Pressure-induced helix–coil transition of DNA copolymers is linked to water activity

We have investigated the effect of reduced water activity on the pressure-stability of double-stranded DNA polymers, poly[d(A-T)] and poly[d(I-C)]. Water activity was modulated by the addition of ethylene glycol and glycerol. The ionic strength of the medium was such that pressure had a destabilising effect on the polymers in the absence of cosolvents. The molar volume change of the heat-induced helix to coil transition (ΔV_T) becomes more positive as the activity of water was reduced, suggesting that the pressure-induced denaturation of DNA polymers would not occur at very low water activity. This would imply that water plays a crucial role in the pressure denaturation of DNA, much like that in pressure denaturation of proteins where the driving force of the process is the penetration of water molecules into the protein core [Hummer et al., Proc Natl Acad Sci USA 1998, 95, 1552–1555].     

Development of hydrophobic,mechanically reliable,and glow-in-the-dark glue using Arabic gum

A smart nanocomposite adhesive was created to facilitate a simple production of long-persistent photoluminescent and hydrophobic commercial products. Even after being left in the dark for up to 90 min, the created photoluminescent adhesive agent continued to generate light. A surface-specific nanocomposite adhesive agent consisting of lanthanide-activated strontium aluminate (LSA) nanoparticles (NPs; 5–14 nm) immobilized in the environmentally friendly Arabic gum (AG) was developed. A light-transmitting nanocomposite adhesive agent was manufactured by dispersing LSA nanoparticles evenly across the AG matrix without agglomeration. An excitation peak at 365 nm and an emission wavelength at 519 nm were observed for the prepared adhesives at different concentrations of LSA NPs. The emission spectra showed either fluorescence or afterglow phosphorescence, depending on the LSA ratio. The photochromic transition from colourless to green beneath an ultraviolet (UV) lamp and greenish yellow in a dark room was tracked. The LSA NPs in the Arabic gum matrix imparted enhanced hydrophobicity and scratch resistance to the LSA@AG nanocomposite. The LSA@AG nanocomposite demonstrated excellent durability and photostability. This study confirmed that the mass production of smart adhesives for applications such as smart windows, smart packaging, and safety directional signs in buildings is possible.     

Novel fabrication of gelatin-encapsulated copper nanoparticles using Aspergillus versicolor and their application in controlling of rotting plant pathogens

The fabrication of copper nanoparticles (CuNPs) with smallest size and more stability, with potential effects in plant disease management, may need a modified protocol for green synthesis. In this study, we could biosynthesize stable CuNPs extracellularly by an eco-friendly route using A. versicolor. The biosynthesis of nanoparticles was confirmed by UV–visible spectroscopy, Fourier transform infrared (FTIR), transmission electron microscope (TEM) and dynamic light scattering (DLS) techniques. CuNPs have a size range of 23–82 nm with round to polygonal shape. Antifungal study showed that CuNPs have potential antifungal activity against rotting plant pathogens, where 3.2 and 2.8 µg ml⁻¹ of nanoparticle solution totally inhibited the growth of both Fusarium oxysporum and Phytophthora parasitica, respectively. Damaged hyphae with limited deformed spores were detected through scanning electron microscope (SEM) analysis after the treatment of both pathogens with CuNPs. Between all tested polymers, gelatin-encapsulated nanoparticles were characterized ‘by their smallest size, 7–33 nm, and regular spherical shape at all experimental conditions. After 6 months of storage, gelatin-CuNPs maintained full nanoscale and antifungal properties compared with uncoated particles which lost these properties after only 1 month. It is concluded that CuNPs can be biosynthesized by an eco-friendly cheap method using A. versicolor and can be preserved stably for a long time with the smallest size and full antifungal activity by their encapsulation with gelatin as a natural polymer. These nanoparticles can be used safely in the management of plant rotting fungi.

     

Polarity, aperture condition and germination in pollen grains ofEphedra (Gnetales)

Pollen grain polarity, aperture condition and pollen tube formation were examined inEphedra americana, E. foliata, E. rupestris, E. distachya, andE. fragilis using LM, SEM and TEM. In the characteristic oblate pollen, as seen in situ in the tetrad configuration, the polar axis is the minor one and the equatorial plane runs between the two narrow ends of the microspore. The intine is thick in fresh fixed mature pollen but we have seen no indication of regions having an exceptionally thick intine that could be considered associated with an aperture or apertures. About three minutes after transferring fresh pollen to the germinating medium the ridged exine splits and twists away from the intine and its enclosed protoplast. The shed exine spreads out and curls into a scroll-like configuration that is as distinctive as that of the pollen shape had been but now having the ridges and valleys perpendicular to the long axis. The pollen tube develops, in our experience with more than a hundred germinating pollen grains, near one of the narrow tips of the pollen grain's equatorial plane. The location of the pollen tube initiation probably is related to the position of the tube cell nucleus. The pollen tube starts to grow about one hour after the exine was shed. The pollen tube emerges close to the narrow end (equator) of the gametophyte. This end emerged first as the exine is shed and is opposite to the prothallial cells. The stout pollen tube is c. 10µm in diameter grown in vitro on agar. In our germination medium the stout tube continued to elongate for about 24 hours reaching a length of c. 100 µm. With respect to exine morphology the aperture condition could be considered as inaperturate. The pollen tube, however, is formed in a germination area near one end of the exineless gametophyte.