Susceptibility to purple blotch (Alternaria porri) in garlic (Allium sativum)

Experiments were conducted to study the progress of purple blotch disease of garlic caused by Alternuria porri in the field, to determine the relationship between garlic leaf age and susceptibility to Alternaria porri, and also to assess loss in bulb characters due to purple blotch of garlic. Per cent disease severity and number of purple blotch lesions on four garlic genotypes of known susceptibility, Sel-10 (highly susceptible), G-41 (highly susceptible), IC-49382 (moderately susceptible) and IC-49373 (moderate to less susceptible) were monitored from bulb formation to bulb maturity at weekly intervals. Lesions appeared early on highly susceptible cultivars, Sel-10 and G-41. Rapid progress of disease development was noticed during the last 3 wk before bulb maturity. Peak severity at the maturity of the crop was significantly higher on highly susceptible genotypes. No definite correlation could be established between number of lesions and disease severity. A logistic curve was fitted to predict the disease progress on different weeks before bulb maturity. Levels of leaf tissue found damaged by A. porri at weekly intervals from bulb initiation to bulb maturity were significantly lower on younger leaves than on older leaves. Leaves that emerged 7 wk before bulb maturity required more than a 5 wk period to reach 50% leaf damage, whereas leaves emerging 2, 3 and 4 wk before bulb maturity exceeded 50% leaf damage within a 2–3 wk period. Individual garlic leaves became more susceptible to purple blotch as they aged and emerging leaves were more susceptible the closer they emerged to bulb maturity. Per cent loss in bulb weight and bulb volume was found to be significantly higher on highly susceptible genotypes. No significant reduction in number of cloves/bulb was observed. We propose 4 wk before bulb maturity as the action threshold for initiation of fungicidal application to prevent damaging levels of disease.     

Development of a genetic system for a purple sulfur bacterium: Conjugative plasmid transfer inChromatium vinosum

Establishment of a system for manipulative genetics in phototrophic sulfur bacteria of the family Chromatiaceae has mainly been hampered by the lack of reliable methods for growth of these organisms on agar surfaces, techniques for streaking, growth on selective media, screening for antibiotic resistance markers, and most importantly by the lack of a system for DNA transfer. We, therefore, developed minimal and complex agar media for Chromatium vinosum strain D (DSM 180^T), a representative of the purple sulfur bacteria. Sensitivity of C. vinosum towards a broad range of antibiotics was tested in liquid cultures and solidified media, allowing us to select appropriate antibiotic resistance markers. Furthermore, a system for conjugative transfer of IncP-mobilizable plasmids from Escherichia coli to C. vinosum was established. Broad-host-range IncQ vectors were mobilized to C. vinosum with the aid of plasmid RP4 either present extrachromosomally or integrated in the chromosome of E. coli S17-1. Conjugation efficiencies of up to 1 were observed. Agarose gel electrophoretic analysis showed that transconjugants contained the transferred plasmids in addition to the two detectable plasmids of wild-type C. vinosum. All genetic markers tested (kanamycin, gentamicin, ampicillin, amikacin, tetracycline) were expressed in C. vinosum. Furthermore, high-frequency transfer of plasmid RP4 from C. vinosum to E. coli and to Rhodospirillum rubrum K100 was demonstrated. Received: 3 March 1995 / Accepted: 22 May 1995     

