Photosynthesis: action spectra for leaves in normal and low oxygen

Re-interpreting the photosynthetically action radiation (PAR) curve in plants

The basis of a plant's spectral response of photosynthesis, or the photosynthetically active radiation (PAR) curve, is derived from earlier studies nearly five decades ago. These studies reported that blue and red light were the primary wavelengths; however, shifting within red and blue peaks (10-40 nm) in addition to different PAR curve shapes was observed. In recent years, the McCree curve, which is considered the standard for spectral response of photosynthesis, has been challenged because of experimental design and differences between photosynthetic and whole-plant growth responses. Therefore, this overview provides an amalgamation of all the PAR curve studies, with a focus on narrow spectrum light characteristics, including light measurement units, full width at half maximums (FWHMs) of narrow light spectra, and light intensity levels. While replicating these pioneering works with higher wavelength resolution and narrower light spectrum across the whole visible spectrum is still challenging, we hope that this re-interpretation of PAR curves in plants can elucidate and provide in-depth insight into spectral responses of photosynthesis. We leave the readers with some different perspectives and prospects that need to be considered for future studies.

Plant Growth Absorption Spectrum Mimicking Light Sources

Plant factories have attracted increasing attention because they can produce fresh fruits and vegetables free from pesticides in all weather. However, the emission spectra from current light sources significantly mismatch the spectra absorbed by plants. We demonstrate a concept of using multiple broad-band as well as narrow-band solid-state lighting technologies to design plant-growth light sources. Take an organic light-emitting diode (OLED), for example; the resulting light source shows an 84% resemblance with the photosynthetic action spectrum as a twin-peak blue dye and a diffused mono-peak red dye are employed. This OLED can also show a greater than 90% resemblance as an additional deeper red emitter is added. For a typical LED, the resemblance can be improved to 91% if two additional blue and red LEDs are incorporated. The approach may facilitate either an ideal use of the energy applied for plant growth and/or the design of better light sources for growing different plants.

Enhanced photosynthetic activity in Spinacia oleracea by spectral modification with a photoluminescent light converting material

The spectral conversion of incident sunlight by appropriate photoluminescent materials has been a widely studied issue for improving the efficiency of photovoltaic solar energy harvesting. By using phosphors with suitable excitation/emission properties, also the light conditions for plants can be adjusted to match the absorption spectra of chlorophyll dyes, in this way increasing the photosynthetic activity of the plant. Here, we report on the application of this principle to a high plant, Spinacia oleracea. We employ a calcium strontium sulfide phosphor doped with divalent europium (Ca0.4Sr0.6S:Eu(2+), CSSE) on a backlight conversion foil in photosynthesis experiments. We show that this phosphor can be used to effectively convert green to red light, centering at a wavelength of ~650 nm which overlaps the absorption peaks of chlorophyll a/b pigments. A measurement system was developed to monitor the photosynthetic activity, expressed as the CO2 assimilation rate of spinach leaves under various controlled light conditions. Results show that under identical external light supply which is rich in green photons, the CO2 assimilation rate can be enhanced by more than 25% when the actinic light is modified by the CSSE conversion foil as compared to a purely reflecting reference foil. These results show that the phosphor could be potentially applied to modify the solar spectrum by converting the green photons into photosynthetically active red photons for improved photosynthetic activity.

