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PubMed2006

UV effects on photosynthesis and DNA in propagules of three Antarctic seaweeds (Adenocystis utricularis, Monostroma hariotii and Porphyra endiviifolium).

Ozone depletion is highest during spring and summer in Antarctica, coinciding with the seasonal reproduction of most macroalgae. Propagules are the life-stage of an alga most susceptible to environmental perturbations therefore, reproductive cells of three intertidal macroalgal species Adenocystis utricularis (Bory) Skottsberg, Monostroma hariotii Gain, and Porphyra endiviifolium (A and E Gepp) Chamberlain were exposed to photosynthetically active radiation (PAR), PAR + UV-A and PAR + UV-A + UV-B radiation in the laboratory. During 1, 2, 4, and 8 h of exposure and after 48 h of recovery, photosynthetic efficiency, and DNA damage were determined. Saturation irradiance of freshly released propagules varied between 33 and 83 mumol photons m(-2) s(-1) with lowest values in P. endiviifolium and highest values in M. hariotii. Exposure to 22 mumol photons m(-2) s(-1 )PAR significantly reduced photosynthetic efficiency in P. endiviifolium and M. hariotii, but not in A. utricularis. UV radiation (UVR) further decreased the photosynthetic efficiency in all species but all propagules recovered completely after 48 h. DNA damage was minimal or not existing. Repeated exposure of A. utricularis spores to 4 h of UVR daily did not show any acclimation of photosynthesis to UVR but fully recovered after 20 h. UVR effects on photosynthesis are shown to be species-specific. Among the tested species, A. utricularis propagules were the most light adapted. Propagules obviously possess good repair and protective mechanisms. Our study indicates that the applied UV dose has no long-lasting negative effects on the propagules, a precondition for the ecological success of macroalgal species in the intertidal.

Antarctic Regions↗
PubMed2003

Legume presence increases photosynthesis and N concentrations of co-occurring non-fixers but does not modulate their responsiveness to carbon dioxide enrichment.

Legumes, with the ability to fix atmospheric nitrogen (N), may help alleviate the N limitations thought to constrain plant community response to elevated concentrations of atmospheric carbon dioxide (CO(2)). To address this issue we assessed: (1) the effects of the presence of the perennial grassland N(2 )fixer, Lupinus perennis, on biomass accumulation and plant N concentrations of nine-species plots of differing plant composition; (2) leaf-level physiology of co-occurring non-fixing species (Achillea millefolium, Agropyron repens, Koeleria cristata) in these assemblages with and without Lupinus; (3) the effects of elevated CO(2) on Lupinus growth and symbiotic N(2) fixation in both monoculture and the nine-species assemblages; and (4) whether assemblages containing Lupinus exhibit larger physiological and growth responses to elevated CO(2 )than those without. This study was part of a long-term grassland field experiment (BioCON) that controls atmospheric CO(2) at current ambient and elevated (560 micromol mol(-1)) concentrations using free-air CO(2) enrichment. Nine-species plots with Lupinus had 32% higher whole plot plant N concentrations and 26% higher total plant N pools than those without Lupinus, based on both above and below ground measurements. Co-occurring non-fixer leaf N concentrations increased 22% and mass-based net photosynthetic rates increased 41% in plots containing Lupinus compared to those without. With CO(2) enrichment, Lupinus monocultures accumulated 32% more biomass and increased the proportion of N derived from fixation from 44% to 57%. In nine-species assemblages, Lupinus N derived from fixation increased similarly from 43% to 54%. Although Lupinus presence enhanced photosynthetic rates and leaf N concentrations of co-occurring non-fixers, and increased overall plant N pools, Lupinus presence did not facilitate stronger photosynthetic responses of non-fixing species or larger growth responses of overall plant communities to elevated CO(2). Non-fixer leaf N concentrations declined similarly in response to elevated CO(2) with and without Lupinus present and the relationship between net photosynthesis and leaf N was not affected by Lupinus presence. Regardless of the presence or absence of Lupinus, CO(2) enrichment resulted in reduced leaf N concentrations and rates of net photosynthesis.

