Plant Reproduction and Development 1 Lecture Notes PDF

Plant Reproduction and Development 1 Concepts 38.1-38.2 Campbell. Biology. 3rd ed Outline • 1. Unique features of the Angiosperm life cycle • Flowers • Double fertilization • Seed development • Fruits • 2. Reproduction in Flowering Plants • Advantages of Asexual vs Sexual •1. Unique features of...

Plant Reproduction and Development 1 Concepts 38.1-38.2 Campbell. Biology. 3rd ed Outline • 1. Unique features of the Angiosperm life cycle • Flowers • Double fertilization • Seed development • Fruits • 2. Reproduction in Flowering Plants • Advantages of Asexual vs Sexual •1. Unique features of the Angiosperm life cycle •Angiosperm Derived Traits • Flowers • Double fertilization • Fruits Flowers Sepals – whorl at base of flower that encloses flower before opening Petals – attract pollinators; colorful/provide landing strip Carpel/Pistil - female part of flower; includes the stigma, style and ovary Stamen – male part of the flower; includes anther and filament Receptacle – point of flower attachment to stem Simple flower = one flower on floral axis Inflorescence = a cluster of flowers arranged on a floral axis (oat panicle) https://canadianagronomist.ca/triallate-resistant-wild-oats-also-cross-resistant-to-four-other-groups/ • Complete flowers = all four floral organs (sepals, petals, stamens, anthers) • Incomplete flowers = lacking one or more floral organs • Perfect flowers = both male and female floral organs • Imperfect flowers = only male or only female floral organs present • Monoecious plant = one house = separate male and female flowers on the same plant (ie. corn) • Dioecious plant = two houses = plants produce only male or only female flowers (ie, papaya, holly) • Bisexual plant = plants with flowers that contain both male and female organs IMPERFECT FLOWERS PERFECT FLOWERS IMPERFECT FLOWERS https://www.knowswhy.com/difference-between-monoecious-and-dioecious/ Hartmann and Kester’s Plant Propagation Principles and Practices 8e Hudson Hartman, Dale Kester, Fred Davies and Robert Geneve Copyright ©2011, 2002, 1997, 1990, 1983, 1975, 1968, 1959 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Monoecious in Corn Monoecious Male and female flowers on the same plant http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1087230040&maxto=9&topicorder=4 Hartmann and Kester’s Plant Propagation Principles and Practices 8e Hudson Hartman, Dale Kester, Fred Davies and Robert Geneve Copyright ©2011, 2002, 1997, 1990, 1983, 1975, 1968, 1959 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Dioecious in Holly (two house) Figure 5–2 Holly (Ilex) plants are dioecious, producing female (a) and male (b) flowers on separate plants, forcing cross-pollination. Many flowers in dioecious plants produce remnant female and male parts that are usually non-functional. Note the non-functional male stamens present in the female flowers. Dioecious plants have pistils (female parts) and stamens (male parts) present on separate plants Hartmann and Kester’s Plant Propagation Principles and Practices 8e Hudson Hartman, Dale Kester, Fred Davies and Robert Geneve Copyright ©2011, 2002, 1997, 1990, 1983, 1975, 1968, 1959 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Methods of Pollination • Do all crops need insect pollinators? • Usually flowers that are “showy” and have colorful petals require insect pollinators • ~80% of angiosperm pollination relies on animal pollinators • ~20% of angiosperm pollination relies on wind (a few rely on water) Pollination Ecology • Pollinators have coevolved with plants. – Twenty thousand bee species among current-day pollinators. – Bee-pollinated flowers: • Generally brightly colored, mostly blue or yellow • Often have lines or other distinctive markings, (function as landing platforms and nectar guides). – Bees see UV light (humans do not). » Some flower markings visible only in UV light. In ordinary light Copyright ©2011, 2002, 1997, 1990, 1983, 1975, 1968, 1959 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. In UV light Pollination Ecology • Beetle-pollinated flowers: – Strong, yeasty, spicy or fruity odor – White or dull in color - Beetles do have keen visual senses. • Fly-pollinated flowers: – Smell like rotten meat – Dull red or brown CORPSE FLOWER -smells of feces, rotting meat and fish, garlic, cheese, sweat https://www.calpoly.edu/news/back-back-blooms-another-corpse-flowe r-comes-alive-third-straight-summer Copyright ©2011, 2002, 1997, 1990, 1983, 1975, 1968, 1959 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Pollination Ecology • Butterfly- and moth-pollinated flowers: – – – – Often have sweet fragrances Light colored flowers (white or yellow) for night-flying moths Colorful flowers (red, often