Optical Modulation of the Diffraction Efficiency in an Indoline Azobenzene/Amorphous Polycarbonate Film.

We have made a diffraction grating in an indoline azobenzene/amorphous polycarbonate film by two-beam interference at 532 nm that periodically photodegrades the indoline azobenzene dye. Subsequent illumination of the film with 532-nm light into the trans-isomer band leads to trans-cis isomerization in the indoline azobenzene dye and results in a decrease in the trans-isomer band absorption coefficient. This causes the diffraction efficiency to decrease when probed at 655 nm. The diffraction efficiency returns to its original value when the 532-nm light is blocked by thermal relaxation from the indoline azobenzene cis-isomer to the trans-isomer. Thus, we have been able to optically modulate the diffraction efficiency in a thin film diffraction grating.

Optically switchable diffraction grating in a photochromic/polymer thin film.

An optically switchable diffraction grating has been made in a thin film containing a photochromic dye and amorphous polycarbonate. We show that a film containing the dye 5-chloro-1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-(3H)naphth[2,1-b](1,4)oxazine] can be optically processed so that a diffraction grating can be completely switched on by ultraviolet light and turned off by thermal relaxation. The ability to switch or modulate the diffraction efficiency has a number of practical applications that include optical switches and add/drop multiplexers.

Detection of DNA methylation changes in micropropagated banana plants using methylation-sensitive amplification polymorphism (MSAP).

The extent of DNA methylation polymorphisms was evaluated in micropropagated banana (Musa AAA cv. 'Grand Naine') derived from either the vegetative apex of the sucker or the floral apex of the male inflorescence using the methylation-sensitive amplification polymorphism (MSAP) technique. In all, 465 fragments, each representing a recognition site cleaved by either or both of the isoschizomers were amplified using eight combinations of primers. A total of 107 sites (23%) were found to be methylated at cytosine in the genome of micropropagated banana plants. In plants micropropagated from the male inflorescence explant 14 (3%) DNA methylation events were polymorphic, while plants micropropagated from the sucker explant produced 8 (1.7%) polymorphisms. No DNA methylation polymorphisms were detected in conventionally propagated banana plants. These results demonstrated the usefulness of MSAP to detect DNA methylation events in micropropagated banana plants and indicate that DNA methylation polymorphisms are associated with micropropagation.

CDC-42 regulates PAR protein localization and function to control cellular and embryonic polarity in C. elegans.

BACKGROUND: The polarization of the anterior-posterior axis (A-P) of the Caenorhabditis elegans zygote depends on the activity of the par genes and the presence of intact microfilaments. Functional links between the PAR proteins and the cytoskeleton, however, have not been fully explored. It has recently been shown that in mammalian cells, some PAR homologs form a complex with activated Cdc42, a Rho GTPase that is implicated in the control of actin organization and cellular polarity. A role for Cdc42 in the establishment of embryonic polarity in C. elegans has not been described. RESULTS: To investigate the function of Cdc42 in the control of cellular and embryonic polarity in C. elegans, we used RNA-mediated interference (RNAi) to inhibit cdc-42 activity in the early embryo. Here, we demonstrate that RNAi of cdc-42 disrupts manifestations of polarity in the early embryo, that these phenotypes depend on par-2 and par-3 gene function, and that cdc-42 is required for the localization of the PAR proteins. CONCLUSIONS: Our genetic analysis of the regulatory relationships between cdc-42 and the par genes demonstrates that Cdc42 organizes embryonic polarity by controlling the localization and activity of the PAR proteins. Combined with the recent biochemical analysis of their mammalian homologs, these results simultaneously identify both a regulator of the PAR proteins, activated Cdc42, and effectors for Cdc42, the PAR complex.

T-lymphoblastic leukaemia and aspartate aminotransferase.

AST levels from 11 untreated children with T-ALL were found to be significantly higher than those from 74 children with non-T disease. The enzyme was not related to haemoglobin or bilirubin levels nor to the presence of hepatosplenomegaly in any of the patients. It was correlated with the white cell count, but only in the T-cell group and not the remainder. It was also correlated with a parallel (but lesser) rise in ALT, but again only in the T-cell group. The blast cells themselves contained little or no transaminase activity, so it is probable that T-ALL produces more extramedullary tissue damage than non-T disease.