CO₂ Photoassimilation by the Spinach Chloroplast at Low Temperature

Abstract

Spinach chloroplasts were used to study the relationship between photosynthetic CO2 fixation and temperature from 30 to -15°C. In saturating light and high concentrations of CO2, the temperature coefficients (Q,.) above 20°C were less than 2 in the intact chloroplast. Below 15°C, the Qlo values were greater than 2 and gradually increased with decreasing (down to 0WC) temperature to approximately 4.4. Photosynthesis responded similarly to temperature in a reconstituted chloroplast preparation fortified with ribose 5-phosphate. In the intact chloroplast, temperature did not alter the Qlo value in low light and high CO2.Elevating the temperature to 25°C after photosynthesizing at -15°C (46 minutes) or 0°C (17 minutes) restored the temperature-depressed photosynthetic rate without a lag in the intact chloroplast to the rate of a chloroplast continually at 25°C. At 0°C, the intact chloroplast photosynthetic rate responded slightly to the inorganic phosphate concentration (0.1-1.0 millimolar) and to pH (7.04.6). Relative to 25°C, the levels of ribulose 1,5-bisphosphate and glycerate 3-phosphate were increased 1300 and 200%, respectively, whereas glycolate decreased 57% during intact chloroplast photosynthesis at 0°C. Chilling temperature impeded the transport of photosynthetic intermediates from the stromal compartment to the external medium. Ethylene glycol was shown to be an appropriate additive to prevent freezing of the reaction mixture down to -15°C for photosynthetic CO2 assimilation.The influence of temperature on photosynthesis is a complex phenomenon. In experiments involving short exposures to low temperature (minutes rather than hours or beyond) where no apparent time-dependent inhibition effects occur, it should be possible to obtain results of the direct effect of temperature on the photosynthetic process. To eliminate the complication of the stomates well known to be influenced by temperature as well as CO2 concentration, light intensity, and the water status of the plant, the algae rather than the higher plant became the principal experimental material. Whenever the illumination was weak and the supply of CO2 high, the rate of photosynthesis was found to be practically equal over a range of temperature from 4 to 30C.At high light intensity, the photosynthetic rate increased with temperature more so in high than in C02-limiting concentrations (see Ref. 24 for a review of the early literature).To

Ecosystem CO2and CH4exchange in a mixed tundra and a fen within a hydrologically diverse Arctic landscape: 1. Modeling versus measurements

“…Increases in GPP with warming were attributed to more rapid carboxylation and respiratory kinetics, represented by the low‐temperature inactivation terms in Arrhenius equations used to model the temperature dependence of CO 2 fixation (C10), R a (C22), and R h (A6). This term caused Q 10 derived from these equations to rise with lower temperatures (Grant 2014), as found in experimental studies on the temperature dependence of CO 2 fixation by Fu and Gibbs [], and of R h by Tuomi et al . [], so that sensitivity of biological reactions to temperature was greater in cooler climates.…”

Chilling-enhanced photooxidation: The production, action and study of reactive oxygen species produced during chilling in the light

“…Brtiggemann (1992) demonstrated that chilling temperatures inhibit photosynthesis by limiting the consumption of reducing equivalents and that this increased the susceptibility of the light reactions to photoinhibition. Additional experimental evidence for a slowing of the dark reactions in the cold comes from Fu and Gibbs (1987) who measured photosynthesis in intact spinach chloroplasts from -15 to 30 °C. They recorded a cold-temperature-dependent inhibition of carboxylation and concluded the cause was an increase in stromal viscosity that impaired the diffusion of substrate(s) to the RuBisCO enzyme.…”

Effects of Temperature Pretreatment in the Dark on Photosynthesis of the Intact Spinach Chloroplast

“…The neutralized mixture was centrifuged and the increase in A340 was taken as the amount of NADPH formed. Esterification of 32p was by a method described in an earlier report (12).…”