Test 3 Book NotesChapter 39: Plant Responses to Internal & External Signals[pg. 821-834 : October 1, 3]Stimuli and Stationary Life (Plants)- Linnaeus noticed flowers opened and closed at specific times of day, creating a “floral clock” also known as a horologium florae. - Plants vs. Animals- Animals are mobile so can move away or toward (+/-) stimuli. - Plants are stationary, so must alter their growth and development according to internal and external cues in their environment. - Therefore, the same species of plants tend to vary much more than the same species of animals.- On a molecular level, both plants and animals use a complex system to respond to changes in the environment.39.1: Signal Transduction Pathways Link Signal Reception to Response- Plants must be able to adapt to changes in their environment ---> increases their ability to survive and reproduce successfully.- E.g. Potato plants grow underground in darkness- Etiolation are the morphological changes occurring in these plants that allow for them to grow in darkness. Most of energy is put towards elongating its shoots instead of growing leaves for photosynthesis since their is no light.- De-etiolation is the process that begins to occur when a shoot reaches light, and the plant undergoes changes making it more like a typical plant.- This is an example of a signal (light) ---> response (greening).- A. Reception- Signals accepted by receptors: proteins that change shape according to certain stimuli. - De-etiolation uses protein phytochrome (functions in light detection), which is a cytoplasmic protein. - Most proteins are in the membrane.- B. Transduction- Some signals transduced are very weak, using second messengers (small ions or molecules in the cell that amplify the signal and transfer it from the receptor to proteins that carry out the response). - Two types used in de-etiolation: Both must be produced for complete de-etiolation response.- Ca2+: changes in this concentration is involved in phytochrome signal transduction. It is generally low at 10^-7M, but phytochrome activation causes Ca2+ channels to open (a 100-fold increase in cytosolic Ca2+ concentration).- cGMP (cyclic GMP) after light is detected by phytochrome, it activates cGMP.BIOL1108: Test 3 Book Notes! Fall 2012- Max Boston- C. Response- Second messengers can regulate one or more cellular activities. - Two main mechanisms a signaling pathway can enhance an enzymatic step:- 1. Post-translational modification: activates pre-existing enzymes.- Proteins modified by phosphorylation of specific amino acids, which alters the hyrophobicity/activity of protein kinases (protein kinase cascades) directly.- Results in stimuli being linked to responses involving gene expression (via phosphorylation of transcription factors). - Can regulate synthesis of new proteins by turning specific genes on/off.- Protein phosphatases are the “off-switch”.- 2. Transcriptional regulation: increases or decreases the synthesis of mRNA encoding a specific enzyme.- Specific transcription factors are activated (by phosphorylation via kinases) and bind to specific portions of DNA controlling the transcription of certain genes.- Activators increase transcription, while repressors decrease it.- De-Etiolation (“Greening”) Proteins- Enzymes that function in photosynthesis or involved in producing chemical precursors for making chlorophyll are either activated by phosphorylation or newly transcribed during De-Etiolation. Concept Check 39.11. What are the morphological differences between dark- and light-grown plants? Explain how etiolation helps a seedling compete successfully.! Dark-grown seedlings are etiolated: They have long stems, underdeveloped root systems, and unexpanded leaves, and their shoots lack ! chlorophyll. Etiolated growth is beneficial to seeds sprouting under the dark conditions they would encounter underground. By devoting more ! energy to stem elongation and less to leaf expansion and root growth, a plant increases the likelihood that the shoot will reach the sunlight ! before its stored foods run out.2. Cycloheximide is a drug that inhibits protein synthesis. Predict what effect cycloheximide would have on de-etiolation.! Cycloheximide should inhibit de-etiolation by preventing the synthesis of new proteins necessary for de-etiolation.39.2: Plant hormones help coordinate growth, development, and responses to stimuli- Hormones is a signaling molecule produced in tiny amounts (not always in plants like so in animals) by one part of organismʼs body and transported to other parts.- Bind to a specific receptor ---> causes response in target area(s).BIOL1108: Test 3 Book Notes! Fall 2012- Max Boston- Also called “plant growth regulator” in plants because there are key differences from animal hormones, but still greatly regulate functioning of plants. - Plants do not have circulatory blood systems (like animals)- Plant hormones sometimes act only locally.- Some plant hormones (e.g. sucrose) exist in much higher quantities than normal.- All functions of plants are under hormonal control to some extent.- One hormone can regulate many different processes.- Multiple hormones can regulate one process. - The discovery of plant hormones- Any response resulting in curvature of organs toward or away from a stimulus is called a tropism. - Tropisms are often caused by hormones.- The growth of a shoot away from or towards light = phototropism- Series of experiments on how stems responded to light carried out by:- 1. Darwin and his son in the late 1800s. - They observed that grass seedling could bend toward light only if the tip of the coleoptile was present.- They postulated that a signal was passed from the tip to the elongating region (right below the tip somewhere).- Hypothesis: reception of light by tip of the plant is necessary for phototropism.- 2. Boysen-Jensen in 1913- Demonstrated that the signal was a mobile chemical substance- Hypothesis: movement of chemical from tip to stem is necessary for phototropism. - 3. Went in 1926- Extracted and determined the chemical messenger for phototropism, auxin, by modifying Boysen-Jensenʼs experiment.- Hypothesis: asymmetric distribution of auxin transport from tip to stem is sufficient for phototropism. - Concluded that a coleoptile curves toward light because its darker side has a higher concentration concentration of the growth-promoting chemical auxin.- Major type of auxin later purified and determined to be