Vol 66, No 6 (2019)

The paradox of misfit between the levels of mRNAs and their protein products in the eukaryotic cells, including plant cells, encountered by researchers, direct their efforts towards the study into fine mechanisms of translation. Translation is an intricate biological process with numerous players, including mRNAs, tRNAs, ribosomes, and manifold protein factors. Certainly, each of them is important for efficient translation. However, the mRNAs itself contain numerous regulatory elements, such as 5'UTR, the context around the AUG start codon, and codon composition; each element separately or in combination can determine the fate of an individual mRNA in translational process. The previous reviews mainly focus on individual key stages in translation or the aspects of its control. Our goal here is (i) to summarize the recent data on the specific structure–function features of plant mRNAs and their correlation with translational efficiency; (ii) to brief new experimental and theoretical approaches to gaining the insight into the complex network of translation; and (iii) to assess the relevance of this knowledge to both the plant functional genomics and biotechnological application.

De-etiolation of plant seedlings is controlled by a complex system of light and hormonal signaling. This process is accompanied by chloroplast development and initiation of chlorophyll biosynthesis leading to cotyledon greening. In this study, peculiaritis of regulation of expression of the key genes encoding enzymes of chlorophyll biosynthesis in wild type plants and mutants of perception and transduction of blue light in Arabidopsis thaliana (L.) Heynh. during cytokinin (CK)-dependent greening of seedlings were investigated. Inactivation of blue-light signaling components (СRY1, CRY2 and HY5) led to retarded chlorophyll accumulation and decrease of the expression of the key genes responsible for its biosynthesis. Exogenous application of cytokinin accelerated de-etiolation of wild type and knockout-mutants cry1cry2 and hy5 seedlings that was manifested itself in elevating chlorophyll a fluorescence and higher level of transcripts of a number of genes involved in chlorophyll biosynthesis. Taken together the results may provide evidence for the significant contribution of blue-light signaling to the greening regulation at early steps of de-etiolation of seedlings and involvement of HY5 protein in realization of the positive effect of CK at early steps of photomorphogenesis.

Transgenic plants containing genes of bacterial phytases represent one of the promising ways to solve the problem of phosphorus deficiency in the nutrition of plants and monogastric animals. Histidine acid phytase PaPhyC from Pantoea agglomerans has a high activity and represents a promising basis for the biotechnology of plants. In this study, the analysis of morphological characteristics, phytase activity, and phosphorus content in tissues of the earlier obtained, genetically modified Arabidopsis thaliana (L.) Heynh. plants producing extracellular phytase (PaPhyC) has been carried out. According to the obtained results, modified plants are able to grow on a medium supplemented with phytate as the sole source of phosphorus. Exterior characteristics (rosette diameter and area) of phytase-expressing plants grown on media containing phytate or inorganic phosphorus do not differ, which confirms that the plants use phytate as the phosphorus source. In the case of plant cultivation on a phytate-containing medium, a high phytase activity is observed in the cell walls of modified plants. The content of inorganic phosphorus in tissues of modified plants does not change in the case of their cultivation on the medium containing phytate as the sole source of phosphorus.