blue, yellow or orange) for butterflies Nectaries at bases of corolla tubes or proboscis (tongues). • Bird-pollinated flowers (hummingbirds and sunbirds): • Often bright red or yellow • Little if any odor • Large, study flowers • Copious amounts of nectar Copyright ©2011, 2002, 1997, 1990, 1983, 1975, 1968, 1959 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Pollination Ecology • Bat-pollinated flowers: • Primarily in tropics • Open at night when bats are foraging • Dull in color • Often aromatic • Large enough for bat to insert head or consist of ball-like inflorescence containing large numbers of small flowers Copyright ©2011, 2002, 1997, 1990, 1983, 1975, 1968, 1959 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Double Fertilization and Endosperm • Double Fertilization • One sperm fuses with egg cell = zygote • One sperm fuses with two polar nuclei = endosperm • Unique feature of angiosperms • Endosperm • Begins to develop before embryo • Nutritive tissue in seeds • Provides energy to developing embryo and germinating seed • Coconut milk and meat are examples of liquid and solid endosperm • Fluffy part of popcorn is endosperm • Double fertilization: • One sperm unites with egg, forming zygote (2N), then embryo. • Other sperm unites with central cell nuclei, producing triploid (3N) endosperm nucleus that develops into endosperm tissue. https://www.quora.com/How-can-you-describe-the-process-of-double-fertilization-in-plants https://propg.ifas.ufl.edu/04-seeds/01-development/05-seedsdevelopment-endosperm.html Seeds and Seed Development • During final stages of seed maturation there is decrease in water content of the seed to about 5-15% of total seed weight • Parts of the embryo in Eudicot • Cotyledons = embryonic seed leaves • Hypocotyl = embryonic stem below cotyledons • Epicotyl = embryonic stem above cotyledons • Radicle = embryonic root • Parts of the embryo in Monocot • Cotyledon (1) = embryonic seed leaf • Grasses have specialized cotyledon called scutellum • Grass seed is embryo is enclosed within two protective sheaths: coleoptile which covers the shoot and coleorhiza which covers the root Figure 38.8 Seed Structure Seed Germination • Seed germination is initiated by imbibition = uptake of water into the seed • Imbibition causes the seed to expand and the seed coat to rupture in addition to triggering metabolism and resumption of growth • Enzymes digest the endosperm and cotyledons • Radicle is first organ to emerge from the seed and anchors the embryo in soil and begin water uptake Epigeal vs Hypogeal Germination • Epigeal Germination= hypocotyl elongates and forms a hook that pulls the cotyledons above ground. First true leaves unfold and begin photosynthesis • Hypogeal Germination = hypocotyl does not elongate and remains below ground along with the single cotyledon. Coleoptile (sheath covering embryonic shoot) pushes through soil and emerges above ground. Shoot emerges from coleoptile and begins photosynthesis Figure 38.9 Two common types of seed germination General Requirements for Seed Germination • Water • Oxygen • Proper temperature • Removal of dormancy factors • **Light or no light (not considered a requirement) The Germination Process • For germination to be initiated, three conditions must be fulfilled: • 1. The seed must be viable; that is, the embryo must be alive and capable of germination. • 2. The seed must be subjected to the appropriate environmental conditions • 3. Any primary dormancy condition present within the seed must be overcome. Primary VS Secondary Dormancy • Primary dormancy • is induced during seed development resulting in seeds that are dormant when dispersed from the mother plant. • condition present within the seed. • induced with the involvement of abscisic acid (ABA) during seed maturation on the mother plant • Secondary dormancy • is induced by unfavorable environmental conditions. Growth and Flowering • After seedling emerges, photosynthesis begins • Sugars made from photosynthesis and water/minerals taken up by the root allow for plant growth and development • Growth includes primary growth (primary meristems – growth in length) and secondary growth (secondary meristems – growth in width) • Vegetative growth precedes reproductive growth • A developmental switch in the primary meristems activates flower production and halts vegetative production in the tip of the shoots • Perception of seasonal changes and daylength Fruits ■ ■ ■ Simple – develops from a single carpel or pistil (tomato) Aggregate – from single flower with many pistils (strawberry) Multiple – cluster of many individual flowers in a single inflorescence (pineapple) https://www.backyardnature.net/frt_aggr.htm http://tomatosphere.letstalkscience.ca/Resources/library/A