The incorporation of nitrogen into products of recent photosynthesis in Anabaena cylindrica Lemm.

In vivo tracer studies with ¹⁴C have been performed to help determine pathways of incorporation of newly assimilated nitrogen into N₂-fixing cells of Anabaena cylindrica. After photosynthesis in Ar:O₂:¹⁴CO₂ for 30 min, the addition of N₂ or NH ₄ ⁺ resulted in increased rates of ¹⁴CO₂-incorporation both in the light and dark, and in increased incorporation of ¹⁴C into amino acids at the expense of sucrose and sugar phosphates. Evidence of enhanced sucrose catabolism and increased pyruvate kinase activity was obtained on adding nitrogen, and, of the ¹⁴C-labelling entering the tricarboxylic acid cycle, more appeared in citrate and 2-oxoglutarate than in malate and oxaloacetate. The kinetics of ¹⁴C-incorporation into various amino acids suggest that in the light and dark the most important route of primary ammonia assimilation involves glutamine synthetase and that glutamate, aspartate, glycine and probably alanine are formed secondarily from glutamine.     

The extracellular products of Anabaena cylindrica Lemm. II. Fluorescent substances containing serine and threonine,and their role in extracellular pigment formation

From aged-culture filtrates of Anabaena cylindrica Lemm., two similar compounds were isolated which fluoresced strongly in ultraviolet light. Hydrolysis of each gave a single different fluorescent moiety, and serine and threonine in a probable ratio of 2 : 1. No carboxy- or amino-terminal amino acid was present. On chromatograms exposed to light, the fluorescent peptides turned yellow-brown. Analysis of the results of this reaction indicated conversion to similar but yellow substances, followed by polymerisation to give a macromolecular brown pigment-peptide, indistinguishable from a similar complex which represents a major extracellular product of the alga.     

Performance and Photosynthetic Ecophysiology of Three Photo-Types of Dioscorea zingiberensis under Differing Light Intensities

Abstract: The performance and photosynthetic ecophysiology of three photo-types of Dioscorea zingiberensis were studied. The three types are designated DzTL, DzTM and DzTH, according to their adaptation to low (LL), medium (ML) and high (HL) light intensities, respectively. Under LL (23 - 55 μmol m^-2 s^-1) and simulated natural light (SNL), DzTM grows well with increased longevity, and green leaves which are unspotted; while its leaves became small, light yellow and short-lived under HL (550 - 850 μmol m^-2 s^-1). In contrast, under LL the leaves of DzTH were very large, spotted, light yellow and short-lived; while they were small, green and long-lived under HL. Under HL, DzTH had a much higher chlorophyll content than DzTM. Under LL, DzTM and DzTL had a higher Chl content than DzTH. Among the three types, DzTM had the highest peroxidase activity. DzTL had a higher electron transport rate (ETR), maximal quantum yield (MQY) and effective quantum yield (EQY) than DzTH and DzTL under LL, while DzTH had higher ETR, MQY and EQY than the other two types under ML and HL. Therefore, three different photo-types can be characterized according to their adaptation to LL, ML and HL: DzTL, DzTM and DzTH, respectively.     

Extension of a biochemical model for the generalized stoichiometry of electron transport limited C3 photosynthesis

The widely used steady‐state model of Farquhar et al. (Planta 149: 78–90, 1980) for C₃ photosynthesis was developed on the basis of linear whole‐chain (non‐cyclic) electron transport. In this model, calculation of the RuBP‐regeneration limited CO₂‐assimilation rate depends on whether it is insufficient ATP or NADPH that causes electron transport limitation. A new, generalized equation that allows co‐limitation of NADPH and ATP on electron transport is presented herein. The model is based on the assumption that other thylakoid pathways (the Q‐cycle, cyclic photophosphorylation, and pseudocyclic electron transport) interplay with the linear chain to co‐contribute to a balanced production of NADPH and ATP as required by stromal metabolism. The original model assuming linear electron transport limited either by NADPH or by ATP, predicts quantum yields for CO₂ uptake that represent the highest and the lowest values, respectively, of the range given by the new equation. The applicability of the new equation is illustrated for a number of C₃ crop species, by curve fitting to gas exchange data in the literature. In comparison with the original model, the new model enables analysis of photosynthetic regulation via the electron transport pathways in response to environmental stresses.     

