Adaptation of photosynthetic electron-transport rate to growth temperature in pea

Genotype Specific Photosynthesis x Environment Interactions Captured by Automated Fluorescence Canopy Scans Over Two Fluctuating Growing Seasons

Photosynthesis reacts dynamic and in different time scales to changing conditions. Light and temperature acclimation balance photosynthetic processes in a complex interplay with the fluctuating environment. However, due to limitations in the measurements techniques, these acclimations are often described under steady-state conditions leading to inaccurate photosynthesis estimates in the field. Here we analyze the photosynthetic interaction with the fluctuating environment and canopy architecture over two seasons using a fully automated phenotyping system. We acquired over 700,000 chlorophyll fluorescence transients and spectral measurements under semi-field conditions in four crop species including 28 genotypes. As expected, the quantum efficiency of the photosystem II (Fv/Fm in the dark and Fq'/Fm' in the light) was determined by light intensity. It was further significantly affected by spectral indices representing canopy structure effects. In contrast, a newly established parameter, monitoring the efficiency of electron transport (Fr2/Fv in the dark respective Fr2'/Fq' in the light), was highly responsive to temperature (R2 up to 0.75). This parameter decreased with temperature and enabled the detection of cold tolerant species and genotypes. We demonstrated the ability to capture and model the dynamic photosynthesis response to the environment over entire growth seasons. The improved linkage of photosynthetic performance to canopy structure, temperature and cold tolerance offers great potential for plant breeding and crop growth modeling.

A novel mechanistic interpretation of instantaneous temperature responses of leaf net photosynthesis

Steady-state rates of leaf CO2 assimilation (A) in response to incubation temperature (T) are often symmetrical around an optimum temperature. A/T curves of C3 plants can thus be fitted to a modified Arrhenius equation, where the activation energy of A close to a low reference temperature is strongly correlated with the dynamic change of activation energy to increasing incubation temperature. We tested how [CO2] < current atmospheric levels and saturating light, or [CO2] at 800 µmol mol(-1) and variable light affect parameters that describe A/T curves, and how these parameters are related to known properties of temperature-dependent thylakoid electron transport. Variation of light intensity and substomatal [CO2] had no influence on the symmetry of A/T curves, but significantly affected their breadth. Thermodynamic and kinetic (physiological) factors responsible for (i) the curvature in Arrhenius plots and (ii) the correlation between parameters of a modified Arrhenius equation are discussed. We argue that the shape of A/T curves cannot satisfactorily be explained via classical concepts assuming temperature-dependent shifts between rate-limiting processes. Instead the present results indicate that any given A/T curve appears to reflect a distinct flux mode, set by the balance between linear and cyclic electron transport, and emerging from the anabolic demand for ATP relative to that for NADPH.

Acclimation of foliar respiration and photosynthesis in response to experimental warming in a temperate steppe in northern China

BACKGROUND

Thermal acclimation of foliar respiration and photosynthesis is critical for projection of changes in carbon exchange of terrestrial ecosystems under global warming.

METHODOLOGY/PRINCIPAL FINDINGS

A field manipulative experiment was conducted to elevate foliar temperature (Tleaf) by 2.07°C in a temperate steppe in northern China. Rd/Tleaf curves (responses of dark respiration to Tleaf), An/Tleaf curves (responses of light-saturated net CO2 assimilation rates to Tleaf), responses of biochemical limitations and diffusion limitations in gross CO2 assimilation rates (Ag) to Tleaf, and foliar nitrogen (N) concentration in Stipa krylovii Roshev. were measured in 2010 (a dry year) and 2011 (a wet year). Significant thermal acclimation of Rd to 6-year experimental warming was found. However, An had a limited ability to acclimate to a warmer climate regime. Thermal acclimation of Rd was associated with not only the direct effects of warming, but also the changes in foliar N concentration induced by warming.

CONCLUSIONS/SIGNIFICANCE

Warming decreased the temperature sensitivity (Q10) of the response of Rd/Ag ratio to Tleaf. Our findings may have important implications for improving ecosystem models in simulating carbon cycles and advancing understanding on the interactions between climate change and ecosystem functions.

The temperature response of C(3) and C(4) photosynthesis

We review the current understanding of the temperature responses of C(3) and C(4) photosynthesis across thermal ranges that do not harm the photosynthetic apparatus. In C(3) species, photosynthesis is classically considered to be limited by the capacities of ribulose 1.5-bisphosphate carboxylase/oxygenase (Rubisco), ribulose bisphosphate (RuBP) regeneration or P(i) regeneration. Using both theoretical and empirical evidence, we describe the temperature response of instantaneous net CO(2) assimilation rate (A) in terms of these limitations, and evaluate possible limitations on A at elevated temperatures arising from heat-induced lability of Rubisco activase. In C(3) plants, Rubisco capacity is the predominant limitation on A across a wide range of temperatures at low CO(2) (<300 microbar), while at elevated CO(2), the limitation shifts to P(i) regeneration capacity at suboptimal temperatures, and either electron transport capacity or Rubisco activase capacity at supraoptimal temperatures. In C(4) plants, Rubisco capacity limits A below 20 degrees C in chilling-tolerant species, but the control over A at elevated temperature remains uncertain. Acclimation of C(3) photosynthesis to suboptimal growth temperature is commonly associated with a disproportional enhancement of the P(i) regeneration capacity. Above the thermal optimum, acclimation of A to increasing growth temperature is associated with increased electron transport capacity and/or greater heat stability of Rubisco activase. In many C(4) species from warm habitats, acclimation to cooler growth conditions increases levels of Rubisco and C(4) cycle enzymes which then enhance A below the thermal optimum. By contrast, few C(4) species adapted to cooler habitats increase Rubisco content during acclimation to reduced growth temperature; as a result, A changes little at suboptimal temperatures. Global change is likely to cause a widespread shift in patterns of photosynthetic limitation in higher plants. Limitations in electron transport and Rubisco activase capacity should be more common in the warmer, high CO(2) conditions expected by the end of the century.

