Temperature dependence of net photosynthesis in Trientalis borealis Raf. in Wisconsin

Summary Multivariate analysis of variance was used in testing 16 gas exchange curves derived from three populations of Trientalis borealis Raf., to demonstrate lack of evidence for ecotypic differentiation with respect to thermal adaptation of net photosynthesis among the populations examined. Limitations of these conclusions are discussed. Although ecotypes within Trientalis borealis may indeed exist, demonstration of their existence requires increase in the precision of experimental techniques, or in sizes of samples that are commonly used in ecophysiological studies of gas exchange capacities of plants.     

Temperature dependence of photosynthesis in Arabidopsis plants with modifications in Rubisco activase and membrane fluidity

Net photosynthesis (Pn) is reversibly inhibited at moderately high temperature. To investigate this further, we examined the effects of heat stress on Arabidopsis plants in which Rubisco activase or thylakoid membrane fluidity has been modified. During heating leaves from 25 to 40 degrees C at 250 ppm CO2 and 1% O2, the wild-type (WT), plants expressing the 43 kDa isoform only (rwt43), and plants accumulating activase 40% of WT (R100) exhibited similar inhibitions in the Pn and Rubisco activation state. Despite better membrane integrity than WT, plants having less polyunsaturation of thylakoid lipids (fad7/8 double mutant) failed to maintain greater Pn than the WT. Plants expressing the 46 kDa isoform only (rwt46) exhibited the most inhibition, but plants expressing a 46 kDa isoform incapable of redox regulation (C411A) were similar to the WT. The null mutant (rca) exhibited a continuous decline in Pn. As measured by fluorescence, electron transport activity decreased concomitantly with Pn but PSII was not damaged. Following a quick recovery to 25 from 40 degrees C, whereas most lines recovered 90% Pn, the rwt46 and rca lines recovered only to 59 and <10%, respectively. As measured by NADP-malate dehydrogenase activation, after an initial increase at 30 degrees C, stromal oxidation in the WT and rwt46 plants did not increase further as Pn decreased. These results provide additional insight into the role of Rubisco activation and activase in the reversible heat inhibition of Pn.     

Temperature acclimation of photosynthesis: mechanisms involved in the changes in temperature dependence of photosynthetic rate

Growth temperature alters temperature dependence of the photosynthetic rate (temperature acclimation). In many species, the optimal temperature that maximizes the photosynthetic rate increases with increasing growth temperature. In this minireview, mechanisms involved in changes in the photosynthesis-temperature curve are discussed. Based on the biochemical model of photosynthesis, change in the photosynthesis-temperature curve is attributable to four factors: intercellular CO2 concentration, activation energy of the maximum rate of RuBP (ribulose-1,5-bisphosphate) carboxylation (Vc max), activation energy of the rate of RuBP regeneration (Jmax), and the ratio of Jmax to Vc max. In the survey, every species increased the activation energy of Vc max with increasing growth temperature. Other factors changed with growth temperature, but their responses were different among species. Among these factors, activation energy of Vc max may be the most important for the shift of optimal temperature of photosynthesis at ambient CO2 concentrations. Physiological and biochemical causes for the change in these parameters are discussed.     

Respiration and intensity dependence of photosynthesis in Chlorella

1. Respiration changes as a result of illumination. 2. In the absence of glucose or other supply of substrate, respiration decays in the dark showing at least two types—a fast decay in a few minutes and a slow decay lasting hours. 3. Respiratory response to illumination is delayed. 4. Intermittent illumination (in the absence of glucose, etc.) produces a periodic variation in respiration with a delay or phase lag. 5. Periodic variation of respiration may produce a higher average value in the dark than in the light due to the lag and depending upon the period of intermittent illumination. 6. Based upon average respiration values our data confirm the Kok effect. 7. Interpolated values of respiration, however, result in photosynthetic rates which are linearly dependent upon intensity of illumination. 8. Thus the quantum efficiency is found to be independent of intensity, over the wide range of intensities investigated.     

Temperature dependence of fast dynamics in proteins

The temperature dependence of the internal dynamics of recombinant human ubiquitin has been measured using solution NMR relaxation techniques. Nitrogen-15 relaxation has been employed to obtain a measure of the amplitude of subnanosecond motion at amide N-H sites in the protein. Deuterium relaxation has been used to obtain a measure of the amplitude of motion of methyl-groups in amino-acid side chains. Data was obtained between 5 and 55 degrees C. The majority of amide N-H and methyl groups show a roughly linear (R(2)>0.75) temperature dependence of the associated Lipari-Szabo model-free squared generalized-order parameter (O(2)) describing the amplitude of motion. Interestingly, for those sites showing a linear response, the temperature dependence of the backbone is distinct from that of the methyl-bearing side chains with the former being characterized by a significantly larger Lambda-value, where Lambda is defined as d ln(1 - O)/d lnT. These results are comparable to the sole previous such study of the temperature dependence of protein motion obtained for a calmodulin-peptide complex. This suggests that the distinction between the main chain and methyl-bearing side chains may be general. Insight into the temperature dependence is gathered from a simple two-state step potential model.     

