Effect of Seed Treatment with Salicylic Acid on the Carbonic Anhydrase Activity, Photosynthesis Rate, Stomatal Conductance, and Pigments Content in Wheat Leaves at Zinc Excess.

The effect of seed treatment with salicylic acid (SA) on the carbonic anhydrase (CA) activity, photosynthesis rate, stomatal conductance, and pigment content in wheat leaves was studied at an optimal zinc content (2 µM) and zinc excess (1500 µM). It was shown for the first time that the CA activity and stomatal conductance increased upon seed treatment with SA at the optimal zinc content as compared with untreated plants, while the photosynthesis rate was not affected. When zinc was in excess in the root zone, seed treatment with SA decreased the CA activity to a greater extent, but the photosynthesis rate was higher than in untreated plants, apparently due to an increase in the contents of chlorophylls and carotenoids and stomatal conductivity. It was concluded that SA is involved in the protective and adaptive responses of wheat plants to excess environmental zinc along with other nonhormonal factors and hormones.

Effect of Methyl Jasmonate on the Gene Expression, Encoding Non-Protein Thiol Enzymes in Wheat under Cadmium.

The effect of the phytohormone methyl jasmonate (MJ) on the expression of the TaGS1 and TaPCS1 genes encoding glutathione synthetase and phytochelatin synthase, respectively, which are key enzymes in the synthesis of glutathione and phytochelatins in wheat (cv. Moskovskaya 39), was studied. It was shown for the first time that pretreatment of plants by exogenous MJ (1 µM) leads to an increase in the accumulation of transcripts of the TaGS1 and TaPCS1 genes in leaves without cadmium effect. When cadmium (CdSO4, 100 µM) was added into the nutrient solution, the transcript level of the TaGS1 gene in the plants pretreated by MJ increased (compared to the untreated plants), whereas the transcript level of TaPCS1 remained unaffected. The pretreatment of plants with MJ leads to a lower accumulation of cadmium in the roots and leaves of wheat. At the same time, MJ had no effect on the linear growth parameters of plants, but had a positive effect on the accumulation of biomass under cadmium. It was assumed that MJ is involved in plant tolerance to cadmium by increasing the expression of the TaGS1 and TaPCS1 genes and, as a result, enhancing the synthesis of chelating compounds, as well as by reducing the supply of metal ions to plants.

Seed Treatment with Salicylic Acid Increases Gene Expression and Activity of Antioxidant Enzymes in Wheat Plants in Zinc or Copper Deficiency.

The effect of wheat seed treatment with salicylic acid (SA) on expression of the TaCu/ZnSOD, TaFeSOD, and TaCAT2 genes and activities of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) in leaves was studied at optimal contents of zinc (2 µM) and copper (0.3 µM) in the root environment and in zinc and copper deficiencies. Seed treatment with SA was for the first time shown to increase of the amount of transcripts of the above genes as compared with untreated plants, both in optimal conditions and in zinc or copper deficiency. Activities of the enzymes, especially catalase, also increased. Judging by the malondialdehyde (MDA) content, the changes make it possible to avoid an increase in lipid peroxidation (LPO) and, therefore, oxidative stress. A positive effect of seed treatment with SA on activities of the main antioxidant enzymes was assumed to underlie the stimulating effect of SA on physiological processes in plants exposed to microelement deficiency.

The HMA2 Gene Expression in Leaves of Introgressive Wheat Lines under Zn Optimum and Deficiency Content in Root Environment.

In two introgressive lines of bread wheat (15-7-1 and 15-7-2), which differ in the allelic status of the Gpc-B1 gene, the expression of the gene encoding the HMA2 transport protein in flag leaves under optimum Zn content in substrate (2 µÐœ) and in its deficiency (0 µÐœ) was investigated. This is the first study to show that the plants carrying functional allele of the Gpc-В1 gene (line 15-7-1) have a higher level of TaHMA2 transcripts than the plants with nonfunctional allele of the Gpc-В1 gene (line 15-7-2) both at optimum Zn content in substrate and at its deficiency. Importantly, the high TaHMA2 gene expression did not affect the wheat shoot growth but correlated with a high Zn concentration in the aboveground part of plants. It is assumed that the NAC transcription factor encoded by the Gpc-В1 gene may be involved in the regulation of the ТаНМА2 gene expression.

Influence of Gold Nanoparticles on the Tolerance of Wheat to Low Temperature.

It was shown for the first time that the treatment of winter wheat (Triticum aestivum L.) seeds with gold nanoparticles (average diameter 15.3 nm; solution concentration 20 µg/mL) increases plant tolerance to low temperature. It was found that an increase in tolerance under the influence of nanoparticles is accompanied by a number of changes depending on temperature conditions. In optimal temperature conditions, gold nanoparticles stimulated plant growth and the activity of the photosynthetic apparatus, whereas in conditions of low-temperature hardening (2°C, 7 days) they inhibited growth but maintained photosynthetic activity, contributing to the accumulation of soluble sugars (cryoprotectants) in the leaves. It is concluded that gold nanoparticles can be considered as adaptogens that increase plant tolerance to low temperatures; however, their effectiveness in this role and the subtle mechanisms of action require further study.

