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Sorption of three pesticides on geologic material ranging in organic carbon content from 0.33 to 6.9 g kg-1 was measured in soil columns using a miscible displacement technique. An octanol-water partitioning model was shown to be inappropriate for predicting sorption of the less hydrophobic pesticides on the low organic carbon materials.
Constant red light (RR) influences the Gonyaulax clock in several ways: (1) Phase resetting by white or blue light pulses is stronger under background RR than in constant white light (WW); (2) frequency of the rhythm is less in RR than in WW; and (3) the amplitude of the spontaneous flashing rhythm is greater in RR than in WW. The phase response curve (PRC) to 4-hr white or blue light pulses is of high amplitude (Type 0) for cells in RR, but is of lower amplitude (Type 1) for cells in WW. In all cases, the PRC is highly asymmetrical: The magnitude of advance phase resetting is far higher than that of delay resetting. Consistent with this PRC, Gonyaulax cells in RR (free-running period greater than 24 hr) will entrain to T cycles of between 21 and 26.5 hr. The bioluminescence rhythms exhibit "masking" by blue light pulses while entrained to these T cycles. The fluence response of phase resetting to light-pulse intensity is not linear or logarithmic--rather, it is discontinuous. This feature is consistent with a limit cycle interpretation of Type 0 resetting of circadian clocks. Light pulses that cause large phase shifts also shorten the subsequent free-running period. The phase angle difference between the clock and the previous LD cycle is within 2 hr of the same phase between 16 degrees C and 25 degrees C, as determined from the light PRCs at various temperatures. Several drugs that inhibit mitochondria and/or electron transport will partially inhibit the phase shift by light.
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The effects of divalent salts and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) upon nicotinamide adenine dinucleotide phosphate (NADP) reduction and P700 in isolated chloroplasts are described and compared with the influence of DCMU on oxygen evolution and P700 in intact cells. Most experiments were carried out with a steady-state relaxation spectrometer. A kinetic mechanism for the estimation of P700 fluxes is proposed and experimentally tested. Good agreement between theory and experiment was found. Concurrent measurements of P700 and NADP reduction revealed two antagonisms: addition of divalent cations caused an increase in the yield of NADP reduction and a decrease in the yield of P700. Conversely, in the presence of Mg2+ low concentrations of DCMU decreased the yield of NADP reduction and increased the yield of P700. Aging of the chloroplasts at 30 degrees C exerted a similar effect. With far-red actinic light, Mg2+ stimulated the yield of NADP reduction without affecting the flux. Also, in the absence of Mg2+, DCMU inhibited both reactions although P700 required a higher herbicide concentration for fractional inhibition than NADP reduction. In the presence of Mg2+, chloroplasts resembled intact algae in which a high rate of oxygen evolution was accompanied by little P700 turn-over. Titration with DCMU decreased the rate of photosynthesis and increased P700 flux. On the whole, the data suggest that P700 relaxing in 20 msec is not directly involved in linear electron transport.
The field indicating electrochromic 515 nm absorption change has been measured under different excitation conditions in DCMU poisoned chloroplasts in the presence of benzylviologen as electron acceptor. It has been found: 1. The amplitude of the 515 nm absorption change is nearly completely suppressed under repetitive single turnover flash excitation conditions which kinetically block the back reaction around system II (P. Bennoun, Biochim. Biophys. Acta 216, 357 [1970]). 2. The amplitude of the 515 nm absorption change measured under repetitive single turnover flash excitation conditions which allow the completion of the back reaction during the dark time between the flashes (measuring light beam switched off) amounts in the presence of 2 mum DCMU nearly 50% of the electrochromic 515 nm amplitude obtained in the absence of DCMU. In DCMU poisoned chloroplasts this amplitude is significantly decreased by hydroxylaminhydrochloride, but nearly doubled in the presence of CDIP+ascorbate. 3. The dependence of the 515 nm amplitude on the time td between the flashes kinetically resembles the back reaction around system ?II. The time course of the back reaction can be fairly described either by a second order reaction or by a two phase exponential kinetics. 4. 1,3-dinitrobenzene (DNE) or alpha-bromo-alpha-benzylmalodinitril (BBMD) reduce the 515 nm amplitude in DCMU poisoned chloroplasts, but seem to influecne only slightly the kinetics of the back reaction. 5. The dependence of the 515 nm amplitude on the flash light intensity (the amplitude normalized to 1 at 100% flash light intensity) is not changed by DNB. Based on these experimental data it has been concluded that in DCMU poisoned chloroplasts the amplitude of the 515 nm absorption change reflects the functional state of photosystem II centers (designated as photoelectric dipole generators II) under suitable excitation conditions. Furthermore, it is inferred that in DCMU poisoned chlorplasts the photoelectric dipole generators II either cooperate (probably as twin-pairs) or exist in two functionally different forms. With respect to BBMD and DNB it is assumed that these agents transform the phtooelectric dipole generators II into powerful nonphotochemical quenchers, which significantly reduce the variable fluorescence in DCMU-poisoned chloroplasts.
