Cytokinin modulates the metabolic network of sulfur and glutathione.

The phytohormone cytokinin is implicated in a range of growth, developmental, and defense processes. A growing body of evidence supports a crosstalk between cytokinin and nutrient signaling pathways, such as nitrate availability. Cytokinin signaling regulates sulfur-responsive gene expression, but the underlying molecular mechanisms and their impact on sulfur-containing metabolites have not been systematically explored. Using a combination of genetic and pharmacological tools, we investigated the interplay between cytokinin signaling and sulfur homeostasis. Exogenous cytokinin triggered sulfur starvation-like gene expression accompanied by a decrease in sulfate and glutathione content. This process was uncoupled from the activity of the major transcriptional regulator of sulfate starvation signaling SULFUR LIMITATION 1 and an important glutathione-degrading enzyme, γ-glutamyl cyclotransferase 2;1, expression of which was robustly up-regulated by cytokinin. Conversely, glutathione accumulation was observed in mutants lacking the cytokinin receptor ARABIDOPSIS HISTIDINE KINASE 3 and in cytokinin-deficient plants. Cytokinin-deficient plants displayed improved root growth upon exposure to glutathione-depleting chemicals which was attributed to a higher capacity to maintain glutathione levels. These results shed new light on the interplay between cytokinin signaling and sulfur homeostasis. They position cytokinin as an important modulator of sulfur uptake, assimilation, and remobilization in plant defense against xenobiotics and root growth.

Cytokinin at the Crossroads of Abiotic Stress Signalling Pathways.

Cytokinin is a multifaceted plant hormone that plays major roles not only in diverse plant growth and development processes, but also stress responses. We summarize knowledge of the roles of its metabolism, transport, and signalling in responses to changes in levels of both macronutrients (nitrogen, phosphorus, potassium, sulphur) and micronutrients (boron, iron, silicon, selenium). We comment on cytokinin's effects on plants' xenobiotic resistance, and its interactions with light, temperature, drought, and salinity signals. Further, we have compiled a list of abiotic stress-related genes and demonstrate that their expression patterns overlap with those of cytokinin metabolism and signalling genes.

Roles of proteome dynamics and cytokinin signaling in root to hypocotyl ratio changes induced by shading roots of Arabidopsis seedlings.

In nature, root systems of most terrestrial plants are protected from light exposure by growing in a dark soil environment. Hence, in vitro cultivation in transparent Petri dishes leads to physiological perturbations, but the mechanisms underlying root-mediated light perception and responses have not been fully elucidated. Thus, we compared Arabidopsis thaliana seedling development in transparent and darkened Petri dishes at low light intensity (20 µmol m(-2) s(-1)), allowing us to follow (inter alia) hypocotyl elongation, which is an excellent process for studying interactions of signals involved in the regulation of growth and developmental responses. To obtain insights into molecular events underlying differences in seedling growth under these two conditions, we employed liquid chromatography-mass spectrometry (LC-MS) shotgun proteomics (available via the PRIDE deposit PXD001612). In total, we quantified the relative abundances of peptides representing 1,209 proteins detected in all sample replicates of LC-MS analyses. Comparison of MS spectra after manual validation revealed 48 differentially expressed proteins. Functional classification, analysis of available gene expression data and literature searches revealed alterations associated with root illumination (inter alia) in autotrophic CO2 fixation, C compound and carbohydrate metabolism, and nitrogen metabolism. The results also indicate a previously unreported role for cytokinin plant hormones in the escape-tropism response to root illumination. We complemented these results with reverse transcription followed by quantitative PCR (RT-qPCR), chlorophyll fluorescence and detailed cytokinin signaling analyses, detecting in the latter a significant increase in the activity of the cytokinin two-component signaling cascade in roots and implicating the cytokinin receptor AHK3 as the major mediator of root to hypocotyl signaling in responses to root illumination.

High cytokinin levels induce a hypersensitive-like response in tobacco.

