The site of inhibition of the chloroplast electron-transport system by 2,3-dithiopropan-1-ol (BAL)

BAL (2,3-dithiopropan-1-ol) treatment of chloroplasts has previously been reported to induce a block in electron transport from water to NADP+ at a site preceding plastocyanin [Belkin et al. (1980) Biochim. Biophys. Acta 766, 563-569]. In the present work the block was further characterized. The following properties of BAL treatment are described. Inhibition of electron transport from water to lipophilic acceptors but not to silicomolybdate. Inhibition of the slow, sigmoidal phase of chlorophyll a fluorescence induction. Inability of N,N,N',N',-tetramethyl-p-phenylenediamine to bypass the inhibition of NADP+ photoreduction with water as the electron donor. Inhibition of electron transport from externally added quinols to NADP+. Inhibition of cytochrome f reduction by photosystem II, but not its oxidation by photosystem I. Inhibition of cytochrome b6 turnover and cytochrome f rereduction after single-turnover flash illumination under cyclic electron-flow conditions. The BAL-induced block is therefore located between the secondary quinone acceptor (QB) and the cytochrome b6f complex. It was further found that (a) the isolated cytochrome complex is not inhibited after BAL treatment; (b) BAL-reacted plastoquinone-1 inhibits electron transport in chloroplasts; (c) BAL does not inhibit electron transport in chromatophores of Rhodospirilum rubrum or Rhodopseudomonas capsulata. It is suggested that the inhibition of electron transport in chloroplasts results from specific reaction of BAL with the endogenous plastoquinone.     

Biochemical Similarities between Soluble and Membrane-Bound Calcium-Dependent Protein Kinases of Barley

The soluble and membrane-bound forms of the calcium-dependent protein kinase from barley leaves (Hordeum vulgare L. cv. Borsoy) have been partially purified and compared. Both forms showed an active polypeptide of 37 kilodaltons on activity gels with incorporated histone as substrate. They eluted from chromatofocusing columns at an identical isoelectric point of pH 4.25 ± 0.2, and also comigrated on several other chromatographic affinity media including Matrex Gel Blue A, histone-agarose, phenyl-Sepharose, and heparin-agarose. Both activities comigrated with chicken ovalbumin during gel filtration through Sephacryl S-200, indicating a native molecular mass of 45 kilodaltons. The activities share a number of enzymatic properties including salt and pH dependence, free calcium stimulation profile, substrate specificity, and Km values. The soluble activity was shown to bind to artificial lipid vesicles. These data suggest strongly that the soluble and membrane-bound calcium-dependent protein kinases from barley are very closely related or even identical.     

Effect of heated naringenin on immunomodulatory properties and cellular antioxidant activity

Naringenin is one of the most popular flavonoids derived from citrus. It has been reported to be an effective anti-inflammatory compound. Citrus fruit may be used raw, cooked, stewed, or boiled. The present study was conducted to investigate the effect of thermal processes on naringenin in its immunomodulatory and cellular antioxidant activities. The effects of flavonoids on B and T cell proliferation were assessed on splenocytes stimulated or not with mitogens. However, their effects on cytotoxic T lymphocyte (CTL) and natural killer (NK) activities were assessed in splenocytes co-incubated with target cells. The amount of nitric oxide production and the lysosomal enzyme activity were evaluated in vitro on mouse peritoneal macrophages. Cellular antioxidant activity in splenocytes and macrophages was determined by measuring the fluorescence of the dichlorofluorescin (DCF). Our findings revealed that naringenin induces B cell proliferation and enhances NK activity. The highest concentration of native naringenin exhibits a significant proliferation of T cells, induces CTL activity, and inhibits cellular oxidation in macrophages. Conversely, it was observed that when heat-processed, naringenin improves the cellular antioxidant activity in splenocytes, increases the cytotoxic activity of NK cells, and suppresses the cytotoxicity of T cells. However, heat treatment maintains the anti-inflammatory potency of naringenin.     

920. CONSTANCEA NEVINII

Constancea nevinii (A. Gray) B.G. Baldwin (Compositae: Heliantheae: Baeriinae) is described and illustrated. The distribution of the species in, and a glimpse at the history and endemic flora of, the California Channel Islands (also known as the Santa Barbara Islands), together with the conservation threats posed by feral goats, is outlined. The historically variable Conservation Status is commented on, although the species is no longer considered under threat of extinction. The position of this monotypic genus in the Heliantheae is commented on. Cultivation, propagation, and availability notes are provided. The species is rarely cultivated in the United Kingdom, but clearly widely so in the western States along the Californian coast.     

