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The effects of various light intensities and spectral compositions on glutathione and amino acid metabolism were compared in wheat. Increase of light intensity (low—normal—high) was accompanied by a simultaneous increase in the shoot fresh weight, photosynthetic activity and glutathione content. These parameters were also affected by the modification of the ratios of blue, red and far-red components (referred to as blue, pink and far-red lights) compared to normal white light. The photosynthetic activity and the glutathione content decreased to 50% and the percentage of glutathione disulfide (characterising the redox state of the tissues) in the total glutathione pool doubled in far-red light. The alterations in the level and redox state of the antioxidant glutathione resulted from the effect of light on its synthesis as it could be concluded from the changes in the transcription of the related genes. Modification of the light conditions also greatly affected both the amount and the ratio of free amino acids. The total free amino acid content was greatly induced by the increase of light intensity and was greatly reduced in pink light compared to the normal intensity white light. The concentrations of most amino acids were similarly affected by the light conditions as described for the total free amino acid content but Pro, Met, Thr, ornithine and cystathionine showed unique response to light. As observed for the amino acid levels, the expression of several genes involved in their metabolism also enhanced due to increased light intensity. Interestingly, the modification of the spectrum greatly inhibited the expression of most of these genes. Correlation analysis of the investigated parameters indicates that changes in the light conditions may affect growth through the adjustment of photosynthesis and the glutathione-dependent redox state of the tissues. This process modifies the metabolism of glutathione and amino acids at transcriptional level.

CBF (C-repeat binding factor) transcription factors show high expression levels in response to cold; moreover, they play a key regulatory role in cold acclimation processes. Recently, however, more and more information has led to the conclusion that, apart from cold, light—including its spectra—also has a crucial role in regulating CBF expression. Earlier, studies established that the expression patterns of some of these regulatory genes follow circadian rhythms. To understand more of this complex acclimation process, we studied the expression patterns of the signal transducing pathways, including signal perception, the circadian clock and phospholipid signalling pathways, upstream of the CBF gene regulatory hub. To exclude the confounding effect of cold, experiments were carried out at 22 °C. Our results show that the expression of genes implicated in the phospholipid signalling pathway follow a circadian rhythm. We demonstrated that, from among the tested CBF genes expressed in Hordeum vulgare (Hv) under our conditions, only the members of the HvCBF4-phylogenetic subgroup showed a circadian pattern. We found that the HvCBF4-subgroup genes were expressed late in the afternoon or early in the night. We also determined the expression changes under supplemental far-red illumination and established that the transcript accumulation had appeared four hours earlier and more intensely in several cases. Based on our results, we propose a model to illustrate the effect of the circadian clock and the quality of the light on the elements of signalling pathways upstream of the HvCBFs, thus integrating the complex regulation of the early cellular responses, which finally lead to an elevated abiotic stress tolerance.

BackgroundAs both abiotic stress response and development are under redox control, it was hypothesised that the pharmacological modification of the redox environment would affect the initial development of flower primordia and freezing tolerance in wheat (Triticum aestivum L.).ResultsPharmacologically induced redox changes were monitored in winter (T. ae. ssp. aestivum cv. Cheyenne, Ch) and spring (T. ae. ssp. spelta; Tsp) wheat genotypes grown after germination at 20/17°C for 9 d (chemical treatment: last 3 d), then at 5°C for 21 d (chemical treatment: first 4 d) and subsequently at 20/17°C for 21 d (recovery period). Thiols and their disulphide forms were measured and based on these data reduction potentials were calculated. In the freezing-tolerant Ch the chemical treatments generally increased both the amount of thiol disulphides and the reduction potential after 3 days at 20/17°C. In the freezing-sensitive Tsp a similar effect of the chemicals on these parameters was only observed after the continuation of the treatments for 4 days at 5°C. The applied chemicals slightly decreased root fresh weight and increased freezing tolerance in Ch, whereas they increased shoot fresh weight in Tsp after 4 days at 5°C. As shown after the 3-week recovery at 20/17°C, the initial development of flower primordia was accelerated in Tsp, whereas it was not affected by the treatments in Ch. The chemicals differently affected the expression of ZCCT2 and that of several other genes related to freezing tolerance and initial development of flower primordia in Ch and Tsp after 4 d at 5°C.ConclusionsVarious redox-altering compounds and osmotica had differential effects on glutathione disulphide content and reduction potential, and consequently on the expression of the flowering repressor ZCCT2 in the winter wheat Ch and the spring wheat Tsp. We propose that the higher expression of ZCCT2 in Ch may be associated with activation of genes of cold acclimation and its lower expression in Tsp with the induction of genes accelerating initial development of flower primordia. In addition, ZCCT2 may be involved in the coordinated control of the two processes.

