In situ experiments on the effect of low pH on the ultrastructure of the seagrasses Cymodocea nodosa and Posidonia oceanica

The present study investigates the impacts of low pH on the cell structure of the seagrasses Posidonia oceanica (L.) Delile and Cymodocea nodosa (Ucria) Ascherson. The study was conducted via in situ experiments performed at the Castello Aragonese of Ischia (Naples, Italy), where shallow submarine vents lower the pH and can be used as natural laboratories. Shoots of the seagrasses were transferred from the control area (pH 8.1) to the two venting areas (pH 7.8 and 6.8) at different times. Epidermal cells of young leaves were examined using transmission electron microscopy (TEM) and tubulin immunofluorescence. After one week at pH 7.8, the cell structure of Posidonia oceanica was normal, while in Cymodocea nodosa, microtubule (MT) network and cell structure were affected. In addition, in C. nodosa, ultrastructural analysis revealed a gradual degradation of the nuclei, a disorganization of the chloroplasts, and an increase in the number of mitochondria and dictyosomes. The exposure of both plants for 3 weeks at pH 6.8 resulted in the aggregation and finally in the dilation of the endoplasmic reticulum (ER) membranes. Tubulin immunofluorescence revealed that after three weeks, the MT cytoskeleton of both plants was severely affected. All these alterations can be considered as indications of an apoptotic-like programmed cell death (AL-PCD), which may be executed in order to regulate stress response. © 202

A contribution to the phylogeny of Albanian Agathylla (Gastropoda, Clausiliidae): Insights using morphological data and three mitochondrial markers

In the present study, we revised Albanian Agathylla, combining the traditional shell morphological approach with a phylogenetic reconstruction based on three mitochondrial DNA markers (COI, COII and 16S rRNA). From the faunistic perspective, Albania was an almost completely unexplored country until the end of the 1990s. Following recent intense field sampling activity in Albania, the number of known Agathylla populations has increased, providing an opportunity to investigate how additional material can contribute to the resolution of the taxonomy of the Albanian Agathylla species. Newly discovered populations indicate greater morphological variability than previously recorded and highlight the presence of various other character state combinations. Based on these findings, we argue that only two Agathylla taxa occur in the region, namely A. neutra and A. biloba. Due to apparent morphological differences, they are still treated as distinct species, but high intraspecific morphological variability makes it unjustifiable to delimit subspecies. The molecular phylogeny indicates a close relationship between A. neutra and A. biloba, but could neither confirm nor refute their reciprocal monophyly, so their possible conspecificity requires further evaluation. © 2013 © The Author 2013. Published by Oxford University Press on behalf of The Malacological Society of London, all rights reserved

Responses of the Mediterranean seagrass Cymodocea nodosa to combined temperature and salinity stress at the ionomic, transcriptomic, ultrastructural and photosynthetic levels

The Little Neptune grass Cymodocea nodosa is a key seagrass species in the Mediterranean Sea, forming extensive and patchy meadows in shallow coastal and transitional ecosystems. In such habitats, high temperatures and salinities, separately and in combination, can be significant stressors in the context of climate change, particularly during heatwave events, and seawater desalination plant effluents. Despite well-documented negative, macroscopic effects, the underlying cellular and molecular processes of the combined effects of increasing temperature and salinities have remained largely elusive in C. nodosa – which are addressed by the present study. High salinity and high temperature, alone and in combination, affected ion equilibrium in the plant cells. Non-synonymous mutations marked the transcriptomic response to salinity and temperature stress at loci related to osmotic stress. Cell structure, especially the nucleus, chloroplasts, mitochondria and organization of the MT cytoskeleton, was also altered. Both temperature and salinity stress negatively affected photosynthetic activity as evidenced by ΔF/Fm’, following an antagonistic interaction type. Overall, this study showed that all biological levels investigated were strongly affected by temperature and salinity stress, however, with the latter having more severe effects. The results have implications for the operation of desalination plants and for assessing the impacts of marine heat waves. © 202

High temperatures alter cross-over distribution and induce male meiotic restitution in Arabidopsis thaliana

de Storme and Geelen show that heat stress has pleiotropic effects on male meiosis in Arabidopsis, causing deviations in cross-over formations, reproduction, and fertility. They show that heat also affects cell wall formation, providing mechanistic insights into karyotype change under high temperatures. Plant fertility is highly sensitive to elevated temperature. Here, we report that hot spells induce the formation of dyads and triads by disrupting the biogenesis or stability of the radial microtubule arrays (RMAs) at telophase II. Heat-induced meiotic restitution in Arabidopsis is predominantly SDR-type (Second Division Restitution) indicating specific interference with RMAs formed between separated sister chromatids. In addition, elevated temperatures caused distinct deviations in cross-over formation in male meiosis. Synapsis at pachytene was impaired and the obligate cross-over per chromosome was discarded, resulting in partial univalency in meiosis I (MI). At diakinesis, interconnections between non-homologous chromosomes tied separate bivalents together, suggesting heat induces ectopic events of non-homologous recombination. Summarized, heat interferes with male meiotic cross-over designation and cell wall formation, providing a mechanistic basis for plant karyotype change and genome evolution under high temperature conditions