915. HIERACIUM TOMENTOSUM

Hieracium tomentosum L. (Compositae: Lactuceae: Hieraciinae) is illustrated and described, the account of the species providing a fairly full synonymy, reference to types and the complication of grexes indicated. Frequently appearing under the name of Hieracium lanatum (L.) Vill., issues with the historical naming of this species are highlighted, together with those of naming many of the European hieracia. The species has been in cultivation in the British Isles for just short of three hundred years, and is apparently only currently available from three suppliers. Cultivation and propagation requirements are discussed. The artist of the plate and the figure, Gustavo Surlo, is the youngest Margaret Mee Fellowship Programme Artist Scholar to have illustrated in Curtis's Botanical Magazine. Having won the Artist Scholarship for 2018, this is his first plate in the Magazine.     

917. CORETHROGYNE FILAGINIFOLIA

Corethrogyne filaginifolia (Hook. & Arn.) Nutt. (Compositae: Astereae: Machaerantherinae) is illustrated and described. The full synonymy of this monospecific North American genus is provided together with the location of known type material and relevant comments made where applicable. The Conservation Status of the species is considered LC (Least Concern), as previous listings in California are shown to refer to Corethrogyne filaginifolia (Hook. & Arn.) var. incana (Lindl.) D.R. Morgan & R.L. Hartman, which is now considered a synonym of the rather variable Dieteria canescens (Pursh) Nutt. The taxonomic placement of Diplopappus incanus Lindl. is discussed, and a synonymy has been provided for Dieteria canescens subsp. canescens var. incana (Lindl.) D.R. Morgan & R.L. Hartman, of which it is the basionym. The location of the probable holotype of Diplopappus leucophyllus Lindl. ex DC. is discussed, together with the relevance of material mounted on a Kew sheet.     

Cytochrome function in the cyclic electron transport pathway of chloroplasts.

Flash excitation of isolated intact chloroplasts promoted absorbance transients corresponding to the electrochromic effect (P-518) and the alpha-bands of cytochrome b6 and cytochrome f. Under conditions supporting coupled cyclic electron flow, the oxidation of cytochrome b6 and the reduction of cytochrome f had relaxation half-times of 15 and 17 ms, respectively. Optimal poising of cyclic electron flow, achieved by addition of 0.1 microM 3-(3,4-dichlorophenyl)-1,1-dimethylurea, increased phosphorylation of endogenous ADP and prolonged these relaxation times. The presence of NH4Cl, or monensin plus NaCl, decreased the half-times for cytochrome relaxation to approximately 2 ms. Uncouplers also revealed the presence of a slow rise component in the electrochromic absorption shift with formation half-time of about 2 ms. Ths inhibitors of cyclic phosphorylation antimycin and 2,5-dibromo-3-methyl-6-isoprophy-p-benzoquinone abolished the slow rise in the electrochromic shift and prolonged the uncoupled relaxation times of cytochromes b6 and f by factors of ten or more. These observations indicate that cytochrome b6, plastoquinone and cytochrome f participated in a coupled electron transport process responsible for cyclic phosphorylation in intact chloroplasts. Estimations of cyclic phosphorylation rates from 40 to 120 mumol ATP/mg chlorophyll per h suggest that this process can provide a substantial fraction of the ATP needed for CO2 fixation.     

Natural Variation for Responsiveness to flg22, flgII-28, and csp22 and Pseudomonas syringae pv. tomato in Heirloom Tomatoes

Tomato (Solanum lycopersicum L.) is susceptible to many diseases including bacterial speck caused by Pseudomonas syringae pv. tomato. Bacterial speck disease is a serious problem worldwide in tomato production areas where moist conditions and cool temperatures occur. To enhance breeding of speck resistant fresh-market tomato cultivars we identified a race 0 field isolate, NC-C3, of P. s. pv. tomato in North Carolina and used it to screen a collection of heirloom tomato lines for speck resistance in the field. We observed statistically significant variation among the heirloom tomatoes for their response to P. s. pv. tomato NC-C3 with two lines showing resistance approaching a cultivar that expresses the Pto resistance gene, although none of the heirloom lines have Pto. Using an assay that measures microbe-associated molecular pattern (MAMP)-induced production of reactive oxygen species (ROS), we investigated whether the heirloom lines showed differential responsiveness to three bacterial-derived peptide MAMPs: flg22 and flgII-28 (from flagellin) and csp22 (from cold shock protein). Significant differences were observed for MAMP responsiveness among the lines, although these differences did not correlate strongly with resistance or susceptibility to bacterial speck disease. The identification of natural variation for MAMP responsiveness opens up the possibility of using a genetic approach to identify the underlying loci and to facilitate breeding of cultivars with enhanced disease resistance. Towards this goal, we discovered that responsiveness to csp22 segregates as a single locus in an F₂ population of tomato.