plant hormones 2

cytokinins

• stimulate cell division

• occur in most plants including mosses, ferns, conifers, algae, and diatoms

chemistry of cytokinins

• adenine derivatives

• occurs as: a free nitrogenous base, a nucleoside, a nucleotide, or glycoside

• ~40 different structures

synthesis of cytokinins

• primarily in the meristematic region of the roots

• also produced in developing embryos and crown gall tissues

how are cytokinin’s transported?

via xylem

cytokinin’s affect crown gall

• a tumor-like mass of undifferentiated cells that typically occurs near the crown (junction of root and stem) of the plant

• caused by the bacterium Agrobacterium tumefaciens

actions of cytokinin’s

• affect crown gall

• regulate the cell cycle/ cell division

• delay senescence

• greening

• lateral bud development

• cell expansion

abscisic acid chemistry

• is a single structure, not a family of related structures like auxin, gibberellins, and cytokinin’s

• is a sesquiterpene - C15- made from 3 isoprene units

• found in all green plants, also some mosses, algae, and fungi

where is abscisic acid made?

• plastids

• most tissues, especially leaves and seeds

• its synthesis involves the terpene pathway

transportation of abscisic acid

• xylem and phloem

• also parenchyma cells

actions of abscisic acid

• growth/ elongation inhibitor

• maintains or “seals” bud and seed dormancy

• prevents vivipary

  • seeds germinating inside the fruit

• stimulates stomatal closure under water stress

ethylene

• made by most plants including angiosperms, gymnosperms, ferns, mosses, liverwarts

• made by all parts of the plant

• production is stimulated by physiological stresses including:

  • wounding

  • anaerobic conditions

  • flooding

  • chilling

  • disease

  • drought

action of ethylene

triggers fruit ripening

climacteric fruits

continue ripening after being picked

• apple

• avocado

• banana

• cantaloupe

• mango

• peach

• pear

• tomato

nonclimacteric fruits

• bell pepper

• cherry

• citrus

• grape

• pineapple

• strawberry

• watermelon