Leaf development, temperature and light stress control of the expression of early light-inducible proteins (ELIPs) in Vitis vinifera L.

Early light inducible proteins (ELIPs) are thylakoid proteins transiently induced by light. They are found in many species, most of which are annual plants. Studies on perennial plants are scarce and in grapevine almost nil. Because grapevines normally grow in sites with high radiation, we aimed to characterize the ELIP expression to evaluate whether they have a role in photoprotection in this species. ELIP expression was characterized in leaves at different temperatures, times of induction and natural light intensities. Very low expression was found in mature leaves. In young leaves, ELIP expression was high but began at temperatures higher than 13 °C. Maximal expression was obtained at 30 °C after 4 h of induction at 1000 μmol PAR m⁻² s⁻¹. At this intensity, the level of photoinhibition was also maximal. We conclude that in grapevine leaves, ELIP expression is developmentally dependent, occurring mainly in developing leaves, Finally, our results showed that the light intensity dependence of the ELIP expression correlated with the extent of photoinhibition indicating that ELIP induction is controlled by the strength of light stress and suggesting a role of these proteins in photoprotection.     

Estimation of Photorespiration Rate by Simultaneous Measurements of CO2, Gas Exchange Rate,and Chlorophyll Fluorescence Quenching in the C3 Plant Vigna Radiata (L.) Wilczek and the C4 Plant Amaranthus Mongostanus L.

So far the photorespiration rate (R _P) in a leaf has been determined as the difference between the net photosynthetic rates (P _N) measured in 21 % O₂ air (P _N21%) and 3 % O₂ air (P _N3%). In the C₃ plant Vigna radiata and the C₄ plant Amaranthus mongostanus L., P _N and chlorophyll fluorescence quenching in leaves were monitored simultaneously. R _P of leaves in situ was estimated as termed R _PE from the electron transport rates through photosystem 2 (PS2), and compared with R _PO (P _N3% – P _N21%). In V. radiata R _PO was 11.9 µmol(CO₂) m^–2 s^–1 and the ratio of R _PO to P _N21% was 42.2 %, whereas the ratio of R _PE to P _N21% was 25.7 %. This suggests that R _PO may be over-estimated for the real R _P in normal air. In A. mongostanus, P _N was almost not changed with a decrease in O₂ concentration from 21 to 3 %, whereas the quantum yield of PS2 was evidently affected by the change in O₂ concentration. This fact shows the presence of photorespiration in this C₄ species, where R _PE was equivalent to 3.8 % of P _N21%.     

Evaluation of the importance of ionic and osmotic components of salt stress on the photosynthetic efficiency of epiphytic lichens

Salt stress can significantly disrupt the functioning of lichens which are self-sufficient symbiotic organisms inhabiting various severe environments. The aim was to test the effect of salt and sucrose on the photosynthetic efficiency of two selected epiphytic lichens inhabiting the interior of the land. Firstly, we compared the effect of salt and sucrose solutions of different concentrations. Secondly, the effect of salt and sucrose solutions with identical osmotic pressures was compared. The results showed that short-term salt stress leads to a significant reduction of F_V/F_M, greater changes in chlorophyll fluorescence parameters and OJIP transients compared to the osmotic effects induced by sucrose. This proved that the negative impact of salt stress is associated primarily with ionic effects. The most symptomatic effect of the ionic stress was a significant reduction of the utilisation of trapped energy in electron transport and thereby down-regulation of electron transfer. Since lichens are resistant to a temporary lack of water, ionic stress could have more serious consequences than osmotic stress itself. Hypogymnia physodes was more sensitive to salt stress than Pseudevernia furfuracea, but the reduction of photosynthetic efficiency was not permanent since after 24 h F_V/F_M returned to the level characteristic for healthy lichens. Nevertheless, repeated exposure to salt may reduce the vitality of lichens growing along communication routes sprinkled with salt in the winter season. Finally, the changes in certain JIP-test parameters were stronger than F_V/F_M, thus they could be better indicators of salt stress in lichens.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-022-01134-2.     

