The photosynthetic gas-exchange has been assessed traditionally either as O2 evolution or CO2 consumption. In this study, we used a liquid-phase O2 electrode combined with CO2 optodes to examine simultaneously photosynthesis in intact leaves of mangrove Rhizophora mucronata. We verified suitable conditions for leaf photosynthetic rates by assessing pH levels and NaHCO3 concentrations and compared these to the gas-exchange method at various PAR levels. The photosynthetic rate in response to pH exhibited a similar pattern both for O2 evolution and CO2 consumption, and higher rates were associated with intermediate pH compared with low and high pH values. The net photosynthetic quotient (PQ) of R. mucronata leaves ranged from 1.04-1.28. The PQ values, which were never lesser than 1, suggested that photorespiration did not occur in R. mucronata leaves under aqueous conditions. The similar maximum photosynthetic rates suggested that all measurements had a high capacity to adjust the photosynthetic apparatus under a light saturation condition. The simultaneous measurements of O2 evolution and CO2 consumption using the Clark oxygen electrode polarographic sensor with the CO2 optode sensor provided a simple, stable, and precise measurement of PQ under aqueous and saturated light conditions., T. Z. Ulqodry, A. Nose, S.-H. Zheng., and Obsahuje seznam literatury
Active control of photosynthetic activities is important in plant physiological study. Although models of plant photosynthesis have been built at different scales, they have not been fully examined for their application in plant growth control. However, we do not have an infrastructure to support such experiments since current plant growth chambers usually use fixed control protocols. In our current paper, an open IoT-based framework is proposed. This framework allows a plant scientist or agricultural engineer, through an application programming interface (API), in a desirable programming language, (1) to gather environmental data and plant physiological responses; (2) to program and execute control algorithms based on their models, and then (3) to implement real-time commands to control environmental factors. A plant growth chamber was developed to demonstrate the concept of the proposed open framework.
The decay of chlorophyll (Chl) fluorescence of etiochloroplasts isolated in various stage of greening of cucumber cotyledons was analysed in order to get structural information on a photosynthetic apparatus. Two model decays, multiexponential and stretched exponential, were applied in the analysis. The quality of fit in these two models was different in various stages of chloroplast greening. The two-exponent model did not provide a good fit at early greening stages. To improve the fit it was necessary to introduce an additional third component which became very low at later stages. However, chloroplasts in the early stage of greening could also be described by a stretched exponential with parameters indicating rather planar (two-dimensional) arrangement of donor and acceptor molecules. The chloroplasts treated by DCMU and/or photooxidized by strong irradiance exhibit a similar character of fractal decay as untreated samples but in the multiexponential model the exact values of lifetimes and amplitudes of components vary. This suggests that the structure of investigated system does not dramatically change as a result of these two types of treatment. and A. Kowalczyk, A. Waloszek, D. Frąckowiak.
Turnover of Dl protein as influenced by actual irradiance and growth irradiance was analyzed in the photoautotrophic suspension cultured cells of Chenopodium rubrum. Proteins were labelled by adding 35S-methionine to the ceU suspension. Following electrophoresis the labelled proteins were detected by autoradiography. Relative label incorporation into the Dl protein containing band was calculated from scans of the autoradiographs and ušed as an estimate of Dl protein synthesis (pulse experiments) and Dl protein degradation (chase experiments). Total label incorporation was not affected by the irradiance during labelling but Dl protein synthesis and degradation were boťh increased at 900 pmol m-2 s*i as compared to 120 pmol m'2 s*^ The effect of growth irradiance was analysed by comparing cells which had been pre-cultured at 120 pmol m'2 s"^ (HL cells) and 900 pmol s‘i (PIL cells) for at least 6 d. The inhibition of chloroplastic protein synthesis by cUoramphenicol exacerbated the effect of photoinhibitory irradiance on the chlorophyll fluorescence parameters in these cells. The inhibitor effect was more pronoímced in PIL cells than in HL ones. This points to a higher chloroplastic protein synthesis capacity of the former cell type. Due to a considerable difference in total label incorporation pulse experiments could not be ušed to check this hypothesis. The chase experiments indicated that the Dl-protein degradation rate was higher in PIL cells tiian in HL cells. Probably a generál increase in the Dl protein tumover occiu^ if the cells are exposed to photoinhibitory irradiances for a prolonged period.
We studied the dominant environmental factors that affect the
gas-exchange characteristics and water potential (ψ) of broad-ovate leaves of Populus euphratica Oliv. in extreme arid area of Tarim River, China, and their correlation to water status of P. euphratica by analyzing on-field monitored meteorological data, soil moisture and salinity, P. euphratica leaf gas exchange and ψ, and revealed the indicative threshold of environmental factors for P. euphratica leaf water changes and growth. The results indicated that meteorological factors such as air relative humidity (RH), air temperature (T air), etc. are the dominant factors. The threshold value of RH is (48.19 ± 1.06)% for P. euphratica growth, i.e. RH from 10.69% to 48.19% is suitable for P. euphratica growth in extremely arid region of Tarim River. This study provides a theoretical basis for reducing drought damage to P. euphratica and maintaining normal growth of P. euphratica by in-time watering. and A. H. Fu ... [et al.].
