Childhood developmental changes in the auditory P300.

In this study we investigated developmental changes in the auditory P3 latency from childhood to adolescence. Event-related potentials evoked by improbable auditory stimuli were recorded from 35 normal children between the ages of 5 and 13 years. Regression analyses showed significant age trends in the auditory P3 latency. Latencies decreased at a rapid rate (Cz: 20.34 msec/yr; Pz: 19.27 msec/yr) from childhood to adolescence, suggesting an increased efficiency in processing information as children mature. This rate was linear or constant in nature as evidenced by the failure of the quadratic and cubic components to significantly increase predictability of the regression equation. The slope of the P3 latency/age regression line was also shown to be influenced by the interactive effects of task difficulty and maturation. It was hypothesized that neuro-developmental processes (increased myelination and dendritic arborization) may underlie the maturational changes observed in the P3 latency during childhood.

Cryopreservation of cultivated and wild Arachis species embryonic axes using desiccation and vitrification methods.

The effects of two methods of cryopreservation involving chemical vitrification and air desiccation) were studied on isolated embryonic axes of A. hypogaea. Vitrification with PVS2 and desiccation in a laminar flow cabinet resulted in high levels (70-90%) of whole plant recovery after cryopreservation. A desiccation protocol based on 1h exposure of explants to the air flow was successfully applied to six wild species of section Extranervosae, resulting in recovery levels of 70-90% after liquid nitrogen treatment.

Cryopreservation of Arachis species by vitrification of in vitro-grown shoot apices and genetic stability of recovered plants.

A storage protocol at cryogenic temperature was established for shoot apices from in vitro plants of the cultivated groundnut (Arachis hypogaea) and wild Arachis species (A. retusa and A. burchellii) using a basic vitrification protocol with direct immersion in liquid nitrogen (LN). The effect of pre-treatments of donor-plants with ABA as well as of different supplements in the post-thaw culture medium was studied. After rapid warming at 40 C, the explants were cultured on MS medium devoid of growth regulators (MS0) or MS supplemented with 4.4(M benzylaminopurine (BAP) and 0.5(M naphthalene acetic acid (NAA) plus 5(M silver nitrate (AgNO3), 0.25% polyvinylpyrrolidone (PVP) or 0.2% activated charcoal. Non-frozen explants from the three species formed one shoot through meristematic amplification when cultured on MS0 medium. These explants also developed callus on MS supplemented with growth regulators (4.4(M BAP and 0.5(M NAA) alone or plus PVP or AgNO3. Callus formation was suppressed in the presence of activated charcoal. Post-thaw regeneration ocurred only through indirect organogenesis on media containing AgNO3 or PVP. Preculturing on medium supplemented with abscisic acid (ABA) improved regrowth rate in these media. Recovery failed to occur in the presence of activated charcoal. The genetic stability of shoots of A. burchellii originated from shoot apices was analyzed through Random Amplified Polymorphic DNA (RAPD) markers.