卷 63, 编号 6 (2016)

Plants of Sorghum bicolor (C₄ species) were grown at different nitrate or ammonium concentrations (0.5, 5, 20 and 50 mM) in order to examine the effect of nitrogen nutrition on growth, phosphoenolpyruvate carboxylase (PEPC) and antioxidant enzymes activities in both roots and leaves of 30-day-old plants. At high NO₃⁻ levels (20 and 50 mM) the fresh weight was significantly higher. When the nitrogen source was in ammonium form, the leaf and root mass increased drastically at low concentration 5 mM and significantly at 20 mM, however similar fresh weight was found at high level of ammonium (50 mM). The leaves catalase (CAT), guaiacol peroxidase (POD), glutathione reductase (GR), and glutathione S-transferase (GST) activities and the roots glutathione reductase and glutathione S-transferase activities were significantly higher in the NH₄⁺-fed plants than those grown in the nitrate medium. Activity and proteins levels of phosphoenolpyruvate carboxylase in both leaves and roots of sorghum plants were increased progressively with increasing external nitrogen concentration. This increase was more pronounced at high level of ammonium (50 mM), being 2-fold at 50 mM of NO₃⁻ and 3-fold at 50 mM of NH₄⁺. Our results suggested that antioxidant enzymes activities and PEPC play a key role in ammonium detoxification and tolerance in sorghum plants.

The induction of thiols including glutathione and phytochelatins as well as the activities of antioxidant enzymes namely superoxide dismutase isoenzymes and those enzymes involved in the ascorbate-glutathione cycle in watercress plants under arsenic stress were investigated. Arsenic concentrations and tissue type-dependent response to arsenic were assessed. Plant was capable of accumulating large amounts of arsenic in the shoots. Superoxide dismutase isoenzymes activity and phytochelatin level was higher in shoots than in roots. In roots, ascorbate levels increased significantly, while no relationship was found between ascorbate contents and arsenic tolerance in shoots. Treatment with arsenic resulted in a remarkable increase in glutathione content of roots at all of the arsenic concentrations, while in shoots, glutathione content increased by lower levels of arsenic. Differences were noted in both roots and shoots for enzymes involved in the ascorbate-glutathione cycle. These results suggest that, the strategy of tolerance to arsenic toxicity in roots of watercress plants is different from that of shoots.

Earlier it was noticed that the supplementary nitrogen to nutritive solution of the cadmium stressed (Cd-stressed) plants can alleviate the toxic effects of this metal on the plants and improve plant growth performance. But the underlying mechanisms of such detoxification effect of nitrogen were not studied. In this study, a ten-day responses of related nitrogen-synthesized genes including γ-glutamylcysteine synthetase (γ-GCs), glutathione synthetase (ECGs) and phytochelatin synthase (PCs) involved in glutathione (ECG) and phytochelation (PC) synthetic pathways were examined. The plant growth performance and leaf chlorophyll content were examined at the final harvest. It was shown that the supplement of additional nitrogen to poplar plants under cadmium stress could significantly up-regulate the expression levels of γ-GCs, ECGs and PCs genes in plant leaves during the first 12 hours. Furthermore, cadmium stressed plants with additional nitrogen supplement showed significant enhancement in growth performance and increase in leaf chlorophyll content compared to sole cadmium stressed plants. Our results suggest that additional nitrogen could stimulate a short-term defense system in poplar plants through ECG and PC synthetic pathways. It is contribute to the alleviation of the toxic symptoms in polar plants caused by cadmium stress. This study provides a potential method to render harmless cadmium toxicity in stressed plants with nitrogen fertilization.

Effect of salinity on vegetative growth and sexual reproduction was investigated in laboratory cultures of a benthic diatom Ardissonea crystallina (C. Agardh) Grunow from the Black Sea and vegetative growth of Ardissonea sp. from the coast of Martinique, the Atlantic Ocean. Typical water salinity in the places where the populations inhabit differs two times. It was shown that the clones of both populations have a broad tolerance and great ability to adapt to changes in salinity. Cells of different size (i.e., in different stages of the life cycle) responded differently to desalination. Salinities optimal for vegetative growth of these species were not the same. Ardissonea from the coast of Martinique was more sensitive to low levels of salinity as compared with A. crystallina from the Black Sea. It was surprising that salinity optimal for vegetative growth and sexual reproduction of the Black Sea species did not coincide with the real salinity level of the Black Sea. Position of physiological optimums indicates an oceanic (or Mediterranean) origin of the Black Sea population of A. crystallina.