The effect of alpha-bromo-alpha-benzylmalodinitril (BBMD) on the oxygen evolution and on the absorption changes at 515 nm and 704 nm has been investigated in spinach chloroplasts. It has been found: 1. Under repetitive flash excitation conditions, where the back reaction around system II is practically excluded for kinetical reasons, BBMD does not resotre the 515 nm absorption change in DCMU poisoned chloroplasts. 2. Under single flash excitation conditions, where the back reaction around system II becomes prominent in the presence of DCMU, BBMD moderately inhibits this back reaction. The deleterious effect is pronounced by preillumination with short flashes during the BBMD incubation period of the chloroplasts in the absence of DCMU. 3. Incubation of the chloroplasts with BBMD leads to an activity loss of oxygen evolution which increases with the time td between the repetitive short excitation flashes and with the dark incubation time. Preillumination during the incubation period with tbbmd significantly enhances the effect. 4. In the absence of artificial electron acceptors BBMD suppresses in DCMU poisoned chloroplasts the 704 nm absorption change reflecting an internal cyclic electron flow around system I. On the other hand the linear electron transport at system I mediated by DCIP plus ascorbate as electron donor couple and benzylviologen as electron acceptor is not distrubed by BBMD. 5. BBMD incubation of chloroplasts accelerates the decay rate of the field indicating 515 nm absorption change. Based on these experimental findings the conclusion has been drawn, that -- in contrast to the assumption of Brandon and Elgersma (Biochim. Biophys. Acta 292, 753--762 [1973]) -- BBMD does not accept electrons from the primary electron acceptor X 320 of system II in DCMU poisoned chloroplasts. BBMD rather acts as a system I electron acceptor. Furthermore, BBMD exerts deleterious effects on the center of photosystem II, accompanied by a weak ADRY-effect on the water-splitting enzyme system Y. As a tentative explanation of the BBMD-action on system II it is assumed that BBMD transforms the photochemical centers of system II into dissipative energy sinks.
A monospecific antiserum to tobacco plastocyanin agglutinates stroma-free swellable chloroplasts from wild type tobacco, (Nicotiana tobacum var. John William's Broadleaf) from the tobacco aurea mutant Su/su2, (Nicotiana tabacum var. Su/su2) from Antirrhinum majus and spinach (Spinacia oleracea). In this condition the antiserum inhibits linear photosynthetic electron flow in tobacco and spinach chloroplasts. This inhibition of electron transport as well as the agglutination are not observed if the chloroplasts have been sonicated prior to antiserum addition. This is due to the fact that plastocyanin is removed by ultasonication. The antiserum stimulates a number of photophosphorylation reactions in tobacco chloroplasts. This stimulation is always larger in the aurea mutant chloroplasts from yellow leaf patches of a variegated tobacco mutant (N. tabacum, var. NC 95) than in the green type chloroplasts. The stimulation appears to be a consequence of the inhibition of linear electron transport. The antiserum does not affect PMS-mediated cyclic photophosphorylation in tobacco chloroplasts from the wild type whereas the reaction appears stimulated in the tobacco mutant chloroplasts. However, menadione-mediated cyclic photophosphorylation is inhibited upon addition of the antiserum. The same is true for noncyclic photophosphorylation coupled to electron transport in the aerobic system diaminodurene/ascorbate leads to methylviologen in the presence of N-tetraphenyl-p-phenylenediamine in spinach chlorplasts. If the lamellar system of Antirrhinum and spinach has lost is swellability neither agglutination nor inhibition of electron transport is observed. However, also in this state antibodies to plastocyanin are specifically adsorbed onto the surface to the thylakoid membrane. This state which is characterized by a morphologically well preserved lamellar system is realized in chloroplast preparations from Antirrhinum and spinach and is termed stroma-freed chloroplasts. In both states of the molecular structure of the thylakoid membrane, plastocyanin is located in the outer surface of the thylakoid. However, it cannot be excluded that functioning plastocyanin is also located in the interior of the thylakoid membrane.