Hydrogenase of purple bacteria: properties and regulation of synthesis

Physico-chemical properties of homogeneous preparations of soluble and membrane-bound hydrogenases from the purple sulfur bacterium Thiocapsa roseopersicina BBS and membrane-bound hydrogenase of Rhodopseudomonas capsulata, strain B10 have been studied. Compared to the enzymes from other sources, the hydrogenase of Thiocapsa roseopersicina is more stable to O₂ and products of its reduction (O ₂ ^- , H₂O₂), temperature and a number of other factors of the medium. A natural electron donor for T. roseopersicina hydrogenase is a low-potential cytochrome C₃, while the natural electron acceptors for hydrogenases of R. capsulata, T. roseopersicina, Ectothiorhodospira shaposhnikovii and Anabaena cylindrica are cytochromes of groups c and b.In different phototrophs, synthesis of hydrogenase can be inhibited by the presence of high concentrations of O₂. In some microorganisms (e.g. Rhodopseudomonas capsulata, strain B10) the repressing effect on hydrogenase formation is also exhibited by organic compounds. H₂ may not necessarily be present for hydrogenase synthesis by purple bacteria, but its presence may considerable increase the level of the enzyme.Abbreviations SDS sodium dodecylsulfate - Hipip high-potential iron — sulfur protein - R Rhodopseudomonas - T Thiocapsa - Rh Rhodospirillum - C Chromatium This paper is dedicated to Professor Dr. H.G. Schlegel in honour of his sixtieth birthday and in recognition of his great contribution in the field of physiology and biochemistry of microorganisms capable of using H₂. Professor H.G. Schlegel had a profound and most fuitful influence on the progress in the research of the laboratory headed by the author     

Endogeneous levels of indole-3-acetic acid and abscisic acid during the rooting of Cotinus coggygria cuttings taken at different times of the year

Cuttings of Cotinus coggyria cv Royal Purple rooted well in the spring but not at all later in the season. Levels of free and conjugated IAA and ABA were measured in cuttings taken at different times of the year. Hormones were measured in the leaf, the upper stem and the lower stem (rooting zone). In cuttings taken in early June the level of IAA was much higher than that of conjugated IAA. In late July the opposite was found. No significant differences in ABA levels were found although the ABA/IAA ratio changed dramatically.     

Short-lived delayed luminescence of photosynthesizing organisms II. The ratio between delayed and prompt fluorescence as studied by the modulation method

The ratio between the intensities of delayed and prompt fluorescence was studied for different photosynthetic objects under different conditions by a modulation method. The method is based on excitation of luminescing objects by light, modulated harmonically, and on a combined study of phase shifts and demodulation coefficients of the luminescence as related to excitation light. The presence of intense delayed emissions was revealed in purple bacteria, Ectothiorhodospira shaposhinokovii, Rhodospirillum rubrum and Rhodopseudomonas sphaeroides, in the micro- and nanosecond range. Under conditions of saturating light, their proportion was several percent of the total emission.The most striking phenomenon was observed under reducing conditions (addition of 1 · 10^?2 M Na₂S₂O₄ to whole-cell suspensions of purple bacteria) where the intensity of the delayed emissions grew dramatically and became comparable to that of prompt fluorescence.The data obtained indicate that, at room temperature, reversal of some early stages of charge separation in bacterial reaction centres may proceed largely via the channel that includes generation of the reaction-centre bacteriochlorophyll in the excited singlet state, followed by excitation-energy migration to antenna bacteriochlorophyll.The relation of these phenomena to the efficiency of solar energy utilization in photosynthetic apparatus is discussed.     

Phylogenetic origins of the plant mitochondrion based on a comparative analysis of 5S ribosomal RNA sequences

Summary The complete nucleotide sequences of 5S ribosomal RNAs fromRhodocyclus gelatinosa, Rhodobacter sphaeroides, andPseudomonas cepacia were determined. Comparisons of these 5S RNA sequences show that rather than being phylogenetically related to one another, the two photosynthetic bacterial 5S RNAs share more sequence and signature homology with the RNAs of two nonphotosynthetic strains.Rhodobacter sphaeroides is specifically related toParacoccus denitrificans andRc. gelatinosa is related toPs. cepacia.These results support earlier 16S ribosomal RNA studies and add two important groups to the 5S RNA data base. Unique 5S RNA structural features previously found inP. denitrificans are present also in the 5S RNA ofRb. sphaeroides; these provide the basis for subdivisional signatures. The immediate consequence of our obtaining these new sequences is that we are able to clarify the phylogenetic origins of the plant mitochondrion. In particular, we find a close phylogenetic relationship between the plant mitochondria and members of the alpha subdivision of the purple photosynthetic bacteria, namely,Rb. sphaeroides, P. denitrificans, andRhodospirillum rubrum.     

