process of flower formation

plant metamorphosis - environment controls how the plant changes phase change - internal development >> competence, ability to reproduce reproductive structures added on to existing structures distinct juvenile, adult phases easier to revert adult into juvenile than to induce phase change flower production pathways - 3 regulated pathways to flowering light-dependent (photoperiodic) pathway - length of day (amount of daily sunlight) affects flowering daylight shorter than critical length (12 hours) >> flowering in short-day plants (blooms in late summer/fall) daylight longer than critical length >> flowering in long-day plants (crop plants, blooms in spring/summer) day-neutral plants - flower when mature, regardless of day length 2 critical photoperiods >> will not flower if day too long/short facultative-long-or-short-day-plants - flower speed depends on day length cryptochrome/phytochrome detect photoperiods repress gene that represses flowering >> flowering takes place temperature-dependent pathway - cold temperatures >> faster flowering vernalization - shoots/seeds chill >> reproduce gibberellin hormones controls flowering, expression of certain genes.zzz

parts of the flower - no direct contact between pollen, ovule

• pollinators - animals that transfer pollen between plants
• complete flower - has all 4 whorls (calyx, corolla, androecium, gynoecium)
• perfect flower - has stamen/carpel (androecium/gynoecium)
• calyx - outermost whorl
  • contains the sepals (protects the flower in the bud)
• corolla - collective name for the petals
  • used to attract pollinators
• androecium - stamens in a flower
  • microsporangia on anthers
  • held up by filaments
• gynoecium - female flower parts
  • contains single/fused carpel
  • ovules - produced in the ovary, become seeds
  • stigma - receives pollen at top of carpel
  • style - connects stigma to ovary
  • floral specialization - floral parts either fused or reduced/lost
    • more advanced angiosperm >> less parts in each whorl
    • modifications sometimes due to pollination techniques (wind replaces animals)
    • artificial selection >> flowers less able to adapt
      • corn (maize) wouldn’t be able to survive as easily w/o human aid
    • floral symmetry - different between primitive/advanced flowers
      • primitive >> radial symmetry
      • advanced >> bilateral symmetry
    formation of angiosperm gametes - gametophytes completely enclosed by sporophyte
    • male gametophytes = microgametophytes, pollen grains
      • forms in 2 pllen sacs in anther
      • microspore mother cells - found in specialized chambers of sac
      • microspore mother undergoes meiosis >> haploid microspores >> 4 pollen grains after mitosis

 female gametophytes = megagametophytes, embryo sac forms in ovules megaspore mother cells - found in each ovule megaspore mother cell undergoes meiosis >> haploid megaspores, only 1 survive >> 8 haploid nuclei after mitosis 1 nucleus >> egg, rest arranged in precise locations (2 polar nuclei in middle of sac, 2 in synergids flanking egg, 3 in antipodal cells)