Vol 66, No 4 (2019)

Modern ideas on the nature and functions of plastid retrograde signals, i.e., plastid retrograde signaling, predominantly of chloroplasts, are summarized. The main attention is focused on the participation of plastid retrograde signals in inter- and intracellular signaling pathways and their role in the processes of plant growth and development. The small amount of data on the little-studied retrograde signaling system of plant mitochondria are outlined as well.

In silico analysis of the promoter region of the At4g01870 gene of Arabidopsis thaliana (L.) Heynh. showed the presence of ABRE, W-box, RAV1-A, MYB, and LFY cis-elements in the sequence. These regulatory motifs bind the transcription factors involved in responses to abscisic acid (ABA) and stresses. Stable transgenic plants carrying the β-glucuronidase gene under the control of the 5'-deletion fragments of the At4g01870 promoter were obtained. According to the results of histochemical staining of transformants, gene expression was induced by abiotic stress and was most significant in the conductive tissues of the root, leaves, and sepals as well as in flowers. The study of At4g01870 gene expression by RT-PCR confirmed that the gene transcript content increased after the exposure of plants to a solution of NaCl or at 37°C and after ABA treatment; however, hypothermia almost unchanged the level of accumulation of the transcripts. Along with ABA, expression of the At4g01870 gene was induced by indolylacetic and salicylic acids and ethylene precursor 1-aminocyclopropane-1-carboxylic acid; it was hardly regulated by methyl jasmonate and inhibited by cytokinin. The TolB-like protein, encoded by the At4g01870 gene, functions as a type of platform, based on which protein complexes are assembled. Given the previously identified ABA-binding properties of the protein At4g01870 and the presence of the ABA-dependent cis-elements in the promoter of its coding gene, it can be assumed that the protein encoded by the At4g01870 gene allows to control the hormonal signals in the cell, providing a structural platform for the interaction of specific effector proteins, trans-factors and ion channels.

The effect of sodium hydrosulfide (NaHS) as a donor of hydrogen sulfide on the resistance to subzero temperatures was investigated in the seedlings of winter wheat (Triticum aestivum L.) and rye (Secale cereale L.). Treatment of nonhardened seedlings with NaHS at concentrations of 0.1 and 0.5 mM improved their survival after freezing at –5°С. Exposure to NaHS at the same concentrations also improved the survival of wheat and rye seedlings hardened at 2–4°С after their freezing at –9°С. Under the effect of the hydrogen sulfide donor, the seedlings of both species at normal temperature (20–22°С) and upon cold hardening accumulated more sugars and proline. After sodium hydrosulfide treatment, the content of anthocyanins rose only in wheat seedlings. The donor of hydrogen sulfide also induced a rise in the activity of catalase and guaiacol peroxidase in the seedlings of both species at normal and hardening temperatures, while the activity of superoxide dismutase remained essentially the same. Under the effect of NaHS, both species accumulated less malonic dialdehyde caused by cryogenic stress. The contribution of different components of stress-protective systems to chilling resistance induced by hydrogen sulfide and hardening is discussed in relation to plant species.

Water stress is the major environmental stress that affect agricultural production worldwide, especially in arid and semi-arid regions. This research investigated the effect of water stress on common reed (Phragmites australis (Cav.) Trin. ex Steud.) grown in the West Lake Wetland of Zhangye City, China. We designed with four water treatments (100, 95, 85 and 75% of water field capacity, i.e. CK (100%), mild (95%), moderate (85%) and severe (75%) water deficit regimes). The effect of water stress on photosynthesis and chlorophyll fluorescence parameters was investigated. There was a midday depression in net photosynthetic rate (P_n) for CK, mild and moderate drought, but not for severe drought. Stomatal limitation was dominant for mild treatment. But under severe drought stomatal limitation to photosynthesis was dominating in the morning and nonstomatal limitation was dominating in the afternoon. Compared with CK treatment, P_n, stomatal conductance (g_s), intercellular CO₂ concentration (C_i), transpiration rate (E) and water use efficiency (WUE) were always lower at drought stress. This result suggests that water stress caused the photosynthesis of common reed to be completely blocked and the common reed was a drought-sensitive plant. We found 75% is the moisture threshold for common reed. The decrease in F_m, F_v, F_v/F_m and increase F₀ suggested that Rubisco activity reduced and PSII partially inactivated during the day under drought. However, part of this inactivation of PSII might be alleviated under mild or moderate drought, but severe drought cannot. Drought stress also affected the photosynthesis P_n-PAR response curve. Drought stress increased LCP, R_D and decreased LSP, P_max and AQY. This indicates that when common reed suffers from drought, the utilization range of light intensity become narrowed and photosynthetic ability or adaptability to light reduced.

