Showing papers on "Photosynthesis published in 1982"

Modelling of Photosynthetic Response to Environmental Conditions

Abstract: Photosynthesis is the incorporation of carbon, nitrogen, sulphur and other substances into plant tissue using light energy from the sun. Most of this energy is used for the reduction of carbon dioxide and, consequently, there is a large body of biochemical and biophysical information about photo synthetic carbon assimilation. In an ecophysiological context, we believe that most of today’s biochemical knowledge can be summarized in a few simple equations. These equations represent the rate of ribulose bisphosphate (RuP2)-saturated carboxylation, the ratio of photorespiration to carboxylation, and the rates of electron transport/photophosphorylation and of “dark” respiration in the light. There are many other processes that could potentially limit CO2 assimilation, but probably do so rarely in practice. Fundamentally this may be due to the expense, in terms of invested nitrogen, of the carboxylase and of thylakoid functioning. To reach our final simple equations we must first discuss the biochemical and biophysical structures — as they are understood at present — that finally reduce the vast number of potentially rate-limiting processes to the four or five listed above. A diagrammatic representation of these processes is given in Fig. 16.1.

Inactivation of Photosynthetic Oxygen Evolution and Concomitant Release of Three Polypeptides in the Photosystem II Particles of Spinach Chloroplasts

Abstract: Photosystem II particles having an oxygen evolution activity as high as 300,ulnol mg-1 chlorophyll hr -1 were prepared from spinach chloroplasts using Triton X-IOO. The oxygen evolution system in these particles was stable; 70% of the original activity remained after storage of the particles at O°C for 7 days. When the particles were treated at pH 9.3, the oxygen evolution was specifically inactivated and three polypeptides having apparent molecular weights of 32,000, 24,000 and 15,000 were simultaneously released. This observation suggests that these polypeptides are associated with the oxygen evolution system of photosynthesis.

Functional Significance of Different Pathways of CO 2 Fixation in Photosynthesis

Abstract: The functional significance of different photosynthetic CO2 fixation pathways is a question which can be answered in many ways, each being appropriate to certain scales of enquiry. In physiological ecology our purpose should be to integrate these different scales of enquiry as comprehensively as possible, and to show how photosynthesis contributes, directly or indirectly, to performance and survival of plants in diverse habitats. Studies of photosynthetic CO2 fixation were afflicted with a post-Calvin cycle chauvinism in the 1950’s, which may have been responsible for the slow and tentative revelation of the C4 pathway of photosynthetic carbon assimilation in the USA and USSR (Burr et al. 1957; Karpilov 1960; Kortschak et al. 1965). Elucidation of this pathway undoubtedly stimulated new interest in the carbon metabolism of photosynthesis in the next decade (Hatch and Slack 1966, 1970; CC Black 1973) and led to an upsurge in comparative studies of higher plant photosynthesis (Black 1971; Bjorkman 1973). Largely as a result of this stimulus, the peculiar dark CO2 fixation processes of succulent plants, known as crassulacean acid metabolism (CAM), were also recognized as a distinctive photosynthetic process (Kluge and Ting 1978; Osmond 1978). It also led to the present revival of interest in the photosynthesis of aquatic plants.

The Close Relationship Between Net Photosynthesis and Crop Yield

Abstract: Crop yield is closely related to the net photosynthetic assimilation of CO2 throughout an entire season, but instantaneous measurements of photosynthesis may be misleading. Increasing the rates of net photosynthesis and translocation and enlarging the storage capacity by selection and breeding may bring about large increases in yield, especially in C3 species. (Accepted for publication 23 April 1982)

Photosynthetic acclimation to variability in the light environment of early and late successional plants.

