Plant Responses/Behavior Cell division, germination, cell differentiation, flowering, fruit ripening, root growth, branching, etc
Tropisms Growth response toward (+) or away from (-) a stimulus
Phototropism Response to light Gravitropism Response to gravity Shoots (stems) + phototropism Roots – phototropism Gravitropism Response to gravity Shoots (stems) – gravitropism Roots + gravitropism Thigmotropism Response to touch
Other Responses Apical dominance Apical bud/shoot represses lateral growth Photoperiodism Plants detect & respond to periods of darkness Abscission Aging of leaves Circadian rhythms Cycles of daily behaviors Controlled by endogenous clocks Sleep movements
(varies) Need specific amt of uninterrupted darkness SHORTER than critical night length Need specific amt of uninterrupted Darkness, MORE than critical night length
So what makes plants behave the way they do? HORMONES!!!! Chemical signals produced in one part of an organisms that influence another Triggers a response at the cellular level, relies on specific hormone receptor binding Effective at extremely small concentrations Overall behavior/growth is a result of a combo of all hormones
Experimenting w/ Hormones Conclusions: Darwin-chemical in tip, light required Boysen-Jenson-signal is mobile,passed thru agar
Went Experiments: Chemical is produced in tip, Concentrates on dark side, Causes elongation of cells
The answer is….. AUXIN
Mechanism of Auxin
Stimulatory Hormones Auxins Elongation of cells in developing shoots Induces cell division in vascular cambium Promotes fruit growth Responsible for photo & gravi tropisms
Stimulatory cont…. Cytokinins Produced in actively dividing tissues(germinating seeds, fruits, roots) Delay senescence Controls differentiation (w/ auxin)
More stimulation… Gibberellins Produced in roots, stimulate stem & leaf growth Promote fruit development (W/ auxin) Stimulate germination (if environmental conditions are right)
Inhibitory Hormones Abscisic acid Prepares for dormancy by inhibiting vascular cambium & slowing bud growth Keeps seeds dormant Produced during water stress (causes guard cells to lose water, closing stomata)
Inhibitory continued… Ethylene Only gaseous hormone Inhibits cell growth & elongation in all plant organs Causes senescence Fruit ripening-degrades cell walls, reduces chlorophyll Leaf abscission-degrades cell wall between stem & petiole
Even more plant behaviors (and you thought they were boring!) O2 deprivation Release of ethylene from roots, holes form High salt Produce extra solutes Heat Heat shock proteins bind to enzymes & prevent denaturing Cold Synthesize more unsaturated FAs Herbivores Pathogens Anti-microbial compounds, alarm chemicals, PR genes