In the heavy fraction of deoxycholate-treated spinach chloroplasts the chlorophyll aII activity is high and the chlorophyll aI activity is low when no artificial electron donor is added. The addition of the photosystem I donor system N-methyl-phenazonium sulphate plus sodium ascorbate (PMS + Asc) leads to a complete reactivation of the chlorophyll aI reaction. The addition of the photosystem II donor system p-benzohydroquinone plus sodium ascorbate (HQ + Asc) leads to an inhibition of the chlorophyll aII activity. From these results we conclude: 1. Besides an interruption of the linear electron flow between the two photosystems deoycholate-treatment leads to a block of the electron flow from water to photosystem II. 2. In deoxycholate-treated chloroplasts the linear electron flow in photosystem II just like in Tris-washed, heat-treated or aged chloroplasts, is replaced by a cyclic one.
In trypsin-treated spinach chloroplasts there is no linear electron flow from water to potassium ferricyanide. The chlorophyll aII reaction, however, is still active but insensitive to 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea. From this we conclude that ferricyanide and trypsin together stimulate a mini-cycle in photosystem II.
The chlorophyll fluorescence of isolated chloroplasts in the presence of phenazine methosulfate (PMS) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) can be quenched in a light-depentdent reaction. This phenomenan has been studied and the following observations were made: 1. Quenching occurs under non-phosphorylating conditions and is stimulated by Mg2+ ions. 2. Under the same conditions, a light-dependent, Mg2+ stimulated transient decrease of absorption at change and binding of PMS. Others, such as methylamine, ammonia, gramicidin and nigericin do not. It is suggested that fluorescence quenching, transient absorption change and binding of PMS are casually related. The concept, postulated by others, that a high-energy state of the chloroplast membrane is involved in the fluorescence lowering is questioned.
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Three polypeptide fractions with the apparent molecular weight 66 000 were isolated from stromafreed Antirrhinum chloroplasts which were solubilized with dodecyl sulfate. Antisera to these fractions affect electron transport in distinctly different ways. For the characterization of the three antisera photochemical reactions of chloroplast preparation with artificial electron donors and acceptors as well the analysis of fluorescence rise curves were used. Antiserum 66 000 PSI-96 inhibits electron transport apparently on the acceptor side of photosystem I, provided the antibodies are adsorbed onto the outer surface of the thylakoid membrane. Antiserum 66 000 PSI-88 probably acts directly on the reaction centre I or on its immediate vicinity, if the antibodies are adsorbed at the inner surface of the thylakoid membrane. Antiserum 66 000 PSII-42 inhibits electron transport in the region of photosystem II. The antigen towards which the antiserum is directed appears to belong to the reaction centre II, as also in the condition of high inhibition degrees, the fluorescence intensity remains unchanged. The determinants are located at the outer surface of the thylakoid membrane.
An antiserum to synthetic Zeaxanthin inhibits photosynthetic electron transport on the oxygen-evolving side of photosystem II in tobacco chloroplasts and thylakoids of the filamentous blue-green alga Oscillatoria chalybea. The inhibition site lies for both species between the site of electron donation of water or tetramethyl benzidine and that of diphenyl carbazide or manganese II ions. Typical photosystem I reactions are not impaired by the antiserum. The effect of the antiserum concerning the inhibition site is practically identical to that of the earlier described antiserum to violaxanthin. However, the degree of inhibition seems to be generally somewhat lower with the antiserum to Zeaxanthin, than with that to violaxanthin which hints at a lesser accessibility of zeaxanthin, in the tylakoid membrane in comparison to violaxanthin. In the course of these investigations new evidence was obtained that the oxygen-evolving side of the electron transport scheme is differently organized in Oscillatoria chalybea when compared to tobacco chloroplasts. Thus, the silicomolybdate reduction with water as the electron donor is sensitive to DCMU in these algae.
Light dependent (35 Klux) chlorophyll bleaching in autotrophically grown Euglena gracilis cells at slightly acidic pH (6.5-5.4) is stimulated by the photosystem II blockers DCMU and DBMIB (both 10(-5) M) as well as by the autooxidizable photosystem I electron acceptor, paraquat (10(-3) M). Chlorophyll photobleaching is accompanied by the formation of thiobarbituric acid -- sensitive material ("malondialdehyde") and ethane. Both chlorophyll photobleaching and light dependent ethane formation are partially prevented by higher concentrations (10(-4) M) of the autooxidizable photosystem II electron acceptor DBMIB or by sodium bicarbonate (25 mM). In vitro studies with cell free extracts (homogenates) from E. gracilis suggest that alpha-linolenic acid oxidation by excited (reaction center II) chlorophyll represents the driving force for both ethane formation and chlorophyll bleaching. Ethane formation thus appears to be a sensitive and non-destructive "in vivo" marker for both restricted energy dissipation in photosystem II and, conditions yielding reactive oxygen species at the reducing side of photosystem I.