Acclimation to the growth temperature and thermosensitivity of photosystem II in a mesophilic cyanobacterium, Synechocystis sp. PCC6803

Differences in the temperature dependence and thermosensitivities of PSII activities in Synechocystis sp. PCC6803 grown at 25 and 35 degrees C were studied. Hill reactions in cells, thylakoid membranes and purified PSII core complexes were measured at high temperatures or at their growth temperatures after high-temperature treatments. In the presence of 2,5-dichloro-p-benzoquinone as an electron acceptor, which can accept electrons directly from Q(A), the temperature dependence of the oxygen-evolving activity was almost the same in thylakoid membranes and in the purified PSII complexes from cells grown at 25 or 35 degrees C. When duroquinone, which accepts electrons only through Q(B) plastoquinone, was used as an electron acceptor, the temperature dependence was the same for purified PSII core complexes but was different between thylakoids isolated from the cells grown at 25 and 35 degrees C. No remarkable difference was observed in protein compositions between thylakoids and between purified PSII complexes from cells grown at 25 or 35 degrees C. However, the fluidity of thylakoids, measured by electron flow to P700, was affected by the growth temperature. These results suggest that one of the major factors which cause the changes in the thermosensitivity of PSII is the change in the fluidity of thylakoid membranes. As for the acclimation of PSII in thylakoids to high temperatures, one of the main causes is the decrease in the high-temperature-induced formation of non-Q(B) PSII due to the decreased fluidity in the cells grown at 35 degrees C.

Differential response of photosynthesis in greenhouse- and field-ecotypes of tomato to long-term chilling under low light

Three greenhouse- and four field-ecotype varieties of domestic tomato (Lycopersicon esculentum) were compared for the sensitivity of their photosynthetic apparatus to chilling under low light intensity. After chilling at 12/7 degrees C under 100 micromolm(-2)s(-1) of light for 10 days, they were allowed to recover at 25/18 degrees C and 600 micromolm(-2)s(-1) of light for 10 days. For both pre-chilling and recovered plants, greenhouse-ecotype varieties did not necessarily show higher net CO(2) assimilation rate (A), quantum yield of electron transport at PSII (Phi(PSII)) and photochemical quenching (q(P)) than field-ecotype varieties. However for the post-chilling period, greenhouse-ecotype varieties, exhibited higher A, and Phi(PSII) values than field-ecotype varieties. The difference in Phi(PSII) was found to be largely due to q(P). The absence of ecotypic differences in pre-chilling plants indicates that the trait was not expressed constitutively, but relied mainly on adaptation/acclimation mechanisms. Greenhouse-ecotype varieties were able to adapt to low temperature and low light more quickly, and then exhibited higher A, Phi(PSII), q(P) values and greater re-growth capacity after chilling than field-ecotype varieties. Plant re-growth capacity after chilling was highly correlated with Phi(PSII) and q(P) measured in chilled plants, suggesting the usefulness of Phi(PSII) and q(P) measured at low temperature after defined chilling stresses as screening indexes for chilling tolerance in breeding programs.

Temperature acclimation of photosynthesis and related changes in photosystem II electron transport in winter wheat

Winter wheat (Triticum aestivum L. cv Norin No. 61) was grown at 25 degrees C until the third leaves reached about 10 cm in length and then at 15 degrees C, 25 degrees C, or 35 degrees C until full development of the third leaves (about 1 week at 25 degrees C, but 2-3 weeks at 15 degrees C or 35 degrees C). In the leaves developed at 15 degrees C, 25 degrees C, and 35 degrees C, the optimum temperature for CO(2)-saturated photosynthesis was 15 degrees C to 20 degrees C, 25 degrees C to 30 degrees C, and 35 degrees C, respectively. The photosystem II (PS II) electron transport, determined either polarographically with isolated thylakoids or by measuring the modulated chlorophyll a fluorescence in leaves, also showed the maximum rate near the temperature at which the leaves had developed. Maximum rates of CO(2)-saturated photosynthesis and PS II electron transport determined at respective optimum temperatures were the highest in the leaves developed at 25 degrees C and lowest in the leaves developed at 35 degrees C. So were the levels of chlorophyll, photosystem I and PS II, whereas the level of Rubisco decreased with increasing temperature at which the leaves had developed. Kinetic analyses of chlorophyll a fluorescence changes and P700 reduction showed that the temperature dependence of electron transport at the plastoquinone and water-oxidation sites was modulated by the temperature at which the leaves had developed. These results indicate that the major factor that contributes to thermal acclimation of photosynthesis in winter wheat is the plastic response of PS II electron transport to environmental temperature.