Respiration and Alternative Oxidase in Corn Seedling Tissues during Germination at Different Temperatures

Publisher Website
Google Scholar
Abstract
Respiration rates of Zea mays L. seedlings tissues grown at 30 and 14.degree. C were measured at 25.degree. C at different stages of seedling growth. Accumulation of heat units was used to define the developmental stages to compare respiration between the two temperatures. At both temperatures, respiration rates of most tissues were highest at the youngest stages, then declined with age. Respiration rates of mesocotyl tissue were the most reponsive to temperature, being nearly twofold higher when grown at 14 compared to 30.degree. C. Alternative pathway respiration increased concomitantly with respiration and was higher in mesocotyls grown in the cold. When seedlings were started at 30 than transferred to 14.degree. C, the increase in alternative pathway respiration due to cold was not observed unless the seedlings were transfected before 2 days of growth. Seedlings transferred to 14.degree. C after growth at 39.degree. C for 2 days had the same alternative oxidase capacity as seedlings grown at 30.degree. C. Seedlings grown at 14.degree.C for 10 to 12 days, then transferred to 30.degree. C, lost alternative pathway respiratory capacity over a period of 2 to 3 days. Western blots of mitochondrial proteins indicated that this loss of capacity was due to a loss of the alternative oxidase protein. Some in vitro characteristics of mitochondria were determined. The temperature optimum for measurement for alternative oxidase capacity was 15 to 20.degree. C. At 41.degree. C, very little alternative oxidase was measured, i.e., the mitochondrial oxygen uptake was almost completely sensitive to cyanide. This inactivation at 41.degree. C was reversible. After incubation at 41.degree. C, the alternative oxidase capacity measured at 25.degree. C was the similar to when it was measured at that temperature directly. Isolatred mitochondria lost alternative oxidase capacity at the same rate when incubated at 41.degree. C as they did when incubated at 25.degree. C . Increasing the supply of electrons is isolated mitochondria increased the degree of engagement of the alternative pathway, whereas lower temperature decreased the degree of engagement. Lower temperatures did not increase the degree of engagement of the pathway in intact tissues. We interpret these observations to indicate that the greater capacity of alternative oxidase in cold-grown seedlings is a consequence of development at these low temperatures which results in elevated respiration rates. Low temperatures itself does not cause greater capacity or engagement of the alternative oxidase in mitochondria that have developed under warm temperatures. Our hypothesis would be that the low growth temperatures require the seedlings to have a higher respiration rate for some reason, e.g., to prevent the accumulation of toxi metabolite, and that the alternative pathway functions in that respiration.