Biology 110

Environmental control of Growth and Development

Cascade of events (examples)

• Perception of environmental cue
• Hormonal response - production or changed sensitivity
• Tissue response

Light as an environmental signal

• Perception by pigment molecules

action spectra

blue light responses - cryptochrome

red light responses - phytochrome

• Phytochrome

two interconvertable forms - Pr and Pfr

reversability of response - e.g. seed germination

Flowering - a dramatic developmental event often cued by environmental signals

• Readiness to flower
• Photoperiod - evidence of signal

Critical day length - determination

Night (dark) controls

Phytochrome response (evidence)

• Florigen - a flowering hormone? (evidence)

Sample question from past exams:

Complete this table by filling in the empty boxes. (I'm unlikely to ask this kind of question again)

plant response	envtl. signal	perception by:	hormone 1	hormone 2
phototropism		cryptochrome		XXXXXX
seed germination	red light			abscisic acid
flower stalk bolting	photoperiod			XXXXXX
stomatal closure		root or leaves		XXXXXX
leaf abscision	drought or cold	leaves

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