Seed Development

• seed propagation is one of the most efficient and widely used propagation methods
• seedlings: plants produced from seeds
• sowing: physical beginning of seedling propagation
• seed propagation advantages:

  • quick and economical
  • only means of propagation for some plants
  • ability to make new cultivars and hybrids
  • may avoid disease transmission
  • genetic diversity
• seed propagation disadvantages:

  • plants may not be true to type
  • long juvenile period
  • may take more time and effort
• characteristics of a seed:

  • sexual reproductive unit
  • product of fertilization
  • a matured ovule containing an embryo, storage reserve tissue, and protective outer coating
• monocotyledonous plants: have a single cotyledon (grasses)
• dicotyledonous plants: have two cotyledons (bean)
• gymnosperms may have as many as 15 cotyledons
• basic embryo types:

  • basal embryos
  • peripheral embryos
  • axial embryos
  • foliate embryos
• monocots storage reserve tissue is in the endosperm
• dicots storage reserve tissue is contained in the endosperm, cotyledons, and perisperm tissue
• gymnosperms storage reserve tissue is in the endosperm
• seeds can be classified as:

  • endospermic
  • non-endospermic
  • unclassified
• endospermic: seeds with dominant endosperm as seed storage organ (most monocots and gymnosperm seeds)
• non-endospermic: seeds with dominant embryo
• unclassified: have negligible seed storage reserves
• protective seed covering may consist of seed coat, the remains of nucellus and endosperm, and sometimes parts of the fruit
• seed coat also called the testa
• sarcotesta: a living, fleshy outer seed coat
• Fruit structures can be included in the seed unit
• Specialized seed structures aid in seed dispersal
• specialized seed structures:

  • aril
  • hairs
  • elaiosome
  • wings
• sporophytic generation: plant like appearance, diploid genetic composition, produce specialized reproductive structures
• gametophytic generations: male and female gametes, haploid genetic composition
• seedless vascular plants reproduce from spores
• pollen development:

  • male gametes are formed in pollen grains
  • pollen microspore mother cells divide by meiosis
  • developing microspores are surrounded by the tapetum
  • at maturity, tetrads separate into individual pollen grains
• microsporogenesis: pollen development
• megasporogenesis: ovule development
• pollination: the transfer of male pollen to the female stigma
• gymnosperms have single fertilization, angiosperms have double fertilization
• double fertilization:

  • one generative nucleus fuses with the egg cell to form zygote
  • second generative nucleus fuses with two polar nuclei to form endosperm
• ovary grows into fruit tissue
• ovule becomes the mature seed
• embryo sac is the inner part of the seed
• polar nuclei plus a generation nucleus become the endosperm
• egg cell fuses with one generative nucleus to form embryo
• integuments form the layers of the seed coat (testa)
• stages of seed development:

  • histodifferentiation
  • cell expansion
  • maturation drying
• Stage I: histodifferentiation