Abstract: Fourteen plant species from early-, mid-, and late-successional habitats were grown for a period of 25 to 50 days in each of two light environments, i.e. full sunlight and in deep shade. The rate of photosynthesis for newly formed leaves was measured as a function of light intensity for plants from each light environment. Photosynthetic flexibility, measured as the difference in response between sun- and shade-grown plants, was determined for each of 5 parameters including dark respiration, quantum yield, light compensation, half-saturating irradiance for photosynthesis, and the photosynthetic rate at 1,400 μE m-2 s-1. We found photosynthetic flexibility to be high for early successional annuals, intermediate for midsuccessional species, and low for late successional species.

Photosynthesis of Intertidal Brown Algae During and After Periods of Emersion: A Renewed Search for Physiological Causes of Zonation

Abstract: CO2-exchange of emersed plants and 0,-exchange of submersed plants were measured in 5 species of brown algae from different tidal heights on shores in Ireland and Helgoland (southern North Sea). The photosynthesis of emersed fucoids and Laminaria digitata increased as up to 25 % of tissue water was lost, but then declined with further desiccation. The relationship between decrease in photosynthesis and loss of tissue water was similar in 3 species of Fucus, and the photosynthetic apparatus of F. spiralisappeared to be no more resistant to desiccation than that of F. serratus. Recovery from severe desiccation took about 2 h in all species, regardless of their typical position on the shore, but the extent of recovery from a given degree of desiccation was greater in upper shore species. Pelvetia canaliculata and F. spiralis showed complete recovery from 80 to 90% water loss, F. vesiculosus from about 70 %, F. serratus from 60 %, and Laminaria digitata from 55 % water loss. The photosynthetic rate of each species after full recovery decreased linearly as water loss increased beyond these values. It is in the extent of recovery of photosynthesis after desiccation that intertidal brown algae show the clearest correlation with their heights in the zonation pattern on European shores.

Growth kinetics of photosynthetic microorganisms

Abstract: Needless to say, any studies on photosynthetic microorganisms should be accompanied by a proper assessment of microbial absorption of light energy whatever the purposes of these works might be — biomass production, analysis of excessive growth of blue- green algae in waters, evaluation of light-energy conversion efficiency, etc.

Vertical separation of light and available nutrients as a factor causing replacement of green algae by blue-green algae in the plankton of a stratified lake

Abstract: (1) A change from the green alga, Dictyosphaerium pulchellum to the blue-green algae Microcystis aeruginosa and Anabaena spiroides occurred in the plankton of Mt Bold reservoir, South Australia, during November and December 1978. (2) The reservoir was 30-34 m deep, thermally stratified with water mixed to 6-7 m, and a euphotic zone of less than 2.7 m. Measurements of photosynthesis and light penetration showed that photosynthesis was restricted probably to the upper 2.5 m. (3) Growth experiments with eight cultured species, and the natural phytoplankton assemblage, showed that during this change there was a decline of the potential of the water for algal growth to undetectable levels at a depth of 8 m. This could be restored by the combined addition of nitrogen, phosphorus and Fe-EDTA. (4) Continuous measurement of concentration of chlorophyll a in the water column demonstrated that the blue-green algal community was able to migrate to a depth of 12 m despite substantial density barriers. (5) In situ growth experiments, using dialysis bags, showed that populations which were artificially circulated between 0.2 and 10 m, were able to grow, whereas those maintained at a single depth (0-2 m or 10 m) were not. (6) The ability of blue-green algae to overcome successfully this spatial separation between light and nutrients was proposed as the probable cause of the change from green to blue-green algae.

Photoinhibition of photosynthesis: effect on chlorophyll fluorescence at 77K in intact leaves and in chloroplast membranes of Nerium oleander.