Carbon Dioxide↗
PubMed2005

Photosynthesis and reflectance indices for rainforest species in ecosystems undergoing progression and retrogression along a soil fertility chronosequence in New Zealand.

Measurements of photosynthesis at saturating irradiance and CO2 partial pressure, Amax, "adjusted" normalised difference vegetation index, RaNDVI, and photochemical reflectance index, RPRI, were made on trees sampled along a soil chronosequence to investigate the relationship between carbon uptake and ecosystem development in relation to nutrient availability. Measurements were made on the three most dominant species at six sites along the sequence in South Westland, New Zealand with soil age ranging from < 6 to 120,000 years resulting from the retreat of the Franz Josef glacier. The decrease in soil phosphorus availability with increasing soil age and high soil nitrogen availability at the two youngest sites, due to the presence of a nitrogen-fixing species, provided marked differences in nutrient availability. Mean Amax was high at the two youngest sites, then decreased markedly with increasing site age. Analysis of the data for individual species within sites revealed separation of groups of species in the response of Amax to Nm and Pm, suggesting complex interactions between the two nutrients. There were strong linear relationships for leaf-level RaNDVI and RPRI with Amax, at high irradiance, showing that measurements of reflectance indices can be used to estimate Amax for foliage with a range in morphology and nutrient concentrations. Notwithstanding the change in species composition from angiosperms to conifers with increasing site age, the presence of nitrogen-fixing species, the variability in foliage morphology from flat leaves to imbricate scales and a wide range in foliar nitrogen and phosphorus concentrations, there were strong positive linear relationships between site average Amax and foliage nitrogen, Nm, and phosphorus, Pm, concentrations on a foliage mass basis. The results provide insights to interpret the regulation of photosynthesis across natural ecosystems with marked gradients in nitrogen and phosphorus availability.

Analysis of Variance↗
PubMed2006

Nocturnal respiration of lichens in their natural habitat is not affected by preceding diurnal net photosynthesis.

Dark respiration (DR) of lichens is reported to be higher in species with a high photosynthetic potential (suggesting a metabolic maintenance cost effect) and also, often in laboratory studies, transiently after photosynthesis (suggesting a substrate-driven effect). We investigated the occurrence of the latter, the effect of diurnal net photosynthesis (NP) on subsequent nocturnal DR, under natural temperate climate conditions in the chlorolichens Lecanora muralis and Cladonia convoluta and the cyanolichen Collema cristatum. Data sets totalling 15 months, 106 and 113 days, respectively, were obtained from automatic cuvettes that continually measured CO2 exchange and ambient conditions at 30 min intervals. For each 24 h period (sunrise to following sunrise), several measures of NP and DR were extracted, including maximal and mean rates and daily sums. No statistically significant correlations between the various measures of DR and preceding NP were found for L. muralis, only one weak correlation for Co. cristatum (the means of DR and NP) and three for Cl. convoluta (sums and means of DR and NP). It is proposed that even these significant correlations are actually a result of embedded codependencies between NP, DR and thallus water content. Overall it is concluded that no substrate-driven dependency of DR on preceding NP under natural conditions could be recognised. The periods of desiccation that often occur between the NP and following DR as well as the wide range of combinations of conditions would certainly contribute to this lack of relationship.

Carbon Dioxide↗
PubMed2006

Changes in stomatal conductance and net photosynthesis during phenological development in spring wheat: implications for gas exchange modelling.

