs , but won't grow. Dormancy § Is a survival mechanism which allows plants to survive in case of unfavorable times (prevent germination until favorable times). § It also allows for__________ staggered germination. Some seeds will not germinate for several years to allow the perpetuation of the species. SPREADS OUT PRODUCTION = staggered germination Types of Dormancy - VIABLE § _______________________ Exogenous Dormacy § _______________________ Endogenous Dormacy § Combination of both is called DOUBLE DORMANCY. EXOGENOUS DORMANCY Exogenous Dormancy § Is dormancy due to _____________ p hysical constraints. § Germination is prevented due to physical, mechanical or seed coat dormancy. testa > - § The hard seed coat (or other tissue) prevents the entry of water or oxygen for germination to begin. Exogenous Dormancy § To overcome exogenous dormancy in nature, weathering of the seed, passing through an animal’s digestive tract or microorganism action is needed. § In the lab ____________, scarification heat treatment, or acid scarification may be performed to overcome exogenous dormancy. Scarification § Is mechanical scratching or rupturing of the seed coat to enable germination. § Plants in the legume family often have very hard seeds that need to be scarified. § Low soil __________ moisture and high ___________ + emperatures during the growing season can increase the occurrence of very hard seeds in the legumes. What is the adaptive advantage of this? - > GROWN IN DROUGHT - make itthrough CONDITION. > drought w/ hard shell. Scarification § In the desert, there is a species of fungus that grows on seed of shadscale plant thereby scarifying the seed. § This fungal growth occurs only when temp and moisture is suitable. Which is in spring, thereby ensuring germination does not occur until spring when the seedlings are most likely to survive. https://commons.wikimedia.org/wiki/File:Atriplex_confertifolia_(5063217522).jpg Heat Treatment § Some plants will have their exogenous dormancy overcome by being exposed to short periods of high heat. § In a lab situation, a seed may be boiled in water to overcome this dormancy. § Fire adaptation > - JACK PINE Jack Pine Note: 120 oF = 49 oC https://www.youtube.com/watch?v =Vji8YPT_SoQ to 4:30 ENDOGENOUS DORMANCY Endogenous Dormancy § Also called embryonic or _________________ Physiological dormancy. § Strategies to overcome endogenous dormancy stratification chemical block Stratification § Many seeds will not germinate until they have been exposed (weeks-months) to ____________ low temperatures with oxygen and moisture present. § Example: § This is called stratification or pre-chilling. Stratification § In nature, stratification prevents the seeds from germinating in the fall when they may be killed over the winter and forces them to wait until spring when conditions are good. § What happens during this cold period that allows germination to begin in spring? Answer not totally understood, may be the accumulation of plant hormones. Chemicals that Block Germination § Some seeds contain chemicals that prevent germination. Chemicals may be salts, cyanide-releasing or ammonia- releasing compounds. § With adequate ____________, moisture the chemicals will leach out of the seed and allow germination. § This ensures that the seeds will begin germination when there is adequate moisture to support growth of the seedling. DORMANCY IN CULTIVATED CROPS Dormancy in Cultivated Crops § Many of our common crops have ________ lost their dormancy or been selected against by plant breeders. § This is beneficial because dormancy can interfere with the production of the crop or the further use of the seed. Dormancy in Cultivated Crops § The loss of dormancy in cultivated crops can be a “______________ Catch 22 ”. Malt barley has no dormancy mechanisms which allows the malster to have rapid, even germination. However, the lack of dormancy may result in problems with ______________ sprouting in the field. - HAPPENING AT THE WRONG TIME VIABILITY AND LONGEVITY Viability § Viability is the ability to germinate if suitable conditions are present. § Loss of viability usually occurs _________________ gradually. Longevity § Longevity is the length of time a seed can remain dormant and still be viable. § Longevity depends on: plant species growing conditions storage conditions Plant Species § Longevity differs among species. § Examples: wheat 6 to 32 years barely 2 to 10 years oat 6 to 29 years wild mustard up to 60 years vegetable seeds 1 to 5 years Longevity § 2,000 year old date palm from the Dead Sea. § In 2012, Russian scientists say they germinated seed that was 32,000 years old. The mature and immature seeds, which had been entirely encased in ice, were unearthed from 124 feet (38 meters) below the permafrost, surrounded by layers that included mammoth, bison, and woolly rhinoceros bones. 32,000 year old seeds https://www.youtube.com/watch?v =MHYGchvcytc&t=70s Growing Conditions § The conditions under which the seed was produced and the subsequent conditions of the seed also affects longevity. § Lower longevity if: § _________________ immature seed - fost § _________________ low food reserves > - DROUGHT CONDITIONS § _________________ disease § _________________ physical damage Storage Conditions § The higher the temp and moisture content, the faster the respiration and more conducive to disease therefore the shorter the longevity. § __________ DrY seeds can withstand varying temps.  Copyright Sourcing Slide 1: Permission: Saskatoon, SK: University of Saskatchewan. Slide 27: Source: https://www.flickr.com/photos/revstan/3668053095 Permission: CC BY 2.0 Courtesy of Rev Stan. Slide 30: Source: https://www.flickr.com/photos/tessawatson/407050327 Permission: CC BY 2.0 Courtesy of Tess Watson.