Chapter 38: Angiosperm Reproduction & Biotechnology

1. Chapter 38: Angiosperm Reproduction & Biotechnology Plants reproduce both sexually & asexually In angiosperms Sporophyte is the dominant generation Sporophyte reproductive flowers Gametophyte is dependant upon sporophyte Male gametophyte anthers Female gametophyte ovule Fertilization occurs within ovule of ovary ovule becomes seed ovary becomes fruit

3. Floral Structure • Determinate shoots attached to stem at receptacle • 4 whorls • Stamens & carpels= reproductive organs • Stamen (male) • Filament=stalk • Anther=terminus to filament in which pollen is located • Carpel (female) • Pistil=single or fused carpel • Ovary at base • Style= slender neck of carpel • stigma= sticky top of style for capturing pollen • Ovules located within ovary • Sepals & petals = sterile • Sepal- protect flower organs • Petals- attract pollinators

5. Gamete development & pollination • Male • Pollen sacs (microsporangia) • contain microsporocytes (2n) that form microspores (n) • Any microspore can become a male gametophyte • Microspore divides by mitosis generative cell & a tube cell • Pollen grain=generative cell + tube cell + spore wall • Maturation of generative cell occurs within the tube cell • Tube cell will form pollen tube • Generative cell divides to form 2 sperm cells

6. Female • Megasporangium in ovary of ovule • Megasporocyte (2n) divides to form megaspores (n) • In most angiosperms: • 1 of 4 megaspores survives • Surviving megaspore divides without cytokinesis to form a large cell with 8 haploid nuclei • Large cell partitioned in gametophyte embryo sac • Embryo sac has 3 cells at one end • 1 egg • 2 synergids (attract/guide pollen tube) • Rest of embryo sac= 3 antipodal cells & 2 polar nuclei

8. Pollination • Transfer of pollen from anther to stigma • Accomplished by: • wind • H2O • Insects • bird or animal transfer Preventing self-fertilization in Dioecious species • Stamens & carpels • Mature at different times • Arranged to prevent selfing • Self-incompatibility • Plant rejects pollen of closely related species • biochemical or pollen tube formation block • Based on ability to recognize self from non-self • Results from S genes

10. Double fertilization • 1 sperm fertilizes egg= zygote • Other sperm combines with 2 polar nuclei to from triploid (3n)=endosperm • Endosperm= food storing tissue of seed • Endosperm develops only in ovules with a fertilized eggconserves nutrients • After double fertilization • Ovule=seed • Ovary=fruit • Endosperm function often taken over by swelling cotyledons of the fruit

11. Embryo development • Zygote divides to form • Basal cell • Form suspensor anchors embryo to parent • Terminal cell • Gives rise to most of embryo • Divides to form proembryo cotyledons • Shoot apical meristem located in shoot apex between cotyledons • Opposite shoot apex=root apex with the root apical meristem • Mature seed structure • Last stages of development • Seed dehydrates • Seed coat forms from integuments of ovule • Embryo becomes dormant & enclosed within the seed coat

13. Ovary to fruit • While seeds develop from ovules flowers develop into fruit to protect seeds & aid in their dispersal • Caused by hormonal changes triggered by fertilization • Ovary wall=pericarp (thickened wall of fruit)

14. Seed germination • Dormancy of seed must be broken by favorable conditions &/or environmental cues Seed to seedling • Germination dependant on imbibition • Uptake of H2O due to low Y of dry seed • Seed expands & ruptures its coat • Triggers metabolic changes • Radicle • Embryonic root • First to emerge • Shoot • Hypocotyl hook forms to break soil surface • Light causes hypocotyl hook to straighten • Raises cotyledons & epicotyl • epicotyl forms leaves • Cotyledons shrivel & fall away • Monocots- coleoptile pushes up through soil; shoot tip grows from coleoptile

16. Asexual reproduction in plants • Large amount of seeds are produced sexually to compensate for those lost to herbivores & environmental hazards- costly energetically; Some species choose asexual reproduction as a result of that cost • Asexual reproduction=vegetative reproduction • Offspring are usually mature, vegetative fragments of parent distributed locally • Offspring at higher risk of local extinction if catastrophic event of new parasite occurs

17. Mechanisms for asexual reproduction • Fragmentation • Separation of parent plant into parts that develop into whole plants • Apomoxis • Seeds produced without pollination or fertilization • Diploid cell in the ovule gives rise to embryo & mature seeds • Clones from cuttings • Shoot or stem cutting with callus (mass of dividing cells) develops adventitious roots or nodes that develop into whole plant • Grafting • Young twig or bud grafted onto a closely related species • Combines qualities of both plants • Stock=plant that contributes root system • Scion= twig grafted onto stock • In vitro cloning of plants • Make multiple copies • Use for production of Genetically Modified Organisms (GMO) • Foreign gene inserted into plant genome; plant expresses foreign gene

18. Plant Biotechnology, Agriculture, & the consequences • Artificial selection • Manipulating reproduction & genetic make-up of plants for human benefit • Biotechnology • Used to insert genes into crops which • Increase crop yields through pest resistance • Increase nutritional value of crops • Consequences of GMOs • Increase in food allergies • Adverse effects on non-target organisms • Possible “superweeds”