Immunolocalization of dually phosphorylated MAPKs in dividing root meristem cells of Vicia faba, Pisum sativum, Lupinus luteus and Lycopersicon esculentum

Key message In plants, phosphorylated MAPKs display constitutive nuclear localization; however, not all studied plant species show co-localization of activated MAPKs to mitotic microtubules. Abstract The mitogen-activated protein kinase (MAPK) signaling pathway is involved not only in the cellular response to biotic and abiotic stress but also in the regulation of cell cycle and plant development. The role of MAPKs in the formation of a mitotic spindle has been widely studied and the MAPK signaling pathway was found to be indispensable for the unperturbed course of cell division. Here we show cellular localization of activated MAPKs (dually phosphorylated at their TXY motifs) in both interphase and mitotic root meristem cells of Lupinus luteus, Pisum sativum, Vicia faba (Fabaceae) and Lycopersicon esculentum (Solanaceae). Nuclear localization of activated MAPKs has been found in all species. Colocalization of these kinases to mitotic microtubules was most evident in L. esculentum, while only about 50 % of mitotic cells in the root meristems of P. sativum and V. faba displayed activated MAPKs localized to microtubules during mitosis. Unexpectedly, no evident immunofluorescence signals at spindle microtubules and phragmoplast were noted in L. luteus. Considering immunocytochemical analyses and studies on the impact of FR180204 (an inhibitor of animal ERK1/2) on mitotic cells, we hypothesize that MAPKs may not play prominent role in the regulation of microtubule dynamics in all plant species

Inter- and intrachromosomal asynchrony of cell division cycle events in root meristem cells of Allium cepa: possible connection with gradient of cyclin B-like proteins

Alternate treatments of Allium cepa root meristems with hydroxyurea (HU) and caffeine give rise to extremely large and highly elongated cells with atypical images of mitotic divisions, including internuclear asynchrony and an unknown type of interchromosomal asynchrony observed during metaphase-to-anaphase transition. Another type of asynchrony that cannot depend solely on the increased length of cells was observed following long-term incubation of roots with HU. This kind of treatment revealed both cell nuclei entering premature mitosis and, for the first time, an uncommon form of mitotic abnormality manifested in a gradual condensation of chromatin (spanning from interphase to prometaphase). Immunocytochemical study of polykaryotic cells using anti-β tubulin antibodies revealed severe perturbations in the microtubular organization of preprophase bands. Quantitative immunofluorescence measurements of the control cells indicate that the level of cyclin B-like proteins reaches the maximum at the G2 to metaphase transition and then becomes reduced during later stages of mitosis. After long-term incubation with low doses of HU, the amount of cyclin B-like proteins considerably increases, and a significant number of elongated cells show gradients of these proteins spread along successive regions of the perinuclear cytoplasm. It is suggested that there may be a direct link between the effects of HU-mediated deceleration of S- and G2-phases and an enhanced concentration of cyclin B-like proteins. In consequence, the activation of cyclin B-CDK complexes gives rise to an abnormal pattern of premature mitotic chromosome condensation with biphasic nuclear structures having one part of chromatin decondensed, and the other part condensed

New species of Langona Simon, 1901 and Neaetha Simon, 1884 (Araneae Salticidae) from Thailand

Żabka, Marek, Patoleta, Barbara M. (2020): New species of Langona Simon, 1901 and Neaetha Simon, 1884 (Araneae Salticidae) from Thailand. Zootaxa 4899 (1): 374-383, DOI: https://doi.org/10.11646/zootaxa.4899.1.1

New species of Helpis Simon, 1901 from Australia (Araneae: Salticidae), with a new definition of the genus

Żabka, Marek, Patoleta, Barbara M. (2014): New species of Helpis Simon, 1901 from Australia (Araneae: Salticidae), with a new definition of the genus. Zootaxa 3873 (5): 571-589, DOI: http://dx.doi.org/10.11646/zootaxa.3873.5.

New species of Taual a Wanless, 1988 from Australia (Araneae: Salticidae: Astioida: Astiae), with a redefinition of the genus

Żabka, Marek, Patoleta, Barbara M. (2015): New species of Taual a Wanless, 1988 from Australia (Araneae: Salticidae: Astioida: Astiae), with a redefinition of the genus. Zootaxa 4000 (5): 501-517, DOI: http://dx.doi.org/10.11646/zootaxa.4000.5.

New record of Gelotia Thorell, 1890 and a new species of Parahelpis Gardzińska & Żabka, 2010 (Araneae: Salticidae) from Australia

Patoleta, Barbara M., Żabka, Marek (2020): New record of Gelotia Thorell, 1890 and a new species of Parahelpis Gardzińska & Żabka, 2010 (Araneae: Salticidae) from Australia. Zootaxa 4899 (1): 280-286, DOI: https://doi.org/10.11646/zootaxa.4899.1.1

On equivalence of semigroup identities

For a given relation $\rho$ on a free semigroup ${\mathcal F}$ we describe the smallest cancellative fully invariant congruence ${\rho}^{\sharp}$ containing $\rho$. Two semigroup identities are s-equivalent if each of them is a consequence of the other on cancellative semigroups. If two semigroup identities are equivalent on groups, it is not known if they are s-equivalent. We give a positive answer to this question for all binary semigroup identities of the degree less or equal to 5. A poset of corresponding varieties of groups is given