Diurnal and seasonal fluctuations in water potential (Ψ), stomatal conductance (gs), transpiration rate (E), and net photosynthetic rate (PN) were monitored in Capparis spinosa L., a Mediterranean plant growing during summer, i.e. at the period considered the most stressful for local plant life. In spite of the complete absence of rain, Ψ exhibited a modest drop at midday (-2.7 MPa), but was fully recovered overnight, indicating sufficient access to water sources. The stomata remained open throughout the day and season and the high E resulted in leaf temperatures up to 3.9 °C below air temperature. Additionally, PN of the fully exposed leaves was higher than 25 μmol m-2 s-1 for more than 10 h per day throughout the summer growth period. No symptoms of photooxidative stress were shown, as judged by maximum photosystem 2 photochemical efficiency (Fv/Fm) and the function of xanthophyll cycle. Indeed, diurnal inter-conversions of the xanthophyll cycle components were modest during the summer and a more intensive function of the cycle was only evident during leaf senescence in autumn. In comparison with a semi-deciduous and an evergreen sclerophyll co-existing in the same ecosystem, C. spinosa assimilated up to 3.4 times more CO2 per m2 during its growth period (May to October) and up to 1.8 times more on an annual basis. and E. Levizou, P. Drilias, A. Kyparissis.
Photosynthetic parameters, growth, and pigment contents were determined during expansion of the fourth leaf of in vitro photoautotrophically cultured Nicotiana tabacum L. plants at three irradiances [photosynthetically active radiation (400-700 nm): low, LI 60 µmol m-2 s-1; middle, MI 180 µmol m-2 s-1; and high, HI 270 µmol m-2 s-1]. During leaf expansion, several symptoms usually accompanying leaf senescence appeared very early in HI and then in MI plants. Symptoms of senescence in developing leaves were: decreasing chlorophyll (Chl) a+b content and Chl a/b ratio, decreasing both maximum (FV/FM) and actual (ΦPS2) photochemical efficiency of photosystem 2, and increasing non-photochemical quenching. Nevertheless, net photosynthetic oxygen evolution rate (PN) did not decrease consistently with decrease in Chl content, but exhibited a typical ontogenetic course with gradual increase. PN reached its maximum before full leaf expansion and then tended to decline. Thus excess irradiance during in vitro cultivation did not cause early start of leaf senescence, but impaired photosynthetic performance and Chl content in leaves and changed their typical ontogenetic course. and B. Radochová, I. Tichá.
The polarized absorption, photoacoustic, fluorescence emission, and fluorescence excitation spectra of whole cells of cyanobacteria Synechocystis sp. embedded in a polymer film were measured. The bacteria cells, as it follows from anisotropy of absorption and fluorescence spectra, were even in a non-stretched polyvinyl alcohol film oriented to a certain extent. The measurements were done for such film in order to avoid the deformation of cyanobacteria shapes. Part of the samples was bleached by irradiation with strong polarized radiation with electric vector parallel to the orientation axis of cells. The anisotropy of photoacoustic spectra was higher than that of absorption spectra and it was stronger changed by the irradiation. Polarized fluorescence was excited in four wavelength regions characterised by different contribution to absorption from various bacteria pigments. The shapes of emission spectra were different depending on wavelength of excitation, polarization of radiation, and previous irradiation of the sample. The fluorescence spectra were analysed on Gaussian components belonging to various forms of pigments from photosystems (PS) 1 and 2. The results inform about excitation energy transfer between pools of pigments, differently oriented in the cells. Energy of photons absorbed by phycobilisomes was transferred predominantly to the chlorophyll of PS2, whereas photons absorbed by carotenoids to chlorophylls of PS1. and J. Goc ... [et al.].
We present a chlorophyll fluorometer module system which adapts the intensity to the individual leaf sample by adjusting the quantum flux density of the excitation light so that the fluorescence signal is kept constant. This is achieved by means of a feedback power adjustment of the fluorescence exciting laser diode. Thus, the intensity of the excitation light is adapted to the actual need of a particular sample for quantum conversion without applying exaggeratedly high quantum flux density. We demonstrate the influence of the initial laser power chosen at the onset of irradiation and kept constant during fluorescence rise transient within the first second. Examples are shown for measuring upper and lower leaf sides, a single leaf with different pre-darkening periods, as well as yellow, light green and dark green leaves. The novel excitation kinetics during the induction of chlorophyll fluorescence can be used to study the yield and regulation of photosynthesis and its related non-photochemical processes for an individual leaf. It allows not only to sense the present state of pre-darkening or pre-irradiation but also the light environment the leaf has experienced during its growth and development. Thus, the individual physiological capacity and plasticity of each leaf sample can be sensed being of high importance for basic and applied ecophysiological research which makes this new methodology both innovative and informative. and A. Barócsi ... [et al.].
