Controlled by guard cells

Flaccid Little water Limp

Turgid Fill with water Bend

http://academic.kellogg.edu/herbrandsonc/bio111/animations/0021.swf

Triggered by blue light Yellow pigments located in membrane

(?)

Activates proton pump H+ out, creates electrochemical

gradient

K+ diffuses in through ion channels, Cl- follows

K+, Cl- accumulate in vacuoles, water moves in

K+ concentration in guard cells decrease during day

Sucrose increases, maintains osmotic pressure

As sucrose concentration decreases, water leaves

Pores close

Blue Light

Low CO2 concentration

Water stress

Hormones Abscisic acid

Transpiration 99% of water plants take in is lost by evaporation Open stomata

Rate of Transpiration affected by: Humidity Temperature Wind

Guttation Liquid water forced out when transpiration

negligible

Allows water to move from roots to leaves

Shedding of leaves

Conifers lose needles year-round

Deciduous trees Survive low temp of

winter Water uptake inhibited Prevents continuous

water loss by transpiration

Controlled by hormones: Ethylene

Essential organic compounds & minerals move to other parts of plant for storage

Chlorophyll breaks down, other pigments seen

Cork forms protective layer on stem side of abscission zone of petiole

Enzymes dissolve middle lamella in abscission zone of petiole

Leaf detaches in breeze