Gas exchange was measured from 1 month before the onset of anthesis until the end of grain filling in field-grown spring wheat, Triticum aestivum L., cv. Vinjett, in southern Sweden. Two g ( s ) models were parameterised using these data: one Jarvis-type multiplicative g ( s ) model (J-model), and one combined stomatal-photosynthesis model (L-model). In addition, the multiplicative g ( s ) model parameterisation for wheat used within the European Monitoring and Evaluation Programme (EMEP-model) was tested and evaluated. The J-model performed well (R (2)=0.77), with no systematic pattern of the residuals plotted against the driving variables. The L-model explained a larger proportion of the variation in g ( s ) data when observations of A (n) were used as input data (R (2)=0.71) compared to when A (n) was modelled (R (2)=0.53). In both cases there was a systematic model failure, with g (s) being over- and underestimated before and after anthesis, respectively. This pattern was caused by the non-parallel changes in g ( s ) and A (n) during plant phenological development, with A (n) both peaking and starting to decline earlier as compared to g ( s ). The EMEP-model accounted for 41% of the variation in g ( s ) data, with g ( s ) being underestimated after anthesis. We conclude that, under the climatic conditions prevailing in southern Scandinavia, the performance of the combined stomatal-photosynthesis approach is hampered by the non-parallel changes in g ( s ) and A (n), and that the phenology function of the EMEP-model, having a sharp local maximum at anthesis, should be replaced by a function with a broad non-limiting period after anthesis.

Carbon Dioxide↗
PubMed2002

Uptake and transfer of nutrients in ectomycorrhizal associations: interactions between photosynthesis and phosphate nutrition.

Energy-dispersive X-ray microanalytical investigations and microautoradiographic studies were carried out to examine whether the uptake and transfer of phosphate (P) by an ectomycorrhizal fungus is affected by the carbohydrate supply of its host plant. For this purpose, non-mycorrhizal seedlings of Pinus sylvestris L. and plants inoculated with the ectomycorrhizal basidiomycete Suillus bovinus (L. ex Fr.) Kuntze were placed in the dark for 7 days in advance of a P supply. The subcellular element distribution and the uptake and distribution of (33)P was analyzed in non-mycorrhizal and mycorrhizal roots of these plants and compared with plants kept constantly under normal light conditions (control plants). The results show that placing non-mycorrhizal plants in the dark in advance of the nutrient supply led to (1) a reduction of the subcellular contents of P, S and K, but to an increase in the cytoplasmic Na content, and (2) an increase of (33)P absorption and translocation to the shoot. It can be assumed that this increased inflow of (33)P in non-mycorrhizal plants was due to P starvation after suppressed photosynthesis and reduced respiration of these plants. The suppression of photosynthesis by an ectomycorrhizal host plant and the resulting lower carbohydrate supply conditions for the ectomycorrhizal fungus led to (1) a decrease of P absorption by the mycobiont, (2) a change of the P allocation in the fungal cell compartments of an ectomycorrhizal root, and (3) a reduction of P transfer to the host plant. However, microautoradiographic studies revealed that, under these conditions, P was also absorbed by the mycorrhizal fungus and translocated via the Hartig net to the host plant. In mycorrhizal roots of plants placed in the dark in advance of the nutrient supply, the cytoplasmic P content of the Hartig net was reduced and, instead, a high number of polyphosphate granules could be detected within the hyphae. The results indicate that the exchange processes between the symbionts in a mycorrhiza are possibly linked and that P uptake and translocation by an ectomycorrhizal fungus is also regulated by the carbohydrate supply of its host plant.

Basidiomycota↗
PubMed2004

Interspecific difference in the photosynthesis-nitrogen relationship: patterns, physiological causes, and ecological importance.

The photosynthesis-nitrogen relationship is significantly different among species. Photosynthetic capacity per unit leaf nitrogen, termed as photosynthetic nitrogen-use efficiency (PNUE), has been considered an important leaf trait to characterise species in relation to their leaf economics, physiology, and strategy. In this review, I discuss (1) relations between PNUE and species ecology, (2) physiological causes and (3) ecological implications of the interspecific difference in PNUE. Species with a high PNUE tend to have high growth rates and occur in disturbed or high productivity habitats, while those with a low PNUE occur in stressful or low productivity habitats. PNUE is an important leaf trait that correlates with other leaf traits, such as leaf mass per area (LMA) and leaf life span, irrespective of life form, phylogeny, and biomes. Various factors are involved in the interspecific difference. In particular, nitrogen allocation within leaves and the mesophyll conductance for CO(2) diffusion are important. To produce tough leaves, plants need to allocate more biomass and nitrogen to make thick cell walls, leading to a reduction in the mesophyll conductance and in nitrogen allocation to the photosynthetic apparatus. Allocation of biomass and nitrogen to cell walls may cause the negative relationship between PNUE and LMA. Since plants cannot maximise both PNUE and leaf toughness, there is a trade-off between photosynthesis and persistence, which enables the existence of species with various leaf characteristics on the earth.

