The use of L-phenylalanine ammonia lyase inhibitors in plant ecophysiological studies / Zastosowanie inhibitorów amoniakoliazy L-fenyloalaniny w badaniach ekofizjologii roslin.

Phenylalanine ammonia lyase (PAL) is a key enzyme controlling the biosynthesis of phenolic compounds in plants. PAL catalyzes ammonia elimination from L-phenylalanine in a reaction that yields cinnamic acid, a precursor of a large group of phenylpropanoid compounds. Phenylpropanoids and their derivatives play an important role in regulating plant resistance mechanisms under environmental stresses. By reducing the level of phenolic compounds, PAL inhibitors can induce changes in plant metabolism. This paper presents the current state of knowledge on the use of PAL inhibitors in plant biology, and draws attention to the possibilities of using PAL inhibitors in agriculture in the context of the witnessed climate changes which increase the frequency and intensity of some disasters such as droughts, floods and storms. By reducing the level of phenolic compounds, PAL inhibitors can induce changes in plant metabolism. This paper presents the current state of knowledge on the use of PAL inhibitors in plant biology, and draws attention to the possibilities of using PAL inhibitors in agriculture in the context of the witnessed climate changes.

Toward resilient agriculture and environmental protection: The role of cell wall-bound phenolics.

Due to their unpredicted scope, duration, and effects, soil droughts pose a serious threat to agriculture. Gradual steppe formation and desertification of farming and horticultural lands are the consequences of climate change. Irrigation systems for field crops do not offer the most viable solution, as they depend heavily on freshwater resources, which are currently scarce. For these reasons, it is necessary to obtain crop cultivars that are not only more tolerant to soil drought, but also capable of effective use of water during and after drought. In this article, we highlight the importance of cell wall-bound phenolics in the efficient adaptation of crops to arid environments and protection of soil water resources.

Cell dehydration of intergeneric hybrid induces subgenome-related specific responses.

The aim was to identify subgenome-related specific responses in two types of triticale, that is, of the wheat-dominated genome (WDG) and rye-dominated genome (RDG), to water stress induced in the early phase (tillering) of plant growth. Higher activity of the primary metabolism of carbohydrates is a feature of the WDG type, while the dominance of the rye genome is associated with a higher activity of the secondary metabolism of phenolic compounds in the RDG type. The study analyzed carbohydrates and key enzymes of their synthesis, free phenolic compounds and carbohydrate-related components of the cell wall, monolignols, and shikimic acid (ShA), which is a key link between the primary and secondary metabolism of phenolic compounds. Under water stress, dominance of the wheat genome in the WDG type was manifested by an increased accumulation of the large subunit of Rubisco and sucrose phosphate synthase and a higher content of raffinose and stachyose compared with the RDG type. In dehydrated RDG plants, higher activity of L-phenylalanine ammonia lyase (PAL) and L-tyrosine ammonia lyase (TAL), as well as a higher level of ShA, free and cell wall-bound p-hydroxybenzoic acid, free homovanillic acid, free sinapic acid, and cell wall-bound syringic acid can be considered biochemical indicators of the dominance of the rye genome.

Drought-Stress Induced Physiological and Molecular Changes in Plants 2.0.

Plant adaptation to soil drought is a topic that is currently under investigation [...].

The role of invasive plant species in drought resilience in agriculture: the case of sweet briar (Rosa rubiginosa L.).

Sweet briar (Rosa rubiginosa) belongs to the group of wild roses. Under natural conditions it grows throughout Europe, and was introduced also into the southern hemisphere, where it has efficiently adapted to dry lands. This review focuses on the high adaptation potential of sweet briar to soil drought in the context of global climatic changes, especially considering steppe formation and desertification of agricultural, orchard, and horticultural areas. We provide a comprehensive overview of current knowledge on sweet briar traits associated with drought tolerance and particularly water use efficiency, sugar accumulation, accumulation of CO2 in intercellular spaces, stomatal conductance, gibberellin level, effective electron transport between photosystem II and photosystem I, and protein content. We discuss the genetics and potential applications in plant breeding and suggest future directions of study concerning invasive populations of R. rubiginosa. Finally, we point out that sweet briar can provide new genes for breeding in the context of depleting gene pools of the crop plants.

Drought-Stress Induced Physiological and Molecular Changes in Plants.

Soil drought is one of the major abiotic stresses that inhibits the growth, development, and yield of crops all over the world [...].

Non-rolling flag leaves use an effective mechanism to reduce water loss and light-induced damage under drought stress.

