Silent Centers Research Articles

Nabumetone and flufenamic acid pose a serious risk to aquatic plants: A study with Chlamydomonas reinhardtii as a model organism

The aquatic environment is constantly under threat due to the release of numerous pollutants. Among them, pharmaceuticals constitute a huge and diverse group. Non-steroidal anti-inflammatory drugs (NSAIDs) are increasingly found in water bodies, but knowledge about their potential toxicity is still low. In particular, there is a lack of information about their influences on aquatic plants and algae. We estimated the susceptibility of the microalgae Chlamydomonas reinhardtii to nabumetone (NBT) and flufenamic acid (FFA), focusing on photosynthesis. Due to the differences in the structures of these compounds, it was assumed that these drugs would have different toxicities to the tested green algae. The hypothesis was confirmed by determining the effective concentration values, the intensity of photosynthesis, the intensity of dark respiration, the contents of photosynthetic pigments, the fluorescence of chlorophyll a in vivo (OJIP test), and cell ultrastructure analysis. Assessment of the toxicity of the NSAIDs was extended by the calculation of an integrated biomarker response index (IBR), which is a valuable tool in ecotoxicological studies. The obtained results indicate an over six times higher toxicity of NBT compared to FFA. After analysis of the chlorophyll a fluorescence in vivo, it was found that NBT inhibited electron transport beyond the PS II. FFA, unlike NBT, lowered the intensity of photosynthesis, probably transforming some reaction centers into “silent centers”, which dissipate energy as heat. The IBR estimated based on photosynthetic parameters suggests that the toxic effect of FFA results mainly from photosynthesis disruption, whereas NBT significantly affects other cellular processes. No significant alteration in the ultrastructure of treated cells could be seen, except for changes in starch grain number and autophagic vacuoles that appeared in FFA-treated cells. To the best of our knowledge, this is the first work reporting the toxic effects of NBT and FFA on unicellular green algae.

The Triterpenes 3β-Lup-20(29)-en-3-ol and 3β-Lup-20(29)-en-3-yl Acetate and the Carbohydrate 1,2,3,4,5,6-Hexa-O-acetyl-dulcitol as Photosynthesis Light Reactions Inhibitors

Three compounds were isolated from Maytenus acanthophylla Reissek (Celastraceae): the pentacyclic triterpenes lup-20(29)-en-3β-ol (lupeol, 1) and 3β-lup-20(29)-en-3-yl acetate (2) and the carbohydrate 1,2,3,4,5,6-hexa-O-acetyldulcitol (3);lupeol was also isolated from Xylosma flexuosa. The compounds’ structures were elucidated by spectroscopic and spectrometric analysis. Compound 1 acts as an energy transfer inhibitor, interacting with isolated CF1 bound to thylakoid membrane, and dulcitol hexaacetate 3 behaves as a Hill reaction inhibitor and as an uncoupler, as determined by polarography. Chlorophyll a (Chl a) fluorescence induction kinetics from the minimum yield F0 to the maximum yield FM provides information of the filling up from electrons coming from water to plastoquinone pool with reducing equivalents. In this paper we have examined the effects of compounds 1 and 3 on spinach leaf discs. Compound 1 induces the appearance of a K-band, which indicates that it inhibits the water splitting enzyme. In vivo assays measuring the fluorescence of chl a in P. ixocarpa leaves sprayed with compound 1, showed the appearance of the K-band and the PSII reaction centers was transformed to “heat sinks” or silent reaction centers unable to reduce QA. However, 3 also induced the appearance of a K band and a new band I appears in P. ixocarpa plants, therefore it inhibits at the water splitting enzyme complex and at the PQH2 site on b6f complex. Compounds 1 and 3 did not affect chlorophyll a fluorescence of L. perenne plants.

Biflavonoids Isolated from Selaginella lepidophylla Inhibit Photosynthesis in Spinach Chloroplasts

Through bioactivity-guided chemical analysis of Selaginella lepidophylla, biflavonoids robustaflavone (1), 2,3-dihydrorobustaflavone (2), and 2,3-dihydrorobustaflavone-5-methyl ether (3) were isolated and their structures confirmed by spectroscopic and spectrometric analyses. Their NMR resonances were unambiguously assigned from HMBC, NOESY, and NOESY-1D experiments, and absolute configurations of 2 and 3 were established. Compound 3 has not been reported, and although structure of 2 was described before, the (13)C NMR assignment does not correlate with the structure reported. Therefore, this is the first report of 2. All compounds inhibited ATP production. Compounds 1 and 2 behaved as Hill reaction inhibitors. 1 interacted with photosystem II, transforming the reaction centers to silent centers at 300 and 600 microM. The interaction and inhibition target of 2 was located on Cyt b6f to PC. The three compounds also behaved as energy transfer inhibitors, 3 being the most active.

