Measurement Of Photosynthetic Activity Research Articles

Photoacoustic measurements of photosynthetic activities in whole leaves. Photochemistry and gas exchange

Photosynthetic activities of sections of intact tobacco leaves ( Nicotina tabacum L. var. Xanthi) were monitored by the photoacoustic effect. A reference signal was obtained using brief simultaneous illumination of the leaf with continuous light of saturating intensity. 1. The effect of the direct continuous light depends on the modulation frequency: A decrease in the photoacoustic signal, ‘negative effect’, is observed at low frequency (under approx. 200 Hz) and an increase of the photoacoustic signal, ‘positive effect’, at high frequency (above approx. 200 Hz). Both effects are reversible. 2. When leaves are water-infiltrated only a ‘positive effect’: of the direct continuous light is observed, at any frequency. Leaves infiltrated with aqueous DCMU solution (50 μM) do not show any direct continuous light effect. 3. The ‘negative effect’ develops, as the leaf is illuminated, in parallel to the (low frequency) photoacoustic signal itself which increases gradually after an initial lag period. This transient phenomenon takes a few minutes under our conditions. The differential increase of the signal during the induction period matches the size of the negative effect obtained by applying the direct continuous light at various times during the induction or in the steady state. 4. In a similar way, the ‘positive effect’ increases during the induction period, due to a transient decrease of the photoacoustic signal measured at high frequency. This change in the ‘positive effect’ is less noticeable, as a sizeable effect is already observed in a dark-adapted leaf, upon illumination, and the extent of the photoacoustic transient is relatively small. 5. No photoacoustic transients are observed when direct continuous light is used continuously. 6. It is concluded that the photoacoustic signal is due to two contributions: At low frequency there is a considerable contribution from modulated oxygen evolution, which tends to zero as the direct continuous light is applied. At high frequency the main contribution is from the conversion of photon energy to heat, and direct continuous light effects reflect mainly photochemical energy storage. Both low and high frequency photoacoustic transients reflect the induction period of photosynthesis. 7. Preliminary calculations on the relative damping of modulated oxygen evolution and thermal photoacoustic contributions with the modulation frequency, are consistent with the above model, taking into account diffusion and the rate-limiting step in O 2 evolution. 8. Photoacoustic data were used to construct a relative quantum yield spectrum for both oxygen evolution and photochemical energy storage.

Modulation of PSI and PSII Organization During Loss and Repair of Photosynthetic Activity in a Temperature Sensitive Mutant of Chlorella pyrenoidosa

Photosynthetic activity and organization of chlorophyll(Chl)-protein complexes in a temperature sensitive mutant of Chlorella pyrenoidosa have been investigated. The mutant is practically indistinguishable from wild type cells when grown at 25 C. However, mutant cells grown at 33 C do not synthesize Chl and lose their ability to evolve O(2). O(2) evolution and Chl synthesis are restored upon incubation of the 33 C grown cells at 25 C in absence of cell division (repair).Based on polarographic measurements of photosynthetic activities, variable fluorescence, 77 K fluorescence emission, excitation spectra, analysis of Chl-protein complexes, membrane polypeptide pattern and radioactive labeling using sodium dodecyl sulfate-polyacrylamide gel electrophoresis techniques during growth at 33 C and/or under repair conditions, it is concluded that: a, polypeptides of chloroplastic translation required for H(2)O-splitting activity are absent from membranes of 33 C grown cells. Their synthesis and/or assembly during the repair process is light-dependent. b, Polypeptides required for the formation of photosystem II and photosytem I reaction centers continue to be formed during growth at 33 C in absence of Chl synthesis. These can be assembled into functional units following Chl synthesis and energization of the membranes during the repair process. c, The Chl-protein complex serving as an antenna of photosystem I is disorganized, and the Chl is used for the formation of functional reaction centers of photosystem I during growth at 33 C.These results show that Chl-protein complexes can be dissociated in vivo and reassembled in a different way; and formation of Chl-protein complexes can occur stepwise from previously synthesized and newly formed components including both polypeptides and Chl.

