Katarzyna Hura

Effect of long-term drought stress on leaf gas exchange and fluorescence parameters in C3 and C4 plants

A field study was performed on triticale, field bean, maize and amaranth, to find differences between studied species in physiological alterations resulting from progressive response as injuries and/or acclimation to long-term soil drought during various stages of plant development. The measurements of leaf water potential, electrolyte leakage, chlorophyll a fluorescence, leaf gas exchange and yield analysis were done. A special emphasis was given to the measurements of the blue, green, red and far-red fluorescence. Beside, different ratios of the four fluorescence bands (red/far-red: F690/F740, blue/red: F440/F690, blue/far-red: F440/F740 and blue/green: F440/F520) were calculated. Based on both yield analysis and measurements of physiological processes it can be suggested that field bean and maize responded with better tolerance to the water deficit in soil due to the activation of photoprotective mechanism probably connected with synthesis of the phenolic compounds, which can play a role of photoprotectors in different stages of plant development. The photosynthetic apparatus of those two species scattered the excess of excitation energy more effectively, partially through its transfer to PS I. In this way, plants avoided irreversible and/or deep injuries to PS II. The observed changes in the red fluorescence emission and in the Fv/Fm for triticale and amaranth could have occurred due to serious and irreversible photoinhibitory injuries. Probably, field bean and maize acclimatized more effectively to soil drought through the development of effective mechanisms for utilising excitation energy in the photosynthetic conversion of light accompanied by the mechanism protecting the photosynthetic apparatus against the excess of this energy.

The Effects of Cold Acclimation on Photosynthetic Apparatus and the Expression of COR14b in Four Genotypes of Barley (Hordeum vulgare) Contrasting in their Tolerance to Freezing and High-light Treatment in Cold Conditions

BACKGROUND AND AIMS Cold acclimation modifies the balance of the energy absorbed and metabolized in the dark processes of photosynthesis, which may affect the expression of cold-regulated (COR) genes. At the same time, a gradual acclimation to the relatively high light conditions is observed, thereby minimizing the potential for photo-oxidative damage. As a result, the resistance to photoinhibition in the cold has often been identified as a trait closely related to freezing tolerance. Using four barley genotypes that differentially express both traits, the effect of cold acclimation on freezing tolerance and high-light tolerance was studied together with the expression of COR14b, one of the best-characterized barley COR genes. METHODS Plants were cold acclimated for 2 weeks at 2 degrees C. Freezing tolerance was studied by means of electrolyte leakage. Changes in photosynthetic apparatus and high-light tolerance were monitored by means of chlorophyll fluorescence. Accumulation of COR14b and some proteins important in photosynthetic acclimation to cold were studied with western analysis. COR14b transcript accumulation during cold acclimation was assessed with real-time PCR. KEY RESULTS Cold acclimation increased both freezing tolerance and high-light tolerance, especially when plants were treated with high light after non-lethal freezing. In all plants, cold acclimation triggered the increase in photosynthetic capacity during high-light treatment. In two plants that were characterized by higher high-light tolerance but lower freezing tolerance, higher accumulation of COR14b transcript and protein was observed after 7 d and 14 d of cold acclimation, while a higher transient induction of COR14b expression was observed in freezing-tolerant plants during the first day of cold acclimation. High-light tolerant plants were also characterized with a higher level of PsbS accumulation and more efficient dissipation of excess light energy. CONCLUSIONS Accumulation of COR14b in barley seems to be important for resistance to combined freezing and high-light tolerance, but not for freezing tolerance per se.

Possible contribution of cell-wall-bound ferulic acid in drought resistance and recovery in triticale seedlings.

Studies were undertaken to estimate whether the presence of free and cell-wall-bound ferulic acid in leaf tissues can support drought resistance and its recovery under rehydration. An experiment was carried out on two genotypes of winter triticale: Lamberto and Ticino, at the propagation phase. Lamberto exhibited high content of ferulic acid bound with carbohydrates of the cell-wall under drought and rehydration. The markedly better parameters of chlorophyll fluorescence for this variety under both treatments correlated strongly and positively with the high contents of cell-wall-bound ferulic acid. The photosynthetic apparatus of Lamberto, in relation to Ticino, proved to be the more efficient after 4 weeks of drought treatment. The after-effects of soil drought better elicited the function disturbances of the photosynthetic apparatus in Ticino, which did not fully recover in comparison to Lamberto. Ferulic acid covalently bound to carbohydrates of the cell wall may act as a light filter limiting mesophyll penetration under drought conditions and can also support drought adaptation by down-regulation of leaf growth. The observed increase in the content of cell-wall-bound ferulic acid, as a response to water deficit in the leaf, could be one of the protective mechanisms induced by drought conditions. The ability to accumulate phenolic compounds in dehydrated leaves might be an additional and reliable biochemical parameter indicating the resistance of plants to drought stress.

