This document provides an overview of how plants respond to internal and external signals in their environment. It discusses how plants use receptors to detect stimuli like light, gravity, temperature, moisture levels and pathogens. It then describes the roles of various plant hormones like auxin, cytokinins, gibberellins, abscisic acid and ethylene in mediating responses to these stimuli, such as phototropism, drought tolerance and leaf abscission. The document also covers biological clocks, photoperiodism, and defense responses against herbivores and pathogens.
13. Fig. 39-5b
RESULTS
Light
Tip
removed
Darwin and Darwin: phototropic response
only when tip is illuminated
Tip covered
by opaque
cap
Tip
covered
by trans-
parent
cap
Site of
curvature
covered by
opaque
shield
50. Fig. 39-28
Recruitment of
parasitoid wasps
that lay their eggs
within caterpillars
Synthesis and
release of
volatile attractants
Chemical
in saliva
Wounding
Signal transduction
pathway
1 1
2
3
4
A maize leaf “recruiting”
a parasitoid wasp as a
defensive response to
an armyworm
caterpillar, an herbivore