Excitation kinetics based on feedback regulation of chlorophyll (Chl) fluorescence of leaves measured with the chlorophyll fluorometer, FluoroMeter Modul (FMM), are presented. These kinetics showed the variation of excitation light (laser power, LP) regulated by the feedback mechanism of the FMM, an intelligent Chl fluorometer with embedded computer, which maintains the fluorescence response constant during the 300-s transient between the dark- and light-adapted state of photosynthesis. The excitation kinetics exhibited a rise of LP with different time constants and fluctuations leading to a type of steady state. The variation of excitation kinetics were demonstrated using the example of primary leaves of etiolated barley seedlings (Hordeum vulgare L. cv. Barke) during 48 h of greening in the light with gradual accumulation of Chl and development of photosynthetic activity. The excitation kinetics showed a fast rise followed by a short plateau at ca. 30 s and finally a slow constant increase up to 300 s. Only in the case of 2 h of greening in the light, the curve reached a stable steady state after 75 s followed by a slight decline. The final LP value (at 300 s of illumination) increased up to 12 h of greening and decreased with longer greening times. The active feedback mechanism of the FMM adjusted the excitation light during the measurement to the actual photosynthetic capacity of the individual leaf sample. In this way, the illumination with excessive light was avoided. The novel excitation kinetics can be used to characterize health, stress, disease, and/or product quality of plant material., C. Buschmann ... [et al.]., and Obsahuje bibliografii
Excitation-emission maps were constructed by measuring emission spectra from tobacco thylakoids and from thylakoids and intact cells of the cyanobacterium Synechocystis 6803. The measurement of such maps is greatly facilitated by the current diode-array detector technology. We show that excitation-emission maps are valuable tools for studies of the structure and energy transfer pathways in photosynthetic systems. and Mika Keränen, Eva-Mari Aro, Esa Tyystjärvi.
Ca2+ has been considered as a necessary ion for alleviation of stress-induced damages in plants. We investigated effects of exogenous Ca2+ on waterlogging-induced damage to pepper and its underlying mechanisms. Pepper seedlings under stress were treated by spraying of 10 mM CaCl2. Applying exogenous Ca2+ increased the biomass of pepper leaves and roots, improved photosynthetic characteristics, membrane permeability, root activity, osmotic substance contents, antioxidant enzyme and alcohol dehydrogenase activities, while it reduced lactate dehydrogenase activity. It maintained hydroxide radical contents and activities of malate dehydrogenase and succinate dehydrogenase relatively high. Our results suggested that applying exogenous Ca2+ could regulate osmotic substance contents, antioxidant system activity, root respiration, and metabolism, and subsequently alleviate waterlogging-induced damages to pepper plants., B. Z. Yang, Z. B. Liu, S. D. Zhou, L. J. Ou, X. Z. Dai, Y. Q. Ma, Z. Q. Zhang, W. C. Chen, X. F. Li, C. L. Liang, S. Yang, X. X. Zou., and Obsahuje bibliografii
The hypothesis that application of exogenous glycine betaine (GBEX) may attenuate the effects of mild water deficit in leaf gas exchange and lipid peroxidation in Carapa guianensis was examined. For this reason, 110-d old plants were sprayed with 0, 25, and 50 mM GBEX and then subjected to two watering regimes. In the first, irrigation was continuously performed to maintain the soil near to field capacity (watered plants). In the second, irrigation was withheld and water deficit resulted from progressive evapotranspiration (water-stressed plants). Treatment comparisons were assessed when predawn leaflet water potential (Ψpd) of stressed plants reached -1.28 ± 0.34 MPa. Regardless of the watering regime, significant (P<0.05) increases in foliar glycine betaine (GBLeaf) concentration were observed in response to increasing GBEX; however, such increases were more expressive in stressed plants. The net photosynthetic rate, stomatal conductance to water vapor, and intercellular to ambient CO2 concentration ratio were significantly lower in water-stressed plants independently of GBEX concentration sprayed on leaves. The application of 25 and 50 mM GBEX caused significant (P<0.05) increases in ascorbate peroxidase (APX) activity in stressed plants, while significant (P<0.05) increases in catalase activity was observed just in the stressed plants treated with 50 mM GBEX. Malondialdehyde concentrations did not differ between watered and stressed plants regardless of GBEX concentration. In conclusion, C. guianensis was able to incorporate GBEX through their leaves and the resulting increases in GBLeaf attenuated lipid peroxidation in stressed plants through positive modulation of APX and CAT activities., F. J. R. Cruz ...[et al.]., and Obsahuje bibliografii
Cyanobacteria Spirulina platensis and Nostoc linckia were grown in the presence of 5 mM and 50 mM glucose or 5 mM mannose, non-metabolisable glucose analogue that effectively triggers the repression of photosynthesis. Glucose evoked active cyanobacterial growth but chlorophyll (Chl) content decreased to some extent and porphyrins were excreted. The content of monogalactosyldiacylglycerol decreased in glucose-grown cyanobacteria and that of phosphatidylglycerol increased substantially. Mannose inhibited cyanobacteria growth as well as Chl synthesis, however, phosphatidylglycerol contents were higher than in respective control samples. In cyanobacterial cells glucose may not only inhibit photosynthetic processes, but also cause structural transformations of membranes which may be necessary for the activity of respiratory electron transport chain components under heterotrophic conditions. and N. F. Mykhaylenko ... [et al.].
Melatonin mediates many physiological processes in animals and plants. To examine the potential roles of melatonin in salinity tolerance, we investigated the effects of exogenous melatonin on growth and antioxidant system in cucumber under 200 mM NaCl stress conditions. The results showed that the melatonin-treated plants significantly increased growth mass and antioxidant protection. Under salinity stress, the addition of melatonin effectively alleviated the decrease in the net photosynthetic rate, the maximum quantum efficiency of PSII, and the total chlorophyll content. Our data also suggested that melatonin and the resistance of plants exhibited a concentration effect. The application of 50-150 μM melatonin significantly improved the photosynthetic capacity. Additionally, the pretreatment with melatonin reduced the oxidative damage under salinity stress by scavenging directly H2O2 or enhancing activity of antioxidant enzymes (including superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) and concentrations of antioxidants (ascorbic acid and glutathione). Therefore, the melatonin-treated plants could effectively enhance their salinity tolerance., L. Y. Wang, J. L. Liu, W. X. Wang, Y. Sun., and Obsahuje seznam literatury