Plant Reproduction Chapter 30

The Plant Kingdom Nearly all are multicellular Eukaryotic Terrestrial Vast majority are photoautotrophs Energy from sun Carbon dioxide from air Minerals dissolved in water

Plant Kingdom Adaptations to land Well developed tissue Cuticle Stomata Protection of embryo Alternations of generations Sporophyte Diploid Produces spores by meiosis Reproductive structure

Plant Kingdom Gametophyte Haploid Produces gametes Egg and sperm Formed by mitosis Egg and sperm fuse to form zygote Undergoes mitosis Forms sporophyte

Evolutionary Trend multicelled sporophyte (2n) mitosis zygote (2n) Diploid Haploid fertilization meiosis gametes (2n) spores (2n) multicelled gametophytes (n) mitosis mitosis

zygote only, no sporophyte sporophyte’s importance gametophyte’s importance green algae bryophytes ferns gymnosperms angiosperms

Imperiled Sexual Partners Impacts, Issues Video Imperiled Sexual Partners

Plants and Pollinators Pollination Transfer of pollen to the stigma Pollen had evolved by 390 million years ago Sperm packed inside a nutritious package Transferred first by wind currents (abiotic) Later transferred by insects Plants that attracted insect pollinators with flowers had a reproductive advantage

Pollinators Pollination vectors Winds Insects Birds Other animals Coevolution with pollinators

Hummingbird drinking nectar of columbine flower Figure 30.6bb Exploring flower pollination (part 2b: hummingbird) Hummingbird drinking nectar of columbine flower 10

Long-nosed bat feeding on cactus Figure 30.6ba Exploring flower pollination (part 2a: long-nosed bat) Long-nosed bat feeding on cactus flower at night 11

Pollinators Visual cues Size, shape, color, pattern Olfactory cues Odors from fruit or flowers Pollinators follow concentration gradient of volatile chemicals to their sources Reinforcements Nectar

Bee-attracting flower pattern Pollen Formation Bee-attracting flower pattern

Common dandelion Common dandelion under ultraviolet under normal light Figure 30.6ac Exploring flower pollination (part 1c: dandelion) Common dandelion under ultraviolet light Common dandelion under normal light 14

Angiosperm Life Cycle Diploid sporophytes (2n) produce spores (n) by meiosis these grow into haploid gametophytes (n) Gametophytes (n) produce haploid gametes (n) by mitosis fertilization of gametes produces a sporophyte 15

DIPLOID HAPLOID fertilization mature sporophyte seed meiosis (within anther) meiosis (within ovary) DIPLOID HAPLOID fertilization gametes (sperm) microspores (mitosis) male gametophyte gametes (eggs) megaspores (mitosis) female gametophyte

Angiosperm Life Cycle In angiosperms, the sporophyte is the dominant generation, the large plant that we see The gametophytes are reduced in size and depend on the sporophyte for nutrients The angiosperm life cycle is characterized by “three Fs”: Flowers Double Fertilization Fruits For the Discovery Video Plant Pollination, go to Animation and Video Files. 17

Flower Structure and Function Flowers are the reproductive shoots of the angiosperm sporophyte they attach to a part of the stem called the receptacle 18

Flower Structure Nonfertile parts Sepals Receptacle Fertile parts STAMEN (male reproductive part) CARPEL (female reproductive part) filament anther stigma style ovary Nonfertile parts Sepals Receptacle Fertile parts Male stamens Female carpel (ovary) OVULE (forms within ovary) petal (all petals combined are the flower’s corolla) sepal (all sepals combined are the flower’s calyx) receptacle

Pollen Formation Microspores to pollen

Development of Male Gametophytes in Pollen Grains Microspore Mother Cell (2n) Goes through meiosis to produce microscpores (n) Microspores (n) give rise to pollen takes place in the microsporangia, or pollen sacs, of anthers each microspore undergoes mitosis to produce two cells the generative cell 2 sperm the tube cell pollen tube 21

Pollen Formation pollen sac anther filament microspore mother cell Diploid Stage Haploid Stage Meiosis microspores pollen grain pollen tube stigma sperm nuclei mature male gametophyte style of carpel

