BIOL1108 Test 3 Book Notes Fall 2012 Max Boston Test 3 Book Notes Chapter 39 Plant Responses to Internal External Signals pg 821 834 October 1 3 Stimuli and Stationary Life Plants Linnaeus noticed owers opened and closed at speci c times of day creating a oral clock also known as a horologium orae 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 On a molecular level both plants and animals use a complex system to respond to changes in animals 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 modi cation activates pre existing enzymes Proteins modi ed by phosphorylation of speci c 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 speci c genes on off 2 Transcriptional regulation increases or decreases the synthesis of mRNA Protein phosphatases are the off switch encoding a speci c enzyme Speci c transcription factors are activated by phosphorylation via kinases and bind to speci c 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 1 1 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 bene cial 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 organism s body and transported to other parts Bind to a speci c 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 tropism Any response resulting in curvature of organs toward or away from a stimulus is called a 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 They postulated that a signal was passed from the tip to the elongating region coleoptile was present right below the tip somewhere Hypothesis reception of light by tip of the plant is necessary for Demonstrated that the signal was a mobile chemical substance Hypothesis movement of chemical from tip to stem is necessary for 2 Boysen Jensen in 1913 phototropism 3 Went in 1926 phototropism Extracted and determined the chemical messenger for phototropism auxin by modifying Boysen Jensen s experiment Hypothesis asymmetric distribution of auxin transport from tip to stem is suf cient 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 puri ed and determined to be indoleacetic acid IAA A Survey of Plant Hormones Plant hormones affect plant growth and development by affecting Division Elongation Differentiation of plant cells Plant hormones are produced in very low concentrations but small amount of them can