plant chemical regulation - plant hormones have multiple functions, unlike that of animals 

• auxin - made in apical meristem
  • if lacking, plant will no longer grow towards light
  • promotes stem, vascular tissue, root growth
  • suppresses lateral bud growth, leaf abscission
  • “agent orange” - derived from auxin to speed up growth, make trees age faster
• cytokinins - stimulates cell division, differentiation
  • promotes lateral growth
• gibberellins - synthesized from leaves
  • apical growth, stimulates protein synthesis
• ethylene - gaseous
  • drops damaged leaves when in contact w/ toxin
  • ripens fruit
• abscissic acid - controls stomata opening
  • stimulates winter dormancy

tropisms - positive/negative growth toward external stimuli 

• photoperiodism - response to light
  • lets plant know what time of year it is
  • bright red light >> Pr converts to Pfr phytochrome>> inhibits flower growth
  • far red light (longer wavelength) >> Pfr converts to Pr phytochrome>> no more flower inhibition
• gravitropism (geotropism) - response to gravity
• thigmotropism - vines curling around objects
• etoliated plant - grown in the dark
  • loses chlorophyll >> becomes white
  • acts as fiber optics >> grows longer

parts of early plant - 

• coleoptile - in grass, 1st leaf sheath
• epicotyl - apical end of embryo
• hypocotyl - between radicle and leaves
• mesocotyl - embryonic stem axis

dicot germination - hypocotyl emerges in an arch 

• 2 cotyledons protect plumule (embryonic leaves) as it emerges
• light >> hypocotyl arch straightens out
• cotyledons start photosynthesis, later drop off

monocot germination - has sharp primary leaf  

• coleoptile acts as needle to penetrate ground