A. Yu. Stepanova

Late Pleistocene-Holocene and Recent Ostracoda of the Laptev Sea and their importance for paleoenvironmental reconstructions

This work is the first detailed description of the Late Pleistocene-Holocene and Recent Ostracoda of the Laptev Sea. A total of 45 species in 22 genera and 13 families have been identified. All these species are described monographically. Three different ecological assemblages of ostracodes corresponding to different combinations of environmental parameters have been established; they are restricted to three regions of the sea: western-central, eastern, and southern. The recent ostracode assemblages of the Laptev Sea have been compared with those from other Arctic areas and are most similar to those of the Beaufort and Kara seas. Data on recent Ostracoda are used for paleoenvironmental reconstructions on the eastern shelf and western continental slope of the Laptev Sea. For this purpose, ostracodes from five sections obtained from these parts of the sea have been examined. The oldest sediments, which are of Late Pleistocene age (15.8 cal. ka BP), have been recovered in a core from the western continental slope. These yielded five ostracode assemblages, which correspond to different paleoenvironments and replaced each other in the course of the rapid postglacial sea-level rise, thus showing variations in the Atlantic water inflow from the west and freshwater discharge from the subaerially exposed shelf. On the outer shelf of the eastern part of the sea, the rapid sea-level rise in the Early Holocene (lowermost dating 11.3 cal. ka BP) led to a rapid transition from assemblages of brackish-water near-shore environments to those of modernlike normal marine environments; modern environments were established about 8.2 cal. ka ago. Since the core sections from the inner shelf correspond to the time when the level of the sea had already reached its modern values, the changes in the taxonomic composition of ostracode assemblages primarily mirror variations in river runoff.

Arctic quaternary ostracods and their use in paleoreconstructions

The paper deals with original and published data on fossil ostracodal assemblages from the Eurasian Arctic Kara, Laptev and Chuckchi seas. As a whole, six ecologically different assemblages were distinguished (freshwater, brackish water, marine of the inner, middle and outer shelves and upper continental slope), they replace each other upcore reflecting a gradual increase in water depth and distance from the coast. These assemblages are stable in the entire Arctic region and can be used for interpretation of environments in different Arctic areas.

Effect of the ipt gene expression on wheat tolerance to root flooding

The effect of enhanced cytokinin synthesis due to expression of the ipt gene from Agrobacterium tumefaciens on plant tolerance to root flooding was studied. Transgenic wheat (Triticum aestivum L.) plants carrying the ipt gene were more tolerant to flooding than wild-type plants. The effect of transformation was manifested in the higher yield and less growth inhibition during flooding. The measurements of activities of antioxidant enzymes, superoxide dismutase and catalase, as well as MDA content during flooding revealed differences between wild-type and transgenic plants that correlated with their tolerance. These results point to the protective role of cytokinins during wheat root flooding.

The Response of Sugarcane (Saccharum officinarum) Cultured Cells to Anoxia and the Selection of a Tolerant Cell Line

The effect of anoxia on the sugarcane (Saccharum officinarum L.) cultured cells was studied in order to elaborate a technique for in vitro selection of cell lines, which would be tolerant to anaerobic stress. Inhibitory and lethal doses of anaerobic incubation were established from the state of the mitochondrial ultrastructure during the anaerobic incubation of cells either with or without exogenous glucose, as well as from the pattern of the post-anaerobic callus growth. An intact state of the mitochondrial ultrastructure and the viability of some cells in the presence of 3% glucose were shown to be maintained for at least 14 days of anaerobic incubation, while the index of post-anaerobic growth decreased by almost 50% even after 72-hour-long anaerobiosis. In the absence of exogenous glucose, a marked destruction of mitochondria and a twofold decrease in the callus growth index were observed as early as after six-hour-long anaerobic stress. A 48-hour-long incubation under these conditions resulted in the maintenance of the intact ultrastructure only in 7–10% of cells, while a 96-hour-long anaerobiosis brought about the complete degradation of the subcellular structure and cell death. A 48-hour-long anaerobiosis without exogenous glucose was chosen for selecting the anoxia-tolerant cell lines. After three cycles of selection, the anoxia tolerance of the selected cell line exceeded the respective index of the initial callus several-fold. In selected line, about 50% of cells retained viability and could resume growth even after 96-hour-long anaerobic incubation. The experimental results obtained were used to determine the possible causes of the heterogeneity of callus cells as regards their anoxia resistance.

Environmental evolution of the southern Chukchi Sea in the Holocene

The molluscan shells from three drill and two piston cores obtained in the southern Russian sector of the Chukchi Sea are dated by the AMS 14C measurement method back to 0.8–3.5 and 9.2–10.5 ka. The period of 9–10 ka was marked by increased sedimentation rates related to the transgression onset. The fossils in the lower Holocene section exhibit the successive upward replacement of brackish-water organisms by their marine counterparts. After the opening of the Bering Strait in the middle Holocene, the sedimentation was under influence of the increased bioproductivity of the waters. The climatic optimum in the Chukotka region corresponds to the early Holocene, while the late Holocene was characterized by the wider development of the ice cover on the shelf.