An increase in the content of cell wall-bound phenolics correlates with the productivity of triticale under soil drought

The objective of this study was to investigate whether the content of cell wall-bound phenolics can simultaneously influence both the productivity and the water status of triticale under soil drought conditions. Two parallel treatments were carried out. The T1 treatment involved plants being subjected to soil drought twice, during the tillering phase and then during the flowering phase. The T2 treatment included drought only during the flowering phase. After T1 treatment, the majority of cultivars exhibited better PSII functioning at the flowering phase in comparison to T2, which could be related to better adaptation of the photosynthetic apparatus to leaf dehydration. Simultaneously, the higher activity of the photosynthetic apparatus of flag leaves for T1 was significantly correlated with the higher content of cell wall-bound phenolics. The dry mass of plants was markedly lower in the T1 treatment and was correlated with a higher content of cell wall-bound phenolics. Moreover, cultivars subjected to the T1 treatment showed a significantly higher water content in comparison to the T2 treatment. The delay in the leaf rolling and the ageing of plants in the T1 treatment, which induced a higher level of cell wall-bound phenolics, was visual proof of the improvement in the water status of plants. Phenolic compounds that form cross-bridges with carbohydrates of the cell wall can be considered a more effective biochemical protective mechanism than free phenolics during the dehydration of leaves. This potentially higher level of effectiveness is likely the result of the double action of phenolic compounds, both as photoprotectors of the photosynthetic apparatus and hydrophobic stabilizers, preventing water loss from the apoplast.

Physiological and biochemical parameters for identification of QTLs controlling the winter triticale drought tolerance at the seedling stage

The genetic map of the triticale is created on the basis of double-haploid (DH) lines, derived from F1 hybrids of a cross between the parental line Saka3006 and Modus. In order to localise drought resistance genes, it is necessary to find a phenotype feature which clearly differentiates between parental lines under drought stress conditions. With the future in mind, the aim of the presented studies was to analyse differences in the response to drought stress, between Saka3006 and Modus. Analyses of the water status of leaves, and the activity of the photosynthetic apparatus and protective mechanisms relating to the accumulation of phenolic compounds, were carried out. The studies were completed during the tillering phase. Statistically significant changes, between genotypes experiencing the drought period, were noticed for the osmotic potential, leaf water content, some parameters of chlorophyll fluorescence, and for phenolics and the ferulic acid content. On the basis of the studies, the Saka genotype can be considered drought resistant due to higher leaf water content caused, probably, by smaller hydraulic resistance relative to Modus. The activity of its photosynthetic apparatus during drought was higher than that for the Modus genotype. The high level of phenolic compounds, which can act as photoprotectors and free radical scavengers, was also maintained. All the mentioned parameters can represent the potential phenotype features, which allow the identification of resistance genes on the genetic map of the triticale, which is currently being created.

Differences in the physiological state between triticale and maize plants during drought stress and followed rehydration expressed by the leaf gas exchange and spectrofluorimetric methods

The studies were carried out in order to estimate differences in the physiological state between triticale and maize plants subjected to drought stress followed by rehydration. The physiological state of the plants was evaluated by measurements of leaf water potential, net photosynthesis, transpiration and stomatal conductance. Spectrofluorimetric methods for the study of blue, green and red fluorescence were applied.We observed that the soil drought induced a greater water loss in triticale leaves than in maize and consequently caused greater injuries to the photosynthetic apparatus. Moreover, triticale plant recovery was slower than in maize plants during the rehydration phase. The effect was probably connected with the higher functional and structural disorganisation of the photosynthetic apparatus observed during drought stress in triticale. Water stress is responsible for damages to photosystem PS II. The worst light utilisation in photosynthetic light conversion was recorded as an increase in the intensity of red fluorescence. Drought stress induced a strong increase in the intensity of blue and green fluorescence in the studied species and it was still high in maize plants during the first day of rehydration. Increase in the intensity of blue and green fluorescence in maize seems to be the effect of the photoprotection mechanism which prevents damage to PS II through utilisation of excess energy.

Changes in response to drought stress of triticale and maize genotypes differing in drought tolerance

Direct effects and after-effects of soil drought for 7 and 14 d were examined on seedling dry matter, leaf water potential (ψ), leaf injury index (LI), and chlorophyll (Chl) content of drought (D) resistant and sensitive triticale and maize genotypes. D caused higher decrease in number of developed leaves and dry matter of shoots and roots in the sensitive genotypes than in the resistant ones. Soil D caused lower decrease of ψ in the triticale than maize leaves. Influence of D on the Chl b content was considerably lower than on the Chl a content. In triticale the most harmful D impact was observed for physiologically younger leaves, in maize for the older ones. A period of 7-d-long recovery was too short for a complete removal of an adverse influence of D.