Tartary buckwheat (Fagopyrum tataricum Gaertn.) is highly nutritious and an excellent dietary source of flavonoid compounds. Chalcone synthase (CHS) is the first key enzyme involved in flavonoid biosynthesis. Here, three putative CHS genes (designated as FtCHS1 (GU172165), FtCHS2 (KT284884), and FtCHS3 (KT284885) were isolated from tartary buckwheat. Nucleotide sequence analysis indicated that FtCHS1 and FtCHS2 each contained one intron of 444 bp and 157 bp, respectively. FtCHS3 included two introns, one of 86 bp and another of 73 bp. The results of quantitative real-time PCR (qRT-PCR) showed the FtCHSs expression presented the same pattern in the stems and flowers, with FtCHS1>FtCHS3>FtCHS2. A different tendency was found in leaves, with FtCHS3>FtCHS2>FtCHS1. However, there was no direct correlation between the three CHS expression and total flavonoids. Furthermore, high-performance liquid chromatography (HPLC) performance reveals rutin is the most abundant flavonoid in all tissues, leaves should be the main location for quercetin storage in tartary buckwheat.

Expression of STENOFOLIA (STF) gene was analyzed in different organs of line R-108 barrel medic plants (Medicago truncatula Gaertn.). Maximum levels of STF expression were observed in the generative organs, fruits and flowers, suggesting its involvement in the reproduction process. The local analysis of STF expression during somatic embryogenesis in M. truncatula showed that the STF promoter is activated directly in somatic embryos. Overexpression of STF gene in the calli of R-108 line leads to increased embryogenicity, accompanied by reduced levels of MtGH3.6 gene expression, which is responsible for auxin metabolism, and also reduced expression levels of gene encoding MtHB1 transcription factor. Comparative analysis of MtGH3.6 and MtHB1 gene expression dynamics in the calli of embryogenic 2HA line and non-embryogenic A17 line of M. truncatula showed that these genes demonstrated reduced level of expression in embryogenic calli compared to non-embryogenic. These data suggested that STF stimulates the formation of somatic embryos, directly or indirectly inhibiting the transcription of MtGH3.6, MtHB1 and, probably, many other genes.

E3 ubiquitin ligases play essential roles in determining the specificity of ubiquitination and subsequent protein degradation. The plant U-box (PUB) family of E3 ligases has been implicated in biotic and abiotic stress signaling and developmental events in various species. A comprehensive bioinformatics analysis identified 56 PUB genes in the grapevine (Vitis vinifera L.) genome. Based on conserved motifs, the VvPUB family was classified into seven subclasses. Expansion of this family was driven by chromosomal, segmental, and tandem duplications. Microarray expression profiling revealed that three PUB genes were preferentially expressed in pollen, four in leaf, and five in root. Moreover, a large number of PUB genes were differentially expressed under abiotic stresses and eight PUB genes likely participated in defense against powdery mildew. The microarray expression data were verified by RT-qPCR. Genome-wide identification of VvPUB genes and examination of their expression will give insights into the functions of U-box genes in grapevine.

Electrical signals in plants, namely, the action potential (AP) and variation potential (VP) alter the activity of many processes, including photosynthesis. The functional responses induced by electrical signals vary in direction and amplitude, which might be determined by variable conditions of plants prior to stimulation, by the development stage in particular. In this work, the parameters of VP-induced photosynthetic responses were analyzed at various stages of wheat seedling development. Local wounding of the second leaf in wheat plants induced the propagation of VP and altered the activity of photosynthesis at a distance from the wound location. The amplitude of VP was enlarged when the seedling age increased from 11 to 18 days. The VP-induced photosynthetic response changed with age both qualitatively and quantitatively. The amplitude of VP-induced changes in CO₂ assimilation and nonphotochemical quenching (NPQ) increased with age, which might be due to the increase in VP amplitude and associated changes in Ca²⁺ and H⁺ concentrations. The quantum yield of photosystem II photoreaction was subject to age-dependent changes: the photochemical quantum yield (γ(PSII)) was found to increase after VP in young leaves, whereas the decline in γ(PSII) was observed after the VP propagation in mature leaves. The results may explain the diversity of photosynthetic responses caused by the electrical signals.