Abstract: The effect of exposing intact leaves and isolated chloroplast membranes of Nerium oleander L. to excessive light levels under otherwise favorable conditions was followed by measuring photosynthetic CO2 uptake, electron transport and low-temperature (77K=-196°C) fluorescence kinetics. Photoinhibition, as manifested by a reduced rate and photon (quantum) yield of photosynthesis and a reduced electron transport rate, was accompanied by marked changes in fluorescence characteristics of the exposed upper leaf surface while there was little effect on the shaded lower surface. The most prominent effect of photoinhibitory treatment of leaves and chloroplasts was a strong quenching of the variable fluorescence emission at 692 nm (Fv,692) while the instantaneous fluorescence (Fo,692) was slightly increased. The maximum and the variable fluorescence at 734 nm were also reduced but not as much as FM,692 and Fv,692. The results support the view that photoinhibition involves an inactivation of the primary photochemistry of photosystem II by damaging the reaction-center complex. In intact leaves photoinhibition increased with increased light level, increased exposure time, and with decreased temperature. Increased CO2 pressure or decreased O2 pressure provided no protection against photoinhibition. With isolated chloroplasts, inhibition of photosystem II occurred even under essentially anaerobic conditions. Measurements of fluorescence characteristics at 77K provides a simple, rapid, sensitive and reproducible method for assessing photoinhibitory injury to leaves. The method should prove especially useful in studies of the occurrence of photoinhibition in nature and of interactive effects between high light levels and major environmental stress factors.

Adaptation of Chloroplast-Ultrastructure and of Chlorophyll- Protein Levels to High-Light and Low-Light Growth Conditions

Abstract: Adaptation In saturating light radish seedlings grown in high-light growth conditions (90 W · m⁻²) possess a much higher photosynthetic capacity on a chlorophyll and leaf area basis than the low-light grown plants (10 W · m⁻²). The higher CO₂-fixation rate of HL-plants is due to the presence of HL-chloroplasts which possess a different ultrastructure and also different levels of the individual chlorophyll-carotenoid-proteins than the LL-chloroplasts of LL-seedlings. 1. Ultrastructure: The high-light adapted chloroplasts are characterized by fewer photo­ synthetic membranes per chloroplast section, by low grana stacks (only few thylakoids per granum), a lower stacking degree of thylakoids, a higher proportion of non-appressed membranes (stroma thylakoids + end grana membranes) and a high starch content. The LL-chloroplasts possess no starch, their grana stacks are higher (up to 17 thylakoids per granum) and also significantly broader than that of HL-chloroplasts. 2. Chlorophyll-proteins: The photosynthetic apparatus of HL-chloroplasts contains a larger proportion of chlorophyll a-proteins of photosystem I (CPIa + CPI) and of photosystem II (CPa, the presumable reaction center of PS II) than the LL-chloroplasts which possess a higher proportion of light-harvesting chlorophyll a/b-proteins (LHCP₁, LHCP₂, LHCP₃, LHCPy). The higher levels of LHCPs in LL-plants are associated with a higher ground fluorescence fo and maximum fluorescence fp of the in vivo chlorophyll. 3. Chlorophyll and carotenoid ratios: The chloroplasts of HL-plants possess a higher proportion of chlorophyll a and β-carotene (higher values for the ratios chlorophyll a /b and lower values for a/c and x/c) which reflect the increased level of the chlorophyll a/β-carotene-proteins CPIa, CPI and CPa. The higher level of light-harvesting chlorophyll a/b-xanthophyll-proteins (LHCPs) in LL-plants is also indicated by an increased content of xanthophylls and chlorophyll b as seen from lower a/b and higher x/c and a/c ratios. 4. The results indicate that plants possess the capacity for an ontogenetic adaptation of their photosynthetic apparatus to the incident light intensity. The HL-chloroplasts of HL-plants which contain less antenna chlorophyll, are adapted for a more efficient photosynthetic quantum conversion at light saturation than the LL-chloroplasts with high grana stacks. The correlation between higher levels of light-harvesting chlorophyll a/b-proteins (LHCPs) and a higher stacking degree of thylakoids, and the involvement of LHCPs in stacking is discussed.

A special fructose bisphosphate functions as a cytoplasmic regulatory metabolite in green leaves.

