39081001 OR Leaves to Measure Light Intensity Dotaz Zobrazit nápovědu
Quantitative measurement of light intensity is a key step in ensuring the reliability and the reproducibility of scientific results in many fields of physics, biology, and chemistry. The protocols presented so far use various photoactive properties of manufactured materials. Here, leaves are introduced as an easily accessible green material to calibrate light intensity. The measurement protocol consists in monitoring the chlorophyll fluorescence of a leaf while it is exposed to a jump of constant light. The inverse of the characteristic time of the initial chlorophyll fluorescence rise is shown to be proportional to the light intensity received by the leaf over a wide range of wavelengths and intensities. Moreover, the proportionality factor is stable across a wide collection of plant species, which makes the measurement protocol accessible to users without prior calibration. This favorable feature is finally harnessed to calibrate a source of white light from exploiting simple leaves collected from a garden.
- Klíčová slova
- actinometry, fluorescence, green materials, irradiance, light intensity, photoactive materials,
- Publikační typ
- časopisecké články MeSH
The present work has explored for the first time acclimation of upper versus lower canopy leaves along an altitudinal gradient. We tested the hypothesis that restrictive climatic conditions associated with high altitudes reduce within-canopy variations of leaf traits. The investigated beech (Fagus sylvatica L.) forest is located on the southern slope of the Hrubý Jeseník Mountains (Czech Republic). All measurements were taken on leaves from upper and lower parts of the canopy of mature trees (>85 years old) growing at low (400 m above sea level, a.s.l.), middle (720 m a.s.l.) and high (1100 m a.s.l.) altitudes. Compared with trees at higher altitudes, those growing at low altitudes had lower stomatal conductance, slightly lower CO(2) assimilation rate (A(max)) and leaf mass per area (LMA), and higher photochemical reflectance index, water-use efficiency and Rubisco content. Given similar stand densities at all altitudes, the different growth conditions result in a more open canopy and higher penetration of light into lower canopy with increasing altitude. Even though strong vertical gradients in light intensity occurred across the canopy at all altitudes, lower canopy leaves at high altitudes tended to acquire the same morphological, biochemical and physiological traits as did upper leaves. While elevation had no significant effect on nitrogen (N) and carbon (C) contents per unit leaf area, LMA, or total content of chlorophylls and epidermal flavonoids in upper leaves, these increased significantly in lower leaves at higher altitudes. The increases in N content of lower leaves were coupled with similar changes in A(max). Moreover, a high N content coincided with high Rubisco concentrations in lower but not in upper canopy leaves. Our results show that the limiting role of light in lower parts of the canopy is reduced at high altitudes. A great capacity of trees to adjust the entire canopy is thus demonstrated.
- Klíčová slova
- CO2 assimilation, LMA, Rubisco, altitudinal gradient, flavonoids, leaf stoichiometry, light environment,
- MeSH
- buk (rod) anatomie a histologie genetika fyziologie MeSH
- dusík analýza MeSH
- fenotyp * MeSH
- fotosyntéza * MeSH
- listy rostlin anatomie a histologie chemie fyziologie MeSH
- nadmořská výška * MeSH
- oxid uhličitý metabolismus MeSH
- průduchy rostlin anatomie a histologie fyziologie MeSH
- ribulosa-1,5-bisfosfát-karboxylasa analýza MeSH
- světlo MeSH
- uhlík analýza MeSH
- voda metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- dusík MeSH
- oxid uhličitý MeSH
- ribulosa-1,5-bisfosfát-karboxylasa MeSH
- uhlík MeSH
- voda MeSH
A model was constructed which includes electron transport (linear and cyclic and Mehler type reaction) coupled to proton translocation, counter ion movement, ATP synthesis, and Calvin-Benson cycle. The focus is on modeling of the light-induced total electric potential difference (ΔΨ) which in this model originates from the bulk phase electric potential difference (ΔΨb), the localized electric potential difference (ΔΨc), as well as the surface electric potential difference (ΔΨs). The measured dual wavelength transmittance signal (ΔA515-560nm, electrochromic shift) was used as a proxy for experimental ΔΨ. The predictions for theoretical ΔΨ vary with assumed contribution of ΔΨs, which might imply that the measured ΔA515-560nm trace on a long time scale reflects the interplay of the ΔΨ components. Simulations also show that partitioning of proton motive force (pmf) to ΔΨb and ΔpH components is sensitive to the stoichiometric ratio of H+/ATP, energy barrier for ATP synthesis, ionic strength, buffer capacity and light intensity. Our model shows that high buffer capacity promotes the establishment of ΔΨb, while the formation of pHi minimum is not 'dissipated' but 'postponed' until it reaches the same level as that for low buffer capacity. Under physiologically optimal conditions, the output of the model shows that at steady state in light, the ΔpH component is the main contributor to pmf to drive ATP synthesis while a low ΔΨb persists energizing the membrane. Our model predicts 11mV as the resting electric potential difference across the thylakoid membrane in dark. We suggest that the model presented in this work can be integrated as a module into a more comprehensive model of oxygenic photosynthesis.
