A considerable proportion of cytosine residues in plants are methylated at carbon 5. According to a well‐accepted rule, cytosine methylation is confined to symmetrical sequences such as CpG and CpNpG, which provide the signal for faithful transmission of symmetrical methylation patterns by maintenance methylase. Using a genomic sequencing technique, we have analysed cytosine methylation patterns within a hypermethylated and a hypomethylated state of a transgene in Petunia hybrida. Examination of a part of the transgene promoter revealed that in both states m5C residues located within non‐symmetrical sequences could be detected. Non‐symmetrical C residues in the two states were methylated at frequencies of 5.9 and 31.9%, respectively. Methylation appeared to be distributed heterogeneously, but some DNA regions were more intensively methylated than others. Our results show that at least in a transgene, a heterogeneous methylation pattern, which does not depend on symmetry of target sequences, can be established and conserved.

The chromatin structures of two epigenetic alleles of a transgene were investigated by measuring the local accessibility of transgene chromatin to endonucleases. The two epialleles represented the active, hypomethylated state of a transgene in line 17-I of Petunia hybrida, and a transcriptionally inactive, hypermethylated derivative of the same transgene in line 17-IV. In nuclear preparations the inactive epiallele was significantly less sensitive to DNasel digestion and nuclease S7 digestion than the transcriptionally active epiallele, whereas no significant differences in accessibility were observed between naked DNA samples of the two epialleles. Our data suggest that a condensed chromatin structure is specifically imposed on transcribed regions of the construct in line 17-IV. In contrast, in both epialleles the plasmid region of the transgene, which is not transcriptionally active in plants, retains the same accessibility to endonucleases as the chromosomal integration site. These data suggest that transcriptional inactivation is linked to the process of transcription, and imply that control of transgene expression via the use of inducible or tissue-specific promoters might prevent transgene silencing and conserve the active state of transgenes during sexual propagation.

A long-chain polyhydroxy polyene amide, zooxanthellamide D (ZAD-D, 1, C54H83NO19), was isolated from a cultured marine dinoflagellate of the genus Symbiodinium. ZAD-D (1) is a polyhydroxy amide consisting of a C22-acid part and a C32-amine part and furnishes three tetrahydropyran rings and six isolated butadiene chromophores. The relative stereochemistry of the tetrahydropyran ring systems was elucidated by NMR techniques. This metabolite showed moderate cytotoxicity against two human tumor cell lines. A phylogenetic tree of Symbiodinium has been updated and compared with the structures of the hitherto isolated polyols of Symbiodinium, zooxanthellatoxins and zooxanthellamides, providing a promising chemotaxonomic perspective for the classification of this morphologically indistinguishable dinoflagellate.