BACKGROUND AND AIMS: The study reports on four different types of flag leaf rolling under soil drought in relation to the level of cell wall-bound phenolics. The flag leaf colonization by aphids, as a possible bioindicator of the accumulation of cell wall-bound phenolics, was also estimated. METHODS: The proteins of the photosynthetic apparatus that form its core and are crucial for maintaining its stability (D1/PsbA protein), limit destructive effects of light (PsbS, a protein binding carotenoids in the antennas) and participate in efficient electron transport between photosystems II (PSII) and PSI (Rieske iron-sulfur protein of the cytochrome b6f complex) were evaluated in two types of flag leaf rolling. Additionally, biochemical and physiological reactions to drought stress in rolling and non-rolling flag leaves were compared. KEY RESULTS: The study identified four types of genome-related types of flag leaf rolling. The biochemical basis for these differences was a different number of phenolic molecules incorporated into polycarbohydrate structures of the cell wall. In an extreme case of non-rolling dehydrated flag leaves, they were found to accumulate high amounts of cell wall-bound phenolics that limited cell water loss and protected the photosynthetic apparatus against excessive light. PSII was also additionally protected against excess light by the accumulation of photosynthetic apparatus proteins that ensured stable and efficient transport of excitation energy beyond PSII and its dissipation as far-red fluorescence and heat. Our analysis revealed a new type of flag leaf rolling brought about by an interaction between wheat and rye genomes, and resulting in biochemical specialization of flexible, rolling and rigid, non-rolling parts of the flag leaf. The study confirmed limited aphid colonization of the flag leaves with enhanced content of cell wall-bound phenolics. CONCLUSIONS: Non-rolling leaves developed effective adaptation mechanisms to reduce both water loss and photoinhibitory damage to the photosynthetic apparatus under drought stress.

Wheat and Barley: Acclimatization to Abiotic and Biotic Stress.

Twelve articles (ten research papers and two reviews) included in the Special Issue entitled "Wheat and Barley: Acclimatization to Abiotic and Biotic Stress" are summed up here to present the latest research on the molecular background of adaptation to environmental stresses in two cereal species. Crucial research results were presented and discussed, as they may be of importance in breeding aimed at increasing wheat and barley tolerance to abiotic and biotic stresses.

Phytohormone synthesis pathways in sweet briar rose (Rosa rubiginosa L.) seedlings with high adaptation potential to soil drought.

The study aimed to determine the phytohormone profile of sweet briar rose (Rosa rubiginosa L.) seedlings and privileged synthesis pathways of individual hormones including gibberellins, cytokinins and auxins in response to long-term soil drought. We detected eight gibberellins, nine auxins and fifteen cytokinins. Abscisic acid (ABA) was also detected as a sensitive indicator of water stress. Thirty days of soil drought induced significant increase of ABA content and species-specific quantitative changes of other phytohormones. We established preferred synthesis pathways for three gibberellins, six auxins and eight cytokinins. Both an increase and decrease in gibberellin and cytokinin levels may modulate sweet briar's response to soil water shortage. In the case of auxins, induction of effective adaptation mechanisms to extremely dry environments is mostly triggered by their rising levels. Under drought stress, sweet briar seedlings increased their gibberellin pool at the expense of reducing the pool of cytokinins and auxins. This may indicate a specific role of gibberellins in adaptation mechanisms to long-term soil water deficit developed by sweet briar.

Physiological traits determining high adaptation potential of sweet briar (Rosa rubiginosa L.) at early stage of growth to dry lands.

Little is known about mechanisms of sweet briar adaptation to dry habitats. The species is highly invasive and displaces native plants from dry lands of the southern hemisphere. This study evaluates physiological basis of Rosa rubiginosa L. adaptation to soil drought. We performed a pot soil drought experiment and assessed water relations, water use efficiency, gas exchange and photosynthetic apparatus activity. The study also measured the content of chlorophyll, soluble carbohydrates and proline and analyzed plant biomass growth. We hypothesized that the drought stress induced an effective mechanism enabling adaptation of young sweet briar roses to soil water deficit. The study identified several adaptation mechanisms of R. rubiginosa allowing the plant to survive soil drought. These included limiting transpiration and stomatal conductance, increasing the level of soluble sugars, reducing chlorophyll content, accumulating CO2 in intercellular spaces, and increasing the quantum yield of electron transport from QA- to the PSI end electron acceptors. As a result, young sweet briar roses limited water loss and photoinhibition damage to the photosynthetic apparatus, which translated into consumption of soluble sugars for growth purposes. This study showed that photosynthesis optimization and increased activity of the photosynthetic apparatus made it possible to avoid photoinhibition and to effectively use water and sugars to maintain growth during water stress. This mechanism is probably responsible for the invasive nature of R. rubiginosa and its huge potential to displace native plant species from dry habitats of the southern hemisphere.

