Plant Hormones and the Endocrine SystemChapters 39 and 45 (in brief)Campbell • Reece

Cell Communication in Plants

Response2 main types of responses:

Increased or decreased transcription of mRNA to make enzymes

Activation of existing enzymes

Plant Hormones AKA Plant Growth Regulator Almost all aspects of plant growth and

development are under hormonal control to some degree

A single hormone may regulate many different processes

Multiple hormones may influence a single process

Response depends mostly on the amount of a hormone compared with other hormones

Plant TropismsGrowth response toward or

away from stimuliPhototropism – response to

lightGravitropism – response to

gravityThigmotropism – response

to touch

Hormones in Animals A molecule that is secreted into the

extracellular fluid, circulates in the blood or hemolymph, and communicates regulatory messages throughout the body

Hormones elicit a specific response from its target cells, but cells lacking the receptor for that hormone are unaffected

Endocrine system – regulates reproduction, development, energy metabolism, growth, and behavior

Types of Signaling Molecules Hormones – secreted by endocrine cells

or glands Travel via blood or hemolymph throughout

body Local regulators – reach target cells

solely by diffusion Paracrine signaling – target cells lie near

secreting cell Autocrine signaling – target cell is itself

Types of Signaling Molecules Neurotransmitters – cross synapses Neurohormones – specialized neurons

secrete molecules into the bloodstream to reach target cells

Pheromones – chemicals that are released into the external environment

Chemical Classes of Hormones

Cellular Response Pathways Water-soluble hormones travel freely

through the bloodstream, bind to cell-surface signal receptors Change molecules in the cytoplasm OR

regulate gene transcription Lipid-soluble hormones travel in the

bloodstream bound to transport proteins, diffuse across the membrane, bind to an intracellular signal receptor Regulates gene transcription

Multiple Effects of Hormones Many hormones

create more than one type of response in the body

The type of response depends on the molecules that receive or produce the response

Negative Feedback

Positive Feedback