Vol 64, No 3 (2017)

Cytokinins (CKs) have a strong influence on plastid development. We used the Arabidopsis thaliana (L.) Heynh. loss-of function insertion mutants ahk2, ahk3 and ahk4 alone or in different combinations to examine the effect of individual membrane cytokinin (CK) receptors on the expression of plastid genes and nuclear genes for the plastid transcription machinery. Quantitative real-time PCR-analyses demonstrate that the CK membrane receptors have overlapping functions in regulating the levels of plastid house-keeping genes in 7-day-old seedlings, relative to the nuclear UBQ10 gene. In contrast, photosynthesis genes responded differently to AHK3 and AHK2 receptor inactivation and the results show a dominant role of the AHK2/AHK3 receptor combination in the CK responses. These differences could be, at least in part, mediated through the regulation by the nuclear-encoded RPOTp and RPOTmp genes for plastid phage-type RNA polymerases. CK positively regulated the transcript abundance of the nuclear encoded SIG2 and SIG6, and negatively that of SIG4 and SIG5 for sigma factors of the plastid transcription apparatus. We propose that these two sigma factors may affect the CK-controlled plastid gene expression.

Photosynthetic bacteria contain one or two homologues of the signal peptide peptidase A Escherichia coli, designated SppA1 and SppA2. SppA2 protein is unique for prokaryotic cells and in cyanobacterium Synechocystis sp. PCC6803 (Synechocystis) is encoded by the gene slr0021. We have established that in cyanobacteria the transcriptional and post-translational levels of SppA2 protein regulated in opposite directions depending on the light intensity. Expression analysis of slr0021 shows a pattern namely a light-induced increase of mRNA levels. Opposite to that the protein levels decrease with increase of light intensity. Later we have found that the post-translational level of SppA2 is regulated by SppA1 or a SppA1-controlled protease. Regulation of SppA2 levels appears to be light specific and is not affected by temperature stress or nitrogen starvation.

The majority of plant species lose their ability to tolerate severe water deficit after germination at the beginning of seedling growth, in the time of emergence of the radical from the seed. The experiment was designed to compare the differences in proteolytic response between 4-and 6-days old spring wheat (Triticum aestivum L.) seedlings of Eta cultivar, respectively tolerant and sensitive to severe drought inducing up to 90% water saturation deficit (WSD). In coleoptiles the changes of proteolytic activity had the same trend regardless on the seedlings age and increased about fourfold upon 85% WSD as compared to the control, from about 4 to 19 (U/mg protein h). The dehydration of roots of 4 day old seedlings resulted in sharp, fivefold activity increase at 85% WSD (from 11 to >50 U/mg protein h). In roots of 6 days old seedlings dehydrated to 55% WSD the proteolytic activity raised twofold and was about 2.5 times higher than in roots of 4 days old seedlings dehydrated to the same WSD. In coleoptiles of both the 4- and 6-days old seedlings subjected to drought appearance of new bands of serine proteinases was observed. Presented results indicate that roots are more sensitive to drought than coleoptiles, which brings an argument for breeders showing that programs involving roots phenotyping have a full biochemical rationale.

Medicinal halophyte Limonium bicolor (Bag.) Kuntze was treated with 200 mM NaCl, the physiological parameters including fresh weight, dry weight, salt gland number, MDA levels and root activity were investigated, comparative proteomic analyses of leaf and root were carried out using 2D-PAGE combined with MALDI-TOF/TOF-MS. The results showed that L. bicolor performed a positive effect on its growth under NaCl stress since increase in different extent of fr wt, dry wt, salt gland number, MDA level and SOD activity of leaves and roots, as well as root activity. More than 460 protein spots in leaves and 600 protein spots in roots were visualized and matched in 2D gels, the results of proteomic analyses showed that 45 proteins were identified in leaves and 49 proteins in roots to be differentially expressed. Based on their functions, these proteins were grouped into categories covering a wide range of molecular processes, including carbohydrate, energy, lipid, nucleotide and amino acid metabolism, glycan biosynthesis and metabolism, metabolism of cofactors and vitamins, biosynthesis of secondary metabolites, redox homeostasis, transcription, cytoskeleton and transport, as well as folding, sorting and degradation. The upregulating and downregulating of differentially- expressed proteins with different physiological function were also reflected in the physiological parameters. These results are helpful for further research work on salt response mechanisms and medicinal utilization of L. bicolor.

