Inhibition of copepod feeding by exudates and transparent exopolymer particles (TEP) derived from a Phaeocystis globosa dominated phytoplankton community

We investigated if (1) dissolved compounds excreted by Phaeocystis globosa and (2) transparent exopolymer particles (TEP) formed from carbohydrates excreted into the water affect the feeding of nauplii and females of the calanoid copepod Temora longicornis during a P. globosa bloom. Copepod grazing on the diatom Thalassiosira weissflogii in the presence of these possible grazing deterrents was measured during three successive weeks of a mesocosm study, simulating the development of a P. globosa bloom. Our results demonstrate no indication for the presence of feeding deterrents in the dissolved phase, but a strong inhibitory effect of transparent exopolymer particles (TEP) on the consumption of algae by both nauplii and adult copepods. The inhibitory effect of TEP was connected to the accumulation of DOM during the progress of the bloom. We suggest that a reduction in the grazing pressure of zooplankton may increase the survival of the liberated single cells during disruption of colonies and allow seeding populations to persist. Furthermore, P. globosa reduces the trophic efficiency of the food web not only by withdrawal of its colonies from grazing but also by a relaxation of the grazing pressure on co-occurring phytoplankton and by alteration of the food web structure via TEP production.     

Plant microbiota modified by plant domestication

Human life became largely dependent on agricultural products after distinct crop-domestication events occurred around 10,000 years ago in different geographical sites. Domestication selected suitable plants for human agricultural practices with unexpected consequences on plant microbiota, which has notable effects on plant growth and health. Among other traits, domestication has changed root architecture, exudation, or defense responses that could have modified plant microbiota. Here we present the comparison of reported data on the microbiota from widely consumed cereals and legumes and their ancestors showing that different bacteria were found in domesticated and wild plant microbiomes in some cases. Considering the large variability in plant microbiota, adequate sampling efforts and function-based approaches are needed to further support differences between the microbiota from wild and domesticated plants. The study of wild plant microbiomes could provide a valuable resource of unexploited beneficial bacteria for crops.     

Effects of macroalgal exudates and oxygen deficiency on survival and behaviour of fish larvae

Filamentous algae may create anoxic, i.e. oxygen free, conditions during night and fish larvae that commonly spend their first months in the littoral may therefore be subject to anoxia. We conducted two different experiments; firstly, we measured behaviour of pike larvae (Esox lucius L.), such as frequency of prey attacks and time in vegetation, in the presence of a chemical predator cue and oxygen deficiency. In the second experimental set-up, pike larval survival was monitored in water with added macro-algal exudates (excreted from Pilayella littoralis) and a low oxygen level (3 mg l^− 1). Our results showed that oxygen concentration and the chemical predator signal, caused by three-spined sticklebacks, had strong significant effects on the larval prey attacks. The prey attacks were strongly reduced at 3 mg oxygen l^− 1. However, survival of the larvae was not affected by low oxygen and macro-algal exudates. Pike larvae are very tolerant to hypoxia and exudates excreted by the littoral vegetation, whereas prey attacks are strongly decreased in hypoxia when a predator is around. This may have negative consequences for pike larval growth and recruitment in eutrophicated environments.     

Effect of Steinernema glaseri-infected host exudates on movement of conspecific infective juveniles

The entomopathogenic nematode's decision to infect a host is paramount because once the decision is made it is irrevocable; nematodes that invade a host either develop and achieve reproductive success, or they die. Entomopathogenic nematodes that have a cruiser foraging behavior, such as Steinernema glaseri, follow host-associated cues to locate insects to infect. Most of the host finding and infection dynamics research has focused on the infective juvenile nematodes' responses to cues from live insects such as host-associated volatiles and host contact cues. Few studies focus on how previously infected hosts influence infective juvenile infection behaviors. We investigated how exudates from nematode-infected hosts affect the behavior of S. glaseri infective juveniles. We hypothesized that the infective juvenile's behavioral response to cadavers would change as the state of a nematode-infected host changes during pathogenesis. We examined the effect of exudates collected from infected hosts on infective juvenile locomotory behavior. We detected no effects on nematode repulsion or attraction from exudates produced within the first 48h post-infection. We observed repulsion from accumulated exudates during the 3-48, 3-72, 3-120, and 3-144h intervals. Repulsion from exudates was observed during the 48-66, 72-90, and 120-138h intervals in experiments evaluating daily exudate emissions. The repellent effect of infected host exudates may result in an infective juvenile discriminating between suitable and unsuitable hosts.     

