A. F. Titov

Expression of WRKY transcription factor and stress protein genes in wheat plants during cold hardening and ABA treatment

Changes in expression of WRKY transcription factor and stress protein genes (Wcor15, Wrab17, Wrab19, and Wcs120) were studied on wheat (Triticum aestivum L., cv. Moskovskaya 39) seedlings exposed to cold hardening for 7 days at 4°C. The high level of WRKY gene expression was noticed already in 15 min after the beginning of cold treatment, but the expression level lowered during longer treatments. Exogenous ABA (0.1 mM) suppressed the WRKY gene expression. The level of Wcor15 gene expression increased gradually, reaching the peak on the second day, and then decreased. Gene expression of Wrab17 remained elevated throughout the period of cold exposure (7 days), and expression of Wrab19 was promoted within the first two days. Exogenous ABA induced expression of Wcor15, Wrab17, and Wrab19 genes both at cold-hardening (4°C) and normal (22°C) temperatures. A significant increase in Wcs120 gene expression during cold hardening was ABA-independent. It is concluded that the increase of wheat plant resistance at the initial stage of cold hardening is related to gene expression of WRKY transcription factor and of stress proteins (Wcor15, Wrab17, Wrab19, and Wcs120), while the resistance increase during prolonged adaptation is related to gene expression of Wcor15 and Wrab17.

Effect of lead on the photosynthetic apparatus of annual grasses

The effect of lead (in the form of Pb(CH3COO)2 ⋅ 3H2O at concentrations of 200, 400, and 800 mg/kg substrate) on the photosynthetic apparatus of barley (cv. Dina) and oat (cv. Falensky) was studied. Exposure to low concentrations of lead (200 mg/kg) slightly increased the content of chlorophyll in leaves and the rate of photosynthesis. Medium concentrations of lead (400 mg/kg) had no marked effect on the parameters analyzed, whereas high concentrations (800 mg/kg) decreased the area of leaves, the content of green pigments in them, and the rate of photosynthesis.

Setaria viridis tolerance of high zinc concentrations.

The effect of high zinc concentrations on the growth and photosynthetic apparatus of Setaria viridis (L.) Beauv. was investigated under laboratory conditions and a vegetation experiment. The experiments showed that zinc concentrations of 10−6 to 10−3 M did not influence seed germination. Moreover, zinc in concentrations of 40 and 80 mg kg substrate had no significant effect on most of the plant growth parameters. However, higher metal concentrations (160 and 320 mg kg substrate) inhibited shoot biomass, leaf area, inflorescence length, and biomass. At the same time, parameters such as the content of chlorophyll (a + b), F 0, Fv, and the Fv/Fm rate were not reduced even in the presence of zinc in the highest concentrations (320 mg kg substrate). S. viridis tolerance of high zinc concentrations, as well as its capacity to accumulate zinc in roots and shoots, suggests the plant can be used for phytoremediation of zinc polluted soils.

Cold-responsive COR/LEA genes participate in the response of wheat plants to heavy metals stress

28 Under natural conditions, plants are often exposed to the action of two or more stress factors, such as a high temperature and water deficiency, or unfavorable temperature and salinization or heavy metals stress. However, the mechanisms of a combined (simultaa neous or sequential) action of different stress factors on plants still remain poorly studied. It is known that COR/LEA (cold responsive/late embryogenesis abunn dant) genes [1, 2], which encode COR/LEA proteins participating in both cold resistance improvement and protection of cells against dehydration, play an imporr tant role in the lowwtemperature adaptation of plants [3]. Moreover, the expression of many of the LEA genes and the synthesis of the corresponding proteins in plants are enhanced under the influence of the drought [4] and salinization [5]. At the same time, there is no information concerning the possible particc ipation of COR/LEA genes in the plant response to heavy metals stress. It is known that abscisic acid (ABA), being a phytohormone, participates in the regg ulation of the expression of many of the COR genes [2]. For example, ABAAdependent pathways of the loww temperature signal transduction and regulation of COR genes (including the WRAB15 and WRAB18 genes) were revealed in wheat [2]. Taking into account this fact, we studied the changes in the level of express sion of WRAB15 and WRAB18 genes induced by a low positive (hardening) temperature and cadmium, one of the most toxic heavy metals, and also by the combii nation of these two stress factors. Our study was the first to demonstrate a positive correlation between the level of expression of the coldd responsive WRAB15 and WRAB18 genes in leaves of wheat seedlings and the resistance of these seedlings to low temperatures, cadmium, and to the combination of these stress factors. Experiments were conducted with winter wheat (Triticum aestivum L.) seedlings of the Moskovskaya 39 cultivar. The seedlings were grown in filter paper rolls moistened with Knops solution supplemented with microelements (pH 6.2), in an environmental chamber at 22°C, a relative humidity of 60–70%, illuu mination of 10 klx, and photoperiod of 14 h. Onee weekkold seedlings were exposed to a low positive temm perature (4°C) or cadmium sulfate (100 µM) or the combination of both factors for 7 days, with other conn ditions remaining unchanged. Cold resistance of seedlings was assessed by the temperature causing the death of 50% of palisade cells in leaves (LT 50) …

