The Effects of Some Chelating Agents and Their Copper Complexes on Photosynthesis in Scenedesmus quadricauda

The effects on apparent photosynthesis in the green alga Scenedesmus quadricauda of four chelating substances, 8-hydroxyquinoline (= oxine), β-isopropyltropolone (=β-thujaplicin), sodium dimethyldithiocarbamate and 3-(β-hydroxyethyl)-C-pentamethylene-3-aza-dithiocarbamate have been investigated. The first three compounds mentioned had all an inhibitory effect on photosynthesis, measured as oxygen production with a manometric, a volumetric or a polarographic method. In combination with certain concentrations of CuSO₄ bimodal dose response curves were observed, similar to those obtained on the growth of different microorganisms. Calculations of the amounts of different complexes that appeared in the nutrient solutions during the experiments are compared with the recorded degrees of inhibition. The results strongly indicate that the 1: 1-complexes between Cu²⁺ and the chelating substances are the most toxic agents at low concentrations of these compounds.     

Observations on the mechanism of copper damage in chlorella

Addition of excess copper to nongrowing cells of a normal, green Chlorella caused a reduction in total pigments and a blue shift of chlorophyll absorption, concurrent with the inhibition of photosynthesis. Chlorophylless yellow and white mutant strains of the same alga showed a rise in nonspecific absorption (i.e., change in light scatter) within 5 to 10 minutes after the addition of CuSO₄; concomitantly a lowering of packed cell volume and a rise in respiration occurred. Glutathione prevented all copper-induced changes, whereas MnCl₂ protected only partially. Selective inhibition of some responses to copper was observed when O₂ was absent or an antioxidant present.     

Stromal acidification mediates in vivo water stress inhibition of nonstomatal-controlled photosynthesis

Stromal acidification has been reported to mediate reduced osmotic potential (ψ_π) effects on photosynthesis in the isolated spinach chloroplast (Berkowitz, Gibbs 1983 Plant Physiol 72: 1100-1109). To determine if stromal acidification mediates osmotic dehydration inhibition of photosynthesis in vivo, the effects of a weak base (NH₄Cl), which raises stromal pH, on CO₂ fixation of vacuum-infiltrated spinach leaf slices, Chlamydomonas reinhardii cells and Aphanocapsa 6308 cells under isotonic and dehydrating conditions were investigated. Five millimolar NH₄Cl stimulated spinach leaf slice CO₂ fixation by 43% under stress (0.67 molar sorbitol) conditions, and had little effect on fixation under isotonic (0.33 molar sorbitol) conditions. Chlamydomonas cells were found to be more sensitive to reduced ψ_π than spinach leaf slices. CO₂ fixation in the cells of the green alga Chlamydomonas reinhardii was 99 and 17 micromoles per milligram chlorophyll per hour, respectively, at 0.1 molar mannitol and 0.28 molar mannitol. Five millimolar NH₄Cl stimulated CO₂ fixation of Chlamydomonas cells by 147% under stress (0.28 molar mannitol) conditions. Aphanocapsa 6308 cells (blue-green alga) were also found to be sensitive to reduced ψ_π, and inhibitions in photosynthesis were partially reversed by NH₄Cl. These data indicate that in vivo water stress inhibition of photosynthesis is facilitated by stromal acidification, and that this inhibition can be at least partially reversed in situ.     

Interactions between carbon dioxide and oxygen in the photosynthesis of three species of marine red macroalgae

Summary

Red algae have the highest known selectivity factor (S_rel) for CO₂ over O₂ of ribulose bisphosphate carboxylase-oxygenase (RUBISCO). This allows the prediction that a red alga relying on diffusive supply of CO₂ to RUBISCO from air-equilibrated solution should have less O₂ inhibition of photosynthesis than would an otherwise similar non-red alga with a lower S_rel of RUBISCO. Furthermore, RUBISCO shows an increased S_rel values at low temperatures. The prediction that O ₂inhibition of photosynthesis should be small for marine red algae relying on diffusive CO₂ entry growing in the North Sea with an annual temperature range of 4–16°C was tested in O₂ electrode experiments at 12°C. Phycodrys rubens and Plocamium cartilagineum, which rely on diffusive CO₂ entry showed, as predicted, only a small inhibition at lower inorganic C concentrations. Palmaria palmata, which has a CO₂ concentrating mechanism, had the expected negligible O ₂ inhibition of photosynthesis at any inorganic C concentration except (non-significantly) for saturating inorganic C.     

