CHAPTER 13
PLANT REPRODUCTIVE BIOLOGY
REVIEW QUESTIONS
1. What is plant reproductive biology?
Plant reproductive biology is the study of the mechanisms and processes of sexual and asexual reproduction in plants.
It may encompass study of pollination mechanisms, gene flow, genetic variation, and propagule dispersal between and
within populations.
2. What is pollination?
Pollination is the transfer of pollen grains from microsporangia to the ovule or stigma, and fertilization, union of
sperm and egg.
3. What two general features have evolved in flowers that function to effect animal pollination?
Angiosperms have largely evolved very specialized floral structures that are adaptive in promoting animal pollination.
Animal pollination is much more directed and precise, necessitation the synthesis of many fewer pollen grains to effect
fertilization of the eggs within the ovules. The basic adaptive strategy is having an attractant and a reward.
4. What products serve as a reward for animal pollinators?
Nectar, pollen, sometimes waxes or resins.
5. What is a nectar guide? A landing platform?
a) Specialized color patterns, which function to attract and orient the bee to maximally effect pollination.
b) Anterior perianth part(s) (usually petals or corolla lobes), on which the bee lands to more efficiently gather nectar
or pollen and more effectively cause pollination.
6. For the following pollination mechanisms, name some floral syndromes (correlated structural modifications): (a) bee; (b)
butterfly; (c) moth; (d) wind; (e) bird; (f) bat.
a) Bees are correlated with flowers that are showy, colorful, and fragrant. These flowers often have nectar guides.
b) Butterflies are associated with showy, colorful, and fragrant flowers, usually with no nectar guides. The flowers
tend to have long, nectar-filled tubes or spurs, preventing all but an insect with a long proboscis from acquiring the
nectar.
c) Moth pollination is correlated with large, white, and fragrant flowers, with no nectar guides; as with butterfly
pollination, the flowers have long, nectar filled tubes or spurs.
d) Wind pollination is correlated with small, numerous, often unisexual flowers that tend to have a reduced,
nonshowy, or absent perianth.
e) Bird pollination tends to occur in red, large tubular flowers that secrete nectar.
f) Bat pollination is correlated with flowers that open at night and are large, white and colorful with copious
production of pollen or nectar.
7. What are the two major or extreme types of breeding systems?
Outbreeding (=outcrossing, allogamy, or xenogamy) and inbreeding.
8. What are the advantages and disadvantages of outbreeding?
The general advantage of outbreeding is to promote an increase in phenotypic variability within a population. This
generally enables plants to adapt to a wider range of environmental conditions and increases the likelihood for
survival and evolutionary change.
One disadvantage of outbreeding is that it requires a transfer of gametes between individuals. If individuals are far
apart, or if pollinators are scarce, sexual reproduction may not occur at all in obligately outbreeding species.
9. What is dichogamy? Name two specific types of dichogamy that can promote outcrossing.
Differences in timing of maturation of male and female floral parts.
10. What is hercogamy?
Spatial separation of anthers and stigmas that enhances outcrossing.
11. Define and explain: heterostyly, distyly (pin and thrum), tristyly, enantiostyly, movement hercogamy, trigger
mechanisms. What is the overall function of these floral mechanisms?
Heterostyly-the relative heights or lengths of stigmas versus anthers vary among different flowers.
Distyly-two floral morphologies occur: pin flowers, with a long style and short stamens, and thrum flowers, with a
short style and long stamens.
Enantiostyly-curvature of the style either to the left or to the right
Tristyly-a rarer condition in which you will find 3 heights of the styles and stamens
Movement hercogamy- rapid closure of the stigmas upon being touch by a potential animal pollinator.
Trigger Mechanisms-mechanism whereby an insect landing on a flower causes the sudden movement of one or more
stamens, dusting the insect with pollen at the point of contact.
These are all mechanisms for promoting outcrossing in the plant.
12. What is self-incompatibility and what is its significance in plant reproductive biology?
Self-incompatibility refers to the inability for fertilization to occur between gametes derived from an individual
genotype.
Its significance is that it promotes outcrossing.
13. What are the advantages and disadvantages of inbreeding?
A major evolutionary advantage of inbreeding is enabling reproduction to occur when there are relatively few (or
even one) individuals present in a population or at times when pollinators are rare, e.g., in ephemeral habitats.
The disadvantage of inbreeding is that it reduces variation in a population and can even result in the accumulation of
deleterious alleles, a phenomenon known as inbreeding depression.
14. What is the difference between allogamy, autogamy, geitonogamy, and allautogamy?
Allogamy-outcrossing.
Autogamy–inbreeding that may occur within a single flower
Geitonogamy–inbreeding that occurs between flowers derived from one individual.
Allautogamy-plant species that have both crossing and selfing flowers.
15. Name some types of inbreeding mechanisms.
Some plants are cleistogamous in which the perianth remains closed, such that pollen produced from within the
flower pollinates only the stigma of that flower.
Vegetative reproduction is another example. The production of genetic clones can reproduce from vegetative tissue.
16. What is agamospermy? How can it be detected?
Agamospermy is the production of seeds without fertilization. In some species, agamospermy requires pollination to
form seeds, though fertilization never occurs. Embryos are genetically identical to the parent plant.
Agamospermy can be detected by the occurrence of viable seed in the absence of males or precocious embryo
formation prior to anthesis or pollen maturation, multiple embryo and seedling formation from a single seed, the
rarity or absence of males in nature.
17. What is hybridization? Introgression?
Hybridization is the sexual reproduction between different species, specifically termed interspecific hybridization.
Introgression is hybridization between two species followed by backcrossing to one or both parents. It can be a
mechanism of promoting gene flow between two different species, ultimately increasing gene flow between two
different species.
18. Define polyploidy.
Polyploidy is a mutation in which offspring have a multiple of some ancestral set of chromosomes.
19. Cite the ways that polyploidy can occur.
Polyploidy can occur in two different ways, by the production of gametes that have one or more set of chromosomes,
and by spontaneous doubling of chromosome number in the individual plant after normal sexual reproduction.
20. How can one test the breeding mechanism in plants? (cite specific ways to test)
Flower buds can be bagged or caged to exclude pollinators. Flower buds can be emasculated in which the anthers are
removed. Florescence microscopy can be used.
21. If the following experiments are performed for plant species A–D, what can you say about the breeding mechanism based
on the pattern of seed set?
Species A is fertile, self-incompatible, and non-apomictic.
Species B is fertile, self-compatible, not self-fertile, and non-apomictic.
Species C is fertile, self-compatible, self-fertile, and non-apomictic.
Species D is apomictic (at least facultatively).