Tomasz 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.

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.

The impact of limited soil moisture and waterlogging stress conditions on morphological and anatomical root traits in maize (Zea mays L.) hybrids of different drought tolerance

Effects of soil drought or waterlogging on the morphological traits of the root system and internal root anatomy were studied in maize hybrids of different drought tolerance. The investigations comprised quantitative and qualitative analyses of a developed plant root system through determining the number, length and dry matter of the particular components of the root system and some traits of the anatomical structure of the seminal root. Obtained results have demonstrated a relatively broad variation in the habit of the root system. This mainly refers, to the number, length and dry matter of lateral roots, developed by seminal root, seminal adventitious and nodal roots as well as to some anatomical properties of the stele, cortex and metaxylem elements.Plants grown under waterlogging or drought conditions showed a smaller number and less dry matter of lateral branching than plants grown in control conditions. The harmful effect of waterlogging conditions on the growth of roots was greater when compared with that of plants exposed to drought. In the measurements of the root morphological traits, the effect of soil drought on the internal root anatomical characteristic was weaker than the effect of soil waterlogging. The observed effects of both treatments were more distinct in a drought sensitive hybrid Pioneer D than in drought resistant Pioneer C one. The drought resistant hybrid Pioneer C distinguished by a more extensive rooting and by smaller alterations in the root morphology caused by the stress conditions than drought sensitive hybrid Pioneer D one. Also the differences between the resistant and the sensitive maize hybrids were apparent for examined root anatomical traits. Results confirm that the hybrid Pioneer D of a high drought susceptibility was found to be also more sensitive to periodieal soil water excess. A more efficient water use and a lower shoot to root (S:R) ratio were found to be major reasons for a higher stress resistance of the hybrid Pioneer C.The reasons for a different response of the examined hybrids to the conditions of drought or waterlogging may be a more economical water balance and more favourable relations between the shoot and root dimensions in the drought resistant genotype. The observed modifications of the internal root structure caused by water deficit in plant tissues may partly influence on water conductivity and transport within roots.The results suggest that the morphological and anatomical traits of the maize root system may be used in practice as direct or indirect selection criteria in maize breeding.

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 impact of different soil moisture and soil compaction on the growth of triticale root system

Effects of different soil moisture (soil drought and waterlogging) and soil compaction (1.33 and 1.50 g·cm−3) on the growth and morphological traits of the root system were studied in four breeding forms and seven cultivars of triticale. Morphological changes, including the restriction of root extension, expansion and proliferation of laterals roots, occur in plants grown in different soil moisture and in compact soil. The investigations comprised quantitative and qualitative analyses of a developed plant root system through determining the number, length and dry matter of the particular components of the root system.Obtained results have demonstrated a relatively broad variation in the habit of the triticale root system. Plants grown under compact soil and low or high soil water content showed a smaller number and less dry matter of lateral branching than plants grown in control conditions. The harmful effects of compact soil and drought conditions on the growth of roots was greater when compared with that of plants exposed to waterlogging. The observed effects of all treatments were more distinct in a drought sensitive strains. The drought resistant forms were a more characterize with extensive rooting and by smaller alterations in the root morphology under the stress conditions compared with drought sensitive one. Results confirm that the breeding forms (CHD-12 and CHD-173) of a high drought susceptibility was found to be also more sensitive to periodical soil water excess. A more efficient water use and a lower shoot to root (S/R) ratio were found to be major reasons for a higher stress resistance of the breeding forms (CHD-220 and CHD-247). The reasons for a different response of the examined breeding forms and cultivars to the conditions of drought or waterlogging may be a more economical water balance and more favourable relations between the shoot and root dimensions in the drought resistant forms and cultivars. The results suggest that the morphological traits of the triticale root system may be used in practice as direct or indirect selection criteria in maize breeding.

Erratum to: The relationship between seedling growth and grain yield under drought conditions in maize and triticale genotypes

The effects of drought stress on seedlings’ growth and grain yield of 13 single cross maize hybrids and 11 breeding lines and cultivars of spring triticale were studied in greenhouse and field experiments. In the field experiment, the drought susceptibility index (DSIGY) was calculated by determining the change in grain yield (GY) in conditions with two soil moisture levels (IR, irrigated; D, drought). In the greenhouse experiment the response to soil drought was evaluated using DSIDW, by determining changes in the dry weight (DW) of vegetative plant parts. Marked variations in GY and DW were observed among the studied genotypes. In control conditions, the GY and DW in drought-sensitive genotypes were higher compared to the drought-resistant ones; but in drought conditions, the decreases in GY and DW in resistant genotypes were smaller than in drought-sensitive ones. DSIGY and DSIDW revealed variations in the degree of drought tolerance among the examined maize and triticale genotypes. The values of DSIGY in the field experiment and DSIDW in the greenhouse experiment enabled a division of the studied genotypes into drought-resistant or -sensitive groups. A close correlation between DSIGY and DSIDW was found. The positive linear correlation and determination coefficients between DSIGY and DSIDW were statistically significant (P = 0.05), being equal to R2 = 0.614 (maize) and R2 = 0.535 (triticale). The ranking of the studied genotypes based on DSIGY was in most cases consistent with the ranking based on DSIDW, which indicates that genetically conditioned drought tolerance is similar for plants in the seedling and reproductive growth stages or may at least partly have a common genetic background.