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The objective of this study was to assess the effect of an elevated atmospheric CO2 molar ratio on freezing tolerance, photosynthetic apparatus performance and expression of CBF6, Cor14b and LOS2 in meadow fescue (Festuca pratensis Huds.). It was shown that cold acclimation under a CO2 molar ratio of 800 μmol mol(air)−1 decreased the freezing tolerance of meadow fescue when compared to the ambient CO2 level. This effect was not related either to changes observed in PSII redox state or to photosynthetic acclimation to cold, which was in fact more effective at an elevated CO2 level. The decrease in freezing tolerance was linked to changes in the expression of CBF6 and LOS2 genes, whereas the protective effect on photosynthetic apparatus was connected with the activation of a non-photochemical mechanism of photoprotection as well as upregulation of FpCOR14b expression.

PsbO, the manganese-stabilizing protein, plays a crucial role in oxygen-evolving complex functioning and stabilization, by maintaining optimal manganese, calcium and chloride concentrations at the active state of PSII. In this paper we present a study focused on recognizing the relationship between psbO gene activity and acclimation of the photosynthetic apparatus under abiotic stresses in the grasses Festuca arundinacea and F. pratensis. PsbO expression was compared between two distinct genotypes within each species which differed in their levels of stress tolerance (drought and frost, respectively) during drought treatment (F. arundinacea) and cold acclimation (F. pratensis). The research involved: (1) the analyses of psbO gene expression profiles using real-time PCR, and (2) the analyses of PsbO protein accumulation profiles using protein gel blot hybridization. The results indicate that PsbO plays a protective function with respect to the photosynthetic apparatus during abiotic stresses. In cold-treated F. pratensis plants the accumulation of PsbO seems to be responsible for differences in the PSII photochemical efficiency. Higher stability of PSII during drought, observed in the high-drought tolerant F. arundinacea genotype, is not associated with PsbO accumulation, although the degradation of this protein affects destabilization of the oxygen-evolving complex in drought.

Drought is the most significant abiotic stress in agriculture; thus, this area of studies seems to be one of the most important challenges in plant biology. Data about gene expression under drought are crucial to study drought response mechanisms and to select the genes for a transgenic approach. Quantitative RT-PCR is a powerful method for gene expression analysis; however, obtaining proper data normalization requires internal reference genes with stable level of expression. In the present paper ten potential reference genes were examined in two developmental stages of barley for their expression stability during leaf growth and increasing drought level. The results indicated that leaf growth per se affects the expression of studied genes to the similar extent as the drought and showed that different genes were most stably expressed in the seedling and the heading stage. As a result, different sets of reference genes were selected for different applications. For instance, ADP-ribozylation factor 1 and ubiquitin encoding genes were most suitable to study drought-induced changes in gene expression at the seedling stage, whereas actin and GAPDH genes were useful during heading, and ADP-ribozylation factor 1 and HSP90 allowed for the comparison between these two stages. Our data proved the necessity for validation of commonly used reference genes. The results indicate that expression of ADP seems to be the least affected by all the factors studied in the present experiment. However, when the effect of only one factor among those investigated in this work will be studied, different genes should be considered to be used as the references due to the higher stability of their expression.

The freezing tolerance of 69 accessions of field-grown, common wheat (Triticum aestivum) was assessed in three consecutive winters. To measure freezing tolerance directly, field-grown plants were subjected to a range of freezing temperatures in a controlled environment and plant regrowth was subsequently assessed. Indirect assessments of freezing tolerance, as measured by chlorophyll fluorescence transient measurements followed by a JIP-test (an in vivo measurement of the adaptive behavior of the photosynthetic apparatus), were performed on detached leaves frozen at the same time as whole plants. Both direct and indirect tests were also used on plants cold acclimated in the laboratory. These results were compared with results of a field survival study performed at seven experimental sites. An analysis of the data indicated that only some of the JIP-test parameters were suitable for the prediction of freezing tolerance and winter survival. Estimates of cold hardiness were very similar, regardless of the experimental year, but were dependent on the method of cold acclimation and time of sampling. Indirect measurements of cold hardiness were more in line with the field survival data for field-cold-acclimated plants sampled in mid-winter than for plants that were either sampled earlier or cold acclimated in the laboratory. Indirect measurements taken on leaves that had not frozen failed to provide accurate estimates of cold hardiness. Our observations, together with previously reported findings, indicate that cold acclimation under natural field conditions activates a greater array of freezing tolerance mechanisms than cold acclimation performed in under controlled environmental conditions in a laboratory.