Dynamics of the photosynthetic apparatus' (PA) structural and functional parameters during the day was investigated in euhalophyte Salicorniaperennans Willd., crynohalophyte Limoniumgmelinii (Willd.) O. Kuntze, and glycohalophyte Artemisiasantonica L. The greatest PA activity judging from the rate of СО₂ consumption/release by the leaves was observed in the morning. In salt-accumulating (S. perennans) and salt-eliminating (A. santonica) species, the rate of photosynthesis was greater than in L. gmelinii plants possessing the systems of salt excretion. In A. santonica and S. perennans, the content of green pigments decreased during the day, while it remained permanent in L. gmelinii. During the day, the ratio between plastid lipids and pigments increased in A. santonica and S. perennans. In chloroplast lipids from S. perennans, a decrease in the relative content of monogalactosyldiacylglycerol (MGDG) was compensated for by a rise in relative content of digalactosyldiacylglycerol (DGDG), with the contribution of sulfoquinovosyldiacylglycerol (SQDG) and phosphatidylglycerol (PG) remaining the same. In the chloroplasts from L. gmelinii, the proportion of neutral lipids MGDG and DGDG did not change in contrast to the level of anionic lipids SQDG and PG. In A. santonica, we detected changes in both neutral and anionic lipids. A high proportion of unsaturated FA (UFA) (over 70%) in the total pool of FA was mainly accounted for by α-linolenic acid. It was found that the proportion of saturated FA tended to increase in the evening. All the revealed structural and functional reorganizations of PA associated with fluctuation of pigment-lipid resources of thylakoid membranes were adaptive and aimed at optimization of photosynthesis under specific environmental conditions.

Cytophysiological adaptive features of apple fruits (Malus domestica Borkh.) were examined as a function of growth altitude—300, 500, 700, and 1200 m above sea level—in the mountains of the North Caucasus. The altitude-related conditions of apple tree cultivation differed by a range of growth-limiting factors, high irradiance and low temperature in particular. With the use of fruit skins of M. domestica, it was found for the first time that the number of cells containing phenolic substances in the outer cell layers and the amount of accumulated phenols increase with the altitude of tree growth. At higher elevation belts, the content of polyunsaturated fatty acids also increased, which accounted for the rise of the unsaturation index. Phenolic substances protect the fruit peripheral tissues by screening the cells from high doses of UV radiation and by exerting their powerful antioxidant effects. The increased degree of fatty acid unsaturation helps to retain the fluidity of cell membranes in the physiological range at low temperatures. Thus, apple fruits grown at high altitudes adapt to mountain conditions by a suite of structural and functional changes in the peripheral tissues, which facilitates the maintenance of homeostasis in the inner cell layers. The complex rearrangements in fruit tissues of M. domestica trees enable them to grow at high elevation belts under frequently changing conditions and to remain fully productive at various altitudes.

Qualitative and quantitative composition of the lipid complex and total content of polyphenols were compared in aqueous alcoholic extracts from three species of marine macrophytes collected in Peter the Great Bay, the Sea of Japan. Examined seaweeds belonged to different phyla: green alga Ulva lactuca L. sea lettuce, brown alga Sargassum pallidum (Turner) C. Agardh sargassum pallidum, and red alga Ahnfeltia tobuchiensis (Kanno et Matsubara) Makijenko ahnfeltia tobuchiensis. It was shown that glycolipids (30.3–41.5%) and neutral lipids (34–48.5%) prevailed among total lipids in the extracts from all three algal species; phospholipids accounted for 10–25.7% of total lipids. Among neutral lipids in all the seaweeds, triacylglycerols and free sterols prevailed. The greatest quantity of triacylglycerols was found in A.tobuchiensis and that of free sterols was in S. pallidum. As to the individual fractions of phospholipids, their composition and content considerably differed. In terms of content, predominant phospholipid fractions in the extract from U. lactuca were phosphatidyl glycerol, phosphatidyl ethanolamine, and phosphatidyl inositol, those from S. pallidum were phosphatidyl ethanolamine and phosphatidyl glycerol, and those from A. tobuchiensis were phosphatidyl choline and phosphatidyl glycerol. As to the percentage of main fatty acids comprising the lipid component of the extracts from the examined algal species, it was found that the extract from brown alga S. pallidum contained the greatest content of PUFA from the family n-6. The extract from green alga U. lactuca contained the greatest content of PUFA from the family n-3. In the extract from red alga A. tobuchiensis, arachidonic (family n-6) and eicosapentaenoic (family n-3) acids prevailed among PUFA. The greatest quantity of polyphenols was detected in the extract from brown alga S. pallidum, which 15–24 times exceeded respective figures in U. lactuca and A. tobuchiensis. Moreover, the extract from S. pallidum showed a much higher level of antiradical activity in respect to ABTS⁺, which was 5–12.5 times greater than in U. lactuca and A. tobuchiensis, respectively.

