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The biochemical basis for thermoregulation in heat-producing flowers.

Umekawa Y, Seymour RS, Ito K - Sci Rep (2016)

Bottom Line: Here, we show that respiratory control in homeothermic spadices of skunk cabbage (Symplocarpus renifolius) is achieved by rate-determining biochemical reactions in which the overall thermodynamic activation energy exhibits a negative value.Moreover, NADPH production, catalyzed by mitochondrial isocitrate dehydrogenase in a chemically endothermic reaction, plays a role in the pre-equilibrium reaction.We propose that a law of chemical equilibrium known as Le Châtelier's principle governs the homeothermic control in skunk cabbage.

View Article: PubMed Central - PubMed

Affiliation: United Graduate School of Agricultural Science, Iwate University, 3-18-8 Ueda, Morioka, Iwate, 020-8550, Japan.

ABSTRACT
Thermoregulation (homeothermy) in animals involves a complex mechanism involving thermal receptors throughout the body and integration in the hypothalamus that controls shivering and non-shivering thermogenesis. The flowers of some ancient families of seed plants show a similar degree of physiological thermoregulation, but by a different mechanism. Here, we show that respiratory control in homeothermic spadices of skunk cabbage (Symplocarpus renifolius) is achieved by rate-determining biochemical reactions in which the overall thermodynamic activation energy exhibits a negative value. Moreover, NADPH production, catalyzed by mitochondrial isocitrate dehydrogenase in a chemically endothermic reaction, plays a role in the pre-equilibrium reaction. We propose that a law of chemical equilibrium known as Le Châtelier's principle governs the homeothermic control in skunk cabbage.

No MeSH data available.


Comparison of the relationship between temperature and Eo for respiration in intact spadices and mitochondria in skunk cabbage.(a) Curve fitting of the respiration rates in intact spadices using a modified Arrhenius model. Data are derived from Seymour et al.7. (b) Curve fitting of the respiration rates in isolated mitochondria using a modified Arrhenius model. Data are from mitochondrial respiration operated by NADP+-ICDH and NDA (NADPH-NDA/ICDH; green), and by NAD+-NDB (NADH-NDB; light blue). Respiration rates were determined under constant temperature at 8 °C, 15 °C, 23 °C or 30 °C in respiration via NADPH-NDA/ICDH and at 15 °C, 23 °C, 30 °C or 37 °C via NADH-NDB (n = 6). (c) Determination of temperature responses of Eo for intact spadices and mitochondrial respiration. Changes of Eo value for intact spadices (red), isolated mitochondria (NADPH-NDA/ICDH (green) and NADH-NDB (light blue)) are depicted (n = 6). Intersection points of Eo are shown for spadices and NADPH-NDA/ICDH at 15.2 °C and 22.3 °C, respectively.
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f3: Comparison of the relationship between temperature and Eo for respiration in intact spadices and mitochondria in skunk cabbage.(a) Curve fitting of the respiration rates in intact spadices using a modified Arrhenius model. Data are derived from Seymour et al.7. (b) Curve fitting of the respiration rates in isolated mitochondria using a modified Arrhenius model. Data are from mitochondrial respiration operated by NADP+-ICDH and NDA (NADPH-NDA/ICDH; green), and by NAD+-NDB (NADH-NDB; light blue). Respiration rates were determined under constant temperature at 8 °C, 15 °C, 23 °C or 30 °C in respiration via NADPH-NDA/ICDH and at 15 °C, 23 °C, 30 °C or 37 °C via NADH-NDB (n = 6). (c) Determination of temperature responses of Eo for intact spadices and mitochondrial respiration. Changes of Eo value for intact spadices (red), isolated mitochondria (NADPH-NDA/ICDH (green) and NADH-NDB (light blue)) are depicted (n = 6). Intersection points of Eo are shown for spadices and NADPH-NDA/ICDH at 15.2 °C and 22.3 °C, respectively.

