Plant Reproduction Concepts

• Plant reproduction can be sexual or asexual.
• Following pollination, fertilization leads to embryo formation.
• The life cycle of a plant includes germination, growing, flowering, pollination, fertilization, and seed dispersal.
• Plants can reproduce asexually through vegetative growth, using a portion of the mature sporophyte.
• Asexual reproduction results in genetically identical progeny, advantageous for plants with superior qualities, such as varietal grapes.
• Asexual reproduction has the disadvantage of lacking genetic variability.

Sexual Reproduction

• This involves the production of sex gametes, their fusion, and embryo development.

Flower Structure

• The nonfertile parts are the sepals and receptacle.
• Fertile parts are the male stamens and female carpel (ovary).
• Perfect flowers have both male and female parts.
• Imperfect flowers are either male or female; the same plant may have both, or sexes may be on separate plants.

Pollination

• This leads to the creation of a pollen tube, sperm discharge, and egg fertilization, resulting in the embryo.
• In angiosperms, pollination involves transferring pollen from an anther to a stigma.
• Pollinators, or agents, move pollen grains from the anther to the carpel's stigma.
• Flower traits attracting different pollinators are known as pollination syndromes.
• Pollination can occur by wind, water, insect, or animal.

Biotic pollination

• pollination by animals(organisms)
• Approximately 80% of pollination is biotic.
• Entomophily refers to pollination by insects, such as bees, wasps, ants, beetles, moths, and butterflies.
• Zoophily refers to pollination by animals like birds and bats.

Abiotic pollination

• pollination by non-animal factors

• Anemophily is pollination by wind, 98% of abiotic pollination.

• Hydrophily is pollination by water and aquatic plants.

• Pollination in agriculture aims to protect and enhance present pollinators.

• Pollination requires an agent that moves the pollen (pollinator) and the plant that provides the pollen (pollenizer).

• Some plants pollinate themselves; others have chemical or physical barriers requiring cross-pollination.

• Pollination can occur through cross-pollination or self-pollination.

• Monoecious plants have mechanisms preventing self-fertilization.

• Recognition factors prevent self-fertilization, similar to an immune system, rejecting "self" proteins in pollen, ensuring genetic variability.

• Self-incompatibility gives a plant the ability to reject its pollen and that of closely related plants.

• Some plants avoid self-fertilization by developing stamens and pistils at different times or arranging reproductive parts to prevent accidental pollen transfer.

• Pin flowers have long styles and short stamens.

• Thrum flowers have short styles and long stamens.

• Dioecious plants cannot self-fertilize because they possess only one type of reproductive structure individually.

• Cross-pollination occurs between a pollinator and an external pollenizer, also called syngamy, where pollen is delivered to another plant's flower.

• Self-pollination involves pollen moving to the female part of the same flower or another flower on the same plant, also called autogamy.

• Self-pollination is limited to plants accomplishing pollination without an external pollinator.

• Some stamens grow in contact with the pistil, while adapted plants have stamens and carpels at the same length.

• Cleistogamy is autogamy pollination occurring inside the flower before it opens, where the flower is called a cleistogamous flower.

• Self-pollinating crop plants include peas, soybeans, sunflowers, and tomatoes.

• Farmers may remove anthers or use sterile male plants to prevent self-fertilization.

• Peach varieties are autogamous but not truly self-pollinated because insects transfer pollen to another flower on the same plant.

• Hybridization is effective pollination between flowers of different species or genera, e.g., orchids.

• Farmers may combine genes with other plants to improve crops.

Fertilization

• This follows successful pollination, leading to a pollen tube, sperm discharge, and fertilization, forming the embryo.

• Male microgametophytes and female megagametophytes also mature.

• The anther has pollen sacs (microsporangia) where diploid microspore mother cells undergo meiosis to generate four haploid microspores.

• Each microspore can develop into the male gametophyte.

• Each microspore undergoes mitosis and cytokinesis.

• Two separate cells are generated under the same envelope: a generative cell and a tube cell; combined, these spore wall = pollen grain.

• The spore wall is unique to the species of plant that creates it.

• An ovary contains multiple ovules.

• Each ovule houses has megasporangium tissue containing a diploid megaspore mother cell that undergoes meiosis to generate four haploid megaspores.

• Only one megaspore survives in most angiosperms.

• Its nucleus divides three times without cytokinesis.

• One large cell with eight haploid nuclei is generated.

• Membranes then form and divide these nuclei to create the female gametophyte or embryo sac.

• Antipodal nuclei, called antipodal cells are at one end of the sac, with unknown function.