Light-induced conductivity changes in purple membrane suspensions

Small light-induced changes in the conductivity of light-adapted purple membrane suspended in strong electrolyte solutions were detected. The method used involved modulated light and a phase sensitive detector and it allowed us to detect accurately changes as small as 0.0001% in the conductivity of the suspension. The light-induced conductivity changes turned out to be composed of at least two different events: a small fast increase in conductivity (t ∼ 2 ms) followed by a slower and larger decrease in this parameter (Τ=70 ms-80 ms). The effects of pH and temperature on these changes were studied. Both events reached maximal values around neutral pH and approached zero at both high and low pH's. Heating the suspension decreased the photoconductivity change and Arrhenius plots of the data showed breaks around 31‡ C. It is suggested that the conductivity changes reflect changes in the surface charge of the membrane and can be used to follow the kinetics of the conformational changes occuring in the system.     

Reaction of the purple membrane with a carbodimide

Purple membrane was reacted with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide at pH 4.5 and 8.0. At pH 4.5, the reaction yields cross-linked bacteriorhodopsin. The cross-linking is inhibited by pretreatment of the membrane with papain, or by the presence of carbohydrazide or glycine ethyl ester in the reaction mixture. The product of the pH 8.0 reaction is not cross-linked, but it displays altered properties. Two measures of photochemical activity (light-induced change in proton binding (Δh?) and decay of photointermediate M) show changes indicative of slowed proton uptake. The Δh? is increased by ethyl dimethylaminopropylcarbodiimide. This increase is unaffected by pretreatment of the membrane with papain, and it is not reversed by NH₂OH. However, the reaction is inhibited by millimolar concentrations of CaCl₂. The altered Δh? is not apparent in detergent-solubilized membranes. Ethyl dimethylaminopropyl-carbodiimide does not appear to cause a large alteration in the membrane surface charge, as measured by Ca²⁺ binding.We conclude that (1) at acid pH, ethyl dimethylaminopropylcarbodiimide can be used for cross-linking or for attachment of specific probes to the C-terminal region of bacteriorhodopsin, and hence to the cytoplasmic side of the purple membrane, and (2) at alkaline pH, ethyl dimethylaminopropylcarbodiimide reacts at a different type of site and appears to inhibit the proton pump.     

Acylated anthocyanins from leaves of Oxalis triangularis

The novel anthocyanins, malvidin 3-O-(6-O-(4-O-malonyl-alpha-rhamnopyranosyl)-beta-glucopyranoside)-5-O-beta-glucopyranoside (2), malvidin 3-O-(6-O-alpha-rhamnopyranosyl-beta-glucopyranoside)-5-O-(6-O-malonyl-beta-glucopyranoside) (3), malvidin 3-O-(6-O-(4-O-malonyl-alpha-rhamnopyranosyl)-beta-glucopyranoside)-5-O-(6-O-malonyl-beta-glucopyranoside) (4), malvidin 3-O-(6-O-(4-O-malonyl-alpha-rhamnopyranosyl)-beta-glucopyranoside) (5) and malvidin 3-O-(6-O-(Z)-p-coumaroyl-beta-glucopyranoside)-5-O-beta-glucopyranoside (6), in addition to the 3-O-(6-O-alpha-rhamnopyranosyl-beta-glucopyranoside)-5-O-beta-glucopyranoside (1) and the 3-O-(6-O-(E)-p-coumaroyl-beta-glucopyranoside)-5-O-beta-glucopyranoside (7) of malvidin have been isolated from purple leaves of Oxalis triangularis A. St.-Hil. In pigments 2, 4 and 5 a malonyl unit is linked to the rhamnose 4-position, which has not been reported previously for any anthocyanin before. The identifications were mainly based on 2D NMR spectroscopy and electrospray MS.