The fungus Leptosphaeria maculans that causes blackleg can attack winter rape throughout the entire growing season. Therefore, appropriate treatments were designed to simulate environmental factors that may occur under field conditions. The callus tissue of winter rape was treated with abiotic stress in the form of cold (2 °C) and temperature change (2/20 °C and 20/2 °C), and biotic stress in the form of secondary metabolites of L. maculans. The following parameters were analyzed: total phenolics, the activity of l-phenylalanine ammonia lyase (PAL), catalase, respiration intensity, heat emission, and metabolic activity determined by means of 2,3,5-triphenyl-tetrazolium chloride (TTC) assay. Additionally, the changes in the electrical potential, known as a sensitive indicator of biochemical changes in the callus tissue, were measured. The obtained results seem to indicate rather increased stress, caused by temperature (2 or 20 °C) or its changes (2/20 °C, 20/2 °C) and the secondary metabolites of L. maculans than a cross reaction. The factor that most strongly affected the metabolism of winter rape callus tissue was the temperature change, which masked the changes caused by the fungal secondary metabolites or intensified their adverse effects. The only parameters that could be regarded as reliable indicators of the callus tissue response to the elicitation with secondary metabolites of L. maculans were catalase activity and respiration intensity. Additionally, a protective function of low temperature involved a reduction in catalase activity, resulting in increased level of reactive oxygen species (ROS), key molecules inducing the defense mechanisms during pathogenesis. Only the changes in l-phenylalanine ammonia lyase (PAL) activity and the accompanying changes in the content of phenolic compounds can be considered as beneficial effects of low temperature (2 °C) on a more efficient callus acclimation to the biotic stress.

Previously published results showed that high relative reduction state of PSII (PSII excitation pressure) during both early seedling growth (prehardening) as well as cold deacclimation caused significant changes in growth pattern. The differences in elongation growth rate were related to the cold acclimation of photosynthetic apparatus and to frost resistance. To study changes in the hormonal balance connected with alterations in elongation growth rate observed during prehardening and deacclimation under different PSII excitation pressure (modulated by day-temperatures), endogenous concentration of ABA, GA3 and GA-like substances (GAs) were analysed. Analyses were also performed during cold acclimation and reacclimation of plants characterized by different elongation growth rate triggered by prehardening or deacclimation under different day-temperatures. Growth under high PSII excitation pressure (prehardening) resulted in a significant increase in ABA and a considerable decrease in GAs contents. On the other hand, different ABA content played almost no role in controlling growth rate during cold deacclimation and subsequent reacclimation, when the induction of elongation growth was connected with the changes in concentration of GAs including GA3. The possible role of ABA and GAs in controlling prehardening, cold acclimation and deacclimation is discussed.