The Depletion of Carbon Dioxide from Lake Water by Phytoplankton

It has long been known that dense populations of phytoplankton tend to deplete the carbon dioxide present in natural waters, with an associated raising of pH. The ecological significance of these reactions, as possible growth-limiting or retarding factors, is far from clear. This situation is remarkable in view of the intensive study given to the relationship between rates of photosynthesis and carbon dioxide supply in some unicellular algae, the numerous measurements of carbon assimilation by phytoplankton in nature, and the attention bestowed on pH as an ecological factor. Recently a controversy has developed around the relative importance of carbon and phosphorus supply in the enrichment ('eutrophication') of inland waters (e.g. Kuentzel 1969, 1971; King 1970; Kerr, Paris & Brockway 1970; Kerr et al. 1972; Schindler 1971; Schindler et al. 1973; Goldmann et al. 1972; Goldman, Oswald & Jenkins 1974), partly sustained by a shortage of detailed information on the dynamics and availability of inorganic carbon in freshwaters. In particular, the exchange of carbon dioxide between atmosphere and water is rarely estimated, the interrelations of various forms of carbon dioxide are rarely assessed, analytical methods are usually unspecific, and the relevant physiological responses of characteristic common species of freshwater phytoplankton are largely unknown. The present work developed from observations on depletions of carbon dioxide and upward pH shifts, occasionally very pronounced, in two English lake waters. Examples are described in relation to the algal crops involved and the stratification of environmental factors. The general limnological background of these environmental events, including details of diurnal changes, will be described more fully elsewhere. Further analysis is based upon systematic laboratory measurements of photosynthetic activity in relation to episodes of algal production in nature, extended to experimental manipulations of media, population density, and time-sequences of carbon dioxide consumption. As the physiological work is based upon natural populations of known history, it is hoped that ecological inferences can be drawn without undue extrapolation between the properties of different species and different media.

Changes in Internal Atmosphere of Submersed Vascular Hydrophytes in Relation to Photosynthesis

Gases were extracted from the internal atmosphere of Elodea canadensis and Ceratophyllum demersum in a closed system under reduced pressure. The volume of extractable gases varied throughout the daily period. Gases separated and quantitatively measured by gas chromatography included CO2, O2, N2, and CH4. Results from diurnal studies showed a lag between peak values for dissolved oxygen in the surrounding water and oxygen in the internal atmosphere. Lags were also observed in the CO2 values. As a result photosynthetic activity by these plants is not immediately reflected by changes in dissolved oxygen content of the surrounding water. The lacunal system apparently functions as a reservoir for metabolic gases. Experiments in whcih light intensity was controlled by floating screens indicated that at low intensities evidence of oxygen production in E. canadensis may be obtained only by observing the changes which occur within the internal atmosphere. At these intensities no increase in dissolved oxygen can be detected in the surrounding water although internal oxygen concentrations may increase slightly. Confirmation that carbon was being fixed by the plants under these conditions has been obtained by carbon—14 uptake studies using gas phase counting procedures. The observations cast furthur doubt on the reliability of using changes in dissolved oxygen as a sole measure of photosynthetic activity in aquatic ecosystems where submersed vascular plants are dominant.

PHOTOSYNTHESIS IN MAIZE AS INFLUENCED BY A TRANSPIRATION-REDUCING SPRAY

A study was made of the influence of a transpiration-reducing emulsion on the daily variations in the soluble carbohydrate content of Maize leaves. Using accumulation of sugars in the leaves as a measure of photosynthetic activity, the maximum accumulation of sugars in the sprayed plants on the day following application of the spray was 62.10% of that in the controls. Analysis of samples collected twenty days after treatment showed that the total sugar content of the leaves of the sprayed plants was about 18% greater than at the time of the earlier study. The relatively low rate of apparent photosynthesis in the sprayed plants probably can be attributed largely to a limited supply of carbon dioxide. The increased rate of production of carbohydrates shown by the sprayed plants on August 30 compared with the rate on August 10 may be explained in either one or both of two ways. A change in the permeability of the waxy covering to carbon dioxide may have occurred during the 20-day interval. Carbon dioxide may also have become more readily available as a result of shrinking or cracking of the spray film. Although conclusive data are not available, the most reasonable inference from themore » results is that the normal supply of carbon dioxide to the photosynthesizing cells of the control plants was not adequate to meet the requirements for maximum photosynthesis under the existing conditions. 12 references, 4 figures, 4 tables.« less