Salinity is one of the most important factors causing limiting growth aspects. Salinity tolerance is a multigenic trait activating mechanisms such as high H⁺ pumping activity, like NHX2 that is a tonoplast localized Na⁺/H⁺ exchanger and actively transfers the excess sodium ions from the cytoplasm into the vacuole. Vacuolar (v-) H⁺-ATPase pump is also a tonoplast localized, providing the ATP energy required for tonoplast antiporters. Evaluation of the expression level of HvNHX2 and subunit A of v-H⁺-ATPase (VHA-A) genes using real-time RT-PCR, in root and shoot tissue of salt-sensitive Reihan and salt-tolerant Afzal barley (Hordeum vulgare L.) cultivars under different salinity concentrations indicated that increasing the concentrations or duration of NaCl stress would decrease the K⁺/Na ratio that is a signal for cascade responses to the stress but fluctuated expression level of studied genes in some time point. However, promoter analysis of studied genes showed that both have CAAT, TATA and W-box promoter motifs which involve pathogen, salt and ABA-responsive signaling pathways but differed in TC-rich repeats, A-box, TCA-element and GARE-motif that may be one of the reason of observed different.

It is well known that excessive zinc accumulation is harmful to plant cells. Though, it is uncertain at which levels of intracellular availability zinc begins to exert its deleterious action on cell physiology, as the current estimations of zinc in vitro acting concentrations seem to be non-physiologically high (micro- or millimolar). Total esterase activity in plant cells is sensitive to different adverse factors and is often used to access cell physiological activity. Therefore, we determined the effect of different zinc availability levels in vitro on the total esterase activity in extracts from rapeseed (Brassica napus L.) roots and leaves. We founded that esterase activity was drastically decreased by different protein-affecting factors, namely chaotropic salts, detergents, elevated temperatures and denaturing agents. The utilization of reaction media with exactly specified concentrations of free Zn²⁺ ions demonstrated that total esterase activity is substantially reduced already at tens of nM Zn²⁺, which is several orders of magnitude lower than was described earlier. Total phosphatase activity in extracts was even more sensitive, being drastically reduced at free Zn²⁺ concentrations of few nM. Therefore, the plant cellular processes can be adversely affected at very low free Zn²⁺ concentrations.

The species diversity of green coccoid algae is often difficult to study using light microscopy due to their complex morphology. Algae, which have morphological and ecological similarities with the genera Bracteacoccus Tereg., Dictyococcus Gerneck, and Pseudomuriella Hanagata, are one of the most taxonomically complex examples. Often, only a comparison of nucleotide sequences allows one to carry out a reliable identification and find out the phylogenetic identity of the studied objects. Pseudomuriella belongs to the group of genetically diverse genera with a homogeneous Bracteacoccus-like morphology. The combined use of two genetic markers (18S rDNA nuclear gene and chloroplast rbcL gene), along with light microscopy and comparison of fatty acid profiles, allowed the identification of the green algae strain isolated from the soil of the artificial pine and robinia plantation in the steppe zone of Ukraine as Pseudomuriella engadinensis (Kol et Chodat) Fučiková, Rada et Lewis—the first find of the species in the flora of algae in Ukraine. Analysis of the fatty acid composition of the studied strain’s cells showed that the total lipid content in the stationary growth phase was at the level of 87.9 ± 2.1 mg/g dry cell mass, and the main fatty acids were palmitic, hexadecadienoic, ruganic, oleic, linoleic, and α-linolenic—their share accounted for 82.4% of the total amount of fatty acids.