Seed aging or deterioration is considered as one of the seed capacity reducing factors and limiting seed germination, hence, realizing the effective physiological factors on seed deterioration is very important. In order to study the germination indices and enzymatic and non-enzymatic antioxidants in wheat (Triticumaestivum L. cv. Pishtaz) seed as affected by accelerated seed aging and gibberellic acid (GA₃) priming, a laboratory experiment was conducted in Ferdowsi University of Mashhad, Mashhad, Iran, during 2017–2018. For this purpose, different levels of seed aging (100% relative humidity at 40°C for 4, 6 and 7 days, respectively) and GA₃-primed seeds (0, 25, 50 and 100 mg/L) were the first and second experimental factors, respectively. The results indicated that seed germination percentage and indices, superoxide dismutase and ascorbate peroxidase activities, vitamin E, glutathione and ascorbic acid contents were reduced with severe deterioration, compared with low deterioration, whereas, the mentioned traits were improved by increasing the levels of GA₃ seed priming. Overall, the results of this experiment suggest that the GA₃-primed seed can be an effective approach to improve the seed germination and seedling growth in wheat under aging conditions.

The earlier-detected effect of the mineral nitrogen form in the nutrient medium (ammonium or nitrate) on the quantity of ribosomes in the cells of chlamydomonas and the callus of soybean requires experimental corroboration of the proposed interpretation of the discovered phenomenon. In order to elucidate the mechanism of ammonium’s action on the formation of protein-producing structures (ribosomes) in the cells of green alga chlamydomonas (Chlamydomonas reinhardtii, strain gr 21), we compared the effect of the form of mineral nitrogen (nitrate and ammonium) on the growth and heterotrophic fixation of ¹⁴С-bicarbonate. Our experiments have shown that the process of cell division (mitosis) was hampered at the beginning of the growing cycle (on days 1–3) when the cells were cultured on nitrate medium. By the end of the growing cycle (days 7–10), the number of cells and the content of dry matter in the cells equalized. It was found that the cells grown on TAP medium with ammonium fixed Н¹⁴С\({\text{O}}_{3}^{ - }\) at a higher rate than the cells cultured on TAP medium with nitrate. The obtained results have shown that the rate of dark fixation of Н¹⁴С\({\text{O}}_{3}^{ - }\) in the cells grown in the medium with ammonium was higher than in the cells on nitrate medium irrespective of the mode of calculation: on the number of cells or per dry weight unit. An assumption that ammonium present in the nutrient medium can activate synthesis of extra amino acids participating in the formation of protein components of ribosomes in the alga chlamydomonas is discussed.

Phytohormones play a key important role in the sink development of the seed. Endogenous content of IAA, PAA, GA, ABA, and kinetin were estimated in two distinct varieties of soybean (Glycinemax (L.) Merr.) during the entire period of seed development. Antibodies against IAA, PAA, GA, ABA, and kinetin were raised in rabbits. By competitive ELISA, hormones were estimated from the two different varieties: Large seeded variety (L seed) and Small seeded variety (S seed). Growth analysis showed that L seed had more dry weight, the rate of dry matter accumulation and water content than S seed. Plant hormones are signal molecules that regulate many developmental processes, including sink size and dry matter accumulation in viable mature seed. In both the varieties, the free IAA increased gradually with the seed age; value was near to double in L seed. PAA was also observed higher in L seed than S seed during cell elongation period. While GA content was higher in S seed in compare to IAA and PAA. ABA content was observed 2–4 times lower as compared S seed. A significant difference was observed in kinetin levels which showed nearly 1.5 times higher in L seed compared to S seed. GA and ABA levels were more in S seed suggest that GA/ABA ratio and total hormonal balance determine the sink size. The probable role of hormones in seed development is discussed.