Photosynthesis research in Canada from 1945 to the early 1970s

This history traces the development of photosynthesis research in Canada from 1945 to 1975, starting with the work of Gleb(1) Krotkov and his students, Paul Vittorio, Tony(1) Bidwell, Don(1) Nelson, Jim(1) Craigie, Bruce Tregunna, Andreas Hauschild, Geoff Lister and others in the Department of Biology at Queen's University, Kingston, Ontario. They focused on the influence of taxonomy and light quality on the path of carbon into early products, photorespiration and photosynthesis in young trees. During the same period, Ken(1) Clendenning and one of the authors (PRG) at the National Research Council of Canada (NRCC) laboratory in Ottawa began studies of chloroplast photoreduction and leaf carboxylases. They were joined by Don(1) Mortimer, who showed that the path of carbon varies with species of plant and by Morris Kates, who studied phospholipid enzymology in chloroplasts and leaves. Stan(1) Holt researched the chemistry and distribution of chlorophylls in different taxa. In 1952, Ralph Lewin joined NRCC's new Atlantic Regional Laboratory in Halifax, Nova Scotia, followed by Jim Craigie, Jack McLachlan and Tony Bidwell who mainly investigated the products of photosynthesis in marine algae. Tony Bidwell continued these studies in 1959 at the Department of Botany, University of Toronto. Dave(1) Canvin joined the staff at Queen's in 1965 and became involved in solving the mystery of photorespiration. Tony Bidwell returned to Queen's in 1969 and studied photosynthesis of algal chloroplasts using an 'artificial leaf.' In 1965, Don Nelson established a group at Simon Fraser University in Burnaby, British Columbia that included his former student, Geoff Lister who produced the first photosynthetic action spectra for trees, and Bill(1) Vidaver, who showed the useful relation between chlorophyll fluorescence and photosynthetic activity. In 1970, Mário Fragata headed a group at the Université du Québec à Trois Rivières, Québec, that began with studies of Photosystem II in chloroplasts and particles.

Evaluation of maize productivity considering solar energy use limitation by environmental factors

Evaluation of maize productivity under different climatic conditions was made by determination of the amount of the incident solar radiation energy in the PAR range, which can be potentially used by plants for photosynthesis. An irradiance, which can be stored in primary photosynthesis, designated as photosynthetic energy, W (ph), was estimated taking into account the action spectra of photosynthesis. Limitation of the W (ph) usage, owing to unfavorable environmental factors was considered. Quantitative evaluation of limitations by two such factors, air temperature and soil water potential, was made by means of the coefficients F(i), which were defined as the ratio between the photosynthetic rate at a given value of a particular environmental factor and that at the optimal value for this factor. The coefficients F(i), were determined from the dependencies of the photosynthesis rate on air temperature and soil water potential as obtained in chamber and field experiments. In general terms, the fraction of W (ph), which can be utilized under a given climatic condition, was named bioclimatic potential, W (pc). In our model, the effect of monodominancy, when strong action of one factor suppresses the influence of any other factor, was considered. In this case, the bioclimatic potential, designated W'(pc), was calculated by multiplying W (ph) times the coefficient F, for the factor which was most limiting during the period of measurement. There was close correlation between values of bioclimatic potential for the period of vegetation, W'(pc,v), and total dry matter. W'(pc,v) use efficiency in the maize crop was also evaluated for five variants of mineral nutrition.

The relationship of CO2 assimilation pathways and photorespiration to the physiological quantum requirement of green plant photosynthesis

The quantum requirement of green cells for CO2 fixation has been evaluated and discussed in view of the recent discovery of photorespiration and of multiple biochemical pathways for photosynthetic CO2 fixation. The reported quantum requirement of algae generally is near 9 quanta per CO2 fixed. It is suggested that the high CO2 concentrations and low O2 concentrations used for these algae experiments would have completely suppressed photorespiration and, therefore, the minimum number of quanta required to fix 1 CO2 molecule was correctly determined in these experiments. With higher plant leaves, when measurements are made under physiological environments, quantum requirements range from about 12 to 20 quanta per CO2 fixed. It is suggested that these physiological quantum requirements are higher because photorespiration is functional in these leaves and that photorespiration requires energy. The energy requirement of photorespiration was derived using biochemical models of leaf photosynthesis combining photorespiration with specific biochemical pathways for CO2 fixation. The calculated physiological quantum requirements for C3, C4 and CAM plant photosynthesis are 13, 15 and 17 respectively. The literature values on quantum requirements correspond well with these biochemical models of net photosynthesis. However, it was concluded that the biochemical models fail to give a complete description of photosynthesis in plants using the C4-dicarboxylic acid cycle.

