Search results for "PHOTOS"
showing 10 items of 701 documents
Influence of Light on the Bioelectric Potential of the Bean (Phaseolus vulgaris) Hypocotyl Hook
1975
By use of surface electrodes electropotenlial measurements were carried out on hypocotyl hooks of Phaseolus vulgaris seedlings. The hooks were illuminated with a small spot of white, blue, red or far red light. The potential changes in bean hypocotyl hooks do not show the red-far red reversible characteristics of phytochrome-mediated processes. By experimenting with inhibitors of photosynthesis we could demonstrate that the light-triggered potential changes in green bean hooks are correlated to photosynthetic electron transport phenomena. The red-light-induced transient is a depolarization, whereas blue light induces a hyperpolarization. Etiolated beans exhibit no bioelectric potential chan…
Effects of Kinetin and Different Light Qualities on the Content of Carbohydrates
1983
Summary The effects of kinetin on the content of soluble redueing sugars, starch, soluble proteins and various components of the photosynthetic apparatus were studied with primary leaves of Sinapis alba, which were grown under different light qualities (white, red, blue Jight conditions). It was especially the content of soluble reducing sugars that was most influenced by kinetin. The enhancement of the sugar content was dependent on the duration of application as well as on the concentration of kinetin. The doseresponse curve shows that the sugar content strongly increased at low kinetin eoneentrations (0.01 to 1 mg · 1-1), whereas from 1 mg · 1-1 onwards the inerease was slower and linear…
Photokinetic examination of (Z,E,E)-4,4′-distyrylazobenzene
1995
Abstract 4,4′-Distyrylazobenzenes demonstrate a photokinetic equilibrium and a superimposed thermal backward reaction in which the absorption coefficient of one of the partners in the equilibrium is principally unknown. Using the dependence of the photostationary state on the irradiation intensity, the photochemical quantum yields ϕ 1 A and ϕ 2 B were determined, as well as the thermal rate constant k , as a function of the irradiation and observation wavelengths. Experimental difficulties and the wavelength dependence of ϕ 1 A and ϕ 2 B are discussed.
Upscaling leaf gas exchange measurements to the whole grapevine canopy: An update
2009
This review first revisits current knowledge about single-leaf function, viz. photosynthesis, chiefly in relation to environmental factors, that underscores the importance of multiple summer stresses. Emphasis is placed on the response different genotypes show under light and heat stress with or without soil-water shortage. Secondly, it tackles the thorny issue of extrapolating single-leaf readings to the whole-canopy level, with special reference to both methodological and physiological implications. Whole-canopy gas-exchange systems deliver and emphasise the usefulness of such an approach in achieving key research goals. One case in point is quantifying the amount and dynamics of canopy g…
Lake zooplankton δ13C values are strongly correlated with the δ13C values of distinct phytoplankton taxa
2016
Analyses of carbon stable isotopes are often used to estimate the contributions of allochthonous and autochthonous dietary resources to aquatic consumers. Most pelagic food web studies assume that all phytoplankton taxa have a similar δ13C value. We studied pelagic food web compartments (dissolved inorganic carbon [DIC], phytoplankton, bacteria, seston, cladoceran zooplankton) in 12 small (< 0.1 km2) lakes in southern Finland. These lakes were classified as oligotrophic, mesotrophic, eutrophic, and dystrophic based on their concentrations of total phosphorus and dissolved organic carbon. Additionally, we studied phytoplankton photosynthetic carbon fractionation (εp) in laboratory conditions…
Wirkung der Insektizide Allethrin, Lindan und Jacutin-Fogetten-Sublimat auf den photosynthetischen Elektronentransport
1977
Summary During our studies of Hill-reactions of isolated chloroplasts we observed an inhibition of electron transport after an application of the smoke of «Jacutine-Fogetten» in the plant growth chamber. Therefore we tested the influence of the insecticides Lindane (Gammexan), the sublimate formed by the fumigation of «Jacutin Fogetten», and of Allethrin on the photosynthetic electron transport reactions of PS II and PS I. 39 μ M Lindane inhibits the basal, coupled and uncoupled electron transport to ferricyanide of broken chloroplasts isolated from leaves of Pisum sativum up to 35%. A higher inhibitory effect with higher concentrations is limited by the low water solubility of Lindane. On …
Oxygen Availability, Energy Metabolism, and Metabolic Rate in Invertebrates and Vertebrates
1988
It has often been emphasized that primitive life originated in an environment devoid of oxygen. The first eukaryotic cells, however, appeared some 1.4 billion years ago when the earth’s atmosphere had already turned from a mildly reducing to an oxidizing one by the photosynthetic action of prokaryotes that used H20 as reducing agent (see Harold 1986, for review). The presence of free oxygen obviously was a major force shaping the evolution of eukaryotic cells. As a consequence all animals are primarily aerobes, using respiratory chains with oxygen as electron acceptor (oxidant) and membrane-bound ATP synthases for the production of ATP.
EFFECTS OF SENSITIZED AND UNSENSITIZED LONGWAVE U.V.-IRRADIATION ON THE SOLUTION PROPERTIES OF DNA
1971
— Two types of photoreactions occur in DNA irradiated in aqueous systems with longwave u.v.-light (Λ > 295 nm), namely, (a) thymine dimerization, and (b) single- and double-strand breakage of the sugar phosphate backbone; these two reactions are unrelated. The presence of acetophenone as a photosensitizer caused an increase in dimerization by a factor of 16, and an increase in single-strand breaks by a factor of 4. The number of thymine dimers per single-strand break is about 100 in the sensitized and 25 in the unsensitized reaction. The alteration of the radius of gyration of DNA molecules is that expected by the degradation observed. At the same time the change in hyperchromicity is very …
Changes in net photosynthesis, chlorophyll fluorescence and xanthophyll cycle interconversions during freeze-thaw cycles in the Mediterranean moss Le…
1999
The tolerance to freezing and thawing of Leucodon sciuroides, a moss growing in mountainous areas of the Mediterranean (south-east Spain), was investigated by means of CO2 gas exchange, modulated chlorophyll (Chl) a fluorescence and pigment analysis by high-performance liquid chromatography. Evidence is presented for freezing-induced decreases in CO2 fixation that enhance non-radiative dissipation of absorbed light energy, a process which protects the photosynthetic apparatus. The photosynthetic apparatus of L. sciuroides remained fully recuperable after freezing, as indicated by the recovery of photosynthetic CO2 fixation and Chl fluorescence parameters to pre-freezing values during thawin…
Changes in chlorophyll a fluorescence, photosynthetic CO 2 assimilation and xanthophyll cycle interconversions during dehydration in desiccation-tole…
1998
The interactions among water content, chlorophyll a fluorescence emission, xanthophyll interconversions and net photosynthesis were analyzed during dehydration in desiccation-tolerant Frullania dilatata (L.) Dum. and desiccation-intolerant Pellia endiviifolia (Dicks) Dum. Water loss led to a progressive suppression of photosynthetic carbon assimilation in both species. Their chlorophyll fluorescence characteristics at low water content were: low photosynthetic quantum conversion efficiency, high excitation pressure on photosystem II and strong non-photochemical quenching. However, dissipation activity was lower in P. endiviifolia and was not accompanied by a rise in the concentration of de-…