Inhibition of photosynthesis by Colletotrichum lindemuthianum in bean leaves determined by chlorophyll fluorescence imaging

Infection of bean leaves by Colletotrichum lundemuthianum causes vein necrosis and subsequent localized wilting of the blade. The effect of infection on photosynthesis was investigated by imaging leaf chlorophyll fluorescence as a means of mapping stomatal and metabolic inhibition of photosynthesis. During infection, CO₂ assimilation (An), stomatal conductance to water vapour, and photosynthetic electron transport rate (J_t) decreased, whereas dark respiration increased. An decreased more than was expected from the reduction in green leaf area, showing that photosynthesis was inhibited in apparently healthy areas. Under subsaturating irradiance, images of J_t in air showed that photosynthesis decreased gradually, with this effect shifting from green to necrotic areas. Sudden increase in CO₂ concentration to 0·74% in the atmosphere around the leaf only partially reversed this inhibition, showing that both stomatal and metabolic inhibition occurred. Under limiting irradiance, decreases in J_t and in maximal J_t during high CO₂ exposure as leaf damage severity increased suggested that metabolic inhibition was mediated through an inhibition of Ribulose 1·5‐bisphosphate (RuBP) regeneration. Finally, the importance of our data in terms of assessing the loss of photosynthetic yield from visible symptoms – as is currently performed in epidemiology – is discussed.     

Role of ethylene in alleviation of cadmium-induced photosynthetic capacity inhibition by sulphur in mustard

Sulphur (S) assimilation leads to the formation of glutathione (GSH) and alleviation of cadmium (Cd) stress. GSH is synthesized from its immediate metabolite cysteine, which also serves as a metabolite for ethylene formation through S‐adenosyl methionine. To assess the role of ethylene in S‐induced alleviation of Cd stress on photosynthesis, the effects of S or ethephon (ethylene source) on GSH and ethylene were examined in mustard (Brassica juncea L. cv. Varuna). Sufficient‐S at 100 mg S kg^?1 soil alleviated Cd‐induced photosynthetic inhibition more than excess‐S (200 mg S kg^?1 soil) via ethylene by increased GSH. Under Cd stress, plants were less sensitive to ethylene, despite high ethylene evolution, and showed photosynthetic inhibition. Ethylene sensitivity of plants increased with ethephon or sufficient‐S, triggering the induction of an antioxidant system, and leading to increased photosynthesis even under Cd stress. The effects of ethephon and S under Cd stress were similar. The effects of S were reversed by ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG), suggesting that ethylene plays an important role in S‐induced alleviation of Cd stress on photosynthesis.     

The Effect of Deleterious Concentrations of Copper on the Photosynthesis of Chlorella pyrenoidosa

If a single salt solution of CuSO₄ is used, Cu penetrates immediately iuto the plasma of Chlorella cells, reducing the rates of photosynthesis at both high and low illumination. If CuSO₄ is added to ordinary Österlind culture-medium (pH 8) it takes some hours before any influence of deleterious concentrations of Cu is observed and initially only at light saturation. The algae must have been illuminated during the whole period. Maximum influence of CuSO₄ is found duriug the first 24 hours of treatment. A significant deleterious influence of Cu concentrations as low as about 1 μg/l is found. The influence of Cu increases with decreasing concentrations of the alga. If a culture medium at pH 5 is used instead of the ordinary one at pH 8, copper concentrations ahout 10 times as high must he used be order to obtain the same deleterious effect. An increase of the cotncentration of K reduces the influence of Cu to some extent. These facts show that the effect of deleterious concentrations of Cu in halanced solutions is not due to a marked penelration of this ion into the plasma but to a binding to the cytoplasmic membrane whereby the celts i.a. become more or less unable to divide. The cells become saturated with assimilation products which have a depressant effect on the rate of photosynthesis. Other cations compete with Cu for the “active sites” on the membranes.     

