Application of an enthalpy balance model of the relation between growth and respiration to temperature acclimation ofEucalyptus globulusseedlings

Abstract

The enthalpy balance model of growth uses measurements of the rates of heat and CO 2 production to quantify rates of decarboxylation, oxidative phosphorylation and net anabolism. Enthalpy conversion ef ciency (h H ) and the net rate of conservation of enthalpy in reduced biosynthetic products (R S G DH B ) can be calculated from metabolic heat rate (q) and CO 2 rate (R C O 2 ). h H is closely related to carbon conversion ef ciency and the ef ciency of conservation of available electrons in biosynthetic products. R S G DH B and h H can be used, together with biomass composition, to describe the rate and ef ciency of growth of plant tissues. q is directly related to the rate of O 2 consumption and the ratio q:R C O 2 is inversely related to the respiratory quotient.We grew seedlings of Eucalyptus globulus at 16 and 28°C for four to six weeks, then measured q and R C O 2 using isothermal calorimetry. Respiratory rate at a given temperature was increased by a lower growth temperature but h H was unaffected. Enthalpy conversion ef ciency-and, therefore, carbon conversion ef ciency-decreased with increasing temperature from 15 to 35°C. The ratio of oxidative phosphorylation to oxygen consumption (P/O ratio) was inferred in vivo from h H and by assuming a constant ratio of growth to maintenance respiration with changing temperature. The P/O ratio decreased from 2.1 at 10-15°C to less than 0.3 at 35°C, suggesting that decreased ef ciency was not only due to activity of the alternative oxidase pathway. In agreement with predictions from non-equilibrium thermodynamics, growth rate was maximal near 25°C, where the calculated P/O ratio was about half maximum. We propose that less ef cient pathways, such as the alternative oxidase pathway, are necessary to satisfy the condition of conductance matching whilst maintaining a near constant phosphorylation potential. These conditions minimize entropy production and maximize the ef ciency of mitochondrial energy conversions as growing conditions change, while maintaining adequate nite rates of energy processing.

Water stress impacts on respiratory rate, efficiency and substrates, in growing and mature foliage of Eucalyptus spp

“…R q at 14.1°C was calculated from R CO 2 at 14.1°C by assuming that the ratio R q /R CO 2 was the same at 14.1 and 20°C. This assumption is supported by previous work with E. globulus shoots (recalculated data from Macfarlane et al 2002Macfarlane et al , 2005.…”

“…The assumption that carbohydrate is the dominant substrate has underpinned nearly all previous studies to separate enthalpy change into anabolic and catabolic components (e.g. Criddle et al 1997;Taylor et al 1998;Macfarlane et al 2002Macfarlane et al , 2005Marcar et al 2002;Matheson et al 2004). This assumption has also been used in conjunction with Eq.…”

“…Rate of ATP production in plant mitochondria is determined by (a) respiratory rate, (b) the nature of substrate, and (c) the efficiency of mitochondrial electron transport, represented as the ratio of oxidative phosphorylation to oxygen consumption, P/O (Macfarlane et al 2002). We developed an expression for R ATP that explicitly included c S in order to explore the influence of c S on the relationship between R ATP and R CO 2 in mature leaves, for which genotypic differences in c S were large.…”

“…We developed an expression for R ATP that explicitly included c S in order to explore the influence of c S on the relationship between R ATP and R CO 2 in mature leaves, for which genotypic differences in c S were large. The following expression for R ATP was given by Macfarlane et al (2002):…”

Oxygen Consumption by Fruits and Vegetables

“…using a modified aqueous phase on-line mass spectrometry-gas chromatography system. Macfarlane et al (2002) estimated ATP production efficiency equivalent to the distribution rate of e − to AOX by measuring enthalpy conversion efficiency in Eucalyptus globulus Labill. seedlings.…”