BIO SCI 152 1st Edition Lecture 14Flowering Plants II - seed production and dispersalLearning ObjectivesAfter suitable revision, you should be able to –• Recognize and explain some of the key evolutionary innovations whichmake Angiosperms so successful as a plant group • Explain the role of the seed in plant reproduction • Explain the role of fruits in seed reproduction • Explain how seed dispersal may differ for fleshy fruits (e.g. apple, peach)from dry fruits (e.g. maple) • Give examples of different vectors in dispersal of different types of seeds • Explain why seeds have a dormancy period and what needs to happento stimulate germination and growth of a seedling • Explain the advantages and disadvantages of asexual reproduction for plants Vocabulary Flower Fleshy fruitCarpel Aggregate fruitAsexual reproduction Fertilization Multiple fruitPlantlets Double fertilization Seed dispersalStolons Endosperm Seed dormancyRhizomes EmbryoCold stratificationApomixis Cotelydons ImbibitionSelf-fertilization (not Seed coat Germinationasexual) Endosperm metabolismAngiosperm Fruit DiversityEvolutionary Indehiscent Monocotinnovation Dehiscent Dicot (eudicot)Successful pollination leads to seed productionAngiosperm Life Cycle – seed development Fig. 21.25Development of embryo in the seed Fig. 24.4• After first mitotic division of zygote • Terminal cell → proembryo → embryo • Basal cell → suspensor – anchors embryoand transfers nutrient from parent plant Seed and Mature EmbryoSeeds• Consist of seed coat, endosperm, embryo • Endosperm (3n) – Rich in nutrients for developing embryo – In many dicots, food reserve of endospermis restocked in cotyledons, so mature seedwill lack endosperm Monocots and Dicots Fig. 26.1Cotyledons – ‘seed leaves’DICOTS - Two cotyledons e.g. peanut, bean MONOCOTS - One cotyledon e.g. Corn kernelFruits form from the carpel• The carpel is composed of : - the ovary (lower part) - the style (middle part) - the stigma (top part) • The carpel develops into the fruit wall (pericarp) after fertilization • The ovules develop into seeds after fertilization Different Fruit types1. Simple fleshy fruits 2. Simple dry fruits 3. Simple Dehiscent – tissues of mature ovary wall break open releasingseeds e.g. birch 4. Simple Indehiscent – seeds remain in fruit after fruit is shed from parentplant e.g. apple 5. Aggregate fruits • Develop from a cluster of separate carpels • Each flower contains many ovaries • E.g. strawberry, blackberry, magnolia, raspberry 6. Multiple fruit• Gynoecia of a ripened inflorescence – many flowers with many ovaries fused • E.g. pineapple, mulberry What are fruits for? Which of the fruit types above will be dispersed by which seed dispersal vectors?Seeds are effectively dispersed by a range of animalsSeed dispersal by wind and waterSeeds are a dried and dormant form of plant life – a potential plant!Seed Dormancy (during dispersal)Dormancy – suspended activity period– Breaking dormancy – growth resumes if moisture, temperature orday length requirements right – Seed germination timing a. Desert – after rain b. Cold climate – in spring (cold stratification) c. Chapparal - after fires (clears away brush) d. Animal dispersal necessary – must pass through digestivetract to weaken seed coat Germination and growth of seedlingImbibition – seed absorbs water and expands• seed coat ruptures • Seed metabolism resumes, cell division and growthGermination – growth of embryo plant resumes Germination processes Fig. 26.4Seed germination Fig. 26.4 Growing plant uses up food in seed but becomes photosyntheticAsexual Reproduction• New individuals without sex (no meiosis) – clones of parent plant – Cuttings, plantlets, rhizomes, stolons, bulbs, apomixes (Fig. 27.12) In-Class group activity: Advantages and disadvantages of AsexualReproduction?Self-pollination of flowers is not asexual reproduction!!Diversity of Flowering PlantsAngiosperms dominate terrestrial ecosystems - Angiosperms have adapted todiverse environmental conditionsSummary• Asexual reproduction – genetic clones of parent – rhizomes, stolons, plantlets,apomixis. Important for many plants esp. in stable environments • Fruit and seed development – major parts of a fruit, major types of fruit • Seed dormancy – reasons and stimuli for breaking dormancy • Germination – imbibition, germination, role of endosperm • Angiosperms dominate sub-boreal terrestrial habitats – sexual reproduction hasgenerated genetic diversity, giving rise to adaptations to diverse