Mepiquat chloride (PIX)-induced changes in photosynthesis and growth of cotton

Mepiquat chloride (N, N-dimethylpiperidinium chloride), well known as PIX, is a potential systemic plant growth regulator. The effects of PIX on plant height, stem elongation, leaf area, net photosynthetic rates, chlorophyll content, sucrose and starch levels, and RuBP carboxylase activity in cotton (Gossypium hirsutum L. cv. DES 119) plants were measured. PIX was sprayed (0, 7.65, 15.3, 30.6 or 61.2 g active ingredient ha^–1) on the plants at first square (25 days after emergence) and measurements were made at frequent intervals. Plant height was clearly reduced by PIX. The total length of vegetative branches and fruiting branches was 40% and 50% less than the control. Total leaf area in PIX treated plants was 16% less than the control. Net photosynthetic rates were 25% less in PIX-treated leaves. PIX treated leaves had more chlorophyll content. The activity of RuBP carboxylase was decreased in PIX treated plants. Starch accumulation was noticed in PIX treated leaves while sucrose content was not changed. The data reported here suggest that reduced growth responses induced by PIX results in partial loss of photosynthetic capacity in cotton at least up to 20 days after application of the growth regulator.     

Light dependence of carboxylation capacity for C3 photosynthesis models

C₃ photosynthesis at high light is often modeled by assuming limitation by the maximum capacity of Rubisco carboxylation (V_Cmax) at low CO₂ concentrations, by electron transport capacity (J_max) at higher CO₂ concentrations, and sometimes by triose-phosphate utilization rate at the highest CO₂ concentrations. Net photosynthetic rate (P_N) at lower light is often modeled simply by assuming that it becomes limited by electron transport (J). However, it is known that Rubisco can become deactivated at less than saturating light, and it is possible that P_N at low light could be limited by the rate of Rubisco carboxylation (V_C) rather than J. This could have important consequences for responses of P_N to CO₂ and temperature at low light. In this work, P_N responses to CO₂ concentration of common bean, quinoa, and soybean leaves measured over a wide range of temperatures and PPFDs were compared with rates modeled assuming either VC or J limitation at limiting light. In all cases, observed rates of P_N were better predicted by assuming limitation by VC rather than J at limiting light both below and above the current ambient CO₂. One manifestation of this plant response was that the relative stimulation of P_N with increasing the ambient CO₂ concentration from 380 to 570 µmol mol^–1 did not decrease at less than saturating PPFDs. The ratio of VC to V_Cmax at each lower PPFD varied linearly with the ratio of P_N at low PPFD to P_N at high PPFD measured at 380 µmol(CO₂) mol^–1 in all cases. This modification of the standard C₃ biochemical model was much better at reproducing observed responses of light-limited P_N to CO₂ concentrations from pre-industrial to projected future atmospheric concentrations.     

The role of induced mutation in conversion of photoperiod dependence in cotton

Wild cotton germplasm resources are largely underutilized because of photoperiod-dependent flowering of "exotic" cottons. The objectives of this work were to explore the genome-wide effect of induced mutation in photoperiod-converted induced cotton mutants, estimating the genetic change between mutant and wild-type cottons using simple sequence repeats (SSRs) as well as understand the pattern of SSR mutation in induced mutagenesis. Three groups of photoperiod-converted radiomutants ((32)P) including their wild-type parental lines, A- and D-genome diploids, and typically grown cotton cultivars were screened with 250 cotton SSR primer pairs. Forty SSRs revealed the same SSR mutation profile in, at least, 2 independent mutant lines that were different from the original wild types. Induced mutagenesis both increased and decreased the allele sizes of SSRs in mutants with the higher mutation rate in SSRs containing dinucleotide motifs. Genetic distance obtained based on 141 informative SSR alleles ranged from 0.09 to 0.60 in all studied cotton genotypes. Genetic distance within all photoperiod-converted induced mutants was in a 0.09-0.25 range. The genetic distance among photoperiod-converted mutants and their originals ranged from 0.28 to 0.50, revealing significant modification of mutants from their original wild types. Typical Gossypium hirsutum cultivar, Namangan-77, revealed mutational pattern similar to induced radiomutants in 40 mutated SSR loci, implying possible pressure to these SSR loci not only in radiomutagenesis but also during common breeding process. Outcomes of the research should be useful in understanding the photoperiod-related mutations, and markers might help in mapping photoperiodic flowering genes in cotton.     

