Chromosomal variations of Lycoris species revealed by FISH with rDNAs and centromeric histone H3 variant associated DNAs.

Lycoris species have various chromosome numbers and karyotypes, but all have a constant total number of chromosome major arms. In addition to three fundamental types, including metacentric (M-), telocentric (T-), and acrocentric (A-) chromosomes, chromosomes in various morphology and size were also observed in natural populations. Both fusion and fission translocation have been considered as main mechanisms leading to the diverse karyotypes among Lycoris species, which suggests the centromere organization playing a role in such arrangements. We detected several chromosomal structure changes in Lycoris including centric fusion, inversion, gene amplification, and segment deletion by using fluorescence in situ hybridization (FISH) probing with rDNAs. An antibody against centromere specific histone H3 (CENH3) of L. aurea (2n = 14, 8M+6T) was raised and used to obtain CENH3-associated DNA sequences of L. aurea by chromatin immunoprecipitation (ChIP) cloning method. Immunostaining with anti-CENH3 antibody could label the centromeres of M-, T-, and A-type chromosomes. Immunostaining also revealed two centromeres on one T-type chromosome and a centromere on individual mini-chromosome. Among 10,000 ChIP clones, 500 clones which showed abundant in L. aurea genome by dot-blotting analysis were FISH mapped on chromosomes to examine their cytological distribution. Five of these 500 clones could generate intense FISH signals at centromeric region on M-type but not T-type chromosomes. FISH signals of these five clones rarely appeared on A-type chromosomes. The five ChIP clones showed similarity in DNA sequences and could generate similar but not identical distribution patterns of FISH signals on individual chromosomes. Furthermore, the distinct distribution patterns of FISH signals on each chromosome generated by these five ChIP clones allow to identify individual chromosome, which is considered difficult by conventional staining approaches. Our results suggest a different organization of centromeres of the three chromosome types in Lycoris species.

Synthesis and Self-Assembly of Multistimulus-Responsive Azobenzene-Containing Diblock Copolymer through RAFT Polymerization.

This paper gathered studies on multistimulus-responsive sensing and self-assembly behavior of a novel amphiphilic diblock copolymer through a two-step reverse addition-fragmentation transfer (RAFT) polymerization technique. N-Isopropylacrylamide (NIPAM) macromolecular chain transfer agent and diblock copolymer (poly(NIPAM-b-Azo)) were discovered to have moderate thermal decomposition temperatures of 351.8 and 370.8 °C, respectively, indicating that their thermal stability was enhanced because of the azobenzene segments incorporated into the block copolymer. The diblock copolymer was determined to exhibit a lower critical solution temperature of 34.4 °C. Poly(NIPAM-b-Azo) demonstrated a higher photoisomerization rate constant (kt = 0.1295 s-1) than the Azo monomer did (kt = 0.088 s-1). When ultraviolet (UV) irradiation was applied, the intensity of fluorescence gradually increased, suggesting that UV irradiation enhanced the fluorescence of self-assembled cis-isomers of azobenzene. Morphological aggregates before and after UV irradiation are shown in scanning electron microscopy (SEM) and dynamic light scattering (DLS) analyses of the diblock copolymer. We employed photoluminescence titrations to reveal that the diblock copolymer was highly sensitive toward Ru3+ and Ba2+, as was indicated by the crown ether acting as a recognition moiety between azobenzene units. Micellar aggregates were formed in the polymer aqueous solution through dissolution; their mean diameters were approximately 205.8 and 364.6 nm at temperatures of 25.0 and 40.0 °C, respectively. Our findings contribute to research on photoresponsive and chemosensory polymer material developments.

Analysis of B chromosome nondisjunction induced by the r-X1 deficiency in maize.

The maize B chromosome typically undergoes nondisjunction during the second microspore division. For normal A chromosomes, the r-X1 deficiency in maize can induce nondisjunction during the second megaspore and first microspore divisions. However, it is not known whether the r-X1 deficiency also induces nondisjunction of the maize B chromosome during these cell divisions. To answer this question, chromosome numbers were determined in the progeny of r-X1/R-r female parents carrying two B chromosomes. Some of the r-X1-lacking progeny (21.2%) contained zero or two B chromosomes. However, a much higher percentage of the r-X1-containing progeny (43.4%) exhibited zero or two B chromosomes, but none displayed more than two B chromosomes. Thus, the results indicated that the r-X1 deficiency could also induce nondisjunction of the B chromosome during the second megaspore division; moreover, the B chromosome in itself could undergo nondisjunction during the same division. In addition, pollen grains from plants with two B chromosomes lacking or exhibiting the r-X1 deficiency were compared via pollen fluorescence in situ hybridization (FISH) using a B chromosome-specific probe. The results revealed that the r-X1 deficiency could induce the occurrence of B chromosome nondisjunction during the first microspore division and that the B chromosome in itself could undergo nondisjunction during the same division at a lower frequency. Our data shed more light on the behavior of the maize B chromosome during cell division.