Environment↗
PubMed2004

Roles of the acidic lipids sulfoquinovosyl diacylglycerol and phosphatidylglycerol in photosynthesis: their specificity and evolution.

Sulfoquinovosyl diacylglycerol (SQDG) and phosphatidylglycerol (PG) are lipids with negative charges, distributed among membranes of chloroplasts of plants and their postulated progenitors, cyanobacteria, and also widely among membranes of anoxygenic photosynthetic bacteria. Thus, these acidic lipids are of great interest in terms of their roles in the function and evolution of the photosynthetic membranes. The physiological significance of these lipids in photosynthesis has been examined through characterization of mutants defective in their abilities to synthesize SQDG or PG, and through characterization of isolated thylakoid membranes or photosynthetic particles, the acidic lipid contents of which were manipulated in vitro, for example, on treatment with phospholipase to degrade PG. Responsibility of SQDG or PG has been clarified so far in terms of the structural and/or functional integrity of photosystems I and/or II in cyanobacterial, green algal, and higher plant species. Also implied were distinct levels of the responsibility in the different photosynthetic organisms. Extreme cases involved the indispensability of SQDG for photosynthesis and growth in two prokaryotic, photosynthetic organisms and the contribution of PG to construction of the photosystem-I trimer exclusively in cyanobacteria. Here, roles of these acidic lipids are discussed with a focus on their specificity and the evolution of photosynthetic membranes.

Biological Evolution↗
PubMed2006

Photosynthesis and water relations in tomato plants cultivated long-term in media containing (+)-usnic acid.

The influence of (+)-usnic acid on rates of gas exchange (photosynthesis, respiration, and transpiration) in long-term cultivation of tomato plants was studied. The effect was dose-dependent. Plants grown in media containing the maximum concentration of (+)-usnic acid (30 muM) had photosynthetic and respiration rates reduced by 41% and 80%, respectively. The effect on photosynthesis rate may be the result of a multidirectional effect at various stages of this process, which at the highest usnic acid concentration underwent reduction: content of chlorophylls by 30%, carotenoids by 35%, and Hill reaction activity by 75%. Usnic acid also raises the susceptibility of chlorophyll to photodegradation. Under some conditions, transpiration was reduced by 2.1-fold in light and 3.7-fold in dark. This result was correlated with (1) an increase in the diffusive resistance of the stomata (3.1-fold in upper and 1.5-fold in lower surface of leaf), (2) a reduction of stomata density (by 60% on upper and 40% on lower surface), and (3) a 12.3-fold decrease in root hydraulic conductance.

Benzofurans↗
PubMed2004

Expression of a yeast acetyl CoA hydrolase in the mitochondrion of tobacco plants inhibits growth and restricts photosynthesis.

Acetyl Coenzyme A (acetyl CoA) is required in the mitochondria to fuel the operation of the Krebs cycle and within the cytosolic, peroxisomal and plastidial compartments wherein it acts as the immediate precursor for a wide range of anabolic functions. Since this metabolite is impermeable to membranes it follows that discrete pathways both for its synthesis and for its utilization must be present in each of these organelles and that the size of the various compartmented pools are independently regulated. To determine the specific role of acetyl CoA in the mitochondria we exploited a transgenic approach to introduce a yeast acetyl CoA hydrolase (EC 3.1.2.1.) into this compartment in tobacco plants. Despite the facts that the introduced enzyme was correctly targeted and that there were marked reductions in the levels of citrate and malate and an increase in the acetate content of the transformants, the transgenic plants surprisingly exhibited increased acetyl CoA levels. The lines were further characterised by a severe growth retardation, abnormal leaf colouration and a dramatic reduction in photosynthetic activity correlated with a marked reduction in the levels of transcripts of photosynthesis and in the content of photosynthetic pigments. The altered rate of photosynthesis in the transgenics was also reflected by a modified carbon partitioning in leaves of these lines, however, further studies revealed that this was most likely caused by a decreased source to sink transport of carbohydrate. In summary these results suggest that the content of acetyl CoA is under tight control and that alterations in the level of this central metabolite have severe metabolic and developmental consequences in tobacco.