Abstract: Fructose 2,6-bisphosphate (Fru-2,6-P2), a regulatory metabolite discovered in animal cells and recently reported to occur in etiolated seedlings, was found to be present in the cytoplasmic fraction of leaves of spinach and peas (typical C3 plants, in which a three-carbon carboxylic acid is a major early photosynthetic product). At concentrations approximating those calculated to occur physiologically, Fru-2,6-P2 modulated two enzymes of the leaf cytoplasm: (i) Fructose-1,6-bisphosphatase (EC 3.1.3.11), a key enzyme of sugar synthesis, was competitively inhibited by Fru-2,6-P2, and (ii) pyrophosphate-linked phosphofructokinase (inorganic pyrophosphate-D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.90), a cytoplasmic enzyme that now seems important in glycolysis of C3 plants, was activated by Fru-2,6-P2. There was no indication of a role for Fru-2,6-P2 in photosynthesis of either chloroplasts or oxygenic prokaryotes. The results suggest that Fru-2,6-P2 functions in the regulation of glycolysis and gluconeogenesis (carbohydrate synthesis) in the cytoplasm of leaves of C3 plants.

Correlation between changes in photosynthetic activity and changes in total protoplast volume in leaf tissue from hygro-, meso- and xerophytes under osmotic stress.

Abstract: Rates of photosynthesis of leaf slices from various hygro-, meso- and xerophytes were measured in the absence of stomatal control in various stages of osmotic dehydration The external osmotic potential π° for a 50% inhibition of photosynthesis varied between 20 bar in some hygrophytes up to 50 bar in xerophytes The response of photosynthetic enzymes to increased salt concentrations in the reaction medium was similar in leaf extracts from hygro-, meso- and xerophytes The total protoplast volume in vacuum-infiltrated leaf discs from various plants was measured as the difference between 3H2O-labeled space and [14C]sorbitol-labeled space In all plants, the protoplast volume could be reduced to about 55% of the maximum volume of tissue in equilibrium with water, without decreasing photosynthesis Reduction of the maximal protoplast volume below 55% decreased photosynthesis in all tissues to the same decreased photosynthesis in all tissues to the same degree At 20% maximal volume, photosynthesis of all plants was completely inhibited The differential decrease of protoplast volumes of various leaf tissues in response to changes in π° was mainly due to the different osmotic potential of the cell sap (πcs) The relative contribution of sugars to the overall osmolarity of the cell sap was up to nineteen times higher in xerophytes than in hygrophytes Short-term recovery of photosynthesis after hypertonic stress was good in xerophytes, incomplete in mesophytes and absent in hygrophytes There was also a large discrepancy between the partial recovery of protoplast volumes and the complete absence of a recovery of photosynthesis in hygrophytes

Salt tolerance in crop plants monitored by chlorophyll fluorescence in vivo.

Abstract: The potential of measurements of chlorophyll fluorescence in vivo to detect cellular responses to salinity and degrees of salt stress in leaves was investigated for three crop plants. Sugar beet (Beta vulgaris L.) (salt tolerant), sunflower (Helianthus annuus L.) (moderately salt tolerant), and bean (Phaseolus Vulgaris L. cv Canadian Wonder) (salt intolerant) were grown in pots and watered with mineral nutrient solution containing 100 millimolar NaCl. The fast rise in variable chlorophyll fluorescence yield that is correlated with photoreduction of photosystem II acceptors increased in leaves of sugar beet plants treated with salt suggesting stimulation of photosystem II activity relative to photosystem I. In sunflower, this fast rise was depressed by approximately 25% and the subsequent slow rate of quenching of the chlorophyll fluorescence was stimulated. These differences were more marked in the older mature leaves indicating an increasing gradient of salt response down the plant. The salt effect in vivo was reversible since chloroplasts isolated from mature leaves of salt-treated and control sunflower plants gave similar photosystem II activities. Unlike in sugar beet and sunflower, leaves of salt-treated bean progressively lost chlorophyll. The rate of slow quenching of chlorophyll fluorescence decreased indicating development of a partial block after photosystem II and possible initial stimulation of photosystem II activity. With further loss of chlorophyll photosystem II activity declined. It was concluded that measurements of chlorophyll fluorescence in vivo can provide a rapid means of detecting salt stress in leaves, including instances where photosynthesis is reduced in the absence of visible symptoms. The possible application to screening for salt tolerance is discussed.

