9357302 Coleman Atmospheric concentrations of carbon dioxide and other greenhouse gases continue to rise. This may lead to increases in the mean global temperature as well as in yearly, and even daily, variations in temperature. One consequence of increasing variation in temperatures is that plants may be exposed to sudden and severe increases of temperature (i.e., heat shocks) at a greater frequency than they are now. The ability of plants to withstand these hyperthermic episodes is most likely related, at least in part, to their capacity for elevating levels of certain heat shock proteins (hsps). A great deal of information regarding the molecular biology of these proteins in plants exists. Yet, little is known regarding how the physiological state of the cell or whole-plant prior to the imposition of heat stress affects the synthesis and accumulation of hsps or the ability of plants to survive heat stress. This NSF Young Investigator Award supports research using several genotypes of eastern cottonwood (Populus deltoides) in environments with different availabilities of carbon, light and nitrogen resulting in plants with different physiological states. These plants will then be exposed to acute increases in temperature, to chronic sub-lethal temperature stress, or to control conditions to answer the following questions. (1) How does the physiological state of the plant affects the kinetics and extent of accumulation of specific stress proteins in response to a single acute heat shock, as well as a prolonged high- temperature event and the recovery rate of normal protein synthesis? (2) How are patterns of heat shock protein synthesis and accumulation in leaves correlated to the functioning of the photosynthetic apparatus during and after acute and chronic heat stress? (3) Does the synthesis of stress proteins occur in lieu of the production or activation of photosynthetic enzymes? (4) Are any tradeoffs exacerbated when nitrogen is limiting? (5) Is there a correlation between the dynamics of stress protein production at the cellular level and whole-plant performance? (6) How are these relationships affected by plant development stage or plant genotype? The results of this work are important for a number of reasons. First, global climate models predict that the future atmosphere will have extremely high concentrations of carbon dioxide, and that the accumulation of carbon dioxide, as well as other factors, may result in temperature patterns that are subject to extreme fluctuations. Furthermore, increasing levels of carbon dioxide, in and of itself, will have substantial effects on the physiological status of plants. Understanding how the stress response of plants might be altered in a high-carbon dioxide world would therefore be an important step towards understanding how plants in both agricultural and natural settings will respond to the predicted changes in the global climate. Second, the role of stress proteins in the acquisition of stress tolerance is in the midst of an intense debate. Understanding the role that plant physiological status plays in governing the heat shock response may provide essential links to understanding when and if stress proteins function in promoting stress tolerance in plant tissues. ***