Developmental studies on microbodies in wheat leaves : III. On the photocontrol of microbody development

1. In etiolated wheat (Triticum aestivum L.) leaves, the development of the microbody enzymes catalase, hydroxypyruvate reductase, and glycolate oxidase was specifically stimulated by short treatments of the seedlings with red light, although the increases were less than observed after treatment with continuous white light. A comparison of the effects of short red and far-red exposures indicated the involvement of phytochrome. 2. Continuous far-red light treatments also enhanced the development of microbody enzymes. Catalase activity continued to increase at a high rate even after return from a prolonged far-red illumination to darkness, while the increase in the activities of glycolate oxidase and hydroxypyruvate reductase fell to the dark rates when the tissue was removed from the light. However, even at higher intensities of continuous far-red light the microbody enzymes reached only considerably lower activities than in white light. During continuous irradiation of equal quantum flux, the microbody enzymes reached higher activities in red than in far-red light, but the highest activities were observed in blue light, which had similar effects as white light. The quantitative difference between the effects of prolonged red or blue light depended also on the seed material and growing conditions. In the presence of the herbicide 3-amino-1,2,4-triazole the increase of glycolate-oxidase activity was reduced in red light but was affected much less, if at all, in blue light. 3. Continuous irradiations with all three light qualities used (red, far-red, blue) influenced the properties of the microbody particles to form a distinct band sharply confined close to an equilibrium density of 1.25 g cm(-3) on sucrose gradients which was not observed in preparations from plant material raised in complete darkness. In preparations from all light-grown plants a special peak in the activity profile of malate dehydrogenase was found in the microbody fraction while it was lacking on gradients from dark-grown leaves. The heights of the activities of malate dehydrogenase as well as of the other enzymes found in the microbody fractions from plants grown in either far-red, red, or blue light differed in the same way as did the activities from total leaf homogenates. 4. Glycolate oxidation by segments of intact leaf tissue was higher with tissue from light- than from dark-grown plants, but after light treatments of different spectral quality its magnitude did not correspond to the extractable activities of glycolate oxidase.

[The effect of monochromatic light on the extracellular excretion of glycolate and the photorespiration in the blue-green alga Anacystis nidulans]

The algae were grown under normal air conditions in a low light intensity (400 lux) and measured in the normal CO2-concentration (0.03 Vol. %). After an illumination period we observed a CO2 gush which is dependent on the temperature and wavelength used during the measurements. At +20°C a CO2 gush occurs only in the blue and far red regions. At +35°C, on the other hand, a CO2 outburst appears over the whole spectrum. The magnitude of the CO2 gush varies with the wavelength used during the light period. On this basis we have measured an action spectrum of photorespiration which is identical with the action spectrum of photosynthetic CO2 uptake.Only at a low temperature (+20°C) and illumination with red light (550 to 651 nm; 10(-s) einsteins/cm(2)·sec) did we find a light induced release of glycolate; in blue (432 and 473 nm; 10(-s) einsteins/cm(2)·sec) and far red light (681 and 703 nm; 10(-8) einsteins/cm(2)·sec) no glycolate excretion occurred. But after addition of α-hydroxy-2-pyridylmethane sulfonate (10(-3)M) glycolate was excreted during illumination with all used wavelengths. The magnitude of glycolate production was nearly the same in all cases. No glycolate excretion occurred at +35°C in the whole region of the spectrum. Here, too, the addition of α-HPMS forced release of glycolate in all wavelengths, indicating that glycolate biosynthesis was occurring.The results are discussed with reference to the physiological behaviour of the algae and activation of photorespiration in blue light. The obtained action spectrum of photorespiration is explained on the basis of a close relationship to photosynthesis.

Significance of enhancement for calculations based on the action spectrum for photosynthesis

Calculations of the errors involved in measuring "photo-synthetically active radiation" in different ways are based on the assumption that the photosynthetic rate of a leaf in "white" light is equal to the sum of the products of (a) the photo-synthetic rate per unit of incident energy flux (action spectrum) by (b) the spectral energy flux distribution of the white light, the products being summed over all wavelengths at which the action spectrum is greater than zero. The calculations are valid only if the effects of different wavelengths are independent and additive. Although interactions are well documented in photo-synthesis ("enhancement"), tests showed that the photosynthetic rates of leaves of six species, in four different types of white light, were within +/-7% of the rates calculated in this way.