Involvement of ethylene in reversal of salt‐inhibited photosynthesis by sulfur in mustard

Sulfur (S) assimilation results in the synthesis of cysteine (Cys), a common metabolite for the formation of both reduced glutathione (GSH) and ethylene. Thus, ethylene may have regulatory interaction with GSH in the alleviation of salt stress. The involvement of ethylene in the alleviation of salt stress by S application was studied in mustard (Brassica juncea cv. Pusa Jai Kisan). First, the effects of 0, 0.5, 1.0 and 2.0 mM SO₄^2? were studied on photosynthetic and growth parameters to ascertain the S requirement as sufficient‐S and excess‐S for the plant. In further experiments, the effects of sufficient‐S (1 mM SO₄^2?) and excess‐S (2 mM SO₄^2?) were studied on the alleviation of salt stress‐induced by 100 mM NaCl, and ethylene involvement in the alleviation of salt stress by S. Under non‐saline condition, excess‐S increased ethylene with less content of Cys and GSH and adversely affected photosynthesis and growth. In contrast, excess‐S maximally alleviated salt stress due to high demand for S and optimal ethylene formation, which maximally increased GSH and promoted photosynthesis and growth. The involvement of ethylene in S‐mediated alleviation of salt stress was further substantiated by the reversal of the effects of excess‐S on photosynthesis by aminoethoxyvinylglycine (AVG), ethylene biosynthesis inhibitor. The studies suggest that plants respond differentially to the S availability under non‐saline and salt stress and excess‐S was more potential in the alleviation of salt stress. Further, ethylene regulates plants' response and excess S‐induced alleviation of salt stress and promotion of photosynthesis.     

Light-dependent reduction of dehydroascorbate by ruptured pea chloroplasts

Glutathione dehydrogenase (EC 1.8.5.1) was partially purified from pea shoots. The pH optimum was 7.6. The K_m values for GSH and dehydroascorbate were 4.4 and 0.44 millimolar, respectively. The enzyme was inhibited by iodoacetate and CuSO₄ but not significantly by ZnCl₂ or NaN₃. Part of the total enzyme activity was associated with isolated chloroplasts.     

INHIBITORY EFFECT OF AMITROLE ON SCENEDESMUS QUADRICAUDA

The multiplication of the alga Scenedesmus quadricauda is inhibited by Amitrole (3-amino-1,2,4-triazole). This inhibition is reversed by addition of adenine to the growth medium. An electron-microscopic study has been made of the cytological changes which accompany the inhibition by Amitrole and the subsequent reversal. In the presence of Amitrole the cells accumulate a large quantity of starch which is lost very rapidly as soon as the Amitrole block is released and cell multiplication is resumed. ³Present address: Department of Biology and Botany, University of British Columbia, Vancouver, Canada.     

Evaluation of the toxicity of stress-related aldehydes to photosynthesis in chloroplasts

