Towards plastid transformation in rapeseed (Brassica napus L.) and sugarbeet (Beta vulgaris L.)

In the current study tissue cultures of rapeseed (cv. “Drakkar”, cv. “Westar”) and sugarbeet (cv. ”Viktoria”, cv. “VRB”, cv. ”31-188”, cv. ”7T1308” and 47 other breeding lines, Appendix 1) have been investigated for the establishment of conditions that make possible plastid transformation in both species. Tobacco leaf protoplasts (cv. ”petite Havana”, cv. ”Wisconsin 38”) were used to develop a novel technique – the TAL (thin-alginate-layers) technique. The TAL technique in combination with new culture media resulted in very rapid protoplast development and fast shoot regeneration (in less than two weeks). This method was also successfully applied to improve protoplast culture of rapeseed and of the extremely recalcitrant species sugarbeet. Factors, which included protoplast source, mineral and organic composition of isolation and culture media, influence of growth regulators etc. were investigated and conditions for protoplast culture and regeneration were established for both species. According to reports in the literature, only protoplasts from guard cells could be regenerated into plants. Thus, an alternative and reproducible method of shoot regeneration from protoplasts isolated from hypocotyl derived callus was successfully developed. While no shoot regeneration was observed from guard cell protoplasts in our experiments, plant regeneration (efficiencies up to 30%) from callus protoplasts could be achieved for the first time in this study. The influence of different parameters on the efficiency of callus formation from etiolated hypocotyl explants was investigated. Protoplasts from callus and hypocotyl derived callus were used for the experiments on nuclear transformation in sugarbeet. Both, the PEG method and the biolistic method were successfully applied to obtain nuclear transformants as confirmed by molecular methods (PCR analysis and Southern blot hybridisation). The biolistic method was applied for plastid transformation experiments in sugarbeet. Species specific vectors containing the aadA cassette were constructed for plastid transformation in rapeseed and sugarbeet. However, difficulties to select plastid transformants were observed due to a high natural resistance to spectinomycin and streptomycin in rapeseed. In sugarbeet spectinomycin at a concentration of 100 mg/l was found efficient for selection and spectinomycin and streptomycin resistant colonies were obtained after callus bombardment. The presence of the aadA gene in antibiotic-resistant lines was proven by PCR analysis, but an integration of DNA into the plastome could not be verified so far. Efficient regeneration systems and methods of DNA transfer were established for rapeseed and sugarbeet and straightened the way for successful plastid transformation in either species

The Enchanted Desna

translated from the Ukrainian by Dzvinia Orlowsk

Dissociation of Trinitrotoluene on the Surface of Porous Silicon Under Laser Irradiation

AbstractDissociation of trinitrotoluene (TNT) sorbed on porous silicon (pSi) surface under UV laser irradiation has been studied. A method based on ion mobility spectrometry (IMS) has been used in this study. Excitation and ionization of TNT molecules has been occurred at atmospheric pressure. A dependence of TNT ion spectrum on standing time of TNT molecules on pSi surface has been demonstrated. The ion type has changed from (TNT-H) – to (TNT-NO2) – which indicates a slow chemical reaction between pSi surface and TNT molecules. The first step of (TNT-NO2) – formation has been found to be a result of laser stimulated surface dissociation and subsequent desorption of a neutral TNT-NO2 fragment. The second step of (TNT-NO2) – formation is a capture of an electron emitted from the pSi surface under laser irradiation. The result of this study could be used in the area of explosive detection

Modulation of quantum dot photoluminescence in porous silicon photonic crystals as a function of the depth of their penetration

International audiencePhotonic crystals doped with fluorescent nanoparticles offer a plenty of interesting applications in photonics, laser physics, and biosensing. Understanding of the mechanisms and effects of modulation of the photoluminescent properties of photonic crystals by varying the depth of nanoparticle penetration should promote targeted development of nanocrystal-doped photonic crystals with desired optical and morphological properties. Here, we have investigated the penetration of semiconductor quantum dots (QDs) into porous silicon photonic crystals and performed experimental analysis and theoretical modeling of the effects of the depth of nanoparticle penetration on the photoluminescent properties of this photonic system. For this purpose, we fabricated porous silicon microcavities with an eigenmode width not exceeding 10 nm at a wavelength of 620 nm. CdSe/CdS/ZnS QDs fluorescing at 617 nm with a quantum yield of about 70% and a width at half-height of about 40 nm were used in the study. Confocal microscopy and scanning electron microscopy were used to estimate the depth of penetration of QDs into the porous silicon structure; the photoluminescence spectra, kinetics, and angular fluorescence distribution were also analyzed. Enhancement of QD photoluminescence at the microcavity eigenmode wavelength was observed. Theoretical modeling of porous silicon photonic crystals doped with QDs was performed using the finite-difference time-domain (FDTD) approach. Theoretical modeling has predicted, and the experiments have confirmed, that even a very limited depth of nanoparticle penetration into photonic crystals, not exceeding the first Bragg mirror of the microcavity, leads to significant changes in the QD luminescence spectrum determined by the modulation of the local density of photonic states in the microcavity. At the same time, complete and uniform filling of a photonic crystal with nanoparticles does not enhance this effect, which is as strong as in the case of a very limited depth of nanoparticle penetration. Our results will help to choose the best technology for fabrication of efficient sensor systems based on porous silicon photonic crystals doped with fluorescent nanoparticles

Enhanced spontaneous emission from two-photon-pumped quantum dots in a porous silicon microcavity

Photoluminescence (PL)-based sensing techniques have been significantly developed in practice due to their key advantages in terms of sensitivity and versatility of the approach. Recently, various nanostructured and hybrid materials have been used to improve the PL quantum yield and the spectral resolution. The near-infrared (NIR) fluorescence excitation has attracted much attention because it offers deep tissue penetration and it avoids the autofluorescence of the biological samples. In our study, we have shown both spectral and temporal PL modifications under two-photon excitation of quantum dots (QDs) placed in one-dimensional porous silicon photonic crystal (PhC) microcavities. We have demonstrated an up-to-4.3-fold Purcell enhancement of the radiative relaxation rate under two-photon excitation. The data show that the use of porous silicon PhC microcavities operating in the weak coupling regime permits the enhancement of the PL quantum yield of QDs under two-photon excitation, thus extending the limits of their biosensing applications in the NIR region of the optical spectrum