Egg Formation Megaspores to eggs

Egg Formation Meiosis in ovule produces megaspores All megaspores but one disintegrate It undergoes mitosis three times without cytoplasmic division Result is a cell with eight nuclei Cytoplasmic division produces seven-celled female gametophyte 6 cells with 1 nucleus 1 being the egg 1 cell with 2 nuclei Dikaryotic Forms the endosperm

Pollination / Double Fertilization transfer of pollen grains to a receptive stigma Germination pollen tube begins to grow delivers the sperm 1 to fertilize the egg (2n) 1 to the polar nuclei gives rise to the triploid endosperm (3n) nutritive tissue of the seed

Pollen Stigma grain Pollen tube Two sperm Tube nucleus Style Ovary Polar nuclei Ovule Figure 30.7-1 Growth of the pollen tube and double fertilization (step 1) Egg Micropyle 26

Pollen Stigma grain Pollen tube Ovule Two sperm Tube Polar nuclei nucleus Polar nuclei Style Egg Ovary Synergid Polar nuclei Ovule Figure 30.7-2 Growth of the pollen tube and double fertilization (step 2) Two sperm Egg Micropyle 27

Pollen grain Stigma Endosperm nucleus (3n) (two polar nuclei plus sperm) Pollen tube Ovule Two sperm Tube nucleus Polar nuclei Style Egg Ovary Synergid Polar nuclei Zygote (2n) (egg plus sperm) Ovule Figure 30.7-3 Growth of the pollen tube and double fertilization (step 3) Two sperm Egg Micropyle 28

Seed Formation Seed A mature ovule encases an embryo sporophyte food reserves inside a protective coat enters a state of dormancy wherein it stops growing and slows metabolism mature seed is only about 5–15% water 29

Nourishing the Embryo Dicot embryo Absorbs nutrients from endosperm Stores them in its two cotyledons Monocot embryo Digestive enzymes are stockpiled in the single cotyledon Enzymes do not tap into the endosperm until the seed germinates

Eudicot seed development Nourishing the Embryo Eudicot seed development

Seed Dormancy: An Adaptation for Tough Times increases the chances that germination will occur at a time and place most advantageous to the seedling Breaking of seed dormancy often requires environmental cues such as temperature or lighting changes 32

Seed Germination / Seedling Development Germination depends on imbibition, the uptake of water due to low water potential of the dry seed The radicle (embryonic root) emerges first Next, the shoot tip breaks through the soil surface 33

Fruit A fruit develops from the ovary It protects the enclosed seeds and aids in seed dispersal

(a) Simple fruit (b) Aggregate fruit (c) Multiple fruit Stigma Style Carpels Stamen Flower Petal Ovary Stamen Stamen Sepal Stigma Ovary (in receptacle) Ovule Ovule Pea flower Raspberry flower Pineapple inflorescence Apple flower Each segment develops from the carpel of one flower Remains of stamens and styles Carpel (fruitlet) Stigma Sepals Seed Ovary Stamen Figure 30.11 Developmental origins of fruits Seed Receptacle Pea fruit Raspberry fruit Pineapple fruit Apple fruit (a) Simple fruit (b) Aggregate fruit (c) Multiple fruit (d) Accessory fruit 35

Seed Dispersal Fruit structure is adapted to mode of dispersal Some modes of seed dispersal: Wind currents Water currents Animals

wing seed (in carpel)

Dandelion “seeds” (actually one-seeded fruits) Dandelion fruit Figure 30.12ac Exploring fruit and seed dispersal (part 1c: dandelion) Dandelion “seeds” (actually one-seeded fruits) 38

Ant carrying seed with attached “food body” Figure 30.12bd Exploring fruit and seed dispersal (part 2d: food bodies) Ant carrying seed with attached “food body” 40

Advantages and Disadvantages of Asexual vs Sexual Reproduction Asexual reproduction is also called vegetative reproduction beneficial to a successful plant in a stable environment a clone of plants is vulnerable to local extinction if there is an environmental change Sexual reproduction generates genetic variation that makes evolutionary adaptation possible 41