The experiments were performed to check the effects of exogenous ABA and gibberellin on photosynthetic apparatus and leaf resistance to freezing. In the experiment, two cultivars (winter and spring) of oilseed rape were used in the experiment. Discs, cut out from leaves of cold acclimated plants grown at 12 and 20 °C at similar PPFD levels, were immersed for 72 hours in growth regulator solutions. Some of discs were additionally subjected to high radiation. Independently on cultivar studied, the effects of growth regulator treatments were significant only in leaves developed at 20 °C. ABA treatment increased frost resistance, promoted photosynthetic activity measured in cold and inhibited expansion of leaf-disc area, whereas GA3 evoked opposite effects. The treatment with growth regulators particularly affected the resistance of photosynthetic apparatus to high light. In this case ABA treatment decreased, whereas GA3 increased photoinhibition of PSII. The outcomes may suggest that in the ABA-treated plants PSII is better protected against photoinduced inactivation both by the increase in effectiveness of photosynthetic dark reactions at high light/low temperature conditions, increased energy dissipation in xantophyll cycle and enhanced accumulation of anthocyanins. GA3 treatment may affect the resistance to photoinhibition directly via decrease in anthocyanins contents and indirectly through increase of elongation growth rate in the tissue.

The presented work was conducted on seedlings of spring barley and meadow fescue which differ in the degree of sensitivity to leaf spot pathogen Bipolaris sorokiniana (Sacc.) Shoem. The seedling reaction to inoculation with mycelium and conidia was examined in glasshouse conditions on the basis of respiration intensity and heat production. The leaf respiration was measured using Clark-type electrode, while heat emission was evaluated by means of isotermic microcalorimeter. The measurements were performed after 1, 3, 6, 10, 24, 48, 72, 168 and 240 hours since the inoculation moment.

Studies on the effects of temperature during the early stage of growth on frost resistance of winter rape seedlings under controlled conditions were performed. It was found that cold acclimation responses of plants were affected to a great extent by the conditions of the seedlings early growth. During this period, when the day temperatures were reduced to the range from +10 °C to +15 °C, a process termed “prehardening” was observed.

During cold acclimation by higher plants, temperature perception via changes in redox state of Photosystem II (PSII) and subsequent acclimation of the photosynthetic apparatus to cold is very important for achieving freezing tolerance. These properties were studied in two groups (A and B) of the same backcross 3 (BC3) progeny derived from a triploid hybrid of Festuca pratensis (2×) × Lolium multiflorum (4×) backcrossed three times onto diploid L. multiflorum cultivars. Leaves of Group A plants formed at 20°C at medium-low light were unable to acclimate their photosynthetic apparatus to cold. Compared to Group B, the Group A plants were also more frost sensitive. This acclimation ability correlated with the freezing tolerance of the plants. However, leaves of the same Group A plants developed at 20°C, but under higher-light conditions had increased ability to acclimate their photosynthetic apparatus to cold. It was concluded that Group A plants may have impaired PSII temperature perception, and this then resulted in their poor capability to cold acclimate.

Plants have developed different strategies to adapt to various stress conditions including drought. In the present study the drought-induced changes in the actin filament (AFs) network was studied, for the first time, in two barley cultivars of contrasting drought tolerance level. Detached leaves of drought-tolerant (cv. ‘CAM/B1/CI’) and drought-susceptible (cv. ‘Maresi’) cultivars were dried under controlled conditions. The water relations as well as the transcript accumulation of actin (ACT11), actin depolymerization factor (ADF1) and dehydrine (HVA1) encoding genes were studied using qRT-PCR. Quantitative (the relative fluorescence index; RFI) and qualitative drought-induced changes in AF cytoskeleton were observed following staining with phalloidin. It was noticed that tolerant cultivar was characterized with relative water content decreased during drought treatment which was accompanied by increase in HVA1 expression together with decrease in ACT11 and ADF1 transcripts accumulation induced by drought. In drought-susceptible cultivar the expressions of both ACT11 and ADF1 were slightly lower than those in the control. Drought triggered an extensive AF cytoskeleton reorganization within different types of leaf-blade cells. Remarkable changes in AF configuration and its increased amount (fluorescence intensity) were observed mainly in drought-tolerant cultivar. In addition, drought-induced changes in AFs were closely associated with chloroplasts. Those AFs probably controlled drought-induced intracellular chloroplast positioning in mesophyll. Based on the results obtained in the present study, the possible role of AF rearrangements in drought response is discussed.