Plant Reproduction and Development

Plant Reproduction and Development

• Plant success is due to biological adaptations that allow them to thrive in many habitats

Reproduction and Development

• It allows plants to colonize environments with diverse conditions.
• Plants evolved reproductive structures to increase successful fertilization and development.

Plant Characteristics

• Multicellular organisms
• Cellulosic cell wall
• Have life cycle with alternation of generations
• Have photosynthetic capacity
• Have plastids in cytoplasm

Major Plant Groups

• Land plants are split into vascular and non-vascular plants
• Non-vascular plants include hornworts, liverworts and mosses and are spore-bearing
• Vascular plants have lignin
• Vascular plants include Pteridophytes which are spore-bearing
• Vascular plants include gymnosperms, which are cone-bearing, and angiosperms which are flowering

Alternation of Generations

• A common life cycle pattern for green plants
• Involves alternation of haploid and diploid phases
• The diploid stage is the sporophyte; the haploid stage is the gametophyte
• Meiosis forms haploid spores
• Mitosis forms haploid gametes
• Fertilization restores the diploid chromosome number

Floral Anatomy

• The pistil consists of the stigma, style, and ovary
• Stigma structure receives pollen grains during pollination
• The style is the stalk of the stigma that leads to the ovary, containing a pollen tube
• The ovary is the female structure that houses the female gametes
• Ovules are small structures within the ovary containing an egg nucleus
• The stamen describes the male portion of the flower
• The stamen has anthers and filaments
• Anthers produce & store pollen grains
• The filament is the stalk of the anther
• Petals are the colorful, leaf-like structures that attract pollinators
• Sepals are green leaf-like structures that protect the structures in a flower bud
• The receptacle is the thickened portion below the ovary where the floral structures grow
• The stalk of the flower supporting all parts is the pedicel

Angiosperm Life Cycle

• Seedlings continuously grow and develop, becoming mature adults
• Embryos undergo development and differentiation to become seedlings
• The seeds inside a fruit contain the developing embryos and are the first sporophyte stage
• Sexually mature adults produce gametophytes in pollen and ovules
• Fusion of the gametes occurs during pollination
• The ovary develops into a fruit and the ovules become seeds after fertilization

Gymnosperm Life Cycle

• Gametophytes are produced in male and female cones, following sexual maturity
• Pollen from the male cones pollinates the ovules in female cones.
• Fertilization transforms ovules into seeds.
• Embryos develop into seedlings, which then turn into mature sporophytes.

Fern Life Cycle

• Fertile ferns produce spores through division by meiosis
• Spores from the sporangium develop into gametophytes
• Mature gametophytes produce eggs and sperm
• Fertilization forms a diploid zygote, which develops into a young sporophyte
• The young sporophyte then matures into adult ferns

Comparison of Reproductive Structures and Processes

Angiosperm Reproduction

• Asexual reproduction requires a single parent; offspring are genetically identical and there is no fusion of gametes
• Sexual reproduction requires sperm & egg cell fusion through fertilization, involving self or cross-pollination, to enhance genetic diversity

Asexual Reproduction: Apomixis

• Apomixis, a genetic feature of some dandelions, allows the production of embryos from unfertilized eggs in ovules, resulting in viable seeds without pollination

Asexual Reproduction: Vegetative Propagation

• Vegetative propagation allows plant parts to produce buds that can develop into new individuals
• Strawberries perform vegetative propagation through buds that emerge from stolons

Sexual Reproduction: Pollen Grains

• Angiosperm pollen grains contain the male gametophytes
• Each pollen grain has two sperm nuclei from a generative nucleus
• The tube nucleus transports the sperm during pollination

Sexual Reproduction: Ovules

• Each ovule or embryo sac in the ovary of the flower contains eight nuclei
• The primary sex cell is the egg nucleus or egg cell
• Only the polar nuclei and egg nucleus produce descendant in seeds

Sexual Reproduction: Double Fertilization

• Pollen grains land on the stigma
• The pollen tube moves toward two sperm nuclei
• Sperm nuclei fertilize the egg nucleus and the polar nuclei
• Double fertilization produces a diploid embryo and a triploid endosperm

Plant Development

• The shoot apical meristem allows the continuous upward growth of the plant
• The cambium allows further growth of stems and roots by increasing their thickness
• The root apical meristem allows the continuous downward growth of roots

Plant Development: Embryogenesis

• Floral tissues are transformed into fruit
• e.g. The ovary develops into fruit and ovules develop into seeds

Plant Development: Organogenesis

• During germination, the seed coat is ruptured by water
• The radicle emerges from the seed and turns into the root
• The hypocotyl emerges from the seed and turns into the stem
• Cotyledons become embryonic leaves
• The epicotyl from the plumule turns into mature leaves