Secondary metabolite signalling in host-parasitic plant interactions

The parasitic weeds Orobanche and Striga spp. are a serious threat to agriculture in large parts of the world. The lifecycle of the parasitic weeds is closely regulated by the presence of their hosts, and secondary metabolites that are produced by host plants play an important role in this interaction. Model plants, such as Arabidopsis and maize mutant collections, have been increasingly used to study these chemical signals, especially those host-produced stimulants that induce the germination of parasite seeds.     

Comparative proteomics of seed maturation in oilseeds reveals differences in intermediary metabolism

Proteomics is increasingly being used to understand enzyme expression and regulatory mechanisms involved in the accumulation of storage reserves in crops with sequenced genomes. During the past six years, considerable progress has been made to characterize proteomes of both mature and developing seeds, particularly oilseeds - plants which accumulate principally oil and protein as storage reserves. This review summarizes the emerging proteomics data, with emphasis on seed filling in soy, rapeseed, castor and Arabidopsis as each of these oilseeds were analyzed using very similar proteomic strategies. These parallel studies provide a comprehensive view of source-sink relationships, specifically sucrose assimilation into organic acid intermediates for de novo amino acid and fatty acid synthesis. We map these biochemical processes for seed maturation and illustrate the differences and similarities among the four oilseeds. For example, while the four oilseeds appear capable of producing cytosolic phosphoenolpyruvate as the principal carbon intermediate, soybean and castor also express malic enzymes and malate dehydrogenase, together capable of producing malate that has been previously proposed to be the major intermediate for fatty acid synthesis in castor. We discuss these and other differences in the context of intermediary metabolism for developing oilseeds.     

The strigolactone germination stimulants of the plant-parasitic Striga and Orobanche spp. are derived from the carotenoid pathway

The seeds of parasitic plants of the genera Striga and Orobanche will only germinate after induction by a chemical signal exuded from the roots of their host. Up to now, several of these germination stimulants have been isolated and identified in the root exudates of a series of host plants of both Orobanche and Striga spp. In most cases, the compounds were shown to be isoprenoid and belong to one chemical class, collectively called the strigolactones, and suggested by many authors to be sesquiterpene lactones. However, this classification was never proven; hence, the biosynthetic pathways of the germination stimulants are unknown. We have used carotenoid mutants of maize (Zea mays) and inhibitors of isoprenoid pathways on maize, cowpea (Vigna unguiculata), and sorghum (Sorghum bicolor) and assessed the effects on the root exudate-induced germination of Striga hermonthica and Orobanche crenata. Here, we show that for these three host and two parasitic plant species, the strigolactone germination stimulants are derived from the carotenoid pathway. Furthermore, we hypothesize how the germination stimulants are formed. We also discuss this finding as an explanation for some phenomena that have been observed for the host-parasitic plant interaction, such as the effect of mycorrhiza on S. hermonthica infestation.     

Isometric force development of some muscle groups in athletes

In a large sample of both male and female athletes, subdivided by age and sex, a development curve of isometric muscule force (F) was analyzed for hand flexors, upper-body flexors and extensors, and knee extensors (PDS). A sample of 1,857 male and 1,009 female athletes, aged 8-30 years, subdivided by their age and sex, was used to measure the mean values of isometric muscle force of certain muscle groups by way of 5 topologically defined tests. Based on the results, isometric muscle force (F) development curves are shown and analyzed for the right-hand and left-hand (PLS) flexors, upper-body flexors (PTR), upper-body extensors (OTR), and knee extensors (ONO). The application of certain statistical programs gave rise to equations of the relationship between isometric force and age. The maximum mean value of PLS was chosen as the reference value or "the gold standard," with which PTR, OTR, and ONO were subsequently compared. The relationships were 1:1:1:2.8:5.9 (for male athletes), and 1:1:1.3:3.2:5.2 (for female athletes). The newly derived relationship was recognized as "the canon." The results may have practical application in athletes' fitness and conditioning. Every topologically defined muscle force has its own patterns and rules that should be closely followed in the training process, because any generalization may lead to false conclusions.     

Tomato strigolactones are derived from carotenoids and their biosynthesis is promoted by phosphate starvation

* Strigolactones are rhizosphere signalling compounds that mediate host location in arbuscular mycorrhizal (AM) fungi and parasitic plants. Here, the regulation of the biosynthesis of strigolactones is studied in tomato (Solanum lycopersicum). * Strigolactone production under phosphate starvation, in the presence of the carotenoid biosynthesis inhibitor fluridone and in the abscisic acid (ABA) mutant notabilis were assessed using a germination bioassay with seeds of Orobanche ramosa; a hyphal branching assay with Gigaspora spp; and by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis. * The root exudates of tomato cv. MoneyMaker induced O. ramosa seed germination and hyphal branching in AM fungi. Phosphate starvation markedly increased, and fluridone strongly decreased, this activity. Exudates of notabilis induced approx. 40% less germination than the wild-type. The LC-MS/MS analysis confirmed that the biological activity and changes therein were due to the presence of several strigolactones; orobanchol, solanacol and two or three didehydro-orobanchol isomers. * These results show that the AM branching factors and parasitic plant germination stimulants in tomato root exudate are strigolactones and that they are biosynthetically derived from carotenoids. The dual activity of these signalling compounds in attracting beneficial AM fungi and detrimental parasitic plants is further strengthened by environmental conditions such as phosphate availability.     

<Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis> transformed calli of the holoparasitic plant <Emphasis Type="Italic">Phelipanche ramosa</Emphasis> maintain parasitic competence

Phelipanche and Orobanche spp. (broomrapes) are economically important parasitic weeds, causing severe damage to many agricultural crops. However, conventional methods to control these parasitic weeds are often not effective. Targeting molecular and biochemical processes involved in the establishment of the connection between the parasite and the host may offer a new perspective for control. However, progress in the understanding of these processes is hampered by the fact that genetic transformation and regeneration of these parasites is difficult if not impossible due to their specific lifecycle. Phelipanche and Orobanche spp. are holoparasites that need to attach to the roots of a host plant to get their assimilates, nutrients and water to develop and reproduce. The present study describes a highly efficient genetic transformation and regeneration protocol for the root holoparasitic Phelipanche ramosa. We present a new transformation system for P. ramosa using Agrobacterium rhizogenes MSU440 carrying a non-destructive selection marker gene coding for a red fluorescent protein (DsRed1). Using this protocol up to 90% transformation efficiency was obtained. We transformed 4 weeks old P. ramosa calli and transgenic calli expressing DsRed1 were then cultured on host plants. For the first time, we present shoot and flower development of the transgenic parasitic plant P. ramosa after successful connection of transgenic calli with the host plant roots. Moreover, we also present, for the first time, growth and development of P. ramosa shoots and flowers in vitro in the absence of a host plant.     

Leptospirosis distribution related to freshwater habitats in the Vojvodina region (Republic of Serbia)

The retrospective study (2002—2007) for human leptospirosis in Vojvodina was undertaken in order to describe the distribution of the disease in relation with some environmental factors. Regarding the presented results, the major detected number of leptospirosis cases concurs with stagnant waters, wetlands, fish pond areas and protected regions, which comprised the basis for mapping of the region in three risk zones: very high risk (incidence rate higher than 5.0), high risk (2.5—5.0) and medium risk of leptospirosis infection (1.0—2.5). During the investigated period, 97 cases were registered with an average of 13.85 cases per year: 2002, 32 cases; 2003, 7; 2004, 22; 2005, 16; 2006, 4 and 2007, 16. Out of these 97 cases only 5 were women. Serovars from 11 presumptive serogroups caused infection, with a predominance of Icterohaemorrhagiae and Bratislava, accounting for 72.72% of cases together. Icterohaemorrhagiae was the commonest infecting serogroup mostly connected with fish ponds. Case fatality ratio was 9.4%.     

Bacterial Communities Associated with Flowering Plants of the Ni Hyperaccumulator Thlaspi goesingense

Thlaspi goesingense is able to hyperaccumulate extremely high concentrations of Ni when grown in ultramafic soils. Recently it has been shown that rhizosphere bacteria may increase the heavy metal concentrations in hyperaccumulator plants significantly, whereas the role of endophytes has not been investigated yet. In this study the rhizosphere and shoot-associated (endophytic) bacteria colonizing T. goesingense were characterized in detail by using both cultivation and cultivation-independent techniques. Bacteria were identified by 16S rRNA sequence analysis, and isolates were further characterized regarding characteristics that may be relevant for a beneficial plant-microbe interaction—Ni tolerance, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and siderophore production. In the rhizosphere a high percentage of bacteria belonging to the Holophaga/Acidobacterium division and α-Proteobacteria were found. In addition, high-G+C gram-positive bacteria, Verrucomicrobia, and microbes of the Cytophaga/Flexibacter/Bacteroides division colonized the rhizosphere. The community structure of shoot-associated bacteria was highly different. The majority of clones affiliated with the Proteobacteria, but also bacteria belonging to the Cytophaga/Flexibacter/Bacteroides division, the Holophaga/Acidobacterium division, and the low-G+C gram-positive bacteria, were frequently found. A high number of highly related Sphingomonas 16S rRNA gene sequences were detected, which were also obtained by the cultivation of endophytes. Rhizosphere isolates belonged mainly to the genera Methylobacterium, Rhodococcus, and Okibacterium, whereas the majority of endophytes showed high levels of similarity to Methylobacterium mesophilicum. Additionally, Sphingomonas spp. were abundant. Isolates were resistant to Ni concentrations between 5 and 12 mM; however, endophytes generally tolerated higher Ni levels than rhizosphere bacteria. Almost all bacteria were able to produce siderophores. Various strains, particularly endophytes, were able to grow on ACC as the sole nitrogen source.