TY - JOUR
T1 - Temperature-dependent changes in respiration rates and redox poise of the ubiquinone pool in protoplasts and isolated mitochondria of potato leaves
AU - Covey-Crump, Elizabeth M.
AU - Bykova, Natalia V.
AU - Affourtit, Charles
AU - Hoefnagel, Marcel H.N.
AU - Gardeström, Per
AU - Atkin, Owen K.
PY - 2007/1
Y1 - 2007/1
N2 - In many environments, leaves experience large diurnal variations in temperature. Such short-term changes in temperature are likely to have important implications for respiratory metabolism in leaves. Here, we used intact leaf, protoplasts and isolated mitochondria to determine the impact of short-term changes in temperature on respiration rates (R), adenylate concentrations and the redox poise of the ubiquinone (UQ) pool in mitochondria of potato leaves. The Q10 (i.e. proportional change in R for each 10°C rise in temperature) of respiration was 1.8, both for intact leaves and protoplasts. In protoplasts, the redox poise of the extracted UQ pool (UQR/UQ T) increased from 0.33 at 22°C, to 0.76 at 15°C. Further decreases in temperature (from 15 to 5°C) resulted in UQR/UQ T decreasing to 0.40. Adenylate ratios in protoplasts were also temperature dependent. At high adenosine 5′-triphosphate (ATP) adenosine 5′-diphosphate (ADP) ratios (i.e. low ADP concentrations), UQ R/UQT values were low, suggesting that adenylates restricted flux via the UQ-reducing pathways more than they restricted flux via pathways that oxidized UQH2. To assess whether high rates of alternative oxidase (AOX) activity could have uncoupled respiratory flux (and thus UQR/UQT) from adenylate restriction of the cytochrome (Cyt) pathway, we constructed kinetic curves of O2 uptake (via the two pathways) vs UQR/UQT in isolated mitochondria, measured at two temperatures (15 and 25°C); measurements were made for mitochondria operating under state 3 (i.e. +ADP) and state 4 (i.e. -ADP) conditions. In contrast to the Cyt pathway, flux via the AOX was temperature insensitive, with maximal rates of AOX activity representing 21-57% of total O2 uptake in isolated mitochondria. We conclude that temperature-dependent variations in UQR/UQT are largely dependent on temperature-dependent changes in adenylate ratios, and that flux via the AOX could in some circumstances help reduce maximal UQ values.
AB - In many environments, leaves experience large diurnal variations in temperature. Such short-term changes in temperature are likely to have important implications for respiratory metabolism in leaves. Here, we used intact leaf, protoplasts and isolated mitochondria to determine the impact of short-term changes in temperature on respiration rates (R), adenylate concentrations and the redox poise of the ubiquinone (UQ) pool in mitochondria of potato leaves. The Q10 (i.e. proportional change in R for each 10°C rise in temperature) of respiration was 1.8, both for intact leaves and protoplasts. In protoplasts, the redox poise of the extracted UQ pool (UQR/UQ T) increased from 0.33 at 22°C, to 0.76 at 15°C. Further decreases in temperature (from 15 to 5°C) resulted in UQR/UQ T decreasing to 0.40. Adenylate ratios in protoplasts were also temperature dependent. At high adenosine 5′-triphosphate (ATP) adenosine 5′-diphosphate (ADP) ratios (i.e. low ADP concentrations), UQ R/UQT values were low, suggesting that adenylates restricted flux via the UQ-reducing pathways more than they restricted flux via pathways that oxidized UQH2. To assess whether high rates of alternative oxidase (AOX) activity could have uncoupled respiratory flux (and thus UQR/UQT) from adenylate restriction of the cytochrome (Cyt) pathway, we constructed kinetic curves of O2 uptake (via the two pathways) vs UQR/UQT in isolated mitochondria, measured at two temperatures (15 and 25°C); measurements were made for mitochondria operating under state 3 (i.e. +ADP) and state 4 (i.e. -ADP) conditions. In contrast to the Cyt pathway, flux via the AOX was temperature insensitive, with maximal rates of AOX activity representing 21-57% of total O2 uptake in isolated mitochondria. We conclude that temperature-dependent variations in UQR/UQT are largely dependent on temperature-dependent changes in adenylate ratios, and that flux via the AOX could in some circumstances help reduce maximal UQ values.
UR - http://www.scopus.com/inward/record.url?scp=33845641004&partnerID=8YFLogxK
U2 - 10.1111/j.1399-3054.2006.00823.x
DO - 10.1111/j.1399-3054.2006.00823.x
M3 - Article
SN - 0031-9317
VL - 129
SP - 175
EP - 184
JO - Physiologia Plantarum
JF - Physiologia Plantarum
IS - 1
ER -