Effect of Pod Removal on Leaf Senescence in Soybeans

Abstract: Depodding soybean (Glycine max [L] Merr. cv Wye) plants results in an apparent inhibition of senescence as indicated by leaf chlorophyll and soluble protein retention. However, leaf photosynthesis and ribulose bisphosphate carboxylase (Rubisco) levels begin to decline earlier in depodded than in control, podded plants. The initial decline in photosynthesis is correlated with a decrease in leaf transpiration, while the latter decline is associated with the loss of Rubisco. Total soluble protein remains high in depodded plants because several polypeptides, three in particular, increase in amounts sufficient to offset the loss of Rubisco. Thus, depodding appears to change the function of the leaf rather than simply delaying or preventing the decline in leaf function. Changes in specific leaf weight and starch content following depodding suggest that the leaf may be changing to a storage organ.

Biogas production from anaerobic digestion of Spirulina maxima algal biomass

Abstract: The photosynthetic spectrum of solar energy could be exploited for the production of chemical energy of methane through the combined algal-bacterial process. In this process, the algae are mass produced from light and from carbon in the first step. The algal biomass is then used as a nutrient for feeding the anaerobic digester, in the second step, for the production of methane by anaerobic bacteria. The carbon source for the production of algal biomass could be either organic carbon from wastewaters (for eucaryotic algae), or carbon dioxide from the atmosphere or from the combustion exhaust gases (for both prokaryotic and eukaryotic algae). The technical feasibility data on the anaerobic digestion of algal biomass have been reported for many species of algae including macroscopic algae and microscopic algae. Research being conducted in the authors' laboratory consists of using the semimicroscopic blue-green alga Spirulina maxima as the sole substrate for this combined algal-bacterial process. This species of alga is very attractive for the process because of its capability of using the atmospheric carbon dioxide as carbon source and its simple harvesting methods. Furthermore, it appeared that the fermentability of S. maxima is significantly higher than other microscopic algae. This communication presents themore » results on the anaerobic inoculum development by the adaptation technique. This inoculum was then used for the semicontinuous anaerobic digestion of S. maxima algal biomass. The evolutions of biogas production and composition, biogas yield, total volatile fatty acids, alkalinity, ammonia nitrogen, pH, and electrode potential were followed.« less

Temperature Dependence of Photosynthesis in Agropyron smithii Rydb. I. FACTORS AFFECTING NET CO2 UPTAKE IN INTACT LEAVES AND CONTRIBUTION FROM RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE MEASURED IN VIVO AND IN VITRO

Abstract: As part of an extensive analysis of the factors regulating photosynthesis in Agropyron smithii Rydb., a C3 grass, we have examined the response of leaf gas exchange and ribulose-1,5-bisphosphate (RuBP) carboxylase activity to temperature. Emphasis was placed on elucidating the specific processes which regulate the temperature response pattern. The inhibitory effects of above-optimal temperatures on net CO2 uptake were fully reversible up to 40°C. Below 40°C, temperature inhibition was primarily due to O2 inhibition of photosynthesis, which reached a maximum of 65% at 45°C. The response of stomatal conductance to temperature did not appear to have a significant role in determining the overall temperature response of photosynthesis. The intracellular conductance to CO2 increased over the entire experimental temperature range, having a Q10 of 1.2 to 1.4. Increases in the apparent Michaelis constant (Kc) for RuBP carboxylase were observed in both in vitro and in vivo assays. The Q10 values for the maximum velocity (Vmax) of CO2 fixation by RuBP carboxylase in vivo was lower (1.3-1.6) than those calculated from in vitro assays (1.8-2.2). The results suggest that temperature-dependent changes in enzyme capacity may have a role in above-optimum temperature limitations below 40°C. At leaf temperatures above 40°C, decreases in photosynthetic capacity were partially dependent on temperature-induced irreversible reductions in the quantum yield for CO2 uptake.