Acetate-CoA Ligase↗
PubMed2004

Genetic analysis of cold-tolerance of photosynthesis in maize.

The genetic basis of cold-tolerance was investigated by analyzing the quantitative trait loci (QTL) of an F2:3 population derived from a cross between two lines bred for contrasting cold-tolerance using chlorophyll fluorescence as a selection tool. Chlorophyll fluorescence parameters, CO2 exchange rate, leaf greenness, shoot dry matter and shoot nitrogen content were determined in plants grown under controlled conditions at 25/22 degrees C or 15/13 degrees C (day/night). The analysis revealed the presence of 18 and 19 QTLs (LOD > 3.5) significantly involved in the variation of nine target traits in plants grown at 25/22 degrees C and 15/13 degrees C, respectively. Only four QTLs were clearly identified in both temperatures regimes for the same traits, demonstrating that the genetic control of the performance of the photosynthetic apparatus differed, depending on the temperature regime. A major QTL for the cold-tolerance of photosynthesis was identified on chromosome 6. This QTL alone explained 37.4 of the phenotypic variance in the chronic photoinhibition at low temperature and was significantly involved in the expression of six other traits, including the rate of carbon fixation and shoot dry matter accumulation, indicating that the tolerance to photoinhibition is a key factor in the tolerance of maize to low growth temperature. An additional QTL on chromosomes 2 corresponded to a QTL identified previously in another population, suggesting some common genetic basis of the cold-tolerance of photosynthesis in different maize germplasms.

Adaptation, Physiological↗
PubMed2006

Effect of altitude on the primary products of photosynthesis and the associated enzymes in barley and wheat.

There is little information available on the primary products of photosynthesis and the change in the activity of the associated enzymes with altitude. We studied the same in varieties of barley and wheat grown at 1300 (low altitude, LA) and 4200 m (high altitude, HA) elevations above mean sea level in the western Himalayas. Plants at both the locations had similar photosynthetic rates, leaf water potential and the chlorophyll fluorescence kinetics. The short-term radio-labelling experiments in leaves showed appearance of (14)CO(2) in phosphoglyceric acid and sugar phosphates in plants at both the LA and HA, suggesting a major role of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in CO(2) fixation in the plants at two altitudes, whereas the appearance of labelled carbon in aspartate (Asp) and glutamate (Glu) at HA suggested a role of phosphoenolpyruvate carboxylase (PEPCase) in photosynthesis metabolism. Plants at HA had significantly higher activities of PEPCase, carboxylase and oxygenase activity of Rubisco, aspartate aminotransferase (AspAT), and glutamine synthetase (GS). However, the activities of malate dehydrogenase, NAD-malic enzyme and citrate synthase were similar at the two locations. Such an altered metabolism at HA suggested that PEPCase probably captured CO(2) directly from the atmosphere and/or that generated metabolically e.g. from photorespiration at HA. Higher oxygenase activity at HA suggests high photorespiratory activity. OAA thus produced could be additionally channelised for Asp synthesis using Glu as a source of ammonia. Higher GS activity ensures higher assimilation rate of NH(3) and the synthesis of Glu through GS-GOGAT (glutamine:2-oxoglutarate aminotransferase) pathway, also as supported by the appearance of radiolabel in Glu at HA. Enhanced PEPCase activity coupled with higher activities of AspAT and GS suggests a role in conserving C and N in the HA environment.

Altitude↗
PubMed2006

Light- and CO2-saturated photosynthesis: enhancement by oxygen.