Photosystem II quantum yields,off-line measured P/I parameters and carbohydrate dynamics inChlorella vulgaris grown under a fluctuating light regime and its application for optimizing mass cultures

The influence of hourly fluctuating irradiance on a continuous culture ofChlorella vulgaris on the quantum yield for stable charge separation at photosystem II (_II,E) was examined. Linear regression analysis between _II,E and Ft or Fm' showed that Ft or Fm' explained 86 and 54% of the variability in _II,E respectively. The total amount of reducible Q_A remained constant during the light period. Only pigments that are known to operate in the xanthophyll cycle were variable. Violaxanthine reversibly decreased during the day, while an opposite pattern was observed for antheraxanthine. The changes in violaxanthine significantly (P 0.001) explained 87% of Fm' and 90% of the estimated values for the rate constant for energy dissipation by non-photochemical pathways. The magnitude of the variability in _II,E was well within range of regulation by the photosynthetic processes itself. The results suggest that _II,E alone can not be used as an index for the optimal cultivation of microalgae. Guidelines are proposed to translate fluorescence-derived parameters into general strategies to optimize productivity. Estimates ofin situ rates of primary photosynthesis derived from _II,E or from P/I derived estimates were significantly different, while predicted concentrations of carbohydrate concentrations were similar.Alfred Wegener Institute for Polar and Marine Research     

Rapid light-response curves of chlorophyll fluorescence in microalgae: relationship to steady-state light curves and non-photochemical quenching in benthic diatom-dominated assemblages

Rapid light-response curves (RLC) of variable chlorophyll fluorescence were measured on estuarine benthic microalgae with the purpose of characterising its response to changes in ambient light, and of investigating the relationship to steady-state light-response curves (LC). The response of RLCs to changes in ambient light (E, defined as the irradiance level to which a sample is acclimated to prior to the start of the RLC) was characterised by constructing light-response curves for the RLC parameters α _RLC, the initial slope, ETR_m,RLC, the maximum relative electron transport rate, and E _k,RLC, the light-saturation parameter. Measurements were carried out on diatom-dominated suspensions of benthic microalgae and RLC and LC parameters were compared for a wide range of ambient light conditions, time of day, season and sample taxonomic composition. The photoresponse of RLC parameters was typically bi-phasic, consisting of an initial increase of all parameters under low ambient light (E < 21–181 μmol m⁻² s⁻¹), and of a phase during which α _RLC decreased significantly with E, and the increase of ETR_m,RLC and E _k,RLC was attenuated. The relationship between RLC and LC parameters was dependent on ambient irradiance, with significant correlations being found between α _RLC and α, and between ETR_m,RLC and ETR_m, for samples acclimated to low and to high ambient irradiances, respectively. The decline of α _RLC under high light (Δα _RLC) was strongly correlated (P < 0.001 in all cases) with the level of non-photochemical quenching (NPQ) measured before each RLC. These results indicate the possibility of using RLCs to characterise the steady-state photoacclimation status of a sample, by estimating the LC parameter E _k, and to trace short-term changes in NPQ levels without dark incubation.     

