Responses of Plants to Acute and Chronic Heat Stress in a High-CO2 Environment: Linking Molecular Biology with Physiological Ecology

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Atmospheric concentrations of CO2 and other greenhouse gases continue to rise. This phenomenon 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 if that plants may be exposed to sudden and severe increases in 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 exist. Yet, little is known how the physiological state of the cell or whole-plant prior to the imposition of heat stress affect the synthesis and accumulation of hsps or the ability of plants to survive heat stress. This void in understanding is particularly critical because plants in natural environmental of plants may not only be characterized by changes in temperature patterns, but will almost certainly contain extremely high levels of air pollutants (e.g., CO2, ozone) and changing nutrient contents in precipitation and soils. Thus, understanding the role that plant physiological status may play in governing the heat shock response may provide new essential data on the roles of heat shock proteins in the acquisition and maintenance of thermotolerance in plant tissues. The overall goal of this research is to assess the relationship between the synthesis and accumulation of heat shock proteins at the cellular level and the overall stress responses of whole-plants and tissues grown under distinctly different physiological environments. Specific genotypes of corn (Zea mays) and tomato (Lycopersicon esculentum) will be grown in environments with different availabilities of carbon (CO2) and nitrogen resulting in plants at different physiological states. These plants will then be exposed to heat stress or to control conditions. The kinetics of heat shock protein synthesis and the patterns of recovery of normal protein synthesis (molecular level); the capacity of plants to harvest light and CO2 for photosynthesis (tissue level); and overall plant performance (whole-plant level), will be examined simultaneously. The results should help to clarify the biological role of hsps by linking molecular phenomena to processes occurring at tissue and whole-plant levels. Furthermore, how plants in both agricultural and natural systems will respond to the predicted changes in the global climate is a critical question, and understanding how the stress response of plants might be altered in a high CO2 environment would be an important step in solving that problem.