Analysis of plant behavior under diverse environmental conditions would be impossible without the methods for adequate assessment of the processes occurring in plants. The photosynthetic apparatus and its reaction to stress factors provide a reliable source of information on plant condition. One of the most informative methods based on monitoring the plant biophysical characteristics consists in detection and analysis of chlorophyll a fluorescence. Fluorescence is mainly emitted by chlorophyll a from the antenna complexes of photosystem II (PSII). However, fluorescence depends not only on the processes in the pigment matrix or PSII reaction centers but also on the redox reactions at the PSII donor and acceptor sides and even in the entire electron transport chain. Presently, a large variety of fluorometers from various manufacturers are available. Although application of such fluorometers does not require specialized training, the correct interpretation of the results would need sufficient knowledge for converting the instrumental data into the information on the condition of analyzed plants. This review is intended for a wide range of specialists employing fluorescence techniques for monitoring the physiological plant condition. It describes in a comprehensible way the theoretical basis of light emission by chlorophyll molecules, the origin of variable fluorescence, as well as relations between the fluorescence parameters, the redox state of electron carriers, and the light reactions of photosynthesis. Approaches to processing and analyzing the fluorescence induction curves are considered in detail on the basis of energy flux theory in the photosynthetic apparatus developed by Prof. Reto J. Strasser and known as a “JIP-test.” The physical meaning and relation of each calculated parameter to certain photosynthetic characteristics are presented, and examples of using these parameters for the assessment of plant physiological condition are outlined.

The effect of phosmidomycin and mevinolin, which inhibit MEP and MVA isoprenoid biosynthetic pathways, respectively, on the growth (biomass accumulation, growth index, specific growth rate), physiological (respiration intensity and ratio between the cytochrome and cyanide-resistant respiration types), and biosynthetic (steroid glycoside biosynthesis) characteristics of the cell suspension culture of Dioscorea deltoidea Wall. has been studied. Both inhibitors decreased the growth index of a cell culture by 20–25%, but their influence on the cell growth dynamics was different. Mevinolin treatment reduced the maximum biomass accumulation by 20% as against the control but did not change the character of a growth curve. Phosmidomycin treatment caused a significant growth delay (a 6-day lag phase) followed by a short active growth period (μ = 0.29 days^-1). Treatment of cells with inhibitors did not significantly influence on their total oxygen uptake rate, whose average value at different growth phases was equal to 100–200 mg О₂/g of dry cell weight per hour, but cardinally changed characteristics of respiratory metabolism. The inhibitors increased the activity of a cyanide-resistant respiration and decreased the intensity of a cytochrome respiration; each inhibitor worked in its specific manner. In the case of mevinolin, the maximum level of cyanide-resistant respiration (70% of the total respiration intensity) was observed at initial growth phases; during the further cell culture growth, this value gradually reduced to 6–8%. Phosmidomycin treatment caused a reverse dynamics: at the initial growth phases, the contribution of cyanide-resistant respiration was 30%, whereas at the stationary and degradation phases it increased to 50–60%. The treatment of cells with phosmidomycin resulted in a double increase in the content of furostanol glycosides at the stationary growth phase, whereas the use of mevinolin-containing medium reduced the content of these compounds as against the control. Inhibitors also influenced on the ratio of individual glycosides, such as protodioscin, deltoside, and their 26-S-isomers. The obtained results confirm the hypothesis of a possible intermediate exchange between the plastid (MEP) and cytosolic (MVA) isoprenoid biosynthetic pathways; this exchange is directed mainly from the plastids to the cytosol.