BACKGROUND AND AIMS: Cytokinins are positive regulators of shoot development. However, it has previously been demonstrated that efficient activation of the cytokinin biosynthesis gene ipt can cause necrotic lesions and wilting in tobacco leaves. Some plant pathogens reportedly use their ability to produce cytokinins in disease development. In response to pathogen attacks, plants can trigger a hypersensitive response that rapidly kills cells near the infection site, depriving the pathogen of nutrients and preventing its spread. In this study, a diverse set of processes that link ipt activation to necrotic lesion formation were investigated in order to evaluate the potential of cytokinins as signals and/or mediators in plant defence against pathogens. METHODS: The binary pOp-ipt/LhGR system for dexamethasone-inducible ipt expression was used to increase endogenous cytokinin levels in transgenic tobacco. Changes in the levels of cytokinins and the stress hormones salicylic, jasmonic and abscisic acid following ipt activation were determined by ultra-performance liquid chromatography-electrospray tandem mass spectrometry (UPLC-MS/MS). Trends in hydrogen peroxide content and lipid peroxidation were monitored using the potassium iodide and malondialdehyde assays. The subcellular distribution of hydrogen peroxide was investigated using 3,3'-diaminobenzidine staining. The dynamics of transcripts related to photosynthesis and pathogen response were analysed by reverse transcription followed by quantitative PCR. The effects of cytokinins on photosynthesis were deciphered by analysing changes in chlorophyll fluorescence and leaf gas exchange. KEY RESULTS: Plants can produce sufficiently high levels of cytokinins to trigger fast cell death without any intervening chlorosis - a hallmark of the hypersensitive response. The results suggest that chloroplastic hydrogen peroxide orchestrates the molecular responses underpinning the hypersensitive-like response, including the inhibition of photosynthesis, elevated levels of stress hormones, oxidative membrane damage and stomatal closure. CONCLUSIONS: Necrotic lesion formation triggered by ipt activation closely resembles the hypersensitive response. Cytokinins may thus act as signals and/or mediators in plant defence against pathogen attack.

The Superiority of Removable Contact Splints in the Healing of Diabetic Foot during Postoperative Care.

OBJECTIVE: Off-loading is one of the crucial components of diabetic foot (DF) therapy. However, there remains a paucity of studies on the most suitable off-loading for DF patients under postoperative care. The aim of our study was to evaluate the effect of different protective off-loading devices on healing and postoperative complications in DF patients following limb preservation surgery. METHODS: This observational study comprised 127 DF patients. All enrolled patients had undergone foot surgery and were off-loaded empirically as follows: wheelchair+removable contact splint (RCS) (group R: 29.2%), wheelchair only (group W: 48%), and wheelchair+removable prefabricated device (group WP: 22.8%). We compared the primary (e.g., the number of healed patients, healing time, and duration of antibiotic (ATB) therapy) and secondary outcomes (e.g., number of reamputations and number and duration of rehospitalizations) with regard to the operation regions across all study groups. RESULTS: The lowest number of postoperative complications (number of reamputations: p = 0.028; rehospitalizations: p = 0.0085; and major amputations: p = 0.02) was in group R compared to groups W and WP. There was a strong trend toward a higher percentage of healed patients (78.4% vs. 55.7% and 65.5%; p = 0.068) over a shorter duration (13.7 vs. 16.5 and 20.3 weeks; p = 0.055) in the R group, as well. Furthermore, our subanalysis revealed better primary outcomes in patients operated in the midfoot and better secondary outcomes in patients after forefoot surgery-odds ratios favouring the R group included healing at 2.5 (95% CI, 1.04-6.15; p = 0.037), reamputations at 0.32 (95% CI, 0.12-0.84; p = 0.018), and rehospitalizations at 0.22 (95% CI, 0.08-0.58; p = 0.0013). CONCLUSIONS: This observational study suggests that removable contact splint combined with a wheelchair is better than a wheelchair with or without removable off-loading device for accelerating wound healing after surgical procedures; it also minimises overall postoperative complications, reducing the number of reamputations by up to 77% and the number of rehospitalizations by up to 66%.