Structural and functional reorganization of the photosynthetic apparatus in adaptation to cold of wheat plants

In seedlings of a cold-resistant wheat variety, the dynamics was studied of the main structural-functional parameters of the photosynthetic apparatus (PSA) and of cold resistance of leaf cells in low-temperature plant adaptation. It has been established that a complex of structural-functional PSA changes takes place in seedling leaves under the influence of cold. As a result, as early as in the first hours of hardening, the formation of chloroplasts begins to occur in mesophyll cells of larger sizes and with a thylakoid system of the “sun type.” Owing to structural and functional readjustment (a change of content of pigments, stabilization of pigment-protein complexes, and enhancement of nonphotochemical quenching of excess energy) in the process of cold adaptation, the rate of photosynthesis stabilizes. It is suggested that the observed structural-functional PSA rearrangement is a necessary condition for formation of increased cold resistance of leaf cells; this, alongside with other physiological-biochemical changes occurring in parallel in cells and tissues of the plants, provides their survival under conditions of low temperatures.

Barley plant response to cadmium action as dependent on plant age

Age-dependent differences in the responses of 3-day-old (the phase of seed germination) and 7-day-old (the phase of seedlings) of barley (Hordeum vulgare L., cv. Zazerskii 85) plants to treatment with cadmium (100 μM). Four-day-long exposure to the cadmium solution retarded root growth and suppression of the photosynthetic apparatus in germinating seeds, whereas in seedlings, the roots continued to grow actively and parameters characterizing functioning of the photosynthetic apparatus were close to control values. In the presence of cadmium, in the roots of plants the level of HvPCS gene encoding phytochelatin synthase and the content of phytochelatins (PC) increased independently of the plant age. Distinctly, changes in the content of reduced glutathione (GSH) depended on the plant age: in 3-day-old seedlings the content of GSH reduced after 40-day-long exposure to cadmium; in contrast, in 7-day-old plants, it increased. We concluded that differences in the tolerance to cadmium of plants differing in age are related to their anatomic, morphological, physiological, and biochemical properties corresponding to particular developmental stages and also to differences in functioning of different mechanisms of metal detoxification, in particular, to activation of GSH synthesis and a great increase in the content of PC in the older plants.

The Effect of Cadmium on Shoot Apical Meristems of Barley

We studied the effects of cadmium acetate at various concentrations (200 to 800 mg/kg substrate) on growth and development of shoot apical meristem of the barley plants (Hordeum vulgare L.) under the conditions of vegetative experiment. It was shown that in the presence of increasing cadmium concentrations in the soil substrate, the apex length and number of inflorescence elements decreased and the rate of organogenesis slowed down, thus affecting the spike potential productivity and morphological parameters of barley plants at the flowering stage. It is possible that the negative effect of cadmium on the shoot apical meristem is associated with its influence on division of the apex cells.

Effect of abscisic acid on the resistance of cucumber seedlings to combined exposure to high temperature and chloride

The effect of abscisic acid (ABA) on heat and salt resistance of cucumber seedlings exposed (consecutively or simultaneously) to high temperature and chloride was studied. Exogenous ABA proved to additionally increase the heat and salt resistance after both consecutive and simultaneous exposure of cucumber seedlings to 38∞N and NaCl. The involvement of this hormone in the common (nonspecific) mechanisms increasing plant resistance to the studied environmental factors is concluded.

Influence of lowered temperature on the resistance and functional activity of the photosynthetic apparatus of wheat plants

The dynamics of cold resistance and the activity of the photosynthetic apparatus (PSA) of wheat germs at 4°C were studied. It was shown that in the first hours of cold, a certain functional readjustment to the changed conditions takes place in the plant organism. A decrease in the activity of the PSA and cessation of the linear growth of the leaf are registered at this stage along with an increase in resistance, as well as an increase in the coefficient of non-photochemical quenching of the fluorescence of chlorophyll. In one to four days, when resistance reaches its maximum, photosynthesis and the rate of electron transport are stabilized, the chlorophyll content in the lightcollecting complex increases, and the growth recommences. The final stage of adaptation (days 4–7) is characterized not only by the steady level of resistance but also by new functional organization of the PSA, which allows the plants to endure the lowered temperature successfully.

Effect of Stress Factors on Expression of the Gene Encoding a CBF Transcription Factor in Cucumber Plants

419 Plant responses to various stress factors differing in their nature are related to the complex of similar changes in their cells, including derepression of definite genes [1, 2]. For example, expression of the family of transcription factors CBF/DREB (C-repeated binding factor/dehydration response elements binding protein) in arabidopsis plants is induced by dehydration [3, 4], low temperature [3, 4], and cadmium [5]. In its turn, CBF transcription factors activate expression of some stress-protein genes and thus could be involved in the improving of plant tolerance to unfavorable environmental factors [6, 7]. In this connection, we studied the expression of the CBF transcription factor in cucumber plants under the effects of low and high hardening temperatures, NaCl, and also of the stress hormone, abscisic acid (ABA).