Stefan Leu - Academia.edu (original) (raw)

Papers by Stefan Leu

Separation and Purification Technology, May 1, 2022

Plant and Cell Physiology, 1988

The relative contents of the mRNAs were analyzed for the 32 kDa herbicide-binding protein and for... more The relative contents of the mRNAs were analyzed for the 32 kDa herbicide-binding protein and for the large subunit of ribulose-l,5-bisphosphate carboxylase in the membrane fraction and in the soluble fraction of chloroplasts from Chlamydomonas reinhardii. The presence of mRNA for the two proteins in both subchloroplast fractions was demonstrated by in vitro translation of isolated RNA in the reticulocyte lysate. The relative amounts of the two mRNAs were measured by hybridizations with cloned chloroplast DNA probes at two stages of the cell cycle. Both mRNAs were distributed in the same ratio between membrane and soluble fractions, about 75% of both mRNAs being in the membrane and 25% in the soluble fraction. Therefore, in chloroplasts the accumulation of mRNAs on thylakoid membranes does not reflect the final localization of soluble and membrane proteins.

The elaborated genetics and the ease of cultivation made the unicellular green alga Chlamydomonas... more The elaborated genetics and the ease of cultivation made the unicellular green alga Chlamydomonas reinhardii a favorite for studying chloroplast biochemistry and development. However, certain studies have been hampered by the difficulty in isolating intact chloroplasts. The recent development of an isolation procedure for intact chloroplasts from Chlam. reinh. sp. [1, 2, 3] renders now possible in vitro experiments with chloroplasts of this alga. We report here on (i) protein synthesis in intact and broken chloroplasts, (ii) the localization of mRNA within the chloroplast, (iii) import and processing of cytoplasmically made proteins, (iv) modifications, e.g. phosphorylation, of chloroplast proteins.

Biochimica Et Biophysica Acta - General Subjects, Oct 1, 2019

Please cite this article as: K. Chekanov, E. Schastnaya, K. Neverov, et al., Nonphotochemical que... more Please cite this article as: K. Chekanov, E. Schastnaya, K. Neverov, et al., Nonphotochemical quenching in the cells of the carotenogenic chlorophyte Haematococcus lacustris under favorable condition and under stress, BBA-General Subjects,

Proceedings in life sciences, 1987

Journal of Vegetation Science, Nov 1, 2017

QuestionsDo tree species with similar canopy structures but distinct litter production volumes af... more QuestionsDo tree species with similar canopy structures but distinct litter production volumes affect the understorey growth in dryland environments differently? How does rainfall impact the magnitude and sign of these effects?LocationWoodland savanna, northern Negev drylands, Israel.MethodsWe determined understorey herbaceous productivity beneath the canopy of two N‐fixing tree species (Acacia victoriae and Acacia salicina) with comparable canopy structures (canopy height and area) but distinct litter production volumes. Biomass was measured beneath A. victoriae trees and in the open area between the trees for 7 yrs and beneath A. salicina and the nearby open area for 2 yrs. Light measurements, litter biomass, fine root density and nutrients and gravimetric water content in the top soil were assessed for both species. Annual rainfall and the coefficient of variation in daily rain were used to determine rainfall effects on tree–grass relations.ResultsAcacia victoriae and A. salicina had contrasting positive and negative effects on understorey growth, respectively. Both species had comparable fine root densities, soil moisture and nutrient content beneath their canopies, with a higher soil water content than the open area. The large amount of leaf litter produced by A. salicina appeared to suppress the understorey growth, likely via light interference at the soil surface, which outweighed the positive effect of moisture conditions. Acacia victoriae that produced significantly lesser amounts of litter facilitated the understorey growth via canopy shading (likely through reducing evaporative loss). Both the rainfall amount and its intra‐annual variability reduced the magnitude of the tree effect but did not change its sign.ConclusionsTree leaf litter production may have a contrasting effect on understorey growth, ranging from positive to negative even in the same environment. Changes in rainfall amount and intra‐annual rainfall variability affect the magnitude of the effect but not its sign.