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Abiotic stresses induce oxidative stress, which modifies the level of several metabolites including amino acids. The redox control of free amino acid profile was monitored in wild type and ascorbate or glutathione deficient mutant Arabidopsis plants before and after hydroponic treatment with various redox agents. Both mutations and treatments modified the size and redox state of the ascorbate (AsA) and/or glutathione (GSH) pools. The total free amino acid content was increased by AsA, GSH and H 2 O 2 in all 3 genotypes and a very large (3-fold) increase was observed in the GSH-deficient pad2-1 mutant after GSH treatment compared to the untreated wild type plants. Addition of GSH reduced the ratio of amino acids belonging to the glutamate family on a large scale and increased the relative amount of non-proteinogenic amino acids. The latter change was due to the large increase in the content of alpha-aminoadipate, an inhibitor of Glu transport. Most of the treatments increased the Pro content, which effect was due to the activation of genes involved in Pro synthesis. Although all studied redox compounds influenced the amount of free amino acids and a mostly positive, very close (r>0.9) correlation exists between these parameters, a special regulatory role of GSH could be presumed due to its more powerful effect. This may originate from the thiol/disulphide conversion or (de)glutathionylation of enzymes participating in the amino acid metabolism.Abbreviations -Aaa, α-aminoadipic acid; AsA, ascorbic acid; Cysta, cystathione; DHA, dehydroascorbate; DTT, dithiotreitol; GSH, glutathione; GSSG, glutathione disulphide; NPPAs, nonproteogenic amino acids; OAT, ornithine aminotransferase; PDH, proline dehydrogenase; P5CR, pyrroline-5-carboxylate reductase; P5CDH, delta-1-pyrroline-5-carboxylate dehydrogenase; P5CS1, delta This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/ppl.12510 This article is protected by copyright. All rights reserved. Accepted Article1-pyrroline-5-carboxylate synthase 1; P5CS2, delta 1-pyrroline-5-carboxylate synthase 2. IntroductionRedox status has a major role in the regulation of metabolism and is controlled by metabolic processes at the same time (Geigenberger and Fernie 2014). The proper redox status during growth and development under optimal and adverse environmental conditions is maintained by the antioxidant system through the removal of the excess of reactive oxygen species (ROS; Dietz 2008, Suzuki et al. 2012, Kocsy et al. 2013, Considine and Foyer 2014. Accumulation of ROS, such as superoxide radical, hydrogen peroxide, hydroxyl radical and singlet oxygen in high concentration may cause serious injuries or even plant lethality under stress conditions (Bartosz 1997). However, a moderate increase in ROS content may have positive functions as well since, ...

A redox-dependent regulatory network of miRNAs and their targets were created using sequencing results, bioinformatics tools and correlation analysis of the examined biochemical and molecular parameters in wheat.

Light-intensity-dependent (low, normal and high) differences in thiol and amino acid metabolism during drought were compared in wheat seedlings. The drought-tolerant genotype (Plainsman) recovered better than the sensitive one (Cappelle Desprez) after the stress as shown by growth and photosynthetic parameters, the levels of which were greater in low and high light, respectively. Glutathione as an antioxidant contributed to this difference, since its level was twofold greater in Plainsman throughout the experiment. In addition, the accumulation of most amino acids even increased in normal light during drought in Plainsman, while such change occurred in Cappelle Desprez only in high light. The higher contents of proline, glutamate and γ-aminobutyrate are especially important because of their involvement in the protection against drought.The transcription of certain genes related to amino acid and glutathione metabolism and various antioxidants was even induced by higher light intensities before drought, which can contribute to the subsequent increase in the amount of the corresponding metabolites during stress. Increase in light intensity activated various protective mechanisms including greater accumulation of glutathione, proline and other amino acids during drought, which contributed to the efficient recovery of wheat after stress. K E Y W O R D S drought, free amino acids, glutathione, light intensity, photosynthesis, wheatThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.