Multiple,concentration-dependent effects of sucrose,auxins and cytokinins in explant cultures of kale and tobacco

We describe complex multiple concentration dependencies for the response of isolated pith tissues to plant biologically active substances. Kale and tobacco stem pith explants were cultured on agar media containing combinations of sucrose, cytokinin [kinetin or benzyladenine (BA)] and auxin [indole-3-acetic acid (IAA) or naphthaleneacetic acid (NAA)]. Absorption of these components by explants and their effects on explant mass, contents of soluble proteins, starch and sugars, and activity of ADP-glucose pyrophosphorylase (AGPase) were studied in relation to their concentration. Up to ten pronounced statistically significant maxima (peaks or waves) were repeatedly detected in the dose–response curves over a concentration range of several logarithmic orders. Slight maxima were observed in the corresponding absorption curves. Pronounced maxima of sucrose absorption were induced by IAA and BA, and those of NAA absorption were induced by sucrose. Both types of multiple maxima (in dose–response and absorption curves) may be due to changes in concentration of intracellular solutes (sugars, auxins and cytokinins), thereby affecting metabolic processes that act as sinks for external solutes and elicit feedback appearance of maxima in absorption curves. Good correspondence between external concentrations at which maxima of different compared curves occur in addition to statistical significance of individual maxima and repeatability of experimental results supports the conclusion that the multiple maxima exhibited are genuine. We consider it possibile that the multiple maxima are associated with endopolyploidy or mixoploidy and/or epigenomic diversity of pith cells that show different sensitivities to biologically active solutes.     

Some new taxa inLotus corniculatus L.

Four new taxa in the variable speciesLotus corniculatus L. has been described: var.alandicus Chrtková-?ertová, var.norvegicus Chrtková-?ertová, var.fallax Chrtková-?ertová and var.posoniensis Chrtková-?ertová.     

Integrator is a genome-wide attenuator of non-productive transcription

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Effect of increasing methanol concentrations on physiology and cytology ofCandida boidinii

Concentration of methanol in the medium strongly affected not only the physiology but also the cytology ofCandida boidinii strain 2 cells in a methanol-limited chemostat at a constant dilution rateD 0.1/h and at low pH 3.0. The formation of large cubic peroxisomes with high alcohol oxidase (AO) activity observed at low methanol concentration (S ₀ 3 g/L) disappeared on increasing the methanol concentration in the inflow medium. The AO activity in the cells sharply decreased, followed by accumulation of riboflavin phosphate and residual methanol in the medium. The activity of catalase was relatively stable. At methanol concentrationS ₀>K _I (K ₁ equal to 12 g methanol per L), which included a substantial increase in methanol dissimilation, documented by higher formaldehyde and formate dehydrogenase activities and by lower yield coefficient on methanol, the yeast cells contained large lobe-shaped peroxisomes and a smaller number of larger mitochondria. The cells formed pseudomycelium with a thick septum between the mother and daughter cells.     

The many faces of Peridinium cinctum (Peridiniaceae,Peridiniales): morphological and molecular variability in a common dinophyte

Peridinium cinctum is a common freshwater dinophyte with a long history of research. Erich Lindemann was the first to assess intraspecific variability in this species focusing on plate pattern variation. Since then, this issue has been neglected but with the application of DNA sequence diagnostics, a combination of morphological and molecular characters may enable taxonomic delimitations. Our aim was to identify distinct morphotypes using plate pattern as the main characteristic and then compare them to the geographic occurrence of particular ribotypes (as inferred from sequences of the Internal Transcribed Spacer: ITS) in samples from Central Europe. Approximately 200 observations were carried out under the inverse light microscope for each of a total of 15 strains. We observed two main variations from the abundant plate pattern in P. cinctum, namely an unusual position of the 2a plate and the irregular shape of the 1a plate. In 88 (predominantly clonal) strains, we identified five different ribotypes (submitted as 71 new GenBank entries) which had no clear correlation to the defined morphotypes and/or spatial occurrences. In four cases, we detected two distinct ribotypes at the same locality. However, samples collected south of the Danube River presented a different predominant morphotype from the rest of the samples, thus implying a potential biogeographic signal as inferred from morphology. In general, there is morphological and molecular variability in P. cinctum, which is under-studied and which may uncover geographic or ecological correlations or even the existence of cryptic species.