• Two polar nuclei share the cytoplasm of the large embryo sac cell.

• Two synergids are at the other end and attract the pollen tube to the egg.

• There is one egg

• Pollen grain absorbs moisture and begins germination after landing on a stigma.

• The pollen tube extends down between the style and the ovary and the ovules.

• The generative nucleus undergoes mitosis into two sperm, with a tube nucleus extending the pollen tube.

• The tip of the tube proceeds to the ovule and releases two sperm through a micropyle (a gap).

• One sperm fertilizes the egg, producing the zygote which divides into the embryo.

• The other sperm unites with the two polar nuclei to form a triploid nucleus, which gives rise to endosperm.

Seed and Fruit Development

• The ovule develops into the seed with the embryo, endosperm, and integuments after double fertilization.
• The first mitotic division of the zygote is asymmetric, providing environmental differences and establishing the root-shoot axis.
• The ovule integuments become the seed coat.
• The ovary tissues (syn.carpel) and sometimes the receptacle become the fruit.
• Fruits may be dry or fleshy to aid seed dispersal.
• There are many kinds of fruits, from the simple to the aggregate and multiple.
• The ovary wall becomes either a dry or fleshy fruit.
• Many dry fruits are wind or animal dispersed.
• Many fleshy fruits are animal dispersed.
• Some fruits disperse seeds explosively or make seeds buoyant for water dispersal.
• Gymnosperms depend on wind to move pollen from male to female cones.
• The ovule exudes sap to trap pollen.
• Insects fed on protein-rich pollen of male cones and sugar-rich secretions of female cones around 150 mya.
• This led to the origin of Angiosperms and animal-mediated pollination.
• Angiosperms have partnered with animals to move their pollen.
• Flowers provide nurseries or food (nectar or pollen) to their pollinators.
• Nectar is usually presented with attractive structures, like showy petals and fragrances.
• Petals capitalize on pollinators' sensory mechanisms to have ultraviolet patterns.
• Some flowers, like the Bee Orchid, trick their pollinators.

Seed Dormancy

• Most seeds become dormant as they mature, not germinating in unfavourable conditions.
• Certain conditions, species-specific, include drying to avoid in-fruit germination, cold may prevent out-of-season germination, and seed coat disruption via acids or soaking.

Asexual Reproduction

• Natural vegetative propagation is when new plants grow parts of a parent plant such as stems, roots and leaves.
• Modified stems, roots and leaves can all contribute to the method of asexual plant reproduction:
  • Modified stem: bulb, tuber, corm, rhizome and stolons
  • Roots
  • Leaves

Modified Stems

• These contribute to natural, vegetative propagation.
• A bulb has short stem bases with one or more buds enclosed in fleshy leaves.
  • Example: onion, lily, hyacinth, and tulip
• A Corm has a thick stem base with scaly leaves and stored foot.
  • Example: Gladiola and Begonia
• A tuber is an enlarged stem because of food storage.
  • Example: Potato
• Rhizomes are underground stems that grows horizontally near the soil surface.
  • Example: Ginger and birds of paradise
• Stolons are stems that grow horizontally above the ground. When touching the ground, the roots and leaves will develop and grow a new plant.
  • Example: Strawberry and Bermuda

Roots can also result in new plant growth

• Turnip, carrot, radish and sweet potato are examples of plants that have storage shoots.
• Storage roots can grow into new plants, when planted.

Leaves can lead to new plant growth

• Katakataka has leaves that produce new plants from the parent plant.
• Begonia also produce new plants from their leaves when they touch soil.

Artificial vegetative propagation

• Methods of developing plants by people.
• These people produce the plants for food or decoration.
• Methods includes: cutting, grafting, layering, budding, marcotting and cloning.
• Method improves the quality of plants.
• A cutting will have new roots, stems or both. The cutting becomes a new plant.
• Layering is when a portion of the stem is encouraged to grow roots when it is still attached the parent plant, before being removed and planted.
• In grafting, the branch or stem cut from one plant is carefully joined to another. The food and water stem shares the food and water from the stem of the mother plant.
• Grafting improves the quality of plants, provide a strong plant stalk and repair a damaged trunk.
• In budding, a bud is chosen and cut from one plant before attaching it to another.
• The used bud is attached to the mother plant. When the bud gets large enough, it will become part of the plant.
• Marcotting involves a healthy, mature plant where the bark of the plant' stem needs to be removed.
• Soil must be put around the stem and wrapped. Roots will grow out of the stem.
• Cloning occurs when a new plant is produced using.
• When cloning starts with a group of cells from the mother plant, a lot of copies can be produced quickly.