root-shoot axis - regulating amount/pattern of cell division >> 3D shape/form

• cells w/ multiple potentials restricted to meristemic regions
• apical meristems establish axis in embryogenesis
• tissue systems organized radially around axis
• food source for embryo - endosperm in angiosperms, megagametophyte in gymnosperms
• 1st division of zygote >> smaller cell becomes embryo, larger cell forms suspensor (links embryo to nutrient tissue in seed)
  • cells near suspensor >> root
  • cells at other end >> shoot
• embryo stops suspensor from developing into another embryo

tissue systems - dermal tissue, ground tissue, vascular tissue

• dermal tissue - from protoderm, outermost cells of embryo
  • divides w/ cell plate perpendicular to surface
• ground tissue - functions in food/water storage
• vascular tissue - from procambium at embryo core
  • functions in water/nutrient transport
• formation of roots/shoots controlled independently
• morphogenesis - generation of form, produces the cotyledon(s)
• seeds need enough nutrients to support sporophyte until it can photosynthesize
  • can’t bury seeds to deep

germination - radicle (1st root) extends through seed coat

• orients so that roots grow down, shoots grow up
• starts when seed absorbs water, metabolism resumes
• most seeds must stratify (spend time in cold conditions) before germinating
  • ensures that seed will not sprout right before cold season
• amyloplasts - starch-storing plastids, provides metabolic reserves for young plant
• cotyledon >> scutellum (food source used before endosperm)
• aleurone - outer layer of endosperm, signaled by gibberellic acid to produce amylase
• seed very susceptible to disease/drought between germination and young plant stage