Chapter 30/38: Angiosperm Reproduction & Biotechnology
Angiosperms
 Seed plants w/ flowers & fruits
 Pollinated by insects, animals, & wind (e.g. grasses)
 Phylum Anthophyta (anthos = flower, Greek); 250,000 of 290,000 plants
 Seeded Plant Characteristics
o Reduced Gametophytes
o Heterospory by sporophylls
o Pollen
o Ovule (inside ovary)
o Seed
 Angiosperm’s Three ‘F’s:
1. Fruits
2. Flowers
3. Double Fertilization
Flowers
 Attract pollinators
o Visual cues (mimic mates)
o Volatile chemicals (pheromones)
o Food (nectar)
 Form symbiotic relationships
 Parts
o Up to four types of floral organs (modified sporophylls) attached to stem by receptacle
o Sterile organs:
 Sepals – enclose flower (green)
 Petals – brightly colored; attract pollinators
o Reproductive Organs
 Stamen (male)
 Filament – base of stamen
 Anther (like antheridium) – head of stamen
o Has microsporangia that produce microspores (i.e. pollen)
 Carpel (female)
 Stigma – head that receives pollen
 Style – middle section
 Ovary – at the base
o 1 or more ovules within
 Integument – protective tissue around megasporangium
 Megasporangium – organ that makes megaspore
 Becomes f. gametophyte (will make egg)
 Flower Types
o Complete Flower
 Has all 4 floral organs
o Incomplete Flower
 Missing one or more floral organs
o Inflorescences
 Cluster of flowers
 Plant Types
o Monoecious (one sex)
 Both sexes on same plant
 1 flower w/ male & female parts
 Separate male & female flowers on 1 plant
o Dioecious (two sexes)
 Male & Female plants
 Plant has only staminate or carpellate flowers (incomplete)
Life Cycle – p. 627
 Anther (on stamen)
o Many microsporangium (organs) w/ many microsporocytes (cells)
 Microsporocyte forms microspores (pollen) via meiosis
o Pollen – sporopollenin wall w/ male gametophyte inside (2 cells)
 Generative cell – becomes 2 sperm
 Tube cell – makes pollen tube
 Ovary (on carpel)
o Contains 1 or more ovules
o Megasporangium
 Has megasporocyte that will become megaspore
 Megaspore becomes f. gametophyte
o Female Gametophyte
 Made of 7 cells w/ 8 nuclei
 1 egg cell – fertilization = zygote
 2 synergid cells – direct pollen tube to egg
 1 central cell w/ 2 polar nuclei – fertilization = endosperm (food)
 3 Antipodal cells – ???
 Pollination
o Pollen grain lands on stigma, absorbs nutrients & germinates
 Tube cell makes pollen tube
 Generative cell (inside tube) divides forming two sperm
 Tube enters ovule thru micropyle
 Double Fertilization
o Two sperm (n) delivered to f. gametophyte…
 Fertilize egg (n) = zygote (2n)
 Fertilize central cell (2n) = endosperm (3n, triploid)
 Seed Development
o After Fertilization
 Each fertilized ovule makes a seed
 Central cell forms endosperm (Nutrient source for embryo)
 Zygote becomes embryo
 Integuments become seed coat
 Ovary develops into fruit
 Embryo Development
o Zygote divides by mitosis to form…
 Basal cell – forms suspensor
 Connection to sporophyte for nutrients
 Lengthens, pushes embryo into protective tissues
 Terminal cell – becomes embryo
o Embryo Parts
 1 or 2 cotyledons – embryonic seed leaf
 Absorb nutrients from endosperm for embryo (before/after germination)
 Epicotyl – area above cotyledons that contains shoot apex
 Hypocotyl – area under cotyledons that has root apex & ends at radicle (embryonic root)
 Mature Seeds
o At end of maturation
 Seed dries out (5-15% water mass left)
 Integument – hard seed coat
 Enters dormancy
 Stops growth
 Metabolism near standstill
 Seed Dormancy
o Increases chance that germination will occur at right time & place
o Dormancy ended by hot/cold temps, light, rain, heat, smoke, chemicals that weaken seed coat
o Length depends on species

Germination
o Seed uptakes water (swells & ruptures)
o Radicle (embryonic root) emerges first
o Shoot tip breaks soil surface
 Eudicots – hypocotyl hooks, breaks surface, then straightens out (epicotyl & cotyledons
pulled up)
 Fruit
o Develops from ovary (sometimes receptacle, e.g. apple & strawberry)
 Outer wall forms pericarp (outer layer(s) of fruit)
o Aids in seed dispersal by wind or animals
o Protects enclosed seeds
o Can be dry or fleshy
o Types of Fruit
 Simple – from a single or several fused carpels
 Aggregate – from 1 flower that has many carpels
 Multiple – from inflorescence (many flowers); ovaries fuse & make 1 large fruit
 Accessory – from other floral parts as well as ovaries (often receptacle)
o Fruit Dispersal Mechanisms
 Animals
 Water
 Wind
 Asexual Reproduction
o 1 parent reproduces via mitosis
 No meiosis or fertilization
o Produces a clone (exact genetic copy)
o Many forms...