Springer eBooks, 1984

Studies on protein synthesis by isolated chloroplasts have contributed a great deal to our presen... more Studies on protein synthesis by isolated chloroplasts have contributed a great deal to our present knowledge of the biogenesis of chloroplast proteins. So far, the available information has been obtained with only a few higher plants and algae. In Chlamydomonas, studies on chloroplast protein synthesis have been carried out indirectly: in vivo by pulse-labelling the cells in the presence of specific inhibitors (Chua, Gillham 1977), or in vitro using polyribosomes, free or thylakoid-bound, or chloroplast DNA (for review, see Ellis 1981).

Statement of the Problem: Many studies were conducted on the ants' life cycles; food supply etc.,... more Statement of the Problem: Many studies were conducted on the ants' life cycles; food supply etc., still their functioning in cultivated arid areas and as result, their rehabilitation efficiency for these areas is poorly analyzed. Aim: Defining the harvester ants' impacts on different cultivated arid areas and their potential use for rehabilitation and sustainable management. Methodology & Theoretical Orientation: A long term study carried out between 2008 and 2017 in the northern Negev (A heavily degraded and desertified area due to maximum levels of mismanagement, by repeated tilling and grazing without fertilizer inputs, fertility or grazing management) in different cultivated areas some conserved and other open lands on the harvester ants Messor ebeninus and M. arenarius functioning. Findings: Our findings indicate that in tilled areas at the first years after conservation, the harvester ants raised yearly the soil organic matter in by 0.5%, due to their foraging, than by 0.5-1% per year by their nests functioning (which serve as sink for spreading nutrients in the area underground zone). At final state in well managed rainfed Triticum aestivum field we found an increase of 15% of the yields (grains and vegetative biomass for grazing) in 30% ants' nests cover. In rangelands we got a yearly continuant increase of 0.5-1% of SOM and for other fertility parameters as nutrients and vegetative biomass an increase of 30% per year caused by their nest-sink functioning and their soil loosening. In cultivated soil terraces the ants encouraged the herbaceous vegetal growth by their soil loosening, accumulated organic matter and enriched clay content. Conclusion & Significance: Using adequate soil practices which do not interfere with ants' activity will accelerate rehabilitation, sustainable and profitable cultivation use for many degraded arid lands all over the globe. Biography Amir Mor-Mussery has his expertise on implementation of sustainable cultivation practices for arid loamy soils. His fields of interests include defying rehabilitation (or depredation) states of different cultivation practices, planning and monitoring grazing plans for arid rangelands, designing and managing agriculture terraces for halting runoff and rehabilitation of cultivated areas, savannas planning for increasing rangelands' productivity. He wrote many papers in peer reviewed journals on these issues and guide students and high school students on these issues.

Algal Research, 2016

Microalgae accumulate the storage lipids triacylglycerols (TAG) in lipid droplets (LDs) in respon... more Microalgae accumulate the storage lipids triacylglycerols (TAG) in lipid droplets (LDs) in response to environmental cues. Mechanistic insights into LD biogenesis in microalgal cells hold great promise for the manipulation of TAG production. In this report, we demonstrate the heterologous expression of a major LD protein of the green microalga Haematococcus pluvialis in the diatom Phaeodactylum tricornutum. The N-terminus of Haematococcus oil globule protein (HOGP) was fused with EGFP and expressed under the control of the strong light-inducible fcpA gene promoter and the novel nitrogen-starvation-inducible DGAT1 gene promoter. Fatty acid feeding enabled fast monitoring of LDs formation under nitrogen-replete conditions and detection of a fluorescent EGFP-HOGP signal as ring-like structures adjacent to the periphery of LDs. During the prolonged nitrogen starvation, EGFP-HOGP was expressed only under the control of the DGAT1 promoter and was similarly associated with LDs. Furthermore, expression of HOGP under nitrogen starvation enhanced TAG accumulation. The tools and approaches described in this report open the door for characterizing endogenous LD proteins in P. tricornutum. The results of this study indicate the significant biotechnological potential of such LD-associated protein genes in the metabolic engineering of microalgae for enhanced oil productivity.

