Plant Physiology

Plant Physiology (Biology 327) - Dr. Stephen G. Saupe; College of St. Benedict/ St. John's University; Biology Department; Collegeville, MN 56321; (320) 363 - 2782; (320) 363 - 3202, fax; ssaupe@csbsju.edu

Exam Questions: Gas Exchange/Transpiration

Both plants and animals must exchange gases with the environment. To do this successfully required them to solve a number of "problems". Identify the gas exchange problems that confront both plants and animals. Then describe how these problems were "solved". Include a discussion of the photosynthesis/transpiration compromise and why stomata are ideally suited for gas exchange (i.e. anatomy, size, distribution, location).
Explain the mechanism by which guard cells open and close the stomata. Include in your response a discussion of guard cell structure and mechanics (e.g., radial micellation, thickened inner walls), turgor pressure, solute (osmotic) potential, and solutes (e.g., potassium ions, carbohydrates, malate, chloride).
Describe the function and action of the H⁺-ATPase in the action of guard cells. How do we know a proton pump is involved in guard cell action (e.g., vanadate, CCCP, fusicoccin)? Explain the mechanism by which this pump is hypothesized to work (e.g., hyperpolarize membrane, voltage gated channels, potassium).
Data suggest that potassium ions are the important solute regulating guard cell opening while sucrose is important for closing guard cells. Explain why potassium levels increase rapidly and then slowly decline during the day while sucrose levels show the reverse pattern (they slowly increase during the day and then decline a little more rapidly).
Blue light is a potent regulator of the proton pump. Include a description of how blue light stimulates the pump through its interaction with zeaxanthin and serine/threonine kinase.
Describe the effect of light (PAR) on guard cell activity. Why do we expect light to play a major regulatory role in guard cell action? How do we know photosynthesis (PAR) is an important regulator of guard cell action? What is the function of PAR/photosynthesis in guard cell action? Include a discussion of starch, sucrose, chloroplastic pH, ATP synthesis, cytoplasmic carbon dioxide levels and cytoplasmic pH.
Calcium ions play a major role in the signal pathway to close guard cells/stomata. Explain the role of calcium in guard cell closure including a discussion of its role in increasing cytoplasmic calcium concentrations (self-catalytic), its effect on chloride and potassium ion concentrations, and its effect on the proton pump.
Describe the effect of water stress on guard cell activity. Why should water play a role in guard cell action? Include a discussion of hydropassive and hydroactive controls. Explain the mechanism of action for both, including the function and source(s) of ABA and its mechanism of action (e.g., effect on calcium, ROS and other signal pathways).