rticleId/4767/the-life-cycle-of-a-tomato-plant.aspx https://en.wikipedia.org/wiki/Strawberry https://www.interflora.com.au/ blog/post/pineapple-flower Simple fruits - Fleshy Drupe – one hard and stony seed Berry – fleshy mesocarp with many seeds Tomato Peach Orange Apple Pome – papery or leathery endocarp Hisperidium – leathery skin with oils Photos: USDA pepos – Pumpkin Photos: USDA fleshy fruit with a hard rind (Cucurbitaceae) Muskmelon Water melon Simple fruits - Dry Dehiscent – split at maturity (beans; cabbage) Indehiscent – do not split at maturity (macadamia) https://www.kullabs.com/classes/subjects/units/lessons/notes/note-detail/2505 Accessory Fruits • Floral parts, usually the receptacle, contribute to what we refer to as the fruit • Ie, the ovary is not the "fruit" but is instead embedded within the "fruit" • Apples and strawberries are accessory fruits https://www2.palomar.edu/users/warmstrong/termfr4.htm 2. Reproduction in Flowering Plants • Asexual Reproduction with vegetative parts • Parenchyma cells in the plant body are also capable of dividing and specializing which enables plants to regenerate lost parts • Detached stem and/or root tissues (including the eye of the potato which is a bud) can regenerate an entire new plant with full structure and function in the process of fragmentation • Apomixis is a mode of asexual reproduction that involves reproduction with seeds as opposed to vegetative parts Asexual Reproduction • Totipotency: the concept that every cell in plant has the inherent genetic ability to reproduce the entire plant. • Clone: A group of organisms descended by mitosis from a common ancestor. • Clone - a group of plants, derived from the same parent plant by asexual (vegetative) propagation. Advantages of Asexual Reproduction • Natural environment •No need for pollinators • Less energy expended on producing showy floral parts • Advantage in areas where plants are sparsely distributed • Beneficial in stable environments • In Plant Propagation setting •All off-spring are true-to-type (identical to the parent) and produce a clone . •Asexual propagation is appropriate for plants that are hard or impossible to propagate from seeds •Decrease time to flowering (esp. cutting & budding); by-passes juvenile phase Using Clones as Cultivars • Uniformity of populations • eliminates less productive individuals found in seedling mixtures • plant size, growth rate, time of flowering, time of harvesting • makes economic industrial production of fruit and nut crops possible • orchards • clonal forests show a 1/3 wood gain yield compared to non clonal forests http://eucalyptusclones.com/clones_and_clonal_plantation.htm Disadvantage of Asexual Reproduction • No genetic diversity •Recall the Irish Potato famine. Only a few varieties of potato with low genetic diversity and all were susceptible to Late Blight disease https://thesocietypages.org/socimages/2009/01/23/monocultures-genetic-diversity-and-the-social-landscape/ Asexual Plant Propagation Methods • Asexual propagation - Uses vegetative parts • Crown division - Plant separated into several pieces, each with crown portion and roots. Crown division of daylily Cuttings - Propagation from parts of plants ● If stem used, produces adventitious roots. • Cells near the wound must dedifferentiate and create a new meristematic region. • Sometimes rooting is stimulated by the hormone auxin. • Identical copies of valuable plants can be made. • Disadvantage - Diseases carried by mother plant carry to progeny. Layering - roots produced on branch or stem • • Works well for some plants that are not easy to propagate by cuttings. • Tip layering - Tips bent until touch ground, and then covered with soil. • Roots form on buried stem. • Blackberries, boysenberries • Air layering - Branch or main stem wounded or girdled to produce roots. • Tropical trees and shrubs Tip layering http://hort201.tamu.edu/YouthAdven tureProgram/AsexualPropagation/A sexaulPropagation.html Grafting - Segments of different plants connected and induced to grow together as one plant. • Common in fruit and nut trees • Scion - Top part of graft • Rootstock - Bottom portion – Selected for winter hardiness, dwarfing and disease resistance • Success depends on good contact between vascular cambium of scion and that of rootstock. http://www.ces.ncsu.edu/depts/hort/hil/grafting.html Micropropagation - Grow and maintain plants in a disease-free status in test tubes • Advantages: • Can grow large numbers of plants in small area. • Minimal maintenance required. • Rapid multiplication • Grown in-vitro in sterile medium and maintained in controlled environments • Relies on totipotency of plant cells • Capacity of a cell to give rise to any structure of a mature organism • Micropropagation