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
• autonomous pathway - controlled by basic nutrition
  • 1st pathway to evolve
  • used by day-neutral plants
  • certain shoots determined/committed to flower >> nodes starts the flower
  • inhibitory signals sent from roots
• ABC model - shows how 3 genes specify floral organs
  • sepals - class A genes
  • petals - class A/B genes
  • stamens - class B/C genes
  • carpels - class C genes
• formation of gametes - floral parts (modified leaves) transition to meiosis >> gamete-producing gametophytes created

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)