Brassinosteroids (BRs) are plant hormones which promote plant growth and development. Their biosynthetic pathway and signal transduction pathway have been well studied in Arabidopsis thaliana and rice. However, their pathways in Solanaceae plants, especially in potato are still elusive. For now, only several candidate genes have been reported by transcriptome sequencing or homologous clones, but there is little information on their characteristics and functions in tuberization and heat defense. In this study, we systematically identified a series of putative homologs of BRs synthesis and signaling genes in potato (Solanum tuberosum L.) cv. Désirée through bioinformatic and molecular technologies, named as StCPD, StDWF4, StDWARF, StDET2, StBRI1, StBIN2, StBZR1-2 and StBZR1-4. Exogenous BR treatment decreased the expression of all synthesis genes and signaling genes except the negative signal gene StBIN2 which was increased, demonstrating that there exists a feedback regulation for all these genes. Tissue expression analysis revealed that the majority of these genes were highly expressed in leaves, and only the downstream transcription factor gene StBZR1-2 was highly expressed in stolons and tubers. The expression of these genes after heat treatment showed the opposite results from BRs treatment, suggesting that BRs signaling can be activated by heat stress. Furthermore, we explored the effects of BRs on tuber formation and found that exogenous BRs application increased both the number and the total weight of potato tuber due to the activated light-period signal for tuberization. All these results indicated that BRs play an important role in potato tuberization and heat stress defense.

Many specific detection assays have been developed in order to efficiently detect GMOs (genetically modified organisms) in feed and food. Existing approaches to screen or detect GM crops always rely on thermal cycling device. Therefore, these rapid visual detection assays were developed and characterized for the four transgenic soybean (Glycine max (L.) Merr.) events MON87701, MON87705, MON87708, and MON87769 using loop-mediated isothermal amplification (LAMP) method. Four sets of specific primers were successfully designed to recognize the junction sequences of specific soybean events. The optimum primers and reaction temperature of each assay were tested respectively. Different kinds of genomic DNAs of transgenic events and non-transgenic crop samples were examined with the methods that indicated the good specificity of GM soybean species. The detection limit of each LAMP assays could reach 0.05%, showing sensitivity 10 times higher than that of the regular PCR method. Due to their simplicity, rapidness and low cost, the established LAMP assays would be practical for detecting the GM soybeans MON87701, MON87705, MON87708, MON87769 and their derivatives.

Using the method of labeled atoms, we investigated the operation of the source–sink system in potato plants grown at the northern border of the cultivation zone. The label was introduced photosynthetically by means of exposing individual leaves or the whole above-ground part of plants to air containing ¹⁴СО₂ in different stages of their growth and development. It was shown that the export of assimilates from the leaves depended on their age, position on the stem, and the stage of ontogenesis. Young leaves of the lower layers became donors early and exported the products of current photosynthesis to the stems and roots maintaining their own growth with the substrates from the parental tuber. The stems attracted two times more ¹⁴С-assimilates than the roots. The leaves of the middle layers had the greatest area, exported ¹⁴С directly to the tubers, and spent up to 40% of assimilated carbon on their own needs. Apical leaves emerging by the end of the vegetation period accumulated approximately 10% of ¹⁴С-products of photosynthesis, and the rest of them were exported directly to the tubers. Exposure to a short-day length stimulated partitioning of carbon to the tubers in potato species notable for an obligate short-day response of tuberization (Solanum andigenum Juz. et Buk.), whereas reduction in the daily duration of photosynthesis suppressed accumulation of biomass of tops and tubers in commercially grown potato with a neutral response (Solanum tuberosum L.). In the course of tuber formation, respiration consumed 35% of initially assimilated ¹⁴С, which points to a high efficiency of storage of carbohydrate polymers in the form of starch. The obtained data broaden the knowledge about organization and operation of source–sink relationships and provide a basis for elaboration of the methods of governing potato plant’s source–sink system in an effort to improve productivity of this major crop.