Reproduction system

1. Reproduction system

2. Reproduction systems in plants • Seed propagated species • self-pollinated • cross pollinated • self- and cross pollinated • Vegetatively propagated species

3. Sexual reproduction • In animals: It’s easy because you have separate male and female individuals. • In flowering plants: Not so easy, because most flowers have both male and female parts in them, called perfect flowers. • So flowering plants have evolved special ways to insure out-breeding/out-crossing – and to prevent inbreeding.

4. Plant Reproduction

5. Plant Reproduction: male gametophyte • Cells within anther undergo meiosis • Produce 4 spores • Each spore undergoes mitosis • Results in pollen grain containing 2 sperm

6. Plant Reproduction: female gametophyte • Within ovule, a cell undergoes meiosis • Produces 4 spores • 1 spore undergoes mitosis • Produces embryo sac • Egg is contained within embryo sac

7. Plant Reproduction • During pollination, pollen lands on stigma • Sperm travels down pollen tube • 1 sperm fertilizes egg • The other contributes to formation of tissue that will provide nourishment to embryo

8. Ovule develops into seed

9. Basic Terms • Outbreeding Sexual reproduction between individuals (cross-pollination). (It involves two individual plants) • Inbreeding Sexual reproduction within an individual • (self-pollination). (It involves one individual plant) • Sexual Reproduction • The sexual process is a mechanism to bring about gene recombination. • Recombination is the chief source of hereditary variation and provides the raw materials for species to adapt to changing environmental conditions.

10. Function of flower attract pollinators with colorful petals, scent, nectar and pollen Carpel/

11. Overview of floral organs

12. Reproductive floral organs: female • Carpel or pistil – female reproductive organs; contains: • Stigma – is where pollen sticks to • Style – is the long tube that connects stigma to ovary • Ovary – enlarged structure at the base of carpel/pistil where the ovules are located; it will become the fruit. • Ovules – contains female gametophyte, becomes the seed • Plants have style! ovary carpel or pistil

13. Reproductive floral organs: male • Stamen – male floral organ, consists of: • Anther – part of the stamen that produces pollen • Filament – stalk-like structure that holds anther • Pollen – immature male gametophyte

14. Non-reproductive floral organs • Petals – whorl of flower organs that are often brightly colored to attract pollinators • Corolla – whorl of petals in a flower • Sepals – whorl of leaf-like organs outside the corolla; help protect the unopened flower bud. • Calyx – whorl of sepals in a flower • Tepals – when sepals and petals look the same

15. Pollination and Fertilization • Pollen contains TWO nuclei: a sperm nucleus and tube nucleus • Sperm nucleus is protected in gametophyte tissue (pollen can travel in the air)

16. Pollination and Fertilization • For pollen sperm to successfully fertilize the egg, there must be pollination: a method to get the pollen from the male anther to the stigma. • Pollen sticks to the stigma, starts growing a pollen tube • Fertilization begins whentube begins to grow toward the egg

17. Double Fertilization • Double fertilization occurs: One sperm nucleus (1n) fertilizes the egg, producing a zygote (2n)  which becomes the plant embryo inside the seed • Another sperm nucleus fuses with the polar nuclei, resulting in a triploid endosperm (3n) • Endosperm is a source of food for the young embryo. Endosperm

18. The seed Parts of the seed: • Seed Coat offers protection • Endosperm supplies food for the seed • Embryo is the young plant

19. Hermaphroditic Flowers • Self-compatible (SC) • Capable of self-fertilization or cross-fertilization • Self-incompatible (SI) • Only capable of cross-fertilization • Inability of hermaphroditic plant to produce zygotes w/ self pollen

20. Autogamy • Self-fertilization • Pollen transfer within or among flowers of same individual • ~25% of plant taxa

21. Advantages of Autogamy • Insures seed set in absence of pollinators. • Overcomes sterility. • Selectively advantageous by transmitting both sets of genes to offspring. • Well-adapted genotypes preserved. • Only single colonizing individual needed.