Root exudates of plants

Summary The release of substances from wheat roots was found to be directly related to the growth of the root system. Plants whose root system did not grow released almost no exudates.When exudate concentration in the vicinity of the roots was lowered by frequent replacements of the nutrient solution or by a simultaneous cultivation of exudate-utilizing bacteria, the release of exudates was enhanced. In axenic wheat cultures, the amount of exudates during a 12-day cultivation with 2- or 4-day intervals between medium replacements represented 50% of root dry weight and 12% of whole plant dry weight.Wheat plants cultivated in the presence of the bacteriumPseudomonas putida released up to double the amount of exudates compared with axenic variants.     

Die zytochemische Identifikation der Mastzellvorstufen bei der Ratte

Zusammenfassung Die Regeneration von Gewebsmastzellen wurde durch Untersuchungen von Peritonealexsudat erwachsener Ratten verfolgt, die häufigen Spülungen der Bauchhöhle unterworfen wurden. Innerhalb von 4–6 Tagen kommt es zu einer starken Vermehrung unreifer Gewebszellen. Die Ausbildung von Alcianblau-positiven unreifen Granula in ungranulierten Vorstufen benötigt etwa 6 Std. Die Ausbildung von Safranin-positiven reifen Granula vollzieht sich in 48 Std. Die Ergebnisse der zytochemischen Untersuchungen unreifer Mastzellvorstufen sprechen für eine monozytogene Entstehung der Gewebsmastzellen.

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Cytochemical identification of rat tissue mast cell precursors

Summary In adult rats, the regeneration of tissue mast cells in peritoneal exudates was studied by repeated peritoneal lavages. After 4–6 days, tissue mast cells appeared in great numbers in peritoneal exudates. Alcian blue positive granules were first noted at 6 hrs in agranular mast cell precursors. Maturation with accumulation of safraninpositive granules was complete after 48 hrs. The cytochemical reactions of the earliest tissue mast cell precursors suggest a monocytogenic origin of tissue mast cells.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Effect of transporters on the secretion of phytochemicals by the roots of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Root exudation, the process by which plants secrete compounds into the soil, is becoming accepted as a communicative process that determines organismal interactions in the rhizosphere. However, the mechanistic processes involved in the root exudation of phytochemicals have not been elucidated; traditionally, exudation has been regarded as a passive process. There is evidence that transporters in plants (and other organisms) have been involved in the movement of chemicals across different membranes. Here, we describe the involvement of different transporters in root exudation of phytochemicals by employing a pharmacological approach. We used a range of concentrations of several compounds known to inhibit different transporters, including potassium cyanide, orthovanadate, quinidine, glibenclamide, nifedipine and verapamil, to examine the effects of transporter inhibition on root exudation profiles in Arabidopsis. Generally, the exudation profile of phenolic compounds in 18-day-old plants shows more than 15 major phytochemicals. In contrast, the inhibitors listed above caused differences in the secretion of specific compounds. For instance, nifedipine and verapamil completely inhibited the exudation of the phytochemicals with molecular masses of 142 and 294, respectively. These results highlight that root exudation of phytochemicals is an active process controlled at the biochemical level and that different transporters may be involved in this root-specific mechanism. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Microbial responses to salt-induced osmotic stress

Summary The construction and assembly of a model root region is described. The model was used to manipulate the soil matrix, soil microorganisms, and to simulate release of root exudates. The design of the apparatus facilitated long-term, direct microscopic observations of microbial activity in soil and on artificial roots. Preliminary studies indicate that microbial responses to osmotic stress and to changes in components of exudate solutions are easily monitored.     

Pistil anatomy and pollen tube development in Polygala vayredae Costa (Polygalaceae)

Low seed ovule ratios have been observed in natural populations of Polygala vayredae Costa, a narrowly endemic species from the oriental pre-Pyrenees. To evaluate physical and nutritional constraints and pollen tube attrition in this endemic species, stigma and style anatomy, as well as pollen tube development along the pistil were investigated using light and fluorescence microscopy. The structural morphology of the stigmatic region was also examined with scanning electron microscopy. Pollen grains that reached the stigmatic papillae came into contact with a lipid-rich exudate and germinated easily. Although a large number of pollen grains reach the stigmatic papillae, few pollen tubes were able to grow into the style towards the ovary. The style was hollow, with the stylar channel beginning a few cells below the stigmatic papillae. Initially, the stylar channel area was small compared to other levels of the style, and was surrounded by lipid-rich, highly metabolic active cells. Furthermore, lipid-rich mucilage was detected inside the stylar channel. At subsequent style levels towards the ovary, no major reserves were detected histochemically. The reduced intercellular spaces below the stigmatic papillae and the reduced area of the stylar channel at its commencement are suggested to physically constrain the number of pollen tubes that can develop. In subsequent levels of the style, the stylar channel could physically support a larger number of pollen tubes, but the lack of nutritional reserves cannot be disregarded as a cause of pollen tube attrition. Finally, the number of pollen tubes entering the ovary was greater than the number of ovules, suggesting that interactions occurring at this level play a major role in the final reproductive outcome in this species.