Temperature dependence of blood surface tension

Whole blood surface tension of 15 healthy subjects recorded by the ring method was investigated in the temperature range from 20 to 40 degrees C. The surface tension omega as a function of temperature t ( degrees C) is described by an equation of linear regression as omega(t) = (-0.473 t + 70.105) x 10(-3) N/m. Blood serum surface tension in the range from 20 to 40 degrees C is described by linear regression equation omega(t) = (-0.368 t + 66.072) x 10(-3) N/m and linear regression function of blood sediment surface tension is omega(t) = (-0.423 t + 67.223) x10(-3) N/m.     

Temperature dependence of collagen fluorescence.

Dermal collagens have several fluorescent moieties in the UV and visible spectral regions that may serve as molecular probes of collagen. We studied the temperature-dependence of a commercial calf skin collagen and acid-extracted Skh-1 hairless mouse collagen at temperatures from 9 degrees C to 60 degrees C for excitation/emission wavelengths 270/305 nm (tyrosine), 270/360 nm (excimer-like aggregated species), 325/400 nm (dityrosine) and 370/450 nm (glycation adduct). L-tyrosine (1 x 10(-5) M in 0.5 M HOAc) acted as a "reference compound" devoid of any collagen structural effects. In general, the fluorescence efficiency of these fluorophores decreases with increasing temperature. Assuming that rate constant for fluorescence deactivation has the form k(d)(T) = k(d) degrees exp (-DeltaE/RT), an Arrhenius plot of log[(1/Phi) - 1] vs. 1/T affords a straight line whose (negative) slope is proportional to the activation energy, DeltaE, of the radiationless process(es) that compete with fluorescence. Because it is difficult to accurately measure Phi(f) for collagen-bound fluorophores, we derived an approximate formula for an activation parameter, DeltaE*, evaluated from an Arrhenius-like plot of log 1/I(N)vs. 1/T, (1/I(N)vs. is the reciprocal normalized fluorescence intensity). Tyrosine in dilute solution affords a linear Arrhenius plot in both of the above cases. Using the known value of Phi(f) = 0.21 for free tyrosine at room temperature, we determined that DeltaE* is accurate to approximately 25% in the present instance. Collagen curves are non-linear, but they are quasi-linear below approximately 20 degrees C, where the helical form predominates. Values of DeltaE* determined from the data at T < 20 degrees C ranged from 6.2-8.4 kJ mol(-1) (1.5-2.0 kcal mol(-1)) for mouse collagen and 10.3-11.4 kJ mol(-1) (2.5-2.7 kcal mol(-1)) for calf skin collagen, consistent with collisional deactivation of the fluorescent state via thermally enhanced molecular vibrations and rotations. Above 20 degrees C, log 1/I(N)vs. 1/T plots from Skh-1 hairless mouse collagen are concave-downward, suggesting that fluorescence deactivation from the denatured coil has a significant temperature-independent component. For calf skin collagen, these plots are concave-upward, suggesting an increase in activation energy above Tm. These results suggest that collagen backbone and supramolecular structure can influence the temperature dependence of the bound fluorophores, indicating the future possibility of using activation data as a probe of supramolecular structure and conformation.     

Temperature dependence of DNA persistence length

We have determined the temperature dependence of DNA persistence length, a, using two different methods. The first approach was based on measuring the j-factors of short DNA fragments at various temperatures. Fitting the measured j-factors by the theoretical equation allowed us to obtain the values of a for temperatures between 5°C and 42°C. The second approach was based on measuring the equilibrium distribution of the linking number between the strands of circular DNA at different temperatures. The major contribution into the distribution variance comes from the fluctuations of DNA writhe in the nicked circular molecules which are specified by the value of a. The computation-based analysis of the measured variances was used to obtain the values of a for temperatures up to 60°C. We found a good agreement between the results obtained by these two methods. Our data show that DNA persistence length strongly depends on temperature and accounting for this dependence is important in quantitative comparison between experimental results obtained at different temperatures.     

