Tonya Thygerson and Dr. Bruce N. Smith, Botany and Range Science
Populations within a species (accessions) are adapted to the particular microclimate of their origin and may, or may not, grow as well when moved to different location. The purpose of this work is to examine how plants adapt their respiratory metabolism to match the temperature of their native climate.
In this study, calorimetry was used to determine the temperature response and high and low stress temperatures of winterfat collected from six locations. (see Table 1.) This was done using the Conceptual model for plant growth, the measurements from calorimetry and the predicted growth rate model proposed by Hansen et al.(1).
Six populations of winterfat were collected and prepared for germination. The seeds were then placed on moistened filter paper in petri dishes to germinate at room temperature. At the time of germination the winterfat was placed in ampules in a microcalorimeter. Heat-rate (Rq) was measured at a given temperature, and then a vial containing NaOH was added to measure the rate of CO2 evolution (RCO2) for the same tissue at the same temperature. The NaOH was then taken out and Rq was measured again. This procedure was repeated for each of the populations in five-degree intervals at temperatures ranging from 0 to 25 °C. Previously I had been measuring temperatures below zero but we discovered that the NaOH freezes at temperatures below zero and cannot be used to measure the RCO2. But the measurements for Rq are still valid at the lower temperatures and we will have to wait until another method becomes available to measure RCO2 to look at samples at the lower temperatures.
Aerobic respiration has two aspects: catabolism and anabolism. In catabolism, organic substrates are oxidized to produce CO2. Part of the energy produced by oxidation is used to convert ADP and inorganic phosphates to ATP, the rest is lost as heat. The ATP produced in catabolism is transient, but is used for cellular work, including anabolism. In anabolism, heat and new plant tissue are produced and ATP is hydrolyzed back to ADP and phosphate. A calorimeter measures the rate of heat loss (Rq) from both catabolism and anabolism. The rate of CO2 production (RCO2) measures the rate of catabolism.
Growth in terms of energy can occur only when the catabolic energy generation rate (455RCO2) exceeds the rate of heat loss (Rq). Metabolic data for winterfat populations from Pinebluffs WY, Sterling, CO, and Matador, Sasketchewan, Canada differ slightly from each other (table 1). Metabolic heat rates and respiration rates are compared for the three populations of winterfat from the Sevilleta National Wildlife Reserve, New Mexico in the Northside population, Westside, Southside also were slightly different from one another (Table 1).
Differences between northern (Colorado, Wyoming, and Saskatchewan) and southern (New Mexico) populations are illustrated (fig. 1) by comparing metabolic efficiency as indicated by the Rq/RCO2 vs. Temperature of the Pinebluffs and the Northside populations. Note that a smaller ratio of Rq/RCO2 indicates greater efficiency. Values greater that 455ìW mg-1 dry weight representing either physical damage or a shift to another substrate (e.g. lipid).
Predicted growth rate vs. temperature for Pinebluffs is compared with that for Northside in figure 2. RSGÄHB values lower than zero indicate no growth or dormancy.
The southern populations did have higher stress points than the northern populations (see Table 1.). The low stress temperature varies from 2-7 C and the higher stress temperatures were +25 C. Where the southern populations low stress points were around 0 C and the high stress temperature stopped around 16-20 C. These results followed the predictions made for this experiment. Further experiments and gathering of additional populations are needed for a more complete study.
References
- Hansen, L.D., M.S. Hopkin, D.R. Rank, T.S. Anekonda, R.W. Breidenbach, and R.S. Criddle. 1994. The relation between plant growth and respiration: A thermodynamic model. Planta 194:77- 85