Plant mitochondria electron partitioning is independent of short‐term temperature changes

Abstract

We tested the hypotheses that relative activity of the less efficient alternative oxidase (AOX) path changes with diurnal temperature changes, and thus changes carbon use efficiency with temperature. The activities of the alternative and cytochrome oxidase (COX) paths in plant tissues of three species were determined by measuring 18 O/ 16 O discrimination and total respiration from 17 to 36°C. A new, more accurate method for calculating oxygen uptake rate from the mass spectrometry data was developed. Total carbon use efficiency was calculated from the ratio of respiratory heat and CO2 rates measured from 10 to 35°C. Oxygen isotope discrimination (22.9 Ϯ 0.4‰) and AOX participation were invariant with temperature in leaf tissue of Cucurbita pepo, Nicotiana sativa and Vicia faba, thus falsifying the first part of the hypothesis. Stress responses of respiration at the temperature extremes limited the range for which carbon use efficiency could be accurately measured to 15-30°C in N. sativa, to 10-25°C in C. pepo and to 20-30°C in V. faba. Carbon-use efficiency was invariant at these temperatures in these species, demonstrating that changes in other pathways that would vary carbon-use efficiency were also invariant with temperature.

Metabolic control and regulation of the tricarboxylic acid cycle in photosynthetic and heterotrophic plant tissues

“…2009). These authors also observed that there is a relatively large temperature dependence of the respiration rate, suggesting that there was little substrate limitation to respiratory rate in the leaves of healthy plants (Macfarlane et al . 2009).…”

“…The enormous variety of alternative respiratory substrates and metabolic pathways makes plant respiration remarkably flexible especially in response to changing environmental circumstance. For instance, it has been shown that oxygen isotope discrimination during plant respiration seems to be independent of temperature over the range of temperature normally encountered during growth (Macfarlane et al . 2009).…”

Alternative Oxidase: A Mitochondrial Respiratory Pathway to Maintain Metabolic and Signaling Homeostasis during Abiotic and Biotic Stress in Plants

“…, minutes to hours), short-term (several hours to several days) and long-term (weeks to months) changes in temperature. In several species, instantaneous changes in temperature were found to have little impact on the relative partitioning of electrons between the cyt pathway and AOX over a wide temperature range [155]. However, in chilling-sensitive maize, a short-term cold treatment (5 days at 5 °C) was associated with a dramatic decline in cyt pathway activity and increase in AOX activity, such that approximately 60% of total respiration was occurring through AOX [156].…”

Steps towards a mechanistic understanding of respiratory temperature responses

“…However, the same study also showed greater temperature sensitivity of the alternative path for mung bean leaves, especially at high temperatures (25–30°C), but not so much at lower temperatures (Table 1). MacFarlane et al. (2009) showed reduced temperature sensitivity of the alternative path relative to the cytochrome pathway at moderate temperatures (17–23°C) in Nicotiana sativa , Cucurbita pepo and Vicia faba (Table 1), but no clear‐cut pattern above this temperature range.…”

“…Past inhibitor experiments may well have systematically underestimated AOX‐activity in vivo (also compare MacFarlane et al. , 2009).…”