Aldehydes produced under various environmental stresses can cause cellular injury in plants, but their toxicology in photosynthesis has been scarcely investigated. We here evaluated their effects on photosynthetic reactions in chloroplasts isolated from Spinacia oleracea L. leaves. Aldehydes that are known to stem from lipid peroxides inactivated the CO₂ photoreduction to various extents, while their corresponding alcohols and carboxylic acids did not affect photosynthesis. α,β-Unsaturated aldehydes (2-alkenals) showed greater inactivation than the saturated aliphatic aldehydes. The oxygenated short aldehydes malondialdehyde, methylglyoxal, glycolaldehyde and glyceraldehyde showed only weak toxicity to photosynthesis. Among tested 2-alkenals, 2-propenal (acrolein) was the most toxic, and then followed 4-hydroxy-(E)-2-nonenal and (E)-2-hexenal. While the CO₂-photoreduction was inactivated, envelope intactness and photosynthetic electron transport activity (H₂O → ferredoxin) were only slightly affected. In the acrolein-treated chloroplasts, the Calvin cycle enzymes phosphoribulokinase, glyceraldehyde-3-phosphate dehydrogenase, fructose-1,6-bisphophatase, sedoheptulose-1,7-bisphosphatase, aldolase, and Rubisco were irreversibly inactivated. Acrolein treatment caused a rapid drop of the glutathione pool, prior to the inactivation of photosynthesis. GSH exogenously added to chloroplasts suppressed the acrolein-induced inactivation of photosynthesis, but ascorbic acid did not show such a protective effect. Thus, lipid peroxide-derived 2-alkenals can inhibit photosynthesis by depleting GSH in chloroplasts and then inactivating multiple enzymes in the Calvin cycle.     

Characteristics of Lipase-Catalyzed Glycerolysis of Triglyceride in AOT-Isooctane Reversed Micelles

Chromobacterium viscosum lipase, solubilized in microemulsion droplets of glycerol containing small amounts of water and stabilized by a surfactant, could catalyze the glycerolysis of triolein. Kinetic analysis of the lipase-catalyzed reaction was possible in the reversed micellar system. Among surfactants and organic solvents tested, bis(2-ethylhexyl)sodiumsulfosuccinate (AOT) and isooctane were respectively most effective, for the glycerolysis of triolein in reversed micelles. Temperature effects, pH profile, K_m,app, and V_max,app were determined. Among various chemical compounds, Fe³⁺, Cu²⁺, and Hg²⁺ inhibited the lipase-catalyzed glycerolysis severely. However, the glycerolysis activity was partially restorable by adding histidine or glycine to the system containing these metal ions. The glycerolysis activity was dependent on water content and maximum activity was obtained at an R value of 1.21. Higher stability of the lipase was obtained in the reversed micellar system.     

Limitation of acetylene reduction (nitrogen fixation) by photosynthesis in soybean having low water potentials

The role of photosynthesis and transpiration in the desiccation-induced inhibition of acetylene reduction (nitrogen fixation) was investigated in soybean (Glycine max [L.] Merr. var. Beeson) using an apparatus that permitted simultaneous measurements of acetylene reduction, net photosynthesis, and transpiration. The inhibition of acetylene reduction caused by low water potentials and their aftereffects could be reproduced by depriving shoots of atmospheric CO₂ even though the soil remained at water potentials that should have favored rapid acetylene reduction. The inhibition of acetylene reduction at low water potentials could be partially reversed by exposing the shoots to high CO₂ concentrations. When transpiration was varied independently of photosynthesis and dark respiration in plants having high water potentials, no effects on acetylene reduction could be observed. There was no correlation between transpiration and acetylene reduction in the CO₂ experiments. Therefore, the correlation that was observed between transpiration and acetylene reduction during desiccation was fortuitous. We conclude that the inhibition of shoot photosynthesis accounted for the inhibition of nodule acetylene reduction at low water potentials.     

Sensitivity of the alga Scenedesmus acutus to some pesticides.

Indoor cultures of the green alga $\text{Scenedesmus}$$\text{acutus}$ were tested for sensitivity to varying concentrations of seven insecticides and three fungicides. The growth rates of the organisms were considerably reduced by BHC and DDT analogues even at low concentrations of 500 ppb and 1 ppm. Lindane above 5 ppm and Technical BHC and DDT at 100 ppm were lethal to this alga. Of the three fungicides, TMTD (Tetra Methyl Thiurum Disulfide) was most toxic resulting in death of the culture at 10 and 100 ppm. Blitox (Copper-oxy chloride) and Zineb (Zinc Ethylene-Bis dithiocarbamate) considerably retarded growth at all concentrations. This alga was more sensitive to Lindane, BHC (Technical), DDT and TMTD. The growth rate appeared to be influenced by the concentration of pesticide present in the algal culture. As $\text{Scenedesmus}$$\text{acutus}$ is being considered as a source of Single Cell Protein (SCP) for human consumption, knowledge on the sensitivity of this alga to pesticide contamination will be useful.     