Siderin from Toona ciliata (Meliaceae) as photosystem II inhibitor on spinach thylakoids

Four natural products were isolated from plants of the Rutaceae and Meliaceae families and their effect on photosynthesis was tested. Siderin ( 1) inhibited both ATP synthesis and electron flow (basal, phosphorylating, and uncoupled) from water to methylviologen (MV); therefore, it acts as Hill reaction inhibitor in freshly lysed spinach thylakoids. Natural products 2– 4 were inactive. Secondary metabolite 1 did not inhibit PSI electron transport. It inhibits partial reactions of PSII electron flow from water to 2,6-dichlorophenol indophenol (DCPIP), from water to sodium silicomolybdate, and partially inhibits electron flow from diphenylcarbazid (DPC) to DCPIP. These results established that the site of inhibition of 1 was at the donor and acceptor sides of PSII, between P 680 and Q A. Chlorophyll a fluorescence measurements confirmed the behavior of the Toona ciliate coumarin 1 as P 680 to Q A inhibitor by the creation of silent centers. May be this is the mechanisms of action of 1 and is the way in which it develops a phytotoxic activity against photosynthesis.

A Diterpene γ-Lactone Derivative from Pterodon polygalaeflorus Benth. as a Photosystem II Inhibitor and Uncoupler of Photosynthesis

6alpha,7beta-Dihydroxyvouacapan-17beta-oic acid (1) was isolated from Pterodon polygalaeflorus Benth. Modification of 1 yielded 6alpha-hydroxyvouacapan-7beta,17beta-lactone (2) and then 6-oxovouacapan-7beta,17beta-lactone (3). Photosynthesis inhibition by 3 was evaluated in spinach chloroplasts. The uncoupled non-cyclic electron transport rate and ATP synthesis were inhibited by 3, which behaved as a Hill reaction inhibitor. Furthermore, 3 acted as an uncoupler because it enhanced the basal and phosphorylating electron transport rate on thylakoids. This last property of 3 was corroborated when it was observed that it enhances the Mg2+-ATPase activity. In contrast, 3 did not affect photosystem I (PSI) activity. Analysis of the partial photosystem II (PSII) reactions from water to DCPIPOX and water to silicomolybdate allowed to locate the inhibition sites at the redox components of PSII. The OJIP test of the chlorophyll a fluorescence transient confirmed that the inhibition sites were 1.) the oxygen-evolving complex (OEC) and 2.) by the formation of silent centers in the non-QA reducing centers.

Vowel perception in varied symmetric CVC contexts

In the three-decade-long debate over static versus dynamic specification of vowels, perceptual studies in which subjects are tasked with identifying naturally spoken vowels under various ablation conditions have been a mainstay. While not directly producing an understanding of how humans go about recognizing this major subclass of phones, this type of study [e.g., Strange, Jenkins, and Johnson, J. Acoust. Soc. Am. 74, 695–705 (1983)] has provided compelling results which must be accounted for in any successful theory of vowel perception. This paper presents results from yet another perceptual study of human vowel identification under ablation conditions. This study uses CVC syllables spoken rapidly by three male speakers in a carrier sentence. Syllables consist of ten American English vowels in each of four consonantal contexts (b—b, d—d, g—g, and h—d). The conditions studied are silent centers (SC), centers only (CO), and the control condition (full). A very robust hierarchy of full>CO>SC is found. Consonantal contexts also have a clear ordering (h—d>b—b>d—d>g—g) with respect to the ease with which they are perceived. Interesting interactions between vowels and their contexts are also evident.

Perception of synthetic silent-center syllables: A replication and extension

The purpose of this study was to replicate and extend the synthetic silent-center vowel perception study of Miranda and Strange [J. Acoust. Soc. Am. Suppl. 1 88, S55 (1990)]. The goal was to generate synthetic syllables that adequately captured the dynamic spectral information in syllable onsets and offsets. Natural and synthetic /dVd/ syllables were presented to subjects in two forms: full syllable and silent center. Natural silent centers were constructed ty retaining the burst and first three and final four pitch periods in order to achieve a desired vowel identification error rate of about 10%. Natural duration was not altered. From ILS analysis of the first three formants, synthetic syllables were generated with Haskins Labs SYN software synthesis. Natural and synthetic full syllable error rates were 2%. Natural silent center error rates were 11%. Synthetic silent centers were 23%, far less than the 60% reported by Miranda and Strange. Thus these synthetic syllables appear to have captured some of the dynamic spectral information in the syllable onsets and offsets. [Work supported by NIDCD.]

Dynamic information specifies vowel identity

Research reported last year [W. Strange, J. J. Jenkins, and T. R. Edman, J. Acoust. Soc. Am. 61, S1 (1977)] was extended to investigate the contribution of dynamic spectral and temporal information to the specification of vowels. Two tokens each of ten American English vowels produced in /b/-vowel-/b/ syllables by four speakers were digitized and several stimulus conditions were constructed: (1) silent-center syllables (in which a variable-duration center “vowel” portion of each syllable was deleted). (2) variable-duration centers (with initial and final transitions removed). (3) fixed-duration centers (52 ms), and (4) long silent centers, and short silent centers (in which the temporal relations of initial and final portions were changed). Vowel identification was best for the silent-center syllables produced by three of four speakers. Vowels in the variable-duration center condition were identified better than in the fixed-duration center condition. Lengthening the silent centers increased errors while shortening did not. Effects of speaking rate, vocal tract differences, and dialect are discussed. [Supported by NIMH.]