Water stress-induced flag leaf senescence may be accelerated by rehydration.

The aim of the study was to determine molecular, biochemical and physiological responses of non-fully recovered DH line of triticale exposed to water stress during generative stage. The study involved two DH lines of winter triticale that produce different number of shoots with ears during rehydration. We analyzed the content of proteins associated with the photosynthetic apparatus and plant senescence. We also determined the content of hydrogen peroxide and assimilation pigments and assessed stomatal conductance and activity of the photosynthetic apparatus. Water stress-initiated senescence did not slow down during rehydration in the not fully recovered DH line. This line showed an increase in pheophorbide a oxygenase (PaO), a protein associated with chlorophyll degradation, and a decrease in the proteins related to its synthesis (chlorophyll synthase - ChS, protochlorophilide oxidoreductase - POR). Pheophorbide a oxygenase is a marker of accelerated cell death as it catalyzes opening of the porphyrin ring in the chlorophyll degradation pathway. The level of hydrogen peroxide remained high during rehydration with the photosynthetic apparatus being one of its sources. Lower content of Rieske protein reduced the quantum yield of electron transport (ϕRo) from the primary acceptors QA/QB to the final acceptors in PSI. Intensification of metabolic processes during rehydration resulted in overloading the electron transport chain in PSII and transfer of electrons from the primary acceptors to oxygen molecule. Overproduction of hydrogen peroxide accelerated senescence during rehydration and significantly reduced plant yield.

Changes in protein abundance and activity induced by drought during generative development of winter barley (Hordeum vulgare L.).

The present study investigated drought-induced changes in proteome profiles of ten DH lines of winter barley, relatively varied in water deficit tolerance level. Additionally, the parameters describing the functioning of the photosynthetic apparatus and the activity of the antioxidative system were analysed. Water deficit (3-week growth in soil with water content reduced to ca. 35%) induced significant changes in leaf water relations and reduced photosynthetic activity, probably due to decreased stomatal conductance. It was associated with changes in protein abundance and altered activity of antioxidative enzymes. From 47 MS-identified proteins discriminating more tolerant from drought-sensitive genotypes, only two revealed distinctly higher while seven revealed lower abundance in drought-treated plants of tolerant DH lines in comparison to sensitive ones. The majority were involved in the dark phase of photosynthesis. Another factor of great importance seems to be the ability to sustain, during drought stress, relatively high activity of enzymes (SOD and CAT) decomposing reactive oxygen species and protecting plant cell from oxidative damages. Low molecular weight antioxidants seem to play less important roles. Our findings also suggest that high tolerance to drought stress in barley is a constitutively controlled trait regulated by the rate of protein synthesis and their activity level. BIOLOGICAL SIGNIFICANCE: According to our knowledge, this is the first comparative proteomic analysis of drought tolerance performed for the model set of several winter barley doubled haploid (DH) lines. We analysed both the drought impact on the protein pattern of individual winter barley DH lines as well as comparisons between them according to their level of drought tolerance. We have identified 47 proteins discriminating drought-tolerant from drought-sensitive genotypes. The majority was involved in the dark phase of photosynthesis. Another factor of great importance in our opinion seems to be the ability to sustain, during drought stress, relatively high activity of antioxidative enzymes (SOD and CAT) decomposing reactive oxygen species and protecting plant cell from oxidative damages. Our findings also suggest that high tolerance to drought stress in barley is a constitutively-controlled trait regulated by the rate of protein synthesis and their activity level.

Wheat and rye genome confer specific phytohormone profile features and interplay under water stress in two phenotypes of triticale.