Mentions: To clarify whether our model for the pre-equilibrium reaction is functional in isolated skunk cabbage mitochondria, we performed in vitro respiratory analyses at four different temperatures (in a range from 8 °C to 37 °C), and compared the changes in Eo with the changes in Eo in intact spadices (Fig. 3). Because citrate is one of the most abundant organic acids in thermoregulatory male tissues of Dracunculus vulgaris20 and because our analysis with isolated mitochondria showed that NADP+-dependent isocitrate dehydrogenase (ICDH) is the major enzyme that catabolizes isocitrate (which was yielded by aconitase using citrate as a substrate; Supplementary Fig. S3), we focused on the pre-equilibrium reaction mediated by ICDH and type-II rotenone-insensitive internal NADPH dehydrogenase (NDA) in the mitochondria (Fig. 3 and Supplementary Fig. S3). A negative respiration control experiment was conducted with type-II rotenone-insensitive external NADH dehydrogenase (NDB). Because there are no dehydrogenases to convert NAD+ back to NADH outside the mitochondria in our experimental system, no pre-equilibrium reaction occurred in vitro. Ultimately the data fit well to the second-order polynomial equations of the modified Arrhenius model (Fig. 3a,b). NDB-mediated oxygen consumption using NADH as a substrate never revealed negative activation energy. In contrast, NADPH-NDA/ICDH-mediated oxygen consumption did exhibit negative activation energy, although the temperature at which Eo was zero (22.3 °C) was higher than it was in intact spadices (15.2 °C; Fig. 3c). Because enzymatic activity for NADP+-ICDH increased with the temperature (Q10 = 2.0; Supplementary Fig. S3b), a reverse endothermic reaction yielding NADPH would be stimulated at a higher temperature, leading to a shift of the equilibrium to increase the ratio of [NADPH]/[NADP+] (Supplementary Fig. S4). It should be noted here that in a new equilibrium, where a higher [NADPH]/[NADP+] ratio occurs, the ratio of [ubiquinone (UQ)]/[ubiquinol (UQH2)] would be also higher, and, hence, oxygen consumption rates mediated by terminal oxidases would be eventually decreased (Supplementary Fig. S4). These results suggest that the equilibrium shifts with temperature changes to counteract the temperature change and re-establish a new equilibrium. Such behaviour follows a law of chemistry known as Le Châtelier’s principle. It is well-known that this principle has a practical effect only for reactions that are thermodynamically reversible, and our results clearly show that pre-equilibrium reactions containing exothermic and endothermic reversible reactions could be reconstituted in vitro using purified mitochondria from thermogenic tissue of skunk cabbage.


The biochemical basis for thermoregulation in heat-producing flowers.

Umekawa Y, Seymour RS, Ito K - Sci Rep (2016)

Comparison of the relationship between temperature and Eo for respiration in intact spadices and mitochondria in skunk cabbage.(a) Curve fitting of the respiration rates in intact spadices using a modified Arrhenius model. Data are derived from Seymour et al.7. (b) Curve fitting of the respiration rates in isolated mitochondria using a modified Arrhenius model. Data are from mitochondrial respiration operated by NADP+-ICDH and NDA (NADPH-NDA/ICDH; green), and by NAD+-NDB (NADH-NDB; light blue). Respiration rates were determined under constant temperature at 8 °C, 15 °C, 23 °C or 30 °C in respiration via NADPH-NDA/ICDH and at 15 °C, 23 °C, 30 °C or 37 °C via NADH-NDB (n = 6). (c) Determination of temperature responses of Eo for intact spadices and mitochondrial respiration. Changes of Eo value for intact spadices (red), isolated mitochondria (NADPH-NDA/ICDH (green) and NADH-NDB (light blue)) are depicted (n = 6). Intersection points of Eo are shown for spadices and NADPH-NDA/ICDH at 15.2 °C and 22.3 °C, respectively.
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Related In: Results  -  Collection