- Klíčová slova
- Electrochromic shift, Ion movements, Photosynthesis,
- MeSH
- biologické modely * MeSH
- časové faktory MeSH
- koncentrace vodíkových iontů účinky záření MeSH
- listy rostlin metabolismus účinky záření MeSH
- membránové potenciály účinky záření MeSH
- počítačová simulace MeSH
- protonmotorická síla účinky záření MeSH
- protony MeSH
- pufry MeSH
- světlo * MeSH
- transport elektronů MeSH
- tylakoidy metabolismus účinky záření MeSH
- uhlík metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- protony MeSH
- pufry MeSH
- uhlík MeSH
Plants have developed many ways to protect reaction centres of photosystems against overexcitation. One of the mechanisms involves reduction of the leaf absorption cross-section by light-induced chloroplast avoidance reaction. Decrease in the probability of photon absorption by the pigments bound within photosystem II (PSII) complexes leads to the increase in quantum yield of PSII photochemistry (ΦPSII). On the other hand, the decrease of PSII excitation probability causes reduction of chlorophyll a fluorescence intensity which is manifested as the apparent increase of determined quantum yield of regulated light-induced non-photochemical quenching (ΦNPQ). Absorption of different light intensity by phototropins led to the different chloroplast distribution within barley leaves, estimated by measurement of the leaf transmittance. Due to a weak blue light used for transmittance measurements, leaves exposed to actinic light with wavelengths longer than 520 nm undergo chloroplast accumulation reaction, in contrast with leaves exposed to light with shorter wavelengths, that showed a different extent of chloroplast avoidance reaction. Based on the ΦNPQ action spectra measured simultaneously with the transmittance, the influence of different chloroplast distribution on ΦNPQ was assessed. The analysis of results showed that decrease in the leaf absorption cross-section due to increasing part of chloroplasts reaching profile position significantly affected the partitioning of excitation energy within PSII and such rearrangement also distorted measured ΦNPQ and cannot be neglected in its interpretation. When the majority of chloroplasts reached profile position, the photoprotective effect appeared to be the most prominent for strong blue light that has the highest absorption in the upper leaf layers in comparison with green or red ones.
- Klíčová slova
- Action spectra, Chlorophyll fluorescence, Chloroplast accumulation reaction, Chloroplast avoidance reaction, Hordeum vulgare, Leaf absorption cross-section,
- MeSH
- chloroplasty chemie metabolismus MeSH
- fluorescenční spektrometrie MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- ječmen (rod) metabolismus MeSH
- listy rostlin metabolismus MeSH
- světlo MeSH
- tma MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- fotosystém II - proteinový komplex MeSH
Understanding the net photosynthesis of plant canopies requires quantifying photosynthesis in challenging environments, principally due to the variable light intensities and qualities generated by sunlight interactions with clouds and surrounding foliage. The dynamics of sunflecks and rates of change in light intensity at the beginning and end of sustained light (SL) events makes photosynthetic measurements difficult, especially when dealing with less accessible parts of plant foliage. High time resolved photosynthetic monitoring from pulse amplitude modulated (PAM) fluorometers has limited applicability due to the invasive nature of frequently applied saturating flashes. An alternative approach used here provides remote (<5 m), high time resolution (10 s), PAM equivalent but minimally invasive measurements of photosynthetic parameters. We assessed the efficacy of the QA flash protocol from the Light-Induced Fluorescence Transient (LIFT) technique for monitoring photosynthesis in mature outer canopy leaves of potted Persea americana Mill. cv. Haas (Avocado) trees in a semi-controlled environment and outdoors. Initially we established that LIFT measurements were leaf angle independent between ±40° from perpendicular and moreover, that estimates of 685 nm reflectance (R685) from leaves of similar chlorophyll content provide a species dependent, but reasonable proxy for incident light intensity. Photosynthetic responses during brief light events (≤10 min), and the initial stages of SL events, showed similar declines in the quantum yield of photosystem II (ΦII) with large transient increases in 'constitutive loss processes' (ΦNO) prior to dissipation of excitation by non-photochemical quenching (ΦNPQ). Our results demonstrate the capacity of LIFT to monitor photosynthesis at a distance during highly dynamic light conditions that potentially may improve models of canopy photosynthesis and estimates of plant productivity. For example, generalized additive modelling performed on the 85 dynamic light events monitored identified negative relationships between light event length and ∆ΦII and ∆electron transport rate using either ∆photosynthetically active radiation or ∆R685 as indicators of leaf irradiance.