The aim of the experiment was to determine phytohormone profile of triticale and quality-based relationships between the analyzed groups of phytohormones. The study involved two triticale phenotypes, a long-stemmed one and a semi-dwarf one with Dw1 gene, differing in mechanisms of acclimation to drought and controlled by wheat or rye genome. Water deficit in the leaves triggered a specific phytohormone response in both winter triticale phenotypes attributable to the dominance of wheat (semi-dwarf cultivar) or rye (long-stemmed cultivar) genome. Rye genome in long-stemmed triticale was responsible for specific increase (tillering: gibberellic acid; heading: N6-isopentenyladenine, trans-zeatin-9-riboside, cis-zeatin-9-riboside; flowering: N6-isopentenyladenine, indolebutyric acid, salicylic acid) or decrease (heading: trans-zeatin) in the content of some phytohormones. Wheat genome in semi-dwarf triticale controlled a specific increase in trans-zeatin content at heading and anthesis in gibberellin A1 during anthesis. The greatest number of changes in the phytohormone levels was observed in the generative phase. In both triticale types, the pool of investigated phytohormones was dominated by abscisic acid and gibberellins. The semi-dwarf cultivar with Dw1 gene was less sensitive to gibberellins and its mechanisms of acclimation to water stress were mainly ABA-dependent. An increase in ABA and gibberellins during drought and predominance of these hormones in the total pool of analyzed phytohormones indicated their equal share in drought acclimation mechanisms in long-stemmed cultivar.

Physiological Responses of Rosa rubiginosa to Saline Environment.

The aim of this work was to analyse the response of Rosa rubiginosa to salinity induced by different concentrations of sodium chloride and calcium chloride (0, 25, 50, 100, 150 and 200 mM). Besides salt accumulation and pH changes, other parameters were investigated including photosynthetic activity, leaf water content, the dynamics of necrosis and chlorosis appearance and leaf drying. The study was complemented with microscopic analysis of changes in leaf anatomy. R. rubiginosa was more sensitive to the salinity induced by calcium chloride than by sodium chloride. Plant response to salinity differed depending of the salt concentration. These differences were manifested by higher dynamics of necrosis and chlorosis appearance and leaf drying. CaCl2 showed greater inhibition of the photosynthetic apparatus and photosynthetic activity. Treatment with CaCl2 caused more visible deformation of palisade cells, reduction in their density and overall reduction in leaf thickness. The study demonstrated higher accumulation of CaCl2 in the soil, and thus greater limitations in water availability resulting in reduced leaf water content and quicker drying of leaves as compared with NaCl-treated plants.

QTLs for cell wall-bound phenolics in relation to the photosynthetic apparatus activity and leaf water status under drought stress at different growth stages of triticale.

The present study aimed at identifying the regions of triticale genome responsible for cell wall saturation with phenolic compounds under drought stress during vegetative and generative growth. Moreover, the loci determining the activity of the photosynthetic apparatus, leaf water content (LWC) and osmotic potential (Ψ o) were identified, as leaf hydration and functioning of the photosynthetic apparatus under drought are associated with the content of cell wall-bound phenolics (CWPh). Compared with LWC and Ψ o, CWPh fluctuations were more strongly associated with changes in chlorophyll fluorescence. At the vegetative stage, CWPh fluctuations were due to the activity of three loci, of which only QCWPh.4B was also related to changes in F v/F m and ABS/CSm. In the other QTLs (QCWPh.6R.2 and QCWPh.6R.3), the genes of these loci determined also the changes in majority of chlorophyll fluorescence parameters. At the generative stage, the changes in CWPh in loci QCWPh.4B, QCWPh.3R and QCWPh.6R.1 corresponded to those in DIo/CSm. The locus QCWPh.6R.3, active at V stage, controlled majority of chlorophyll fluorescence parameters. This is the first study on mapping quantitative traits in triticale plants exposed to drought at different stages of development, and the first to present the loci for cell wall-bound phenolics.

Different allocation of carbohydrates and phenolics in dehydrated leaves of triticale.

Carbohydrates are used in plant growth processes, osmotic regulation and secondary metabolism. A study of the allocation of carbohydrates to a target set of metabolites during triticale acclimation to soil drought was performed. The study included a semi-dwarf cultivar 'Woltario' and a long-stemmed cultivar 'Moderato', differing in the activity of the photosynthetic apparatus under optimum growth conditions. Differences were found in the quantitative and qualitative composition of individual carbohydrates and phenolic compounds, depending on the developmental stage and water availability. Soluble carbohydrates in the semi-dwarf 'Woltario' cv. under soil drought were utilized for synthesis of starch, soluble phenolic compounds and an accumulation of cell wall carbohydrates. In the typical 'Moderato' cv., soluble carbohydrates were primarily used for the synthesis of phenolic compounds that were then incorporated into cell wall structures. Increased content of cell wall-bound phenolics in 'Moderato' cv. improved the cell wall tightness and reduced the rate of leaf water loss. In 'Woltario' cv., the increase in cell osmotic potential due to an enhanced concentration of carbohydrates and proline was insufficient to slow down the rate of leaf water loss. The mechanism of cell wall tightening in response to leaf desiccation may be the main key in the process of triticale acclimation to soil drought.

