Plant Reproductive Biology

• Plant Reproductive Biology


  The study of the mechanisms and processes of sexual and asexual reproduction in plants. It may encompass the study of pollination mechanisms, gene flow, genetic variation, and propagule dispersal between and within populations.
• Types of Plant Reproduction

  • Sexual Reproduction
  • Asexual Reproduction
• In non-seed plants, sexual reproduction entails the release of motile sperm from a free-living gametophyte into the outside environment. Completion of this phase of the life cycle is dependent on survivorship of the gametophytes, on the effective development and operation of antheridia and archegonia, and on the proper external conditions.
• In seed plants, separate male and female gametophytes are produced within male and female spores. Sperm cells are ultimately released (into or just outside of the female gametophyte of the ovule), where one sperm cell fuses with the egg, initiating development of an embryo within the seed. Seeds are then transported by a variety of mechanisms to a new environment.
• In gymnosperms, pollen grains are mostly transported by wind. Because transport by wind is indirect, it necessitates the production of relatively large numbers of pollen grains to overcome the very low probability that any given pollen grain will make it to the ovule.
• Flowering Plant Parts


  • Perianth (corolla and/or calyx)
  • Stamens
  • Staminodes
  • Corona
  • Gynoecium
• Visual Attractant


  Showy perianth (corolla and/or calyx) that may be brightly colored or otherwise contrasting with the external environment, e.g., a white perianth at night. Other floral parts, such as stamens, staminodes, corona, or even the gynoecium, may replace or augment the perianth as a visual attractant.
• Olfactory Attractant


  Volatile compounds emitted by flowers, usually from the surface of the perianth. Most odiferous flowers have a sweetish smell, but some smell like rotting flesh or feces.
• Floral Reward


  Nectar, a fluid primarily rich in sugars, secreted from specialized regions or organs of the flower called nectaries.
• Nectaries are specialized tissues or organs that may be located within the gynoecium, on the perianth, or at the base of and often surrounding the gynoecium or androecium.
• Some nectaries are "extra-floral," produced outside the flower, and function as a reward not for pollination but for protection of the plant, most commonly in plant interactions with ants (myrmecophily).
• In certain water lilies and orchids, the nectar may actually function to trap or even drown the insect to promote pollination. Flowers of some species emit compounds that mimic the smell of rotting flesh or feces, attracting flies. The flies enter sometimes complex floral structures, perceiving the tissue as real rotting flesh, and in the process effecting pollination.
• Insect Pollination (Entomophily)


  The most common type of pollination in angiosperms. Bee pollination (Melittophily or Hymenopterophily) is correlated with flowers that tend to be showy, colorful, and fragrant, often with specialized color patterns called nectar guides.
• Beetle Pollination (Cantharophily)


  Often thought to have been the ancestral type in the angiosperms, correlated with open flowers, the sexual organs exposed, often with a fruity or foul odor. Some beetle pollinated flowers (and cycad cones) produce heat internally, presumed to function in more effectively dispersing odor-generating compounds.
• Butterfly Pollination (Psychophily)


  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.
• Moth Pollination (Phalaenophily)


  Correlated with night-blooming large, white, and fragrant flowers, with no nectar guides; as with butterfly pollination, the flowers often have long, nectar-filled tubes or spurs.
• Fly Pollination (Sapromyiophily)


  Correlated with flowers that are often maroon or brown in color and emit a fetid odor that simulates the smell of rotting flesh, these visual and olfactory attractants effecting deceptive pollination.
• Bat Pollination (Cheiropterophily)


  Correlated with flowers that open at night (have a nocturnal anthesis), and are large, white or colorful, with copious production of pollen or nectar (often secreted into a hypanthium or perianth tube), either or both of which may serve as a reward.
• Bird Pollination (Ornithophily)


  Tends to be correlated with red, relatively large, and often tubular flowers that secrete copious nectar as a reward.
• Wind Pollination (Anemophily)


  Correlated with small, numerous, often unisexual flowers that tend to have a reduced, nonshowy, or absent perianth. Pollen is produced in large quantities and pollen grains tend to have a smooth wall sculpturing. Styles tend to be highly branched as a more efficient means of catching pollen grains in air currents.
• Water Pollination (Hydrophily)


  May occur in aquatic plants with flowers either at or under the water surface. Some sea grasses have very elongate, filiform pollen grains, making them considerably more efficient in being captured by the styles and stigmas of female flowers in ocean currents.
• Breeding Systems


  • Outbreeding (Outcrossing, Allogamy, Xenogamy)
  • Inbreeding
• Outbreeding (Outcrossing, Allogamy, Xenogamy)

  The transfer of gametes from one individual to another, genetically different individual. The general advantage is to promote an increase in phenotypic variability within a population.
• Dioecy


  Individual plants have either male (staminate) or female (pistillate) flowers, ensuring that outbreeding will always occur.
• Gynodioecy


  Some individuals with pistillate flowers only, others with perfect flowers.
• Androdioecy


  Some individuals with staminate flowers only, others with perfect flowers.
• Trioecy


  Some individuals with staminate flowers only, some with pistillate flowers only, and some with perfect flowers.
• Dichogamy


  Differences in timing of maturation of male and female floral parts, promoting outcrossing.
• Protandry


  The precocious development of the androecium, where the pollen matures and is released prior to the maturation and receptivity of the gynoecium.
• Protogyny


  The precocious development of the gynoecium, where the gynoecium matures and becomes receptive prior to the maturation and release of pollen.
• Hercogamy


  Evolutionary changes in floral structure, particularly the spatial separation of anthers and stigmas, promoting outcrossing.
• Heterostyly


  The relative lengths or heights 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.
• Tristyly


  Three heights of styles and stamens, the principle for cross-pollination is the same as in distyly.
• Enantiostyly (Enantiomorphy)


  The curvature of the style to either the left or the right (as seen in face-view), defining "left-styled" and "right-styled" flowers.
• Movement Hercogamy


  Rapid closure of the stigmas upon being touched by a potential animal pollinator, or trigger mechanisms where an insect pollinator triggers the sudden movement of one or more stamens, dusting the insect with pollen.
• Insect visiting left-styled flower

  • Pollen deposited on the right side of its body
• Movement hercogamy


  1. Rapid closure of stigmas upon being touched by a potential animal pollinator

  2. Physically prevents pollen from the same flower being transferred to the stigmatic region, effectively preventing intra-floral self-pollination

  3. May function to clear the stigma from the path of a potential pollinator
• Plants with movement hercogamy

  • Diplacus (Phyrmaceae)
  • Stylidium (Stylidiaceae)
• Trigger mechanism hercogamy


  1. Insect pollinator triggers the sudden movement of one or more stamens

  2. Dusts the insect with pollen at the point of contact

  3. Pollen is then at a location to be effectively transmitted to the stigma of another flower