This study was performed to understand the mechanisms for Se-enhanced resistance of parsley (Petroselinum crispum L.) plants to salinity stress. Plant growth was negatively affected by salt stress; however, Se treatments at 1 mg/L significantly improved the growth rate and enhanced the salt tolerance of seedlings. This increased tolerance in Se-supplied plants was obtained by reduced damaging effect on maximal quantum yield of photosystem II (PSII) (F_v/F_m) coupled with higher levels of carotenoids and non-photochemical quenching (NPQ). The performance index (PI_ABS), as evidence for modulation of PSII function, was downregulated by salt stress; while Se mitigated this effect. Moreover, analysis of OJIP transients demon-strated that Se reduced salt damaging effect on PSII function through improvement of excitation energy trapping (TR₀/CS) and electron transport (ET₀/CS) per excited cross-section of leaf. The Na concentrations in shoots and roots of parsley seedlings considerably enhanced after NaCl treatment. Interestingly, treatment of salt-stressed plants with Se decreased the Na contents in shoots via the limitation of the root-to-shoot translocation of Na and exclusion of Na from cell sap, as well as the retention of K/Na and Ca/Na ratios. These data provide the first evidence that the Se application alleviates salinity stress by enhancing PSII function and by decreasing Na content in the shoot via binding of Na to the root cell wall.

Three-amino-acid-loop-extension homeodomain proteins affect various aspects during root development, such as root skewing or lateral root initiation and growth. Crossed lines of the BP overexpressor in Arabidopsis thaliana (L.) Heynh. were used to elucidate the role of BREVIPEDICELLUS (BP) in root development. The potential heterodimerization partner of BP, BEL1-like homeodomain protein 6 (BLH6), could be an important modulator of BP function. BLH6 is a member of BEL-like family of homeodomain proteins consisting of all conserved domains and motifs. We identified a new BLH-specific TERM motif at the C terminus of BLH proteins. BLH6 was expressed in different root tissues, including the meristematic zone and bases of lateral roots, and overlap the BP expression zone, enabling coordinated function of these transcription factors. To elucidate potential interactions of BP and BLH6, crossed lines of BP overexpressor were analyzed. While other tested BLH mutations do not affect BP overexpression phenotype, knock-out mutation blh6-1 weakened 35S-BP influence on shoot and root development. We demonstrated that growth of lateral roots was modulated by BP overexpression and auxins, and that this effect was dependent on lateral root position along the primary root. In the upper part of the primary root, BP inhibited lateral root growth despite indol-3-acetic acid treatment and this effect correlated with predicted activity of BLH6 in crossed lines of 35S-BP and blh6 mutants.