 Fragmentation
 Vegetative (growing or can grow) part of plant falls off & new plant develops
 Adventitious (forms at unusual spot) stem, leaf, or root grows
 Apomixis
 Diploid cell in ovule forms seed
 No sperm, egg, or fertilization needed
o Asexual Advantages
 No pollinators needed
 No neighbors needed
 Intact genes
 If you’re awesome, why split your genes?
 Offspring not frail (vs. seedling)
 Come from vegetative fragments
 aka Vegetative Reproduction
 Saves resources
 No seed, flower, fruit production
 Many made for 1 child to live
o Asexual Disadvantages
 All offspring exact replicas
 Harder to adapt to pathogens or changing conditions
 Catastrophic changes can lead to extirpation/extinction
Why Sexual Reproduction?
 Genetic diversity
 Faster to adapt
 Selfing – self fertilization
 Selfing Prevention
o Dioecious (separate sex plants)
o Carpel & stamens mature at different times
o Structural arrangement
 Pollinator unlikely to pollinate same flower
o
Self-Incompatibility
 Ability to reject plant’s own pollen
 Most common defense
 Plant recognizes own pollen; triggers signal that blocks pollen tube growth
 Like human immune response, except plant rejects ‘self’
Humans & Asexual Reproduction
 Cuttings can form new plants
o Cut the shoot
o Cut a single leaf
o Cut portion of storage structure
 Potato – cut off eye (vegetative bud)
 Grafting
o Twig or bud from one plant grafted onto another plant
o Same or closely related species
o Scion – plant providing stem system (leaves, flowers, fruits)
o Stock – plant providing root system
 Human Modification
o Artificial selection – thousands of years old
o Hybridization – common in nature; used by breeders to introduce new genes
 Mutations arise spontaneously or induced (x-ray, radiation, chemical)
 Beneficial mutations used in breeding experiments (many crosses)
 Desirable traits can come from different species
o Genetic Engineering
 Biotechnology – innovations in use of plants to make useful products
 Transgenic (or GM) plants – have genes from a different organism
 New DNA added to cells
 Not limited to transfer of genes b/w closely related species anymore
 GM Crops
 Produce proteins that act as pesticides (potato)
 Tolerate herbicides
 Resist diseases, cold, warm, salt, drought
 Nutritional supplement
 Biofuels
 Fast growing crops can be harvested (like poplars)
 Cellulose (cell wall) is digested into sugars by enzymes
 Sugars are fermented into alcohol by yeast
 Alcohol distilled = biofuel
 Problems
 Human Health
o May transfer allergens from a gene source to food plant
 Bee allergy into corn
 Nontarget Organisms
o Bt maize pollen kills butterflies
o Bt pesticides will broadly kill insects
 Transgene Escape
o Introduced gene escaping into related weed through hybridization
o Herbicide resistance to a weed = ‘superweed’
 Prevention Already?
 Male sterility
o Seeds & fruit made (fertilization from non-GM crop)
o No pollen produced
 Apomixis
o No pollen made, just clones