22. Disadvantages of Autogamy • Decreases genetic variability. • Inability to adapt to changing conditions. • Increases inbreeding depression. • Reduces heterozygosity and increases homozygosity of deleterious alleles. • More uniform populations.

23. Cleistogamy • Flowers never open and only capable of self-fertilization in bud. • Inconspicuous, bud-like apetalous flowers that form directly into seed capsules. • Has evolved independently multiple times • throughout the angiosperms, including some basal lineages. • 488 species, across 212 genera and 49 families. • Violaceae, Fabaceae, Poaceae

24. Outbreeding (Cross-pollination) • Advantages: Increases genetic variability Strong evolutionary potential Adaptation to changing conditions Successful long-term • Disadvantages: Can destroy well-adapted genotypes Relies on effective cross-pollination, seed dispersal and establishment

25. How do plants get pollen from one plant to another? • Because plants are rooted in the ground, they must use different strategies: • WIND POLLINATION: • Gymnosperms and some flowering plants (grasses, trees) use wind pollination. • Flowers are small, grouped together • Not a very efficient method(too chancy and wasteful)

26. ANIMALS Many flowering plants rely on animals for cross-pollination: • Insects – bees, wasps, flies, butterflies, moths • Birds – hummingbirds, honey creepers • Mammals – bats, mice, monkeys • Even some reptiles and amphibians!

27. Coevolution • Coevolution interactions between two different species as selective forces on each other, resulting in adaptations that increase their interdependency. • Animal-flowering plant interaction is a classic example of coevolution: 1. Plants evolve elaborate methods to attract animal pollinators 2. Animals evolved specialized body parts and behaviors that aid plant pollination

28. A word about pollen… • The shape and form of pollen is related to its method of pollination… • Insect-pollinated specieshave sticky of barbedpollen grains • Wind-pollinated speciesis lightweight, small andsmooth (corn pollen)

29. Palynology: the study of pollen • Palynology is useful in many fields: • Petroleum geology – fossil pollen can determine if a field will have oil-rich deposits • Archeology – studying ancient pollen samples, archeologists can determine agricultural practices, diet, etc. • Anthropology – uses of pollen in rituals • Criminology – to determine the whereabouts of an individual, examine pollen clinging to clothes • Aerobiology – to determine what plants cause hay fever and allergic reactions – in landscaping

30. Animal pollinators: Bees • Bees – the most important group of flower pollinators • They live on the nectar and feed larvae, also eat the pollen. • Bees are guided by sight andsmell • See yellow and blue colors,also ultraviolet light (not red) • Flowers have “honey guides” and bee landing platforms..

31. Butterflies and moths • Also guided by sight and smell • Butterflies can see red and orangeflowers • Usually shaped as a long tube because of insect’sproboscis – to get nectar • Moth-pollinated flowersare usually white or pale,with sweet, strong odor – for night pollination.

32. Flies and beetles • Flies like flowers that smelllike dung or rotten meat. • Lay their eggs there, but larvae die due to lack of food • Beetles pollinate flowersthat are dull in color, buthave very strong odor

33. Birds • Birds have a good senseof color, they like yellow orredflowers… • But birds do not have a goodsense of smell, so bird-pollinatedflowers usually have little odor. • Flowers provide fluid nectar ingreater quantities than insects • Hummingbird-pollinated flowersusually have long, tubular corolla • Pollen is large and sticky

34. Mammals: bats and mice • Bats pollinate at night,so flowers are white • Mouse-pollinated flowersare usually inconspicuous,they open at night

35. Why do animals pollinate plants? • They get a REWARD: food! In exchange for moving their pollen to another flower • Nectar – a sugary solution produced in special flower glands called nectaries • Nectar concentration matches energy requirements of the pollinator: bird- and bee-pollinated flowers have different sugar conc. • Pollen – is high in protein, some bees and beetles eat it. • Flowers can produce two kinds of pollen: a normal and a sterile, but tasty, kind, for the insect.