Fractional control of photosynthesis by the QB protein,the cytochrome f/b 6 complex and other components of the photosynthesic apparatus

In order to obtain information on fractional control of photosynthesis by individual catalysts, catalytic activities in photosynthetic electron transport and carbon metabolism were modified by the addition of inhibitors, and the effect on photosynthetic flux was measured using chloroplasts of Spinacia oleracea L. In thylakoids with coupled electron transport, light-limited electron flow to ferricyanide was largely controlled by the Q_B protein of the electron-transport chain. Fractional control by the cytochrome f/b ₆ complex was insignificant under these conditions. Control by the cytochrome f/b ₆ complex dominated at high energy fluence rates where the contribution to control of the Q_B protein was very small. Uncoupling shifted control from the cytochrome f/b ₆ complex to the Q_B protein. Control of electron flow was more complex in assimilating chloroplasts than in thylakoids. The contributions of the cytochrome f/b ₆ complex and of the Q_B protein to control were smaller in intact chloroplasts than in thylakoids. Thus, even though the transit time for an electron through the electron-transport chain may be below 5 ms in leaves, oxidation of plastohydroquinone was only partially responsible for limiting photosynthesis under conditions of light and CO₂ saturation. The energy fluence rate influenced control coefficients. Fractional control of photosynthesis by the ATP synthetase, the cytochrome f/b ₆ complex and by ribulose-1,5-bisphosphate carboxylase increased with increasing fluence rates, whereas the contributions of the Q_B protein and of enzymes sensitive to SH-blocking agents decreased. The results show that the burdens of control are borne by several components of the photosynthetic apparatus, and that burdens are shifted as conditions for photosynthesis change.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DNP-INT 2,4-dinitro phenylether of 2-iodo-4-nitrothymol - pCMBS p-chloromercuribenzosulfonate     

Quantification of excitation energy distribution between photosystems based on a mechanistic model of photosynthetic electron transport

Absorbed light energy is converted into excitation energy. The excitation energy is distributed to photosystems depending on the wavelength and drives photochemical reactions. A non‐destructive, mechanistic and quantitative method for estimating the fraction of the excitation energy distributed to photosystem II (f) was developed. For the f values for two simultaneously provided actinic lights (ALs) with different spectral distributions to be estimated, photochemical yields of the photosystems were measured under the ALs and were then fitted to an electron transport model assuming the balance between the electron transport rates through the photosystems. For the method to be tested using leaves with different properties in terms of the long‐term and short‐term acclimation (adjustment of photosystem stoichiometry and state transition, respectively), the f values for red and far‐red light (R and FR) were estimated in leaves grown (~1 week) under white light without and with supplemental FR and adapted (~10 min) to R without and with supplemental FR. The f values for R were clearly greater than those for FR and those of leaves grown with and adapted to supplemental FR tended to be higher than the controls. These results are consistent with previous studies and therefore support the validity of the proposed method.     

Cyclic electron flow around photosystem I via chloroplast NAD(P)H dehydrogenase (NDH) complex performs a significant physiological role during photosynthesis and plant growth at low temperature in rice

The role of NAD(P)H dehydrogenase (NDH)-dependent cyclic electron flow around photosystem I in photosynthetic regulation and plant growth at several temperatures was examined in rice (Oryza sativa) that is defective in CHLORORESPIRATORY REDUCTION 6 (CRR6), which is required for accumulation of sub-complex A of the chloroplast NDH complex (crr6). NdhK was not detected by Western blot analysis in crr6 mutants, resulting in lack of a transient post-illumination increase in chlorophyll fluorescence, and confirming that crr6 mutants lack NDH activity. When plants were grown at 28 or 35°C, all examined photosynthetic parameters, including the CO(2) assimilation rate and the electron transport rate around photosystems I and II, at each growth temperature at light intensities above growth light (i.e. 800 μmol photons m(-2) sec(-1)), were similar between crr6 mutants and control plants. However, when plants were grown at 20°C, all the examined photosynthetic parameters were significantly lower in crr6 mutants than control plants, and this effect on photosynthesis caused a corresponding reduction in plant biomass. The F(v)/F(m) ratio was only slightly lower in crr6 mutants than in control plants after short-term strong light treatment at 20°C. However, after long-term acclimation to the low temperature, impairment of cyclic electron flow suppressed non-photochemical quenching and promoted reduction of the plastoquinone pool in crr6 mutants. Taken together, our experiments show that NDH-dependent cyclic electron flow plays a significant physiological role in rice during photosynthesis and plant growth at low temperature.     