Inhibition of Photosynthesis by Ethylene—A Stomatal Effect

Abstract: Ethylene at hormonally significant levels inhibited net photosynthesis of the cultivated peanut (Arachis hypogaea L.) as measured by gas analysis. Upon the removal of ethylene, the inhibition was naturally overcome at the concentration-exposure duration combinations tested. Increased length of exposure of 1 microliter of ethylene per liter of air up to 6 hours increased the degree of net photosynthesis inhibition (68% reduction after 6-hour exposure). Significantly greater inhibition of photosynthesis by ethylene was detected on peanut genotypes having higher photosynthetic efficiency. In contrast to peanut, hormonal concentrations of ethylene only moderately inhibited sweet potato, Jerusalem artichoke, and sunflower photosynthesis and was without effect on beans, peas, Irish potato, Mimosa pudica, and white clover. No inhibition could be found by ethylene on ribulose 1,5-biphosphate carboxylase activity in vitro. Photosynthesis was lowered at all CO2 concentrations below ambient at an O2 concentration of 1.5%, indicating that the action of ethylene was not affected by low O2; concomitantly, an increase in the CO2 compensation point occurred. Diffusion resistance measurements of leaf water vapor loss made on ethylene-treated peanut leaves showed a measurable decrease in leaf conductance which correlated with net photosynthesis decrease. Ethylene influenced the conductance of abaxial stomata more so than adaxial.

Effects of water stress on photosynthetic electron transport, photophosphorylation, and metabolite levels of Xanthium strumarium mesophyll cells.

Abstract: Several component processes of photosynthesis were measured in osmotically stressed mesophyll cells of Xanthium strumarium L. The ribulose-1,5-bisphosphate regeneration capacity was reduced by water stress. Photophoshorylation was sensitive to water stress but photosynthetic electron transport was unaffected by water potentials down to-40 bar (-4 MPa). The concentrations of several intermediates of the photosynthetic carbon-reduction cycle remained relatively constant and did not indicate that ATP supply was limiting photosynthesis in the water-stressed cells.

Biochemical Changes that Occur during Senescence of Wheat Leaves: I. Basis for the Reduction of Photosynthesis

Abstract: Changes in activities of photosynthetic enzymes and photochemical processes were followed with aging of vegetative and flag leaves of wheat (Triticum aestivum L. cv Roy). Activities of stromal enzymes began to decline prior to photochemical activities. In general, total soluble protein and the activities of ribulose-1,5-bisphosphate carboxylase and NADP-triose-phosphate dehydrogenase declined in parallel and at an earlier age than leaf chlorophyll (Chl), leaf photosynthesis, and photosynthetic electron transport activity. Leaves appeared to lose whole chloroplasts as opposed to a general degradation of all chloroplasts based on three lines of evidence: (a) electron transport activity calculated on an area basis declined much earlier than the same data expressed on a Chl basis; (b) Chl content per chloroplast was similar for mature and senescent tissue; and (c) the absorbance at 550 nanometers (light scattering) per unit of Chl remained essentially constant until the end of senescence. Chloroplasts did, however, undergo some modifications before they were lost (e.g. loss of stromal enzyme activities), but the reduction in leaf photosynthesis was apparently caused by a loss of whole chloroplasts.

Photosynthetic dynamics in varying light environments: a model and its application to whole leaf carbon gain'

Abstract: The light environment of a plant microsite can be highly dynamic with sunflecks lasting from seconds to minutes in length. Whole leaf photosynthetic response to such variations is complex and species-specific. A mathematical model based on a single enzyme pool is derived to mimic leaf response in varying light. The model is used to analyze carbon gain in Fragaria virginiana. I find that sunflecks can be responsible for an appreciable proportion of leaf carbon gain throughout a day, especially under light-limited conditions. Model results also indicate that the standard methods of estimating carbon gain in varying light using steady-state photosynthetic rates often give overesti- mates.