- MeSH
- chlorofyl MeSH
- fluorescence MeSH
- fotosyntéza fyziologie MeSH
- listy rostlin fyziologie MeSH
- Persea fyziologie MeSH
- stromy fyziologie MeSH
- světlo MeSH
- technologie dálkového snímání přístrojové vybavení metody MeSH
- teoretické modely MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- chlorofyl MeSH
Plants in the field are commonly exposed to fluctuating light intensity, caused by variable cloud cover, self-shading of leaves in the canopy and/or leaf movement due to turbulence. In contrast to C3 plant species, only little is known about the effects of dynamic light (DL) on photosynthesis and growth in C4 plants. Two C4 and two C3 monocot and eudicot species were grown under steady light or DL conditions with equal sum of daily incident photon flux. We measured leaf gas exchange, plant growth and dry matter carbon isotope discrimination to infer CO2 bundle sheath leakiness in C4 plants. The growth of all species was reduced by DL, despite only small changes in steady-state gas exchange characteristics, and this effect was more pronounced in C4 than C3 species due to lower assimilation at light transitions. This was partially attributed to increased bundle sheath leakiness in C4 plants under the simulated lightfleck conditions. We hypothesize that DL leads to imbalances in the coordination of C4 and C3 cycles and increasing leakiness, thereby decreasing the quantum efficiency of photosynthesis. In addition to their other constraints, the inability of C4 plants to efficiently utilize fluctuating light likely contributes to their absence in such environments as forest understoreys.
- MeSH
- Amaranthaceae růst a vývoj fyziologie účinky záření MeSH
- fotony MeSH
- fotosyntéza * MeSH
- izotopy uhlíku analýza MeSH
- lipnicovité růst a vývoj fyziologie účinky záření MeSH
- listy rostlin růst a vývoj fyziologie účinky záření MeSH
- oxid uhličitý metabolismus MeSH
- světlo MeSH
- transpirace rostlin MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- izotopy uhlíku MeSH
- oxid uhličitý MeSH
Of the three isomers of the aromatic amine phenylenediamine (PDA), only o-PDA, but not m- and p-PDA, induced DNA damage (as measured by the Comet assay), and somatic mutations in the leaves of the chlorophyll-deficient tester strain Nicotiana tabacum var. xanthi. With increasing light intensity (0, 30, 80 or 140 micromol m(-2)s(-1) photosynthetic photon fluence rate) during a 72h mutagenic treatment of tobacco seedlings, o-PDA-induced DNA damage and the yield of somatic mutations were significantly increased. The peroxidase inhibitor diethyldithiocarbamate (DEDTC) repressed o-PDA-induced DNA damage. The effect of light is caused by the light-dependent increase of peroxidase activity and the accumulation of hydrogen peroxide, which participate in the metabolic activation of the promutagen o-PDA to mutagenic product(s). In contrast, DNA damage induced by the direct-acting alkylating mutagen ethyl methanesulphonate was the same whether treatment was in the light or in the dark, and was not repressed by the peroxidase inhibitor DEDTC.