Mesophyll structure and content of photosynthetic pigments in the leaves of three species of steppe plants, Centaurea scabiosa L., Euphorbia virgata Waldst. et Kit., Helichrysum arenarium (L.) Moench, were investigated in four geographical sites of the Volga region and the Urals located in the forest-steppe and steppe zones. Variations of the studied parameters between geographical points depended both on the species and on the structural organization of the leaf. The highest level of variation was observed for leaf area and pigment content per unit leaf area, the size and the number of chloroplasts in the cell changed to a lesser extent. The leaf thickness, leaf area and mesophyll cell sizes mostly depended on the plant species. C. scabiosa had large leaves (40–50 cm²) with large thickness (280–290 μm) and large mesophyll cells (up to 15000 μm³). The leaves of H. arenarium and E. virgata were ten times smaller and characterized by 1.5 times smaller thickness and 2−3 times smaller cell size. Geographical location and climate of the region affected leaf density, proportion of partial tissue volume, and the ratio of the photosynthetic pigments. In the southern point of Volga region with the highest climate aridity, all studied species were characterized by maximum values of volumetric leaf density (LD), due to the high proportion of sclerenchyma and vascular bundles, and specificity of the mesophyll structure. With the decline in latitude, chlorophyll (Chl) and carotenoid (Car) contents in leaf area were reduced, the ratio Chl/Car was increased, and the ratio Chl a/b was declined. The reduction of the pigment content in the leaf in all species was associated with a reduction in the amount of Chl per chloroplast, and for C. scabiosa and H. arenarium it was associated also with the reduction of chloroplast amount in the leaf area. In turn, chloroplast number per leaf area and the total cell area (A_mes/A) depended on the ratio of the number and size of mesophyll cells inherent to this plant species. At the same time, we found a similar mechanism of spatial organization of leaf restructuring for all studied species—decrease in A_mes/A was accompanied by increasing in the proportion of intercellular air spaces in the leaf. It is concluded that variations in structural and functional parameters of the photosynthetic apparatus of steppe plants were associated with plant adaptation to climate features. General direction of the changes of leaf parameters of the studied species with aridity was the increase of LD and the decrease of pigment content per leaf area however the cellular mechanisms of changes in the pigment content and integral parameters of mesophyll were determined by the plant species properties.

Effect of weak horizontal alternating magnetic field (AMF) with a frequency of 50 Hz and intensity of 400 A/m on seed formation and morphophysiological characteristics was investigated in radish (Raphanus sativus L.) plants of major types of magnetic orientation (TMO): North–South (NS) and West–East (WE). AMF retarded the passage through all the stages of ontogenesis; as compared with control material, the next leaves emerged slower, and the transition to formation of flower-bearing stems, budding, flowering, and production of pods and mature seeds was delayed. In plants of NS TMO exposed to AMP, the number of pods and seeds and the weight of seeds decreased, while these characteristics rose in WE TMO. AMF acted as an environmental factor differentiating plants’ response depending on their type of magnetic orientation. Dissimilar response to the magnetic field is associated with their physiological status.

Changes in the content of acyl-lipid desaturases gene transcripts in Arabidopsis (Arabidopsis thaliana Heynh. (L.), ecotype Columbia) plants subjected to low temperature hardening for 5 days at 2°C were investigated. In the course of the experiments with hourly dynamics of plant chilling, it was established that the genes under study by their responses to cold action can be separated into two groups. The genes of the first group represented by ADS2, FAD2, and FAD7 are characterized by the amount of their transcripts that rapidly increase even for the first 2–4 h of cold exposition, while the same value for the genes FAD3, FAD6, and FAD8 belonging to the second group remained unchanged under the same conditions. The experiments with the above hardening dynamics provided evidence for consecutive character of genes ADS2, FAD2, and FAD7 transcript accumulation, where the process for ADS2 was sharply intensified even for the first days of hardening, while that for other two genes achieved maximal intensity only on the fourth day of hardening. These results, taken together, lead to the conclusion that the agreeing in time increase in the transcript content of genes ADS2, FAD2, and FAD7 encoding Δ9-, Δ12-, and ω3-desaturases resulted in the change of FAs composition of chloroplast lipids. Increasing portion in them of triene FAs during hardening time provided the maintenance of chloroplast membranes in a native state allowing the Arabidopsis plant to successfully adapt to hypothermia.

A new method for quantitative determination of water potential of mesophyll cells’ apoplast in substomatal cavity of the leaves of herbaceous (maize, millet, wheat, amaranth, and seepweed) and woody (larch, pine, and birch) plants by means of modern instruments designed to assess photosynthetic(СО₂/Н₂О) gas exchange is described. The method consists in determination in the light of such a level of humidity above the leaf surface, which would nullify transpiration without a noticeable suppression of photosynthetic assimilation of СО₂; this makes it possible to calculate the value of water potential at the interface between aqueous and gaseous phases of mesophyll cells’ apoplast in the substomatal cavity.