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f3: Comparison of the relationship between temperature and Eo for respiration in intact spadices and mitochondria in skunk cabbage.(a) Curve fitting of the respiration rates in intact spadices using a modified Arrhenius model. Data are derived from Seymour et al.7. (b) Curve fitting of the respiration rates in isolated mitochondria using a modified Arrhenius model. Data are from mitochondrial respiration operated by NADP+-ICDH and NDA (NADPH-NDA/ICDH; green), and by NAD+-NDB (NADH-NDB; light blue). Respiration rates were determined under constant temperature at 8 °C, 15 °C, 23 °C or 30 °C in respiration via NADPH-NDA/ICDH and at 15 °C, 23 °C, 30 °C or 37 °C via NADH-NDB (n = 6). (c) Determination of temperature responses of Eo for intact spadices and mitochondrial respiration. Changes of Eo value for intact spadices (red), isolated mitochondria (NADPH-NDA/ICDH (green) and NADH-NDB (light blue)) are depicted (n = 6). Intersection points of Eo are shown for spadices and NADPH-NDA/ICDH at 15.2 °C and 22.3 °C, respectively.
Mentions: To clarify whether our model for the pre-equilibrium reaction is functional in isolated skunk cabbage mitochondria, we performed in vitro respiratory analyses at four different temperatures (in a range from 8 °C to 37 °C), and compared the changes in Eo with the changes in Eo in intact spadices (Fig. 3). Because citrate is one of the most abundant organic acids in thermoregulatory male tissues of Dracunculus vulgaris20 and because our analysis with isolated mitochondria showed that NADP+-dependent isocitrate dehydrogenase (ICDH) is the major enzyme that catabolizes isocitrate (which was yielded by aconitase using citrate as a substrate; Supplementary Fig. S3), we focused on the pre-equilibrium reaction mediated by ICDH and type-II rotenone-insensitive internal NADPH dehydrogenase (NDA) in the mitochondria (Fig. 3 and Supplementary Fig. S3). A negative respiration control experiment was conducted with type-II rotenone-insensitive external NADH dehydrogenase (NDB). Because there are no dehydrogenases to convert NAD+ back to NADH outside the mitochondria in our experimental system, no pre-equilibrium reaction occurred in vitro. Ultimately the data fit well to the second-order polynomial equations of the modified Arrhenius model (Fig. 3a,b). NDB-mediated oxygen consumption using NADH as a substrate never revealed negative activation energy. In contrast, NADPH-NDA/ICDH-mediated oxygen consumption did exhibit negative activation energy, although the temperature at which Eo was zero (22.3 °C) was higher than it was in intact spadices (15.2 °C; Fig. 3c). Because enzymatic activity for NADP+-ICDH increased with the temperature (Q10 = 2.0; Supplementary Fig. S3b), a reverse endothermic reaction yielding NADPH would be stimulated at a higher temperature, leading to a shift of the equilibrium to increase the ratio of [NADPH]/[NADP+] (Supplementary Fig. S4). It should be noted here that in a new equilibrium, where a higher [NADPH]/[NADP+] ratio occurs, the ratio of [ubiquinone (UQ)]/[ubiquinol (UQH2)] would be also higher, and, hence, oxygen consumption rates mediated by terminal oxidases would be eventually decreased (Supplementary Fig. S4). These results suggest that the equilibrium shifts with temperature changes to counteract the temperature change and re-establish a new equilibrium. Such behaviour follows a law of chemistry known as Le Châtelier’s principle. It is well-known that this principle has a practical effect only for reactions that are thermodynamically reversible, and our results clearly show that pre-equilibrium reactions containing exothermic and endothermic reversible reactions could be reconstituted in vitro using purified mitochondria from thermogenic tissue of skunk cabbage.

Bottom Line: Here, we show that respiratory control in homeothermic spadices of skunk cabbage (Symplocarpus renifolius) is achieved by rate-determining biochemical reactions in which the overall thermodynamic activation energy exhibits a negative value.Moreover, NADPH production, catalyzed by mitochondrial isocitrate dehydrogenase in a chemically endothermic reaction, plays a role in the pre-equilibrium reaction.We propose that a law of chemical equilibrium known as Le Châtelier's principle governs the homeothermic control in skunk cabbage.

View Article: PubMed Central - PubMed

Affiliation: United Graduate School of Agricultural Science, Iwate University, 3-18-8 Ueda, Morioka, Iwate, 020-8550, Japan.

ABSTRACT
Thermoregulation (homeothermy) in animals involves a complex mechanism involving thermal receptors throughout the body and integration in the hypothalamus that controls shivering and non-shivering thermogenesis. The flowers of some ancient families of seed plants show a similar degree of physiological thermoregulation, but by a different mechanism. Here, we show that respiratory control in homeothermic spadices of skunk cabbage (Symplocarpus renifolius) is achieved by rate-determining biochemical reactions in which the overall thermodynamic activation energy exhibits a negative value. Moreover, NADPH production, catalyzed by mitochondrial isocitrate dehydrogenase in a chemically endothermic reaction, plays a role in the pre-equilibrium reaction. We propose that a law of chemical equilibrium known as Le Châtelier's principle governs the homeothermic control in skunk cabbage.

No MeSH data available.