Temperature dependence of superoxide dismutase activity in plankton

The effect of temperature (from 1 to 37 °C) on in vitro effective superoxide dismutase (SOD) activity of several organisms was investigated and compared. Antarctic plankton, cultures of the alga Nannochloropsis sp., and the cyanobacterium Synechococcus strain WH 7803, and pure bovine erythrocyte SOD was studied. It was found that in all cases SOD activity increased with decreasing temperature within the temperature range assayed, in the Polar as well as the temperate plankton cells. This behavior of SOD is counterintuitive in terms of our experience when looking at enzyme activity or any other chemical reaction. We suggest a theoretical explanation for this apparently odd behavior. The advantage of such behavior is that the same amount of antioxidant will act better under low temperatures when reactive oxygen species (ROS) increase. Moreover, this protective process would act in vivo at a faster pace than the ex novo enzyme synthesis.     

Temperature dependence of histidine ionization constants in myoglobin

The standard enthalpy of ionization of six titratable histidines in horse metaquomyoglobin was determined by repeating proton NMR titrations as a function of temperature and using the van't Hoff relationship. It was found that deltaH degrees varies between 16 and 37 kJ mol(-1) in the protein, compared with a value of 29 kJ mol(-1) in free histidine. The standard entropy change was evaluated by combining the enthalpy and free energy changes derived from the pKa values. Although the entropy change could not be precisely and accurately obtained by this method, it could be established that it spans a wide range, from -60 to 0 J K(-1) mol(-1), about the value of -23 J K(-1) mol(-1) for the free histidine. The entropy change was used within the framework of enthalpy-entropy compensation to partition the solvation component from the standard thermodynamic quantities for each of the titrating residues. It was shown that the partitioning of the values in the protein is not readily understood in terms of solvent accessibility or electrostatic interactions. The contribution of solvation effects to the temperature response appeared to be significant only in the case of His-119 and His-48. The standard quantities were also used to explore the energetics of proton binding in the native state at temperatures below the onset of thermal denaturation.     

Temperature dependence of D-glucose transport in reconstituted liposomes

Sodium-dependent D-glucose uptake into proteoliposomes reconstituted from dimyristoylphosphatidylcholine (DMPC) and hog kidney brush border membrane extract is strongly affected by temperature and the physical state of the membranes. This dependence is defined by a nonlinear Arrhenius plot with a break point at 23 degrees C, a temperature not significantly different from the phase transition temperature of the pure lipid (24 degrees C). The transport process is characterized by different activation energies: 35.1 kcal/mol below and 5.5 kcal/mol above the transition temperature. The shift in the break point for the D-glucose transport activity from 15 degrees C, in the brush border membranes, to 23 degrees C in the reconstituted system leads us to conclude that the lipids surrounding the sodium/D-glucose cotransport system can exchange readily with the bulk lipid used for reconstitution. The results thus provide no evidence for the presence of an annulus of specific lipids surrounding the transport system.     

Temperature dependence of fluctuations in HIV1-protease

Revealing the structure and the intrinsic dynamics of a protein is paramount to understand its function and other properties of evolutionary importance. Several schemes to obtain such insight in silico were developed over the decades. A computationally efficient protocol approximates the molecular dynamics around its native state by a harmonic potential. In this paper, we introduce a new methodology to combine the various harmonic approaches to understand the folding/unfolding dynamics and the dynamics around the native structure of the protein in a temperature dependent way. We apply this new protocol to the HIV1-protease and discuss the results in the light of events in the adaptive evolution towards drug resistance, which is a major problem in HIV infection.     

Interactive effects of elevated carbon dioxide and growth temperature on photosynthesis in cotton leaves

Cotton (Gossypium hirsutum L., cv DPL 5415) plants were grown in naturally lit environment chambers at day/night temperature regimes of 26/18 (T-26/18), 31/23 (T-31/23) and 36/28 °C (T-36/28) and CO2 concentrations of 350 (C-350), 450 (C-450) and 700 L L-1 (C-700). Net photosynthesis rates, stomatal conductance, transpiration, RuBP carboxylase activity and the foliar contents of starch and sucrose were measured during different growth stages. Net CO2 assimilation rates increased with increasing CO2 and temperature regimes. The enhancement of photosynthesis was from 24 mol CO2 m-2 s-1 (with C-350 and T-26/18) to 41 mol m-2 s-1 (with C-700 and T-36/28). Stomatal conductance decreased with increasing CO2 while it increased up to T-31/23 and then declined. The interactive effects of CO2 and temperature resulted in a 30% decrease in transpiration. Although the leaves grown in elevated CO2 had high starch and sucrose concentrations, their content decreased with increasing temperature. Increasing temperature from T-26/18 to 36/28 increased RuBP carboxylase activity in the order of 121, 172 and 190 mol mg-1 chl h-1 at C-350, C-450 and C-700 respectively. Our data suggest that leaf photosynthesis in cotton benefited more from CO_2 enrichment at warm temperatures than at low growth temperature regimes.