begins with establishment of explants in tissue culture. • Explant – Excised (removed/cut) piece of stem or leaf tissue • Plant parts disinfested and inserted into growth medium in test tubes or plates. • Induced with hormones to develop multiple shoots = microshoots • Microshoots separated and placed in new medium by subculturing. • Roots induced by transferring to rooting medium with rooting hormones. • Plants transferred back to outdoor environment. Figure 17–1 Typical structures formed in tissue culture include (a) shoots, (b) roots, (c) flowers, (d) bulbs, (e) callus, (f) somatic embryos. Hartmann and Kester’s Plant Propagation Principles and Practices 8e Hudson Hartman, Dale Kester, Fred Davies and Robert Geneve Apomixis and Parthenocarpy • Apomixis – production of seed without sexual union • No fusion of gametes and no zygote • Embryo derived from a diploid cell of the maternal tissues of the ovule • Clone?? • Parthenocarpy - Fruits develop from ovaries with unfertilized eggs (generally due to mutation). • Results in seedless fruits • Navel oranges and bananas Advantages of Sexual Reproduction •In Natural Environment • Advantageous in unstable environments where greater genetic diversity increases chances of survival of species •In Propagation Environment • Produces large numbers of seedlings in a short period of time • Produce hybrids (hybrid corn industry) Disadvantages of Sexual Reproduction • some plants produce no viable seeds (e.g. sterile seeds in cultivated banana). • Some plants do not regularly produce viable seeds (potato) • Some seeds are very difficult or slow to germinate. • Growth from seed extends time to flowering and fruit production (eg. Fruit orchards) Sliced wild banana, containing seeds http://bananasweb.com/do-bananas-have-seeds Self-Pollination • Self-pollination (transfer of pollen from anther to stigma in same plant) • Limits genetic diversity • Offspring don't always perform as well as those from cross pollination (hybrid = hybrid vigor) • May be advantageous in environments where pollinators are scarce • Hundreds of species of plants are self-pollinating species • Self-pollination in crop plants is a domesticated trait that has been selected for over thousands of years by farmers Mechanisms to Ensure Self Pollination • Cleistogamy = flowers never open (Oxalis, groundnut, soybean, common blue violet) • Chasmogamy = flowers open after shedding pollens (rice, wheat, tomato, cotton, pepper) • Only in perfect flowers (must have both male and female floral organs) Cross Pollination • In dioecious plants, self-pollination is not possible • In bisexual plants with perfect flowers, self-pollination is possible if not prevented • A plant rejects its own pollen • Floral adaptation exist such that pollen and ovule cannot reach each other or are not receptive at the same time • Self-incompatibility is a mechanism by which self-pollination is prevented in some plants, even though the flowers are perfect, pollen is viable, and stigma is receptive • Dichogamy and heterostyly are mechanisms where flowers are perfect but not in sync Mechanisms to Ensure Cross Pollination POLLEN GRAIN Self incompatibility A pollen tube will not grow unless genotype of pollen grain is unique to genotype of stigma. Prevents self fertilization (ie, discriminates against self) https://plantlet.org/self-incompatibility/ • DICHOGAMY • Breeding system to induce cross pollination • Flowers are perfect but not in sync • PROTODANDROUS: Male flower parts shed pollen before female flower parts are receptive • PROTOGYNOUS: Female flower parts are receptive at a time when male flower parts have not begun to shed pollen HETEROSTYLY • Breeding system to induce cross pollination • Flowers are perfect but not in sync due to different lengths of stamens or carpels • THRUM FLOWERS: Male filament is long and anthers are elevated. Female has a short style which keeps the stigma inside the corolla tube • PIN FLOWERS: Female stigma is elevated by a long style and male anthers are on a short filament Breeding systems Use Self and Cross Pollination • SELFING increases homozygosity which “fixes” or stabilizes the genotype. Reduces genetic variability in a population • CROSSING increases heterozygosity or increases genetic variability in a population • Inbred = repeated self pollination of a hybrid (AA or aa) • Hybrid = cross between two inbreds (Aa) http://b4fa.org/bioscience-in-brief/plantbreeding/intraspecific-f1-hybrids/maize-f1-hybrids/ Hybrids • A hybrid seedling population is usually uniform in appearance and shows increased growth and productivity. This phenomenon is called • heterosis or hybrid vigor • Hybrids are created by crossing Inbred (homozygous) lines The End • Thank you • Questions? • Have a wonderful day!