Ultrastructural Changes in Chloroplasts of Cucumis sativus L. and Secale cereale L. during Low-Temperature Hardening

Russian Journal of Plant Physiology - Chloroplast ultrastructural changes were investigated in chilling-sensitive (cucumber, Cucumis sativus L.) and cold-tolerant (winter rye, Secale cereale L.)...     

Study of the amount of oxidative damage to mitochondrial and chloroplast DNA in clones of white poplar (Populus alba L.) during long-term in vitro cultivation for 26 years

Plant Molecular Biology - Measurement of the amount of damage in non-nuclear DNA can be a convenient method for assessing the senescing of clones in vitro during long-term cultivation. In vitro...     

Evolutionary significance of a middle Cambrian (Series 3) in situ occurrence of the pedunculate rhynchonelliform brachiopod Nisusia sulcata

Exceptionally preserved, silicified and articulated complete shells of the rhynchonelliform kutorginate brachiopod Nisusia sulcata are redescribed from the middle Cambrian (Series 3) Marjum Limestone, Utah. Cylindroid sausage‐like protrusions, emerging posteriorly between the valves, were originally interpreted as faecal in origin, but restudy under the SEM shows that these features represent silicified pedicles as they are attached in situ to other Nisusia. The Nisusia host most likely was alive at the time of attachment. Restudy of the pedicles of Nisusia provides new phylogenetic information on the anatomy of the earliest rhynchonelliforms. The silicified pedicles differ considerably from the pedicles of living crown group rhynchonelliforms in being strongly annulated, distally tapering, and were likely to have been rather more flexible. The Nisusia pedicles are more similar to the exceptionally preserved pedicles from other Cambrian rhynchonelliform brachiopods, including Kutorgina, Longtancunella and Alisina, but these emerge from the ventral apical foramen rather than from between the valves as in Nisusia. Although generally similar, these two types of pedicles are unlikely to represent homologous structures as Nisusia is provided with both an apical foramen (possibly larval attachment) and a posterior adult pedicle. The similarities may be explained by similar type of accretionary growth from two different types of epithelia. The Nisusia‐like pedicle appeared early within the kutorginates and rhynchonellates. The discovery of hollow spines in Nisusia sulcata further supports the generic assignation of the species.     

Iridoid patterns of genus Plantago L. and their systematic significance

The distribution of 14 iridoid glucosides in 14 Plantago L. species (44 samples corresponding to 18 taxa) was shown. P. tenuiflora and P. gentianoides were studied for iridoids for the first time. The iridoid patterns showed a good correlation with morphological and other chemical features of the representatives of genus Plantago. The studied species are grouped together according to the iridoid patterns: species containing mainly aucubin (P. major, P. cornuti, P. gentianoides); species containing aucubin and aucubin derivatives (P. subulata, P. media); species containing aucubin and catalpol (P. lanceolata, P. altissima, P. argentea, P. lagopus, P. atrata); species containing aucubin and plantarenaloside (P. afra, P. scabra).     

Behavioural response and winter survival of mated and unmated diapausing females of the Tetranychus atlanticus-urticae complex (Acari, Tetranychidae)

Behavioural responses were studied in mated and unmated females of a Dutch strain of the spider mite Tetranychus urticae which were destined to enter diapause. Observations were confined to the period between acquirement of the winter coloration by the females (a few days after the last moult) and their entering of artificial hibernation sites offered to the mites on the host leaves. Unmated females were found to stay longer on the leaf surface than mated females; they entered the hibernation sites significantly later than mated females. The delay in the search for hibernation sites shown by unmated females may be seen as a behavioural adaptation to enhance the chance of being fertilized before hibernation. Winter survival of mated and unmated diapausing females of the same strain of mites was studied both in the laboratory at a constant temperature of 2±1°C and outdoors under natural climatic conditions in Amsterdam during the winter of 1990–1991. Survival was high under both conditions for mated as well as unmated females; no significant differences in survival were found between both types of female. Observations on post-diapause females of Tetranychus atlanticus (a mite belonging to the T. urticae complex) sampled from strawberry fields near Moscow in spring, showed that at most 10% of the females of this natural spider mite population were unmated. Both mated and unmated females had survived winter temperatures of -28 to -30°C.     