Journal of Analytical & Bioanalytical Techniques, 2015

Treated water effluent from Phakalane waste water secondary maturation ponds in Gaborone City (Bo... more Treated water effluent from Phakalane waste water secondary maturation ponds in Gaborone City (Botswana) enters the Limpopo River via Notwane River. Effluent samples from these ponds were collected and investigated using molecular and analytical methods to determine presence of mcy genes and microcystins (MCs), respectively. It was observed that, potentially toxic algal blooms were present in this effluent and therefore algal toxins. Using Polymerase Chain Reaction (PCR) method; cyanobacterial 16S-rRNA and mcyA,-B,-C,-D,-E and-G genes were amplified and PCR products separated by gel electrophoresis and visualized after ethidium bromide staining. DNA sequence for mcyA gene was obtained using PCR products from a newly designed primer pair for the amplification of mcyA gene. BLAST results of the obtained DNA sequence were evaluated and aligned to NCBI database for species identification. The alignment gave the highest similarity (100%) in nucleotide sequence that was aligned to the DNA sequence of a toxigenic M. novacekii T20-3 based on the published data. Microcystin-RR,-YR,-LR and-WR were chromatographed, identified and quantified from M. novacekii T20-3 cell extracts using LC-ESI-MS technique after liquid-partitioning (LP) and solid-phase extraction (SPE) steps complementing PCR findings. Higher quantities of MC-RR,-LR and YR: 53.620 ± 0.063, 12.114 ± 0.024 and 5.280 ± 0.035 µg/g DW were observed, respectively.

Proceedings in Life Sciences, 1987

FEBS Journal, Sep 6, 2011

We have identified and isolated a cDNA encoding a novel acyl‐CoA:diacylglycerol acyltransferase (... more We have identified and isolated a cDNA encoding a novel acyl‐CoA:diacylglycerol acyltransferase (DGAT)1‐like protein, from the diatom microalga Phaeodactylum tricornutum (PtDGAT1). The full‐length cDNA sequences of PtDGAT1 transcripts revealed that two types of mRNA, PtDGAT1short and PtDGAT1long, were transcribed from the single PtDGAT1 gene. PtDGAT1short encodes a 565 amino acid sequence that is homologous to several functionally characterized higher plant DGAT1 proteins, and 55% identical to the putative DGAT1 of the diatom Thalassiosira pseudonana, but shows little homology with other available putative and cloned algal DGAT sequences. PtDGAT1long lacks several catalytic domains, owing to a 63‐bp nucleotide insertion in the mRNA containing a stop codon. Alternative splicing consisting of intron retention appears to regulate the amount of active DGAT1 produced, providing a possible molecular mechanism for increased triacylglycerol (TAG) biosynthesis in P. tricornutum under nitrogen starvation. DGAT mediates the last committed step in TAG biosynthesis, so we investigated the changes in expression levels of the two types of mRNA following nitrogen starvation inducing TAG accumulation. The abundance of both transcripts was markedly increased under nitrogen starvation, but much less so for PtDGAT1short. PtDGAT1 activity of PtDGAT1short was confirmed in a heterologous yeast transformation system by restoring DGAT activity in a Saccharomyces cerevisiae neutral lipid‐deficient quadruple mutant strain (H1246), resulting in lipid body formation. Lipid body formation was only restored upon the expression of PtDGAT1short, and not of PtDGAT1long. The recombinant yeast appeared to display a preference for incorporating saturated C16 and C18 fatty acids into TAG.DatabaseNucleotide sequence data are available in the GenBank/EMBL/DDBJ databases under accession number HQ589265, sequence to be released November 15 2011.