The occurrence of rapidly reversible non-photochemical quenching of chlorophyll a fluorescence in cyanobacteria

Cyanobacteria have previously been considered to differ fundamentally from plants and algae in their regulation of light harvesting. We show here that in fact the ecologically important marine prochlorophyte, Prochlorococcus, is capable of forming rapidly reversible non-photochemical quenching of chlorophyll a fluorescence (NPQf or qE) as are freshwater cyanobacteria when they employ the iron stress induced chlorophyll-based antenna, IsiA. For Prochlorococcus, the capacity for NPQf is greater in high light-adapted strains, except during iron starvation which allows for increased quenching in low light-adapted strains. NPQf formation in freshwater cyanobacteria is accompanied by deep Fo quenching which increases with prolonged iron starvation.     

Freezing of isolated thylakoid membranes in complex media. V. Inactivation and protection of electron transport reactions

When chloroplast thylakoid membranes isolated from spinach leaves (Spinacia oleracea L. cv. Monatol) were frozen in media containing the predominant inorganic electrolytes of the chloroplast stroma, linear photosynthetic electron transport became progressively inhibited. After onset of freezing, both PSII- and PSI-mediated electron flow were inactivated almost to the same extent. Prolonged storage of the membranes in the frozen state increased damage to PSII relative to PSI activity. Under these conditions, a preferential injury of the water oxidation system was not observed. In thylakoids stored at 0 °C, PSI activity remained fairly unimpaired but inactivation of PSII occurred with strongest inhibition at the oxidizing side.The addition of low-molecular-weight cryoprotectants such as glycerol, sugars, certain amino acids and carbonic acids to thylakoid suspensions prior to freezing provided almost complete preservation of PSI activity and considerable but incomplete stabilization of PSII.Abbreviations BQ 1,4-benzoquinone - Chl chlorophyll - DAD 1,4-diamino-2,3,5,6-tetramethylbenzene - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-dichlorophenolindophenol - DMBQ 2,5-dimethyl-p-benzoquinone - DPC 1,5-diphenylcarbazide - Hepes 4-(2-hydroxyethyl)-1-piperazineeth-anesulfonic acid - MV methylviologen - PD 1,4-diaminobenzene - SOD superoxide dismutase (EC 1.15.1.1) - TMHQ tetramethyl-p-hydroquinone - TMPD N,N,N,N-tetramethyl-1,4-diaminobenzene - Tris 2-amino-2-(hydroxymethyl)-1,3-propandiol Dedicated to Professor Dr. Wilhelm Simonis, Würzburg, on the occasion of his 80th birthday     

Isolation and characterization of a 23 kDa protein essential for photosynthetic oxygen evolution

A 23 kDa protein has recently been demonstrated to participate in photosynthetic oxygen evolution by reconstitution experiments on inside-out thylakoid vesicles (Åkerlund H-E, Jansson C and Andersson B (1982) Biochim Biophys Acta 681:1–10). Here we describe the isolation of the 23 kDa protein from a spinach chloroplast extract using ion-exchange chromatography. The protein was obtained in a yield of 25% and with less than 1% of contaminating proteins. The ability of the protein to stimulate oxygen evolution in inside-out thylakoids was preserved throughout the various fractionation steps. The isolated protein was highly water soluble and appeared as a monomer. Its isoelectric point was at pH=7.3. The amino acid composition showed a high content of polar amino acids, resulting in a polarity index of 49%. The isolated protein lacked metals and other prosthetic groups. Its function as a catalytic or regulating subunit in the oxygen evolving complex is discussed.Abbreviations kDa kiloDalton - PAGE polyacrylamide gel electrophoresis     

