Karyology of Some Coastal and Water Plants from Far East (Russia)

Cytogenetic studies on four species of vascular coastal and water plants from Russian Far East are presented. During the present investigation the next chromosome numbers have been revealed: Gypsophila pacifica (2 n = 34), Allium sacculiferum (2 n = 32), Mertensia maritima (2 n = 24), and Nelumbo komarovii (2 n = 16). Unusual chromosome numbers for these species have not been noted but it was the first case of karyological studies of Nelumbo komarovii from the Jewish Autonomous Region and most northern habitat. The number of nucleoli in interphase nuclei of these species was counted. Interphase nuclei of studied species contain 1–4 nucleoli except in A. sacculiferum so far which have 1–2 nucleoli per cell. Different points of view on polyploidy of studied species are discussed.

Circumscription of three annual species of Paspalum Plicatula Group (Poaceae: Paspaleae) in the light of morphological and chromosomic data

Paspalum comprises 350 species worldwide and is the largest genus of Poaceae in Brazil (211 species). The reticulated evolutionary pattern within the informal Paspalum Plicatula Group makes it a challenging species complex to treat taxonomically. The present work aims to study the three annual species P. cordaense, P. macranthecium and P. plowmanii, characterized by spikelet morphology and anthecium appearance, supported by a comprehensive review of herbaria and fieldwork collections of all related species. When ascertaining the identity of P. cordaense, we realized that it is distinct from P. plowmanii, while these two species are closely related to P. macranthecium. These findings are supported by morphological differences and by the first report of unusual chromosome number for P. plowmanii 2n = 38, whereas the numbers in P. cordaense are 2n = 40 and in P. macranthecium 2n = 20, from previously published research. We clarify the circumscription of the three species and provide a key, descriptions, comments, illustrations, distribution maps and conservation status for all species. The lectotypification of P. cordaense is also proposed.

Meiosis I chromosome segregation is established through regulation of microtubule–kinetochore interactions

During meiosis, a single round of DNA replication is followed by two consecutive rounds of nuclear divisions called meiosis I and meiosis II. In meiosis I, homologous chromosomes segregate, while sister chromatids remain together. Determining how this unusual chromosome segregation behavior is established is central to understanding germ cell development. Here we show that preventing microtubule–kinetochore interactions during premeiotic S phase and prophase I is essential for establishing the meiosis I chromosome segregation pattern. Premature interactions of kinetochores with microtubules transform meiosis I into a mitosis-like division by disrupting two key meiosis I events: coorientation of sister kinetochores and protection of centromeric cohesin removal from chromosomes. Furthermore we find that restricting outer kinetochore assembly contributes to preventing premature engagement of microtubules with kinetochores. We propose that inhibition of microtubule–kinetochore interactions during premeiotic S phase and prophase I is central to establishing the unique meiosis I chromosome segregation pattern.