Endogenous ethylene and reversing methyl jasmonate inhibition of Amaranthus caudatus seed germination by benzyladenine or gibberellin

BA at 10^–5 M, GA₃ at 3×10^–4 M or GA₄₊₇ at 3×10^–5 M partially or largely reversed the inhibition of Amaranthus caudatus seed germination due to JA-Me. BA or GA₃ did not affect ethylene production and ACC oxidase activity in vivo in the presence of JA-Me before radicle protrusion. However, both increased ethylene production after 72 h of incubation, when the reversal of the JA-Me inhibition of seed germination was observed. AVG at 3×10^–4 M decreased ethylene production when it was applied simultaneously with BA and JA-Me or GA₃ and JA-Me, but it had no effect on seed germination. NBD almost completely reversed the stimulatory effect of BA, GA₃ or GA₄₊₇ on the germination of seeds in the presence of JA-Me. Exogenous ethylene reversed the inhibitory effect of NBD. The results indicate that action of endogenous ethylene is involved in the response of JA-Me inhibited seeds to BA or GA_s.     

Over‐expression of bacterial γ‐glutamylcysteine synthetase (GSH1) in plastids affects photosynthesis,growth and sulphur metabolism in poplar (Populus tremula × Populus alba) dependent on the resulting γ‐glutamylcysteine and glutathione levels

We compared three transgenic poplar lines over‐expressing the bacterial γ‐glutamylcysteine synthetase (GSH1) targeted to plastids. Lines Lggs6 and Lggs12 have two copies, while line Lggs20 has three copies of the transgene. The three lines differ in their expression levels of the transgene and in the accumulation of γ‐glutamylcysteine (γ‐EC) and glutathione (GSH) in leaves, roots and phloem exudates. The lowest transgene expression level was observed in line Lggs6 which showed an increased growth, an enhanced rate of photosynthesis and a decreased excitation pressure (1‐qP). The latter typically represents a lower reduction state of the plastoquinone pool, and thereby facilitates electron flow along the electron transport chain. Line Lggs12 showed the highest transgene expression level, highest γ‐EC accumulation in leaves and highest GSH enrichment in phloem exudates and roots. This line also exhibited a reduced growth, and after a prolonged growth of 4.5 months, symptoms of leaf injury. Decreased maximum quantum yield (F_v/F_m) indicated down‐regulation of photosystem II reaction centre (PSII RC), which correlates with decreased PSII RC protein D1 (PsbA) and diminished light‐harvesting complex (Lhcb1). Potential effects of changes in chloroplastic and cytosolic GSH contents on photosynthesis, growth and the whole‐plant sulphur nutrition are discussed for each line.     

A model of carbon dioxide assimilation in Chlamydomonas reinhardii

A simple model of photosynthetic CO₂ assimilation in Chlamydomonas has been developed in order to evaluate whether a CO₂-concentrating system could explain the photosynthetic characteristics of this alga (high apparent affinity for CO₂, low photorespiration, little O₂ inhibition of photosynthesis, and low CO₂ compensation concentration). Similarly, the model was developed to evaluate whether the proposed defects in the CO₂-concentrating system of two Chlamydomonas mutants were consistent with their observed photosynthetic characteristics. The model treats a Chlamydomonas cell as a single compartment with two carbon inputs: passive diffusion of CO₂, and active transport of HCO ₃ ^- . Internal inorganic carbon was considered to have two potential fates: assimilation to fixed carbon via ribulose 1,5-bisphosphate carboxylase-oxygenase or exiting the cell by either passive CO₂ diffusion or reversal of HCO ₃ ^- transport. Published values for kinetic parameters were used where possible. The model accurately reproduced the CO₂-response curves of photosynthesis for wild-type Chlamydomonas, the two mutants defective in the CO₂-concentrating system, and a double mutant constructed by crossing these two mutants. The model also predicts steady-state internal inorganic-carbon concentrations in reasonable agreement with measured values in all four cases. Carbon dioxide compensation concentrations for wild-type Chlamydomonas were accurately predicted by the model and those predicted for the mutants were in qualitative agreement with measured values. The model also allowed calculation of approximate energy costs of the CO₂-concentrating system. These calculations indicate that the system may be no more energy-costly than C₄ photosynthesis.Abbreviations Chl chlorophyll - RuBPC/O ribulose 1,5-bisphosphate carboxylase-oxygenase - CA carbonic anhydrase     