The quantum efficiency of photosystem II and its relation to non-photochemical quenching of chlorophyll fluorescence; the effect of measuring-and growth temperature

The relation between the quantum yield of oxygen evolution of open photosystem II reactions centers (_p), calculated according to Weis and Berry (1987), and non-photochemical quenching of chlorophyll fluorescence of plants grown at 19°C and 7°C was measured at 19°C and 7°C. The relation was linear when measured at 19°C, but when measured at 7°C a deviation from linearity was observed at high values of non-photochemical quenching. In plants grown at 7°C this deviation occurred at higher values of non-photochemical quenching than in plants grown at 19°C. The deviations at high light intensity and low temperature are ascribed to an increase in an inhibition-related, non-photochemical quenching component (q_I).The relation between the quantum yield of excitation capture of open photosystem II reaction centers (_exe), calculated according to Genty et al. (1989), and non-photochemical quenching of chlorophyll fluorescence was found to be non-linear and was neither influenced by growth temperature nor by measuring temperature.At high PFD the efficiency of overall steady state electron transport measured by oxygen-evolution, correlated well with the product of q _N and the efficiency of excitation capture (_exe) but it deviated at low PFD. The deviations at low light intensity are attributed to the different populations of chloroplasts measured by gas exchange and chlorophyll fluorescence and to the light gradient within the leaf.Abbreviations F₀ basic fluorescence - F₀ basic fluorescence, thylakoid in energized state - F_m maximal fluorescence - F_m maximum fluorescence in energized state - F_s steady state fluorescence - F_v maximal variable fluorescence - PFD photon flux density - PS II_rc Photosystem II reaction center - q_F0 quenching of basic fluorescence - q_E energy related quenching - q_N non-photochemical quenching:-q_f-total quenching - q_I inhibition-related quenching - q_p photochemical quenching - q_r quenching due to state transition - R_d dark respiration - _p PS II efficiency of excitation capture of open PS II_rc - _pe extrapolated minimal value of _p - _p0 extrapolated maximal value of _p - _si quantum efficiency of linear electron transport, calculated from gas exchange measurements based on incident light - _sf quantum efficiency of linear electron transport, calculated from fluorescence measurements, based on incident measuring light     

The effects of spacer length on the fluorescence quantum yields of the benzofurazan compounds bearing a donor–acceptor system

We studied the effects of spacer length on the fluorescence quantum yields (Φ) of photoinduced electron transfer (PET) reagents, using nitrobenzoxadiazole (NBD) derivatives that have the –NMe₂ moiety and NBD–NH– fluorophore as electron donor (D) and electron acceptor (A), respectively. The Φ values were reduced as the spacer length became shorter (n ≤ 4; n is the number of methylene units of the spacer) and the fluorescence recovered by suppression of the PET process. It is necessary for the useful PET reagents to link D and A with a short spacer to obtain a difference in the Φ values between fluorescent ‘off‐state’ and ‘on‐state’. Copyright © 2002 John Wiley & Sons, Ltd.     

青藏高原药用植物唐古特山莨菪和唐古特大黄光合作用对强光的响应

与唐古特大黄相比,唐古特山莨菪的表观光合量子效率(AQY)较高,但最大净光合速率(Pmax)较低。在光强小于1200μmolm-2s-1时,后者用于碳同化的电子传递占总光合电子传递的比例(JC/JF)比前者高,而分配于光呼吸的电子传递(JO/JF)及Rubisco氧化和羧化速率的比值(VO/VC)则相反;光强大于1200μmolm-2s-1以后两种植物的这些参数都趋向稳定。随光强增加,后者叶片吸收光能分配于热耗散(D)的增加斜率较前者高,表明两高山植物对强辐射的适应方式略有不同。加强光呼吸途径的耗能代谢和PSII天线热耗散份额是唐古特山莨菪适应高原强辐射的主要方式,而提高叶片光合能力则是唐古特大黄的一种适应方式。