The male sterile mutant, ms35, of Arabidopsis thaliana was produced by X-irradiation of seeds. The mutant produces fertile pollen, but is male sterile because the anthers do not dehisce. Anther development in ms35 plants occurs as in wild-type Arabidopsis until shortly after microspores are released from meiotic tetrads. Thereafter, in the wild type, bands of lignified, cellulosic secondary wall thickenings are laid down around the cells of the anther endothecium. In contrast, wall thickenings are not formed in the endothecium of the ms35 mutant. Development of other lignified tissues, for example the vascular tissue of the stamen, occurs normally in ms35 plants. In mutant anthers, as pollen maturation is completed, the stomium is cleaved but the anther wall does not retract to release pollen. The block in anther dehiscence in ms35 plants is specifically correlated with the absence of endothecial wall thickenings. The ms35 mutation represents the first genetic evidence in support of the proposed role of the endothecium in anther dehiscence. The ms35 gene was mapped to the top arm of chromosome 3 (hy2-(4.17p 2.31 cM)-ms35-(32.14p5.45 cM)-gl1).

Cistus (Cistaceae) comprises a number of white- and purple-flowering shrub species widely distributed in the Mediterranean basin. Within genus Cistus, many taxa are subject to various taxonomic uncertainties. Cistus creticus, a prominent member of the purple-flowered clade, is a prime case of the current taxonomic troubles. Floras and databases approve different species names and utilise different or additional/fewer synonyms. Various intraspecific classification systems based on subspecies or varieties are in use. The inconsistent determination of plant material makes it difficult to compare literature regarding the phytochemical diversity and biological activities of plant material and impedes a systematic utilization of the manifold medicinal properties of C. creticus. In the present investigation, we used DNA sequence data from one nuclear region (ITS) and two chloroplast regions (trnL-trnF, rpl32-trnL) to test the intraspecific genetic diversity of C. creticus and its evolutionary relationships to the closely related C. albidus. The combined DNA data confirmed C. creticus as a rather heterogeneous species that integrates two major evolutionary lineages with clearly different genetic characteristics. The ‘Eastern Mediterranean clade’ seems to represent old and ancestral characteristics. This lineage exhibits a close relationship to the geographically distant C. albidus, expressed by very closely related ribotypes and an interspecifically shared chlorotype. The ‘Western Mediterranean clade’ is characterized by a distinctive ITS polymorphism (co-occurring paralogous ribotypes) and more distantly related chlorotypes. The formation of the genetically complex ‘Western Mediterranean clade’ seems to have involved hybridization and recurrent formation or migration movements.

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