- MeSH
- chlorofyl nedostatek genetika MeSH
- ethylmethansulfonát toxicita MeSH
- fenylendiaminy metabolismus toxicita MeSH
- jedovaté rostliny * MeSH
- kometový test MeSH
- listy rostlin účinky léků enzymologie MeSH
- mutace * MeSH
- mutageny metabolismus toxicita MeSH
- peroxid vodíku metabolismus MeSH
- peroxidasa metabolismus MeSH
- poškození DNA * MeSH
- světlo škodlivé účinky MeSH
- tabák účinky léků enzymologie genetika účinky záření MeSH
- vztah dávky záření a odpovědi MeSH
- vztah mezi dávkou a účinkem léčiva MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- 1,2-diaminobenzene MeSH Prohlížeč
- chlorofyl MeSH
- ethylmethansulfonát MeSH
- fenylendiaminy MeSH
- mutageny MeSH
- peroxid vodíku MeSH
- peroxidasa MeSH
A laser-scanning microscope using second harmonic generation (SHG) as a probe is shown to produce high-resolution images of duckweed Lemna minuta leaves. These leaves are multi-cell layer thick. Second harmonic light is generated by a tightly focused short pulse laser beam and is collected by two objectives yielding forward and backward second harmonic digital images. This measurement shows that the signal of the second harmonic imaging in the forward and backward directions depends on the thickness of the chloroplast and that the forward-SH image was brighter than the backward-SH image. The image intensity also depended on the orientation of the chloroplast in relation to the illuminating polarization direction. Their light-induced re-orientation which was affected by the intensity of the illumination could be observed during the experiments. The novelty of this work is to establish new compact technique in which one can use the SH imaging to investigate the true architecture of the sensitive samples, the unknown samples and the samples which is not producing auto-fluorescence. Moreover, investigation of new or unknown samples needs a long time for looking at details of the sample. Thereby the sample will be exposed for long time to the laser radiation that will cause photobleaching and photodamage. Since the SHG does not undergo photobleaching and photodamage this will be the promising technique for investigating the sensitive and new unknown samples. Then one can move to acquire fluorescence images after complete investigation of the true architecture of the sample. The other advantage of SHG is that it has the ability to image highly ordered structural proteins without any exogenous labels. The SHG is an intrinsic and a coherent process. Imaging of intrinsic compounds avoids the complications of slicing and labeling, and samples can be investigated under physiological conditions.
Abstract- An unconventional band in the thermoluminescence glow curve of barley leaves at about +50°C was examined. In contrast to bands usually observed around +50°C, this band (designated as CL) is not related to photosynthetic electron transport in photosystem II. The appearance of the CL band (1) requires previous freezing of the sample, (2) is not influenced by light excitation and (3) depends on the presence of oxygen. In pure oxygen the glow curves for both leaves and chloroplast suspension exhibit three maxima at about +40°C, +65°C and +90°C. Based on the emission spectra of the CL band and measurements with etiolated leaves, we suppose that the majority of emission corresponding to the CL band originates from chlorophyll. A lipoxygenase inhibitor, butylated hydroxytoluene, and sodium azide decrease the intensity of the CL band. We propose that the mechanism leading to emission of the CL band involves thermally stimulated production of an active oxygen species that results in lipid peroxidation.
- Publikační typ
- časopisecké články MeSH
Chloroplast movement has been studied in many plants mainly in relation to the local light, mechanical or stress effects. Here we investigated possible systemic responses of chloroplast movement to local light or burning stress in tobacco plants (Nicotiana tabacum cv. Samsun). Chloroplast movement was measured using two independent methods: one with a SPAD 502 Chlorophyll meter and another by collimated transmittance at a selected wavelength (676 nm). A sensitive periodic movement of chloroplasts was used in high or low (2 000 or 50 micromol/m(2) per s photosynthetically active radiation, respectively) cold white light with periods of 50 or 130 min. Measurements were carried out in the irradiated area, in the non-irradiated area of the same leaf or in the leaf located on the stem below the irradiated or burned one. No significant changes in systemic chloroplast movement in non-irradiated parts of the leaf and in the non-treated leaf were detected. Our data indicate that chloroplast movement in tobacco is dependent dominantly on the intensity and spectral composition of the incident light and on the local stimulation and state of the target tissue. No systemic signal was strong enough to evoke a detectable systemic response in chloroplast movement in distant untreated tissues of tobacco plants.
