5,449 research outputs found
Time-of-flight analysis of charge mobility in a Cu-phthalocyanine-based discotic liquid crystal semiconductor
We used a time-of-flight method to study the charge carrier mobility properties of a molecular-aligned discotic liquid crystal semiconductor based on Cu-phthalocyanine. The heated isotropic-phase semiconductor material was sandwiched between transparent electrodes coated onto glass substrates without conventional alignment layers. This was then cooled, and a discotic liquid crystal semiconductor cell was obtained, which we used to make mobility measurements. The material had a fixed molecular alignment due to the supercooling of the hexagonal columnar mesophase. It was clarified that the carrier mobility for electrons was as high as it was for holes at room temperature. The maximum value of negative charge mobility reached 2.60x10(-3) cm(2)/V s, although negative carrier mobility is often much lower than positive carrier mobility in other organic semiconductors, including conventional Cu-phthalocyanine vacuum-deposited films.ArticleAPPLIED PHYSICS LETTERS. 85(16):3474-3476 (2004)journal articl
Hydrotropism: analysis of the root response to a moisture gradient
Hydrotropism is a genuine response of roots to a moisture gradient to avoid drought. An experimental system for the induction of hydrotropic root response in petri dishes was designed by pioneering groups in the field. This system uses split agar plates containing an osmolyte only in a region of the plate in order to generate a water potential gradient. Arabidopsis seedlings are placed on the MS agar plate so that their root tips are near the junction between plain MS medium and the region supplemented with the osmolyte. This elicits a hydrotropic response in Arabidopsis roots that can be measured as the root curvature angle
Establishment of endomycorrhizal fungi on micropropagated teak (Tectona grandis L.f.)
No abstract available
Time-of-flight analysis of charge mobility in a Cu-phthalocyanine-based discotic liquid crystal semiconductor
We used a time-of-flight method to study the charge carrier mobility properties of a molecular-aligned discotic liquid crystal semiconductor based on Cu-phthalocyanine. The heated isotropic-phase semiconductor material was sandwiched between transparent electrodes coated onto glass substrates without conventional alignment layers. This was then cooled, and a discotic liquid crystal semiconductor cell was obtained, which we used to make mobility measurements. The material had a fixed molecular alignment due to the supercooling of the hexagonal columnar mesophase. It was clarified that the carrier mobility for electrons was as high as it was for holes at room temperature. The maximum value of negative charge mobility reached 2.60x10(-3) cm(2)/V s, although negative carrier mobility is often much lower than positive carrier mobility in other organic semiconductors, including conventional Cu-phthalocyanine vacuum-deposited films.ArticleAPPLIED PHYSICS LETTERS. 85(16):3474-3476 (2004)journal articl
In vitro cryopreservation of date palm caulogenic meristems
Cryopreservation is the technology of choice not only for plant genetic resource preservation but also for virus eradication and for the efficient management of large-scale micropropagation. In this chapter, we describe three cryopreservation protocols (standard vitrification, droplet vitrification, and encapsulation vitrification) for date palm highly proliferating meristems that are initiated from vitro-cultures using plant growth regulator-free MS medium. The positive impact of sucrose preculture and cold hardening treatments on survival rates is significant. Regeneration rates obtained with standard vitrification, encapsulation-vitrification, and droplet-vitrification protocols can reach 30, 40, and 70%, respectively. All regenerated plants from non-cryopreserved or cryopreserved explants don't show morphological variation by maintaining genetic integrity without adverse effect of cryogenic treatment. Cryopreservation of date palm vitro-cultures enables commercial tissue culture laboratories to move to large-scale propagation from cryopreserved cell lines producing true-to-type plants after clonal field-testing trials. When comparing the cost of cryostorage and in-field conservation of date palm cultivars, tissue cryopreservation is the most cost-effective. Moreover, many of the risks linked to field conservation like erosion due to climatic, edaphic, and phytopathologic constraints are circumvented. (Résumé d'auteur
Quince (Cydonia oblonga) in vitro plant root formation through an automated temporary inmersion system, and its acclimation
Artículo científicoQuince (Cydonia oblonga) is a non-traditional fruit tree found in Costa Rica that has
therapeutic and nutritional properties; however its slow growth and root formation prevents the production
of a homogeneous population when using conventional farming techniques. Hence, the aim of this research
project was to generate uniform plant material in a reduced time span using a temporary immersion bioreactor
system (RITAS ®). A semisolid rooting MS culture medium supplemented with 0.1 mg L-1 NAA; 0.3 mg L-1
IBA and 3% sucrose (pH 6.5), developed in the Centro de Investigación en Biotecnología (CIB), Instituto
Tecnológico de Costa Rica (ITCR), in Cartago, was used as a reference medium. Four different variations
in the sucrose concentration (1%, 2%, 3%, and 4%) were performed in liquid medium. Each trial was
evaluated with in vitro plants which had been previously exposed to the culture medium of the corresponding
treatments, in a stationary mode and for a 15 day long period, and with in vitro plants without any previous
treatment (a total of eight treatments). The comparison of the root formation percentages evidenced the clear
effect of sucrose concentration used, with the best results obtained when using the 2% sucrose trial with no
pre-treatment (73.3%). The in vitro plants were acclimated in cylinders made out of peat, have previously
been disinfected with fungicide, and placed in a humidity chamber at a 20.5°C average temperature and a
75,5% relative humidity for the establishment of weekly fertilizing cycles. The acclimation process generated
an 80% survival rate, since several seedlings experienced stem strangulation caused by a fungal attack.
The conidiophores identified through optical and scanning electron microscopy evidenced the presence of
Cladosporium spp., which was controlled with carbendazim and iprodione fungicides
Organogenesis and embryogenesis in several hypericum perforatum genotypes
St John’s wort (Hypericum perforatum) is a valuable plant used as a herbal remedy or in phytopharmaceutical drugs to
treat a variety of physical ailments. Much research has been performed to study the biochemical production of secondary
metabolites of in vitro cultured plants or organs. However, all of these studies have looked at the regeneration of plants
from explants in only one genotype. In addition, no study has revealed the mechanism of plant regeneration in
H. perforatum, i.e. organogenesis or somatic embryogenesis. We found that different genotypes Helos, Topas, Elixir, and
Numi responded similarly to regeneration medium. The regeneration responses (i.e. callus, root, or shoot production) of
identical explants from different genotypes were similar. However, the source of explant material (leaves, hypocotyls, and
roots) from the same genotype had significant effects on the response to media and plant regeneration frequency. Using
scanning electron microscopy and light microscopy, the progress of organogenesis and embryogenesis under similar
culture conditions was recorded. Root segments were the most responsive explants, producing the maximum number of
shoots per explant of all the genotypes.Fundação para a Ciência e a Tecnologia (FCT) -
POCTI/AGR/40 283/2001, SFRH/BPD/17102/2004
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