Mitochondria were extracted from seedling radicles of Pima S-5 and Pima E-14 cottons and the state 3 respiration, state 4 respiration, ADP:O ratio and respiratory control (RC) ratio were measured in vitro over a range of temperatures from 6 to 18C. Mitochondria from E-14 seedlings exhibited a mean state 3 respiration rate of 13.42 μMO₂/min/gm tissue while mitochondria from S-5 seedlings showed a mean state 3 rate of 17.94 μMO₂/min/gm tissue. Mean state 4 respiration exhibited a similar trend with measurements of 73.4 μMO₂/min/gm tissue and 11.73 μMO₂/min/gm tissue for E-14 and S-5. Mitochondria from E-14 seedlings exhibited a mean ADP:O ratio of 3.73 compared to an ADP:O of 3.28 for S-5, across all assay temperatures. Mean respiratory control ratio was 1.79 for E-14 and 1.53 for S-5. These lower respiration rates of E-14 coupled with higher ADP:O ratios and RC ratios support a greater respiratory efficiency at low temperatures of this variety compared to S-5. Additionally, the E-14 mitochondrial membranes exhibited an ability to remain in a fluid state to a lower temperature than Pima S-5 mitochondrial membranes as judged by Arrhenius plots of respiration. Since mitochondrial respiration is considered to be regulated by membrane-bound enzymes, any change in membrane fluidity would conceivably affect mitochondrial enzyme activity and thus alter respiration rates. Changes in respiration rates will be reflected as a break in an Arrhenius plot. The mean break point temperature of state 3 respiration was 10.7C for E-14 and 13.4C for S-5. The mean break point temperature for state 4 respiration was 10.9C for E-14 and 13.6C for S-5. The ability of E-14 to withstand a greater degree of chilling under field conditions can be attributed, in part, to the greater fluidity of seedling mitochondrial membranes at low temperatures and concomitant conservation of respiratory energy through a lower rate of respiration. Assays of mitochondrial respiration and Arrhenius plots of mitochondrial respiration versus temperatures could be used to select cotton lines more tolerant to chilling temperatures.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/184792 |
| Date | January 1982 |
| Creators | CENTNER, MICHAEL STEPHEN. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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