Effect of Zinc Excess and Low Temperature on the IRT1 Gene Expression in the Roots and Leaves of Barley.

We studied the effect of zinc excess (1000 µM) and low positive temperature (4°C) on the IRT1 gene expression in barley roots and leaves. Exposure at each of the stress factors separately induced an increase in the content of the HvIRT1 gene transcripts, which was more pronounced in leaves. At the same time, the growth of seedlings continued. Under the combined action of the stress factors in the first 3 days, the amount of mRNA also increased, but after 7 days of exposure it significantly declined, which correlated with the complete inhibition of seedling growth. It is assumed that the seedling growth inhibition under the combined effect of zinc excess and low temperature is associated with a decrease in the transcriptional activity of the HvIRT1 gene, due to the deficiency in a number of trace elements under these conditions.

Effect of Methyl Jasmonate on the Expression of Wcs Genes and the Activity of Antioxidant Enzymes at Wheat Cold Adaptation.

We studied the effect of phytohormone methyl jasmonate (MJ) on the expression of WCS (wheat cold specific) family genes and the activity of the key antioxidant enzymes in wheat seedling leaves at a low hardening temperature (4°C). Incubation at 4°C induced an increase in the cold tolerance of seedlings, which was accompanied by an increase in the levels of transcripts of WCS120 and WCS19 genes as well as an increase in the activity of superoxide dismutase (SOD) and peroxidase (PO). The pretreatment of seedlings with MJ significantly increased the mRNA content of WCS120 and WCS19 genes and, at the same time, caused an increase in the activity of SOD and PO, thus contributing to further increase in the cold tolerance of the plants (i.e., enhanced the hardening effect induced by low temperature).

The level of proapoptotic gene transcripts in wheat leaves under high temperature stress.

Under exposure of wheat plants to high temperatures (33, 37, and 43°C), the level of transcripts of the genes encoding proapoptotic proteins-TaMCAII (encodes type II metacaspase) and TaBAX (functional homologue of the CDF1 gene of Arabidopsis thaliana)-in leaf cells increased. This process at temperatures of 37 and 43°C passed ahead of (in the case of TaBAX mRNA) or was accompanied by (in the case of TaMCAII mRNA) the emergence of signs of nucleosomal DNA degradation in leaves. The accumulation of malondialdehyde in the leaves of seedlings exposed to temperatures of 37 and 43°C coincided in time with a change in the TaMCAII gene expression and the emergence of signs of programmed cell death.

The abscisic acid influence on the gene expression of pro- and anti-apoptotic proteins in the leaves of cucumber plants at low temperatures.

We studied the effect of abscisic acid (ABA) on the expression of genes encoding the functional homologues of proapoptotic (CsBAX) and antiapoptotic (CsBI-1) proteins in cucumber leaves at low temperatures. The exposure to a hardening temperature of 12°C caused a slight increase in the level of CsBAX gene transcript and a sharp increase in the CsBI-1 gene transcript. At a damaging temperature of 4°C, the content of the CsBAX gene mRNA significantly increased, whereas the content of the CsBI-1 gene mRNA remained virtually unchanged. The treatment of seedlings with ABA reduced the release of electrolytes from cells and both 12 and 4°C, i.e., increased the cold resistance and simultaneously decreased the level of CsBAX gene transcripts, but drastically increased the content of CsBI-1 gene mRNA.

[Similarities and Differences in Wheat Plant Responses to Low Temperature and Cadmium].

A comparative study was performed on the accumulation of biomass, dynamics of indicators of the activity of photosynthetic apparatus, and cold tolerance in the seedlings of frost-tolerance wheat varieties under the effect of a low hardening temperature and cadmium. It was found that the plant responses to the effects of the stressors studied are similar: an increase in cold tolerance of leaves, slowing rates of plant growth and photosynthesis, and increased non-photochemical fluorescence quenching were observed in both cases. At the same time, it was noted that the plant responses to the actions of low temperature and Cd have certain differences associated with the negative effect of Cd on growth and photosynthetic activity.

[The resistance of plants Setaria veridis (L.) Beauv. to the influence of cadmium].

It was shown that cadmium causes a slowdown of green foxtail Setaria veridis (L.) Beauv. shoots; however it had no effect on root growth or accumulation of underground and above-ground biomass. In the analysis of the effect of cadmium on the water regime and photosynthesis of plants, it was found that it had a negative effect on the stomatal-apparatus, which led to a decrease in the transpiration rate and stomatal conductance. It was noted that the water content of tissues, as well as the rate of photosynthesis in the presence of cadmium, reinained at the level of those in'control planrits. A high resistance of green foxtail to the effects of cadmium was established, which is provided with different adaptive mechanisms and anatomical and physiologicdal characteristics associated with its affiliation to the group of C4-plants.

[Effect of low 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 degrees 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 nonphotochemical extinguishing 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.

[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(-1) substrate had no significant effect on most of the plant growth parameters. However, higher metal concentrations (160 and 320 mg kg(-1) substrate) inhibited shoot biomass, leaf area, inflorescence length, and biomass. At the same time, parameters such as the content of chlorophyll (a + b), F0, F(v), and the F(v)/F(m) rate were not reduced even in the presence of zinc in the highest concentrations (320 mg kg(-1) 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.