Free and Cell Wall-Bound Polyamines under Long-Term Water Stress Applied at Different Growth Stages of ×Triticosecale Wittm.

BACKGROUND: Long-stemmed and semi-dwarf cultivars of triticale were exposed to water stress at tillering, heading and anthesis stage. Quantitative determination of free and cell wall-bound polyamines, i.e. agmatine, cadaverine, putrescine, spermidine and spermine, was supplemented with an analysis of quantitative relationships between free and cell wall-bound polyamines. RESULTS: The content of free and cell wall-bound polyamines varied depending on the development stage, both under optimal and water stress conditions. Drought-induced increase in free agmatine content was observed at all developmental stages in long-stemmed cultivar. A depletion of spermidine and putrescine was also reported in this cultivar, and spermidine was less abundant in semi-dwarf cultivar exposed to drought stress at the three analyzed developmental stages. Changes in the content of the other free polyamines did not follow a steady pattern reflecting the developmental stages. On the contrary, the content of cell wall-bound polyamines gradually increased from tillering, through heading and until anthesis period. CONCLUSION: Water stress seemed to induce a progressive decrease in the content of free polyamines and an accumulation of cell wall-bound polyamines.

Endogenous ABA concentration and cytoplasmic membrane fluidity in microspores of oilseed rape (Brassica napus L.) genotypes differing in responsiveness to androgenesis induction.

KEY MESSAGE: A better understanding of androgenesis with a focus on the changes in plasma membrane fluidity and endogenous ABA content affecting embryogenesis induction in microspore suspension of B. napus. Changes in plasma membrane fluidity (MF) and ABA content associated with androgenesis induction were under the study. Both parameters were monitored in microspores of two Brassica napus L. genotypes differing in their response to androgenic induction under heat (1 day at 32 °C). MF was assessed by DPH method. ABA content was evaluated by ELISA. Heat caused microspores' plasma membrane to become more rigid. Lower MF in microspores of 'DH 4079' (of high androgenic potential) seems to maintain proper cell protection and leads to efficient embryogenesis induction. Plasma membrane remodelling coincided with changes of ABA content in microspores and in the culture medium in both genotypes. ABA concentration (µM) and ABA content (fmol per 10(4) microspores or pmol g(-1) FW) were for the first time measured in microspores. ABA concentration (µM) in microspores and in the culture medium (nM) differed significantly for the genotype and the treatment. The interaction between both variables was also significant. In general, ABA content ranged from <3.5 to 87.1 fmol per 10(4) microspores. The highest content of ABA was detected in 'DH 4079' microspores at 32 °C. Assuming a mean microspores' radius of 10 µm, it corresponds to ABA concentration of 2.1 µM. Heat shock resulted in quantum of medium pH reduction (0.1-0.2) and increased levels of ABA in microspores and in the medium of both tested genotypes. However, heat induced increase of ABA content in microspores of non-responsive 'Campino' had no clear-cut impact, on androgenesis induction efficiency, which suggests a more complex mechanism of process initiation.

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.

Early stage de-etiolation increases the ferulic acid content in winter triticale seedlings under full sunlight conditions.

In the presented work an attempt has been made to estimate the phenolics content and its implication for the protection of the photosynthetic apparatus in course of a plant's de-etiolation. The experiments were carried out on two genotypes of winter triticale varying in their resistance to drought. The activity of the photosynthetic apparatus was monitored by taking measurements of chlorophyll fluorescence and chlorophyll/carotenoids content. Analyses of the total pool of phenolic compounds and ferulic acid as well as l-phenylalanine ammonia lyase activity were completed. The first illuminations of etiolated seedlings induced a chlorophyll synthesis, which was followed by the increasing activity of the photosynthetic apparatus in both studied genotypes. Piano exhibited a higher values of the maximum quantum efficiency of photosystem II primary photochemistry during de-etiolation than Imperial. These results may just indicate that for Imperial, the delivery of photons to the reaction centres exceeded the capacity of the photosynthetic apparatus to transduce this energy via electron transport. An increase in the content of ferulic acid was more noticeable for Piano and seems to be a consequence of adaptation to the new light conditions. It should be taken into account, that an increase of ferulic acid content during early stage of de-etiolation, may limit the photoinhibition of photosynthesis whenever radiation is excessive for the photosynthetic apparatus.