Late pleistocene-holocene ostracod assemblages of the Northern Caspian Sea shelf

Analysis of the ostracod assemblages and the distribution of benthic foraminifera Ammonia beccarii in the core section GS 194-08-1 recovered at a depth of 7.5 m near the Volga delta front showed changes in environmental conditions in response to sea-level fluctuations. The pre-Novocaspian ostracod assemblage reflects the conditions that were dominant during the Late Khvalynian transgression, with a depth of about 20–30 m, and a salinity range of 12–13‰. The Early Novocaspian sediments contain an ostracod assemblage that represents a deeper water environment compared to the present, with an inferred depth of 12–16 m. The faunas from the younger Novocaspian sediments with abundant monospecific populations of Cyprideis torosa and co-occurring benthic foraminifera Ammonia beccarii represent modern-like environmental conditions.

Mitochondria-targeted antioxidant provides for enhanced morphogenetic potential in plant tissue cultures

An ability to regenerate plants from tissue cultures is important for biotechnology; however, many species and cultivars a have low morphogenetic potential. Since oxidative stress is one of the factors affecting morphogenesis, we assessed an ability of a membrane-penetrating mitochondria-targeted antioxidant SkQ1 to improve plant regeneration from cultured tissues of Zea mays L., Triticum aestivum L., Saccharum officinarum L., Medicago falcate L., and M. glutinosa M.Bieb. SkQ1 at nanomolar concentrations was found to stimulate both the set of morphogenenic structures and their subsequent development with the formation of plantlets of all plant species tested. SkQ1 constituents, dodecylplastoquinone and dodecyltriphenylphosphonium, could also exert stimulatory effects on plant regeneration from morphogenic callus, although these effects were less prominent than that of SkQ1. SkQ1-mediated stimulation was most pronounced (up to sevenfold) for cultured tissues with a low morphogenetic potential. The observed properties of SkQ1 suggest its possible application in promoting morphogenesis in a wide range of genotypes.

Obtaining transgenic alfalfa plants for improved phytoremediation of petroleum-contaminated soils

The possibility of using transgenic plants and their complexes with microorganisms to clean up soil from pollution is a topical research area. In our work the transgenic alfalfa plants with the rhlA gene, responsible for the biosynthesis of biosurfactant–rhamnolipids, were obtained. Rhamnolipids help reduce the surface tension of the hydrocarbon oil and its desorption from soil particles, thereby facilitating its recycling by microorganism. Cultivation of the control and the transgenic alfalfa plants in soil polluted with 4% oil showed the advantage of plants emitting rhamnolipids: oil utilization was 20% higher than with the control plants. When used together, the transgenic plants and Candida maltosa microorganism increased the degree of degradation of the oil to 86%. The results suggest bright prospects for the application of transgenic plants and the complex of transgenic plants and microorganisms to increase the efficiency of bioremediation.

Physiological role of nitrate under anaerobic stress in Saccharum officinarum callus cells tolerant and sensitive to anoxia

The physiological role of nitrate as a protective factor against anaerobic stress was studied in experiments with tolerant to anoxia sugarcane (Saccharum officibarum L.) callus lines obtained by in vitro selection in the absence of exogenous carbohydrates. Original cell lines, which were not subjected to selection and therefore more sensitive to oxygen shortage, served as a control. In these lines, anaerobic stress was created in the presence or absence of nitrate in nutrient medium. The presence of nitrate in nutrient medium increased markedly tolerance to anaerobic stress of both lines differing in their sensitivity to anaerobiosis. However, the degree of tolerance differed substantially in compared lines. In the presence of exogenous nitrate, in tolerant cells there were no signs of mitochondrial membrane destruction or degradation even after 72 h of anoxia, whereas in control cells 48-h anaerobic incubation led to the complete degradation of mitochondrial membranes and membranes of other organelles. It is concluded that significant increase in the tolerance of S. officinarum cells in the process of in vitro selection most likely occurred due to induction and stimulation of not only the processes of glycolysis and fermentation, but also nitrate and maybe nitrite utilization.

Effect of NtDCN1 gene activated during embyogenesis on organogenesis in tobacco tissue culture

The role of NtDCN1 gene in organogenesis in the culture of tobacco (Nicotiana tabacum L.) somatic tissues was studied. This gene is specifically expressed in tobacco microspores induced for somatic embryogenesis. This gene knockout resulted in a disturbance of formation and development of embyoids from microspores. In leaf disks and calli derived from tobacco lines with active and inactivated NtDCN1 gene, we studied induction of shoots and roots. A comparative analysis of tobacco line morphogenetic responses in vitro showed that NtDCN1 gene inactivation enhanced shoot formation and suppressed rhizogenesis, whereas this gene reactivation returned organogenesis processes to control level. Difference between lines was manifested only at a definite ratio between exogenous hormones supplied. The involvement of NtDCN1 gene in line responses to exogenous auxin is discussed. The results obtained permit a supposition that the NtDCN1 gene is critical for regulation not only somatic embryogenesis but also organogenesis.