Oxygen may enhance CO2-saturated photosynthesis in intact leaves, which display the Warburg effect when illuminated at the current atmospheric level of CO2 and O2, of about 350 microl l(-1) and 21%, respectively. The magnitude of the stimulation depends on irradiance. The K(M)(O2) of the stimulation is 128 microM (10.6% O2). Maximum enhancement in wheat leaves is 6.1 and 5.3 micromol m(-2) s(-1 )under 27.9 and 18.7 mW cm(-2), respectively, corresponding to a 25-30% increase in the ribulose 1,5-bisphosphate (RuBP) turnover rate if compared with O2-free ambient gas phase. The stimulation appears in 5-10 s after a sharp increase in O2. In response to a decrease in O2, the new stabilized rate is reached in 5-7 min. The stimulation does not involve any increase in the activity of Rubisco. The effect correlates with increased concentration of RuBP. Oxygen enhances CO2-saturated photosynthesis by acting as a terminal electron acceptor in the photosynthetic electron transport. The magnitude of the effect may be adopted as an index of the pseudocyclic photophosphorylation in vivo.

Carbon Dioxide↗
PubMed2006

Twenty years of biophysics of photosynthesis in Padova, Italy (1984-2005): a tale of two brothers.

This paper tells the history of two brothers, almost a generation apart in age, who met again, after having followed different academic paths, to introduce biophysical research in photosynthesis at the University of Padova. The development of two research groups, one in the Chemistry Department, the other in the Biology Department led to a comprehensive interdisciplinary group across academic barriers. The group of Giovanni Giacometti developed in Physical Chemistry, during the years before his retirement, with some roots which can be traced to the famous Linus Pauling school of the mid 1950s, and made possible, by the work of many students (especially Donatella Carbonera and Marilena Di Valentin) and of an older associate (Giancarlo Agostini). The group participated quite actively with a number of European and American laboratories in the application of physical techniques, especially Electron Spin Resonance (EPR) associated with Optical Spectroscopy (Optically Detected Magnetic Resonance; ODMR), and contributed to the development of the understanding of the structure-function relationships in photosynthetic membrane complexes, stimulated by the determination of the X-ray structure of the purple photosynthetic reaction center in the mid 1980s ( J. Deisenhofer, H. Michel, R. Huber and others). The younger brother of Giovanni, Giorgio Mario Giacometti, came to Padova after obtaining biochemical knowledge from the Rossi-Fanelli school in Rome, where Jeffries Wyman, Eraldo Antonini and Maurizio Brunori were the world masters of hemoglobin research. In Padova, together with a group of young scientists (at first Roberto Bassi and Roberto Barbato, now leaders of their own groups in Verona and in Alessandria respectively, followed soon by brilliant coworkers such as Fernanda Rigoni, Elisabetta Bergantino and more recently Ildikò Szabò and Paola Costantini), Giorgio approached more biochemical themes of oxygenic photosynthesis, such as purification and characterization of antenna chlorophyll-protein complexes, Photosystem II (PS II) particles and subunits, having always in mind structural and molecular problems at the level of the largest integrated particles, which are more difficult to investigate in detail by the spectroscopic techniques.

Biophysics↗
PubMed2006

A re-investigation of the path of carbon in photosynthesis utilizing GC/MS methodology. Unequivocal verification of the participation of octulose phosphates in the pathway.

A GC/EIMS/SIM methodology has been developed to re-examine the path of carbon in photosynthesis. Exposing isolated spinach chloroplasts to 13CO2 on a solid support for a defined period followed by quenching and work-up provided a mixture of labelled sugar phosphates. After enzymatic dephosphorylation and derivatization, the Mox-TMS sugars were analysed using the above method. The purpose of the study was to try to calculate the atom% enrichment of 13C in as many of the individual carbons in each of the derivatized sugars as was practical using diagnostic fragment ions. In the event, only one 45 s experiment provided sufficient data to enable a range of enrichment values to be calculated. This confirmed that D-glycero-D-altro-octulose phosphate was present in the chloroplasts and was heavily labelled in the C4, C5 and C6 positions, in keeping with the hypothesis that it had an inclusive role and a labelling pattern consistent with a new modified pathway of carbon in photosynthesis.

