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)
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