Structure-functional organization of the secretin molecule. II. Direct conformation problem

Spatial structure of peptide hormone secretin was investigated by the theoretical conformational method. A solution of the "direct conformational problem" for this hormone indicated that the possible structure of the secretin molecule under polar conditions may be described only by two families of low-energy conformations, possessing relatively conformational valid (Thr7-Leu22) and variable (His1-Phe6 and Leu23-Val27NH2) fragments. One of these families is comprised by five twists of the alpha-helix, while the second isoenergetic family possesses two short segments of the alpha-helix, divided by an irregular structure of the tetrapeptide.     

Stacking-interactions in the control-gear binding of kynurenic acid with NR2A- and GluR2-subunits of glutamate ionotropic receptors

Kynurenine products in tryptophan metabolism are of crucial importance in modulation of neurodegenerative processes in the CNS. Kynurenic acid (KYNA): the endogenous antagonist of ionotropic glutamate receptors, displays specific affinity towards glycine site ofNMDA-receptor NR1 subunit. Mechanisms for the selective interaction of KYNA and its derivatives with other glutamate receptor subtypes are studied insufficiently. Ab initio quantum chemical calculations for KYNA-imidazole dimer, as a model for ligand interaction with His88 fragment of NR2A-subunit, along with KYNA-phenol dimer, as a model for ligand interaction with Tyr61 fragment of GluR2-subunit, were carried out in order to investigate stacking-interaction role of KYNA binding by NR2A subunit of NMDA-receptor and GluR2 subunit of AMPA-receptor. Stacking-interaction energy of KYNA-H88 for the assumed ligand orientation in the binding site is 3.0-5.0 kcal/mol and 102. kcal/mol for the optimized dimer KYNA-imidazole geometry. Stacking-interaction energy of KYNA-Tyr61 for the assumed ligand orientation in the binding site is 6.7-8.5 kcal/mol. The obtained values are comparable with the energies of hydrogen bonds. Thus, stacking-interaction should be taken into account while studing ligand glutamate receptor binding mechanisms. Stacking-interaction is evidently important for the initial ligand orientation inside the receptor binding site after which the delicate tuning of hydrogen bonding pattern is realized. On the other hand, the specific affinity of KYNA derivatives to the receptor subunits could be explained by ligand-aromatic receptor aminoacid stacking-interaction geometry difference.     

Subcellular localization and properties of glyoxylate cycle enzymes in the liver of rats with alloxan diabetes.

Key enzymes of the glyoxylate cycle (isocitrate lyase and malate synthetase) were found in the liver and kidney of rats suffering from alloxan diabetes. The activities of these enzymes in the liver were 0.080 and 0.0430 U/mg protein, respectively. Isocitrate lyase activity in the kidney was 0.030 U/mg protein, and that of the malate synthetase was 0.018 U/mg protein. Peroxisomal localization of the enzymes was shown. A novel malate dehydrogenase isoform was found in a liver of rats suffering from the alloxan diabetes. The isocitrate lyase was isolated by selective (NH4)2SO4 precipitation and DEAE-Toyopearl chromatography. The resulting enzyme preparation had specific activity 6.1 U/mg protein, corresponding to 76.25-fold purification with 32.6% yield. The isocitrate lyase was found to follow the Michaelis--Menten kinetic scheme (Km for isocitrate, 0.08 mM) and to be competitively inhibited by glucose 1-phosphate (Ki = 1. 25 mM), succinate (Ki = 1.75 mM), and citrate (Ki = 1.0 mM); the pH optimum of the enzyme was 7.5 in Tris-HCl buffer.