Calibration↗
PubMed1984

Search for an endotherm in chloroplast lamellar membranes associated with chilling-inhibition of photosynthesis.

The phase transition of chloroplast lamellar membrane lipids has been proposed to be the underlying cause of chilling-induced inhibition of photosynthesis in sensitive plants. Differential scanning calorimetry has been used to search for any endotherms arising from lipid state changes in chloroplast lamellar membranes of the chilling-sensitive plants cantaloupe , kidney bean, domestic tomato, and soybean. For comparison, calorimetric scans of chloroplast lamellar membranes from the chilling-insensitive plants spinach, pea, and wild tomato were made. A large reversible endotherm, extending from below 10 degrees to nearly 40 degrees C, was observed in chloroplast membranes from tomatoes of both chilling-sensitive (Lycopersicon esculentum Mill. cv. Floramerica ) and chilling-insensitive (L. hirsutum LA 1361) species. A much smaller endotherm, approximately 5 to 10% of the area of that seen in the two tomato species, and extending over a similar temperature range, was detected in chloroplasts from chilling-insensitive spinach and peas, and also was generally observed in chloroplasts from chilling-sensitive cantaloupe , kidney bean, and soybean. The enthalpy of these smaller endotherms indicates that, if the endotherm arose entirely from a lipid transition, then it corresponded to the melting of less than about 10% of the total membrane polar lipid. On the basis of these data it is concluded that there is no correlation between chilling sensitivity of photosynthesis and the presence or absence of a phase transition of bulk membrane lipids of the chloroplast lamellar membrane at temperatures above 5 degrees C.

Chloroplasts↗
PubMed1977

The kinetic behavior of P-700 during the induction of photosynthesis in algae.

The kinetics of P-700 were examined spectrophotometrically during the induction of photosynthesis in algae. A pronounced oscillation was observed in the redox level of P-700 upon illumination of dark-adapted cells. The dark adaptation required approximately 1 min. The oscillation may be described as an initial rapid oxidation reaching a peak at approx. 50 ms followed by complete reduction of the pool of P-700. A subsequent slower oxidation resulted in attainment of the final state around 1 s. The main features of the oscillation were qualitatively the same in a wide variety of algae. The modulation in redox level of P-700 required high intensity activation of both photosystems and was eliminated by pre-illumination of the cells with weak short wavelength light but not by longer wavelengths absorbed primarily by Photosystem I. We propose that the P-700 modulation is directly related to the fast redox changes in Photosystem II which occur during the induction of photosynthesis. Cells incubated with methyl viologen did not show the P-700 oscillation confirming the suggestion previously advanced that exhaustion of Photosystem I acceptor and kinetic limitations in the carbon reduction cycle partially control the fast phase of photosynthetic induction.

Bacteria↗
PubMed1979

The differential action of metronidazole on nitrogen fixation, hydrogen metabolism, photosynthesis and respiration in Anabaena and Scenedesmus.

Metronidazole (2-methyl-5-nitroimidazole-1-ethanol) at 1--2 mM levels has been shown to be a selective inhibitor of nitrogenase activity in Anabanena. Two constitutive hydrogenases and photosynthesis are insensitive to metronidazole at these same concentrations. At higher concentrations metronidazole inhibits photosynthesis in Anabaena while photoreduction and to a lesser extent photohydrogen production are retarded in Scenedesmus. Respiration is slightly stimulated at high metronidazole levels in both algae. The reductant source for nitrogenase in Anabaena and photohydrogen production and photoreduction electron transport in Scenedesmus are discussed. Due to the activity to metronidazole as a selective inhibitor of ferredoxin-associated processes, it should prove to be useful in N2 fixation studies and in distinguishing between ferredoxin-linked reactions of different sensitivities and other activities not associated with low reduction potential components.

Cyanobacteria↗