The photochemical reflectance index (PRI), based on reflectance signatures at 531 and 570 nm, and associated with xanthophyll pigment inter-conversion and related thylakoid energisation, was evaluated as an indicator of photosynthetic function in a Mediterranean holm oak (Quercus ilex L.) coppice. The chlorophyll fluorescence pulse-amplitude-modulation and the eddy correlation techniques were used to estimate the photosystem 2 photochemical efficiency of leaves and the CO2 flux over the canopy, respectively. The reflectance and fluorescence techniques yielded identical estimates of the photosynthetic activity in leaves exposed to dark-light-dark cycles or to a variable irradiance in laboratory. However, there was no such correlation between photosynthetic performance and PRI when applied to a sun-exposed canopy in field conditions. Fluorescence profiles inside the canopy and especially a helpful use of multispectral reflectance imaging highlight the limitations of such method.
Nitrogen (N) starvation resulted in degreening, inhibition of photosynthetic oxygen evolution and dark respiration, reduced survival, and increased age-specific mortality in both Chlorella fusca and Chlorella vulgaris. Analysis of in vivo chlorophyll (Chl) fluorescence induction kinetics revealed the presence of N-starvation-induced changes at the level of degreened thylakoids in both species. These changes included decreased yield of the photochemistry of photosystem 2 (PS2), and a declined photosynthetic efficiency. Synthesis of secondary carotenoids represented a biochemical change in carotenogenesis that had a photoprotective effect in degreened C. fusca. This inferred photoprotection was reflected in the delayed inhibition of oxygen evolution and improved survival of C. fusca under N-starvation. The effect was further elucidated by comparison with C. vulgaris which was not able to synthesize secondary carotenoids under the same conditions.
Redox polymer/protein biophotoelectrochemistry was used to analyse forward electron transfer of isolated PSII complexes with natural PsbA-variants. PsbA1- or PsbA3-PSII was embedded in a redox hydrogel that allows diffusion-free electron transfer to the electrode surface and thus measurement of an immediate photocurrent response. The initial photocurrent density of the electrode is up to ~2-fold higher with PsbA1-PSII under all tested light conditions, the most prominent under high-light [2,300 μmol(photon) m-2 s-1] illumination with 5 μA cm-2 for PsbA3-PSII and 9.5 μA cm-2 for PsbA1-PSII. This indicates more efficient electron transfer in low-light-adapted PsbA1-PSII. In contrast, the photocurrent decays faster in PsbA1-PSII under all tested light conditions, which suggests increased stability of high-light-adapted PsbA3-PSII. These results confirm and extend previous observations that PsbA3-PSII has increased P680+/QA- charge recombination and thus less efficient photon-to-charge conversion, whereas PsbA1-PSII is optimised for efficient electron transfer with limited stability., V. Hartmann, A. Ruff, W. Schuhmann, M. Rögner, M. M. Nowaczyk., and Obsahuje bibliografické odkazy
The adaptation of barley (Hordeum vulgare L. cv. Akcent) plants to low (LI, 50 µmol m-2 s-1) and high (HI, 1000 µmol m-2 s-1) growth irradiances was studied using the simultaneous measurements of the photosynthetic oxygen evolution and chlorophyll a (Chl a) fluorescence at room temperature. If measured under ambient CO2 concentration, neither increase of the oxygen evolution rate (P) nor enhancement of non-radiative dissipation of the absorbed excitation energy within photosystem 2 (PS2) (determined as non-photochemical quenching of Chl a fluorescence, NPQ) were observed for HI plants compared with LI plants. Nevertheless, the HI plants exhibited a significantly higher proportion of QA in oxidised state (estimated from photochemical quenching of Chl a fluorescence, qP), by 49-102 % at irradiances above 200 µmol m-2 s-1 and an about 1.5 fold increase of irradiance-saturated PS2 electron transport rate (ETR) as compared to LI plants. At high CO2 concentration the degree of P stimulation was approximately three times higher for HI than for LI plants, and the irradiance-saturated P values at irradiances of 2 440 and 2 900 µmol m-2 s-1 were by 130 and 150 % higher for HI plants than for LI plants. We suggest that non-assimilatory electron transport dominates in the adaptation of the photosynthetic apparatus of barley grown at high irradiances under ambient CO2 rather than an increased NPQ or an enhancement of irradiance-saturated photosynthesis. and I. Kurasová ... [et al.].
Six barley chlorophyll (Chl) mutants, viridis, flavoviridis, chlorina, xanhta, lutea, and albina, differed in the contents of Chl (a+b) and carotenoids (Cars). In accordance with their Chl-deficient phenotype, the Chl a and b and Car contents of mutants decreased from viridis to albina, only xantha had the same or even higher concentration of Cars as the wild type plant. The albina mutant completely lacked and xantha had a significantly reduced photosynthetic activity. We found quantitative differences in protein contents between wild type and mutant plants, with the lowest concentration per fresh mass in the albina mutant. Chl fluorescence analysis revealed that heat-treated barley leaves of both the wild type and Chl mutants had a lower photosystem 2 efficiency than the untreated ones. With 35S-methionine labelling and SDS-PAGE we found that six to nine de novo synthetized proteins appeared after heat shock (2 h, 42 °C) in the wild type and Chl mutants. In albina the expression of heat shock proteins (HSPs) was reduced to 50 % of that in the wild type. Hence mainly albina mutants, with a completely destroyed proteosynthetic apparatus of the chloroplasts, are able to synthesize a small set of HSPs. The albina mutant is a very useful tool for the study of different gene expression of chloroplast and nuclear DNA. and E. Gálová, B. Böhmová, A. Ševčovičová.