36. Getting the pollinator’s attention • Plants advertise their pollen and nectar rewards with • Colors – bees see blue, yellow, UV; while birds see red. Bats don’t see well, so flowers are white. • Nectar or honey guides – a visual guide for pollinator to locate the reward (pansy flower) • Aromas – for insects, nectar.Can also be carrion or dung smell

37. Plant Mimicry • Some plants take advantage of the sex drive of certain insects… • Certain orchids look like female wasps, and even smell like them! • Males try to mate with them,and in the process theypollinate the plant • The orchid gets pollinated,but the male wasp only getsfrustrated!

38. SC Small flowers (few) Unscented flowers Nectaries & nectar guides absent Maturation of reproductive parts Anthers near stigma Style included All fruits mature Low pollen/ovule ratio SI or SC Large showy flowers (many) Scented flowers Nectaries & nectar guides present Differential maturation of reproductive parts Anthers far from stigma Stigma well-exserted Only some fruits mature High pollen/ovule ratio Selfers vs. Outcrossers

39. Strategies to Prevent Self-fertilization

40. Strategies to avoid self-pollination Perfect flowers have both male and female organs, so plants have strategies to avoid self-pollination: 1. Timing – male and female structures mature at different times 2. Morphological– structure ofmale and female organs preventsself-pollination (imperfect flower) 3. Biochemical – chemical on surface of pollen and stigma/stylethat prevent pollen tube germinationon the same flower (incompatible)

41. Physical Separation of Reproductive Parts Herkogamy:Pollination by the neighbor individual, population or species • Within flowers • Among flowers

42. Heterostyly A polymorphism among flowers that ensures cross-fertilization through pollination by visiting insects Flowers have anthers and styles of different length Flowers in different individuals of the same species having 2 or 3 different style lengths • With stamen lengths varying inversely • Distyly • Tristyly

43. Distyly • 2 floral morphs. • “Thrum” flower • long filaments with short styles • “Pin” flower • short filaments with long styles • Only pollinations between different floral morphs are successful. • E.g.: Primula

44. Tristyly • 3 floral morphs • Style long, stamens short and medium • Style medium, stamens short and long • Style short, stamens medium and long

45. Physical Separation of Reproductive Parts • Unisexual flowers • Staminate and carpellate flowers • Monoecy • Dioecy

46. Monoecy • Common in wind-pollinated plants. • Common in temperate regions. • Self-pollination possible but less likely.

47. Dioecy • 4% of angiosperms • Scattered throughout • Common in tropical regions and oceanic islands • Gen small fl size • 100% out-crossing, but inefficient • Often controlled by sex chromosomes • Silene

48. Polygamous Flowers • Both bisexual and unisexual flowers on the same plant. • Androdioecy = bisexual and staminate individuals in a population. • Andromonoecy = bisexual and staminate flowers on same individual. • Euphorbia, Solanum • Gynodioecy = bisexual and carpellate individuals in a population. • Sidalcea hendersonii, Silene • Gynomonoecy = bisexual and carpellate flowers on same individual. • Silene, Solidago • Polygamodioecy = some plants with bisexual and staminate flowers & some plants with bisexual and carpellate flowers in a population. • Polygamomonoecy = bisexual, staminate, and carpellate flowers on same individual.

49. Evolution of Dioecy • From hermaphroditism • Vestigial sex organs • Few families entirely dioecious • From monoecy • From SC • Within groups that have lost original GSI system • From distyly • Unequal pollen flow & gender function • Change in pollinator frequency • Non-functional anthers at low level in female flowers • Non-functional pistil in male flowers

50. Temporal Separation of Reproductive Parts (Dichogamy) • Protandry • Anthers release pollen before stigma receptive • Common in insect-pollinated plants • Geranium maculatum • 1st day flower • 2nd day flower