Chapter 39- The Response in Plants to Internal and External Stimuli

Background The goal of all plants in a response is to enhance survival and reproductive success Signal Transduction Pathways- Reception of stimulus and then a response

Background Example- Potatoes - Etiolation- Potato is left in the dark. All resources are being used by the potato to lengthen the stem, and there is no energy being used to produce leaves. - De-etiolation- Plant exposed to light. Resources are shifted into the production of leaves.

Signal Transduction Pathways How it works 1. Reception of Stimulus - Signals detected by receptors, which are often proteins embedded in the membrane

Signal Transduction Pathways - Receptors produce secondary messenger chemicals which amplify the signal inside of the plant

Signal Transduction Pathways 3. Response - Signal is received somewhere inside of the plant, and usually increases an enzymatic activity (might be the transcription of new mRNA or the activation of proteins already present)

Plant Hormones - Chemical signals - Produced in one part of the plant and then is spread throughout the entire plant - Only needed in small quantities in order to work - Interact with each other to either inhibit or to promote the hormones effect

Plant Hormones - Discovered by looking at tropisms (a reaction to a stimulus) - The Darwin family discovered phototropism- a plant will grow towards light, and it is controlled strictly by hormones in the plant

Effects of Light on Plants - Photomorphogenesis- A plant changing because of light. Two important spectrums of light: - Blue- Absorbed by blue light photoreceptors - Red- Absorbed by phytochromes - Circadian Rhythms- Changes based on a 24 hour day, but not influenced by external stimuli - Biological Clock- Can be desynchronized (ie- “jet lag”) - Controlled by light - Photoperiodism- Length of daylight and/or darkness affects the flowering of most plants

Effects of Gravity on Plants - Gravitropism - Positive gravitropism- growth with gravity (roots) - Negative gravitropism- growth away from gravity (the shoots) - Controlled by statoliths- specialized plastids inside of each cell that tells position of the cell

Effects of Mechanical Stimuli on Plants - Thigmomorphisms- Reacting to being disturbed (wind, touch…) - Thigmotropism- Attraction to mechanical supports (many vines)