Leaf Dehydration Induces Different Content of Phenolics and Ferulic Acid in Drought-Resistant and -Sensitive Genotypes of Spring Triticale

Analyses of the total pool of phenolic compounds and ferulic acid, as a photoprotector of the photosynthetic apparatus, and the activity of L-phenylalanine ammonia-lyase (PAL), as a key enzyme in phenolics synthesis, were carried out. Measurements were performed on drought-resistant (CHD 12, CHD 147) and -sensitive (CHD 220, CHD 247) genotypes of spring triticale during flowering under increasing leaf water deficit. Additionally, the emission of blue and red fluorescence from leaves were estimated. The exclusively in the resistant triticale genotype CHD 247 observed simultaneous increase in the content of ferulic acid and the total pool of phenolic compounds as a response to the leaf water deficit seems to be a promising biochemical indicator for a reliable selection of genotypes most resistant to drought stress. For the other genotypes, an increase in the total pool of phenolic compounds is accompanied by a decrease in the content of ferulic acid. An increase in the emission of red fluorescence, correlated with the high content of phenolic compounds, indicates the possibilities of these substances participating in the mechanisms of adaptation of the photosynthetic apparatus to water deficit in leaf tissues.

The relations between drought susceptibility index based on grain yield (DSIGY) and key physiological seedling traits in maize and triticale genotypes

The physiological reasons for the differences in sensitivity of C3 and C4 plant species to environmental stresses have not been thoroughly explained. In this study the effects of drought stress on the growth and selected physiological traits were examined in the seedlings of 13 single cross maize (C4 plant) hybrids and 11 spring triticale (C3 plant) breeding lines and varieties differing in drought sensitivity. For plants in the seedling stage the results demonstrated a genetic variation in dry matter accumulation of shoots and roots (DWS, DWR), number (N) and length (L) of particular components (seminal, seminal adventitious, nodal) of the root system, membrane injury by soil drought (LID), osmotic and high temperature stress (LIOS, LIHT), water potential (ψ), water loss (WL), grain germination in osmotic stress (FG, PI), and seedling survival (SS). Seedlings grown under moderate soil drought showed a decrease in dry matter of the top parts and roots and a decrease in the length of seminal, seminal adventitious and nodal roots in comparison to seedlings grown in control conditions. The observed harmful effects of drought stress were more distinct in drought sensitive genotypes. Used in this paper drought susceptibility indexes (DSIGY) were calculated in other experiment by determining the changes in grain yield (GY) under two soil moisture levels (irrigated and drought). The variation of DSIGY for maize ranges from 0.381 to 0.650 and for triticale from 0.354 to 0.578. The correlations between DSIGY and laboratory tests (LI, FG, SS) confirmed that they are good indicators of drought tolerance in plants. The highest values of genetic variation were observed in LI, DWS, SS and WL and the lowest in the measurements of ψ FG, PI, LS, LSA and LN. The correlation coefficients between LIOS and LIHT tests were, in most of the considered cases, statistically significant, which indicates that in maize and triticale the mechanisms of membrane injury caused by simulated drought or high temperature are physiologically similar. It can be concluded that an approach to the breeding of maize and triticale for drought tolerance using these tests can be implemented on the basis of separate selection for each trait or for all of them simultaneously. In that case, it would be necessary to determine the importance of the trait in relation to growth phase, drought timing and level, as well as its associations with morphological traits contributing to drought tolerance. The obtained values of the correlation coefficient between laboratory tests suggest that the same physiological traits may be applied as selection criteria in drought tolerance of maize and triticale genotypes.

Reaction of winter oilseed rape callus to different concentrations of elicitors: pectinase or chitosan

The aim of the presented methodical experiments was 1) the evaluation if callus of winter oilseed rape (Brassica napus var. oleifera L.) initiates a defence reaction to fungal elicitors: pectinase (polygalacturonase) or chitosan, and 2) the choice of the elicitor doses, which evoke the strongest tissue reaction. The results obtained will be used in the next experiments relating the studies of pathogenesis mechanisms proceeding in rape plants infected by necrotrophic fungi. The defence response was estimated on the basis of changes in electrolyte leakage from cells, metabolic efficiency, phenolic content and catalase activity. In the experiment pectinase was used at concentration of 3, 8, 16, 133 and 166 µl per 1 cm3 of culture medium while chitosan at: 25, 50, 75 and 100 µg·cm−3. Both elicitors increased cell membrane permeability: pectinase at the doses equal or greater to 16 µl·cm−3 while chitosan of 25 µg·cm−3. The greatest metabolic inefficiency was observed in calli elicited with 16 µl·cm−3 pectinase and with chitosan of 100 µg·cm−3. The decrease in phenolic content was noted under influence of most doses of both elicitors. The highest catalase activity was evoked by pectinase of 8 µl·cm−3 and chitosan of 75 and 100 µg·cm−3. The results indicated that 8–16 µl·cm−3 of pectinase and 100 µg·cm−3 of chitosan caused the strongest defence reaction of oilseed rape tissue.