Ethylene reverses photosynthetic inhibition by nickel and zinc in mustard through changes in PS II activity,photosynthetic nitrogen use efficiency,and antioxidant metabolism

We investigated the influence of exogenously sourced ethylene (200 μL L^?1 ethephon) in the protection of photosynthesis against 200 mg kg^?1 soil each of nickel (Ni)- and zinc (Zn)-accrued stress in mustard (Brassica juncea L.). Plants grown with Ni or Zn but without ethephon exhibited increased activity of 1-aminocyclopropane carboxylic acid synthase, and ethylene with increased oxidative stress measured as H₂O₂ content and lipid peroxidation compared with control plants. The oxidative stress in Ni-grown plants was higher than Zn-grown plants. Under metal stress, ethylene protected photosynthetic potential by efficient PS II activity and through increased activity of ribulose-1,5-bisphosphate carboxylase and photosynthetic nitrogen use efficiency (P-NUE). Application of 200 μL L^?1 ethephon to Ni- or Zn-grown plants significantly alleviated toxicity and reduced the oxidative stress to a greater extent together with the improved net photosynthesis due to induced activity of ascorbate peroxidase and glutathione (GSH) reductase, resulting in increased production of reduced GSH. Ethylene formation resulting from ethephon application alleviated Ni and Zn stress by reducing oxidative stress caused by stress ethylene production and maintained increased GSH pool. The involvement of ethylene in reversal of photosynthetic inhibition by Ni and Zn stress was related to the changes in PS II activity, P-NUE, and antioxidant capacity was confirmed using ethylene action inhibitor, norbornadiene.     

Reduced osmotic potential effects on photosynthesis : identification of stromal acidification as a mediating factor

Addition of sorbitol, which facilitated reductions in reaction medium osmotic potential from standard (0.33 molar sorbitol, −10 bars) isotonic conditions to a stress level of 0.67 molar sorbitol (−20 bars), inhibited the photosynthetic capacity of isolated spinach (Spinacia oleracea) chloroplasts. This inhibition, which ranged from 64 to 74% under otherwise standard reaction conditions, was dependent on reaction medium inorganic phosphate concentration, with the phosphate optimum for photosynthesis reduced to 0.05 millimolar at the low osmotic potential stress treatment from a value of 0.25 millimolar under control conditions.

Stromal alkalating agents such as NH₄Cl (0.75 millimolar) and KCl (35 millimolar) were also found to affect the degree of low osmotic potential inhibition of photosynthesis. Both agents doubled the rate of NaHCO₃-supported O₂ evolution under the stress treatment, while hardly affecting the control rate at optimal concentrations. These agents also reduced the length of the lag phase of photosynthetic O₂ evolution under the stress treatment to a much greater degree. The rate-enhancement effect of these agents under the stress treatment was reversed by sodium acetate, which is known to facilitate stromal acidification.

The reaction medium pH optimum for photosynthesis under the stress treatment was higher than under control conditions. In the presence of optimal NH₄Cl, this shift was no longer evident.

Internal pH measurements indicated that the stress treatment caused a 0.43 and 0.24 unit reduction in the stromal and intrathylakoid pH, respectively, under illumination. This osmotically induced acidification was not evident in the dark. The presence of 0.75 millimolar NH₄Cl partially reversed the osmotically induced reduction in the illuminated stromal pH. It was concluded that stromal acidification is a mediating mechanism of the most severe site of low osmotic potential inhibition of the photosynthetic process.