Mutants of Anacystis R 2 with different amino acid exchanges in positions 255 and/or 264 in copy I of the psbA gene, leading to different tolerances to DCMU-type herbicides, are compared with the respective wild type concerning pigmentation and incorporation of 35S into the D 1 protein upon growth in the presence of [35S]methionine. All mutants have shade-type appearance compared to the wild type, although to different extents depending on site and mode of the amino acid exchange in the D 1 protein. Except for 3 mutants, there is no correlation between shade-type appearance on one hand and resistance towards a certain inhibitor on the other hand. Not only the molar ratio of phycocyanin (PC) to chlorophyll (Chl) is higher in all mutants compared to the respective wild type, but also the rate of synthesis of the D 1 protein. On the background of different levels of total 35S incorporation within 18 min, D 1 synthesis can be related to shade adaptation. Degradation of the D 1 protein remains to be thoroughly studied in this context. No reproducible differences in whole chain electron transport were observed between mutants and wild type.
The D2 protein contains an extended loop (the D-de loop) between helices D and de at the reducing side of photosystem II (PS II). Characterization of D2 mutants of the cyanobacterium Synechocystis sp. PCC 6803 has indicated that the length and amino acid composition of the D-de loop are not critical for basic PS II functions, although most of the residues in that region are conserved phylogenetically. Here we show using herbicide binding and electron-flow inhibition measurements that drastic modifications in the D-de loop of the D2 protein modify the interaction of some PS II-directed herbicides with their binding niche. The stability of (semi)-reduced QB in its binding pocket is altered in at least two of the mutants, as indicated by a shifted peak temperature of the thermoluminescence signal originating from charge recombination involving QB. These results suggest a close functional association between the D-de loop of the D2 protein and the QB/herbicide-binding environment, which is viewed as being coordinated mostly by residues of the D1 protein. This represents one of the first examples of modification of the QB/herbicide-binding domain by mutations in the D2 protein.
Mutations conferring herbicide resistance have been detected in two new strains (ZR250 and ZR480) of Euglena gracilis Z by partial gene cloning and sequencing. These mutants were originally derived from Z cells grown in medium containing progressively increasing concentrations of DCMU. Each of these strains have been characterized by measuring their growth kinetics, O2 evolution, and resistance to DCMU and atrazine. Partial sequences of the psbA gene of these strains were compared to those published for strains Z and ZR25. The ZR250 and ZR480 strains were found to be double mutants. Besides the expected mutation S265A, they showed an additional point mutation at codon 219 (equivalent to codon 218 of other organisms). This mutation results in leucine being substituted by phenylalanine. For each of the ZR strains, two growth conditions (with or without DCMU in the medium) have been compared. The presence of the second mutation (at codon 219) leads to notable increase (20-fold) in resistance to DCMU, whereas the resistance to atrazine is only 2-fold. The presence of DCMU, as the selective agent, was responsible for an enhanced herbicide resistance, irrespective of the concentrations used. Substantial modifications in the rate of cell growth and O2 yields were observed when the maximal concentration (480 microM) of DCMU was used. These modifications were reversible on withdrawal of the DCMU. Thus the reversible adaptative modifications also adds to the mutational effect observed.
Physiological conditions which lead to changes in total carotenoid content in tomato plantlets were identified. Carotenoid levels were found to increase after the onset of a dark period during a normal 24 h cycle. This rapid initial increase is followed by a steady decrease in carotenoid content throughout the night. A decrease in the expression of several carotenogenic genes, namely pds, zds (carotenoid desaturases) and ptox (plastid terminal oxidase), was observed following the removal of the light (when carotenoid content is at its highest). An increase in gene expression was observed before the return to light for pds and zds (when carotenoid levels were at their lowest), or following the return to light for ptox. The phytoene desaturation inhibitor norflurazon leads to a decrease coloured carotenoid content and, in the light, this correlated with pds and zds gene induction. In the dark, norflurazon treatment led to only a weak decrease in carotenoid content and only a small increase in pds and zds gene expression. The striking absence of phytoene accumulation under norflurazon treatment in the dark suggests a down-regulation of carotenoid formation in darkness However, prolonged dark conditions, or treatment with photosynthetic inhibitors, surprisingly led to higher carotenoid levels, which correlated with decreased expression of most examined genes. In addition to light, which acts in a complex way on carotenoid accumulation and gene expression, our results are best explained by a regulatory effect of carotenoid levels on the expression of several biosynthetic genes. In addition, monitoring of protein amounts for phytoene desaturase and plastid terminal oxidase (which sometimes do not correlate with gene expression) indicate an even more complex regulatory pattern.