Primary photochemistry in the facultatively aerobic green photosynthetic bacterium Chloroflexus aurantiacus

Abstract: Photochemical activity was examined in membrane fragments and a purified membrane preparation from Chloroflexus. Flash-induced absorption difference spectroscopy strongly suggests a primary donor (P865) that is more similar to the P870 bacteriochlorophyll a dimer found in the purple photosynthetic bacteria than it is to P840 found in the anaerobic green bacteria. Redox measurements on P865 and an early acceptor also indicate a photochemical system characteristic of the purple bacteria. The membrane preparation contains a tightly bound type c cytochrome, c554, that is closely coupled to the reaction center as indicated by its ability to rereduce photooxidized P865. Chloroflexus thus appears to be distinct photochemically from other families of photosynthetic bacteria and may occupy an important role in photosynthetic evolution.

Distribution of phototrophic microorganisms in the anaerobic and microaerophilic strata of Lake Vechten (The Netherlands). Pigment analysis and role in primary production

Abstract: Ahstruct Dense populations of photoautotrophic bacteria (total chlorophyll concentrations up to 200 mg-m-“) were found sequentially layered in meta- and upper hypolimnion during summer stratification of Lake Vechten (Netherlands). Pigment analysis by Chromatographic and spectrophotometric techniques and phase microscopy were used to reveal the structure and relative seasonal abundance of the populations. The predominant bacteria were identified as members of the genera Synechococcus, Chloronema, Chromatium, and Thiopedia. Unidentified brown Chlorobiaceae also were present. Maximal development of the populations was found in late August and September. The primary production, distribution of sulfide, oxygen, chlorophyllous pigments and ATP, and temperature profiles were determined through the summer. Oxygenic (algal) and anoxygenic (bacterial) photosynthesis were distinguished by using the inhibitor DCMU. The phototrophic sulfur bacteria accounted for 3.9-17.5% of the total daily primary production. The contribution of bacterial photosynthesis to the total pelagic annual primary production of the lake was 3.6%. The main factors determining the growth of photosynthetic sulfur bacteria in Lake Vechten arc light and sulfide concentration.

Chlorophyll‐protein levels and degree of thylakoid stacking in radish chloroplasts from high‐light, low‐light and bentazon‐treated plants

Abstract: The level of 7 chlorophyll-carotenoid-proteins was determined in chloroplasts from radish seedlings (Raphanus sativus L. var. Saxa Treib) grown in high-light (HL; 90 W m−2 and low-light (LL; 10 W m−2) growth conditions with and without application of the photosystem 2 herbicide bentazon (10−4M) and compared with the degree of thylakoid stacking. 1 The photosynthetic apparatus of HL-chloroplasts contains higher proportions of the photosystem 1 chlorophyll a-proteins CPI and CPIa than LL-chloroplasts or chloroplasts from bentazon-treated plants. 2 In LL-chloroplasts and in chloroplasts from bentazon-treated plants a higher proportion of light-harvesting chlorophyll a/b-proteins (LHCP1, LHCP2, LHCP3, LHCPy) is found. Bentazon treatment changes the proportion of LHCPs to about the same levels under both HL and LL-growth conditions. The amounts of free chlorophyll found in bentazon chloroplasts (27–29%) is higher than in the HL or LL-controls (16–18%). 3 The increase in degree of thylakoid stacking (% proportion of appressed membranes per total chloroplasts membranes) of LL-chloroplasts as compared to HL-chloroplasts of 7 to 9% (3rd to 5th day of illumination) is paralleled by a similar increase in the LHCPs of 5% and 8% (3rd and 5th day). The importance of light harvesting chlorophyll a/b-proteins as a prerequisite for thylakoid stacking is discussed.