BACKGROUND: Hormonal homeostasis plays a critical role in the regulation of microspore embryogenesis (ME). The balance between endogenous phytohormones must be altered to induce microspore reprogramming from the classical pollen-formation pathway to embryogenic development, but too extensive changes may be detrimental. In the present study, the levels of auxins, cytokinins and abscisic acid were monitored in the anthers of two Polish winter wheat F1 lines and the spring cultivar Pavon highly differentiated in terms of ME effectiveness. Analyses were carried out at subsequent steps of the ME induction procedure that combined low temperature, sodium selenate and mannitol tiller pre-treatment. RESULTS: Of all the factors tested, mannitol induced the most profound effect on phytohormones and their homeostasis in wheat anthers. It significantly increased the accumulation of all auxins and decreased the levels of most cytokinins, while the change in ABA content was limited to cv. Pavon. In an attempt to alleviate this hormonal shock, we tested several modifications of the induction medium hormonal composition and found thidiazuron to be the most promising in stimulating the embryogenic development of wheat microspores. CONCLUSIONS: The lack of ABA-driven stress defence responses may be one of the reasons for the low effectiveness of ME induction in winter wheat microspore cultures. Low cytokinin level and a disturbed auxin/cytokinin balance may then be responsible for the morphological abnormalities observed during the next phases of embryogenic microspore development. One possible solution is to modify the hormonal composition of the induction medium with thidiazuron identified as the most promising component.

• Keywords
• Triticum aestivum, Abscisic acid, Auxins, Cytokinins, Hormonal homeostasis, Microspore embryogenesis,
• MeSH
• Cytokinins metabolism   MeSH
• Abscisic Acid metabolism   MeSH
• Indoleacetic Acids * metabolism   MeSH
• Mannitol * pharmacology   MeSH
• Triticum * embryology   drug effects   metabolism   MeSH
• Pollen * embryology   drug effects   metabolism   MeSH
• Plant Growth Regulators * metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cytokinins MeSH
• Abscisic Acid MeSH
• Indoleacetic Acids * MeSH
• Mannitol * MeSH
• Plant Growth Regulators * MeSH

The classic plant growth-promoting phytohormone cytokinin has been identified and established as a mediator of pathogen resistance in different plant species. However, the resistance effect of structurally different cytokinins appears to vary and may regulate diverse mechanisms to establish resistance. Hence, we comparatively analysed the impact of six different adenine- and phenylurea-type cytokinins on the well-established pathosystem Nicotiana tabacum-Pseudomonas syringae. The efficiency of resistance effects was evaluated based on impacts on the host plant defence response by scoring infection symptoms and the direct impact on the pathogen by assessment of proliferation in planta. To identify common and cytokinin-specific components involved in resistance effects, transcriptome profiling and targeted metabolomics were conducted in leaves treated with the different cytokinins. We observed clearly different potentials of the tested cytokinins in either suppressing infection symptoms or pathogen proliferation. Gene regulation and metabolite analyses revealed cytokinin-type specific impacts on defence components, such as salicylic acid and related signalling, expression of PR proteins, and regulation of specialised metabolism. Cytokinins also strongly affected plant cell physiological parameters, such as a remarkable decrease in amino acid pools. Hence, this study provides comparative information on the efficiency of diverse cytokinins in mediating resistance in one well-studied pathosystem and insights into the specific regulation of resistance effects mediated by different cytokinin molecules. This is particularly relevant for studies on the function of cytokinins or other phytohormones and compounds interacting with cytokinin activities in the context of pathogen infections and other stress scenarios, considering the diverse cytokinins present in plants.

• MeSH
• Cytokinins * metabolism   MeSH
• Plant Leaves microbiology   metabolism   genetics   MeSH
• Plant Diseases * microbiology   immunology   genetics   MeSH
• Disease Resistance * genetics   MeSH
• Pseudomonas syringae * physiology   pathogenicity   MeSH
• Gene Expression Regulation, Plant drug effects   MeSH
• Plant Growth Regulators metabolism   MeSH
• Nicotiana * microbiology   genetics   immunology   drug effects   metabolism   MeSH
• Structure-Activity Relationship MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Cytokinins * MeSH
• Plant Growth Regulators MeSH

Smoke-water (SW) and Karrikinolide1 (KAR1) release dormancy and improve seed germination in many plant species. Therefore, we tested SW (1:2500 v/v) and KAR1 (10-7 M) to break the morphological dormancy of celery cultivar (Apium graveolens L.). In the first trial, seeds were subjected to a 21-day incubation period at 20 °C with SW and KAR1 applied as single treatments. KAR1 showed significantly improved germination (30.7%) as compared to SW (17.2%) and a water control (14.7%). In seed soaking experiments, SW, KAR1, and gibberellic acid (GA3) treatments showed higher germination percentages than the water control after 3 and 6 h of soaking. However, prolonged soaking (12 h) reduced germination percentages for all treatments, indicating a detrimental effect. Analysis of KAR1 content dynamics in 7-day- and 21-day-old celery seeds indicated its prolonged effects on germination and dormancy alleviation. Phytohormones, including auxins in 7-day-old and cytokinins in 7-day- and 21-day-old celery seedlings, along with their precursors and metabolites, were analyzed using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) after treatment with KAR1 and SW. The analysis of auxin levels in 7-day-old seeds revealed a negative correlation between seed germination and auxin (indole-3-acetic acid, IAA) content. Notably, it was found that KAR1-treated seeds significantly reduced IAA levels in all treatments. SW and KAR1 did not significantly affect cytokinin levels during celery germination except for N6-Isopentenyladenine. Hence, further research is needed to understand their precise role in celery seed germination. This work will improve our understanding of the role of bioactive compounds from plant-derived smoke and how they regulate hormonal responses and improve germination efficiency in celery.

• Keywords
• Karrikinolide, biostimulants, celery, phytohormones, smoke-water,
• Publication type
• Journal Article MeSH

BACKGROUND: Bread wheat (Triticum aestivum) is a major source of nutrition globally, but yields can be seriously compromised by water limitation. Redistribution of growth between shoots and roots is a common response to drought, promoting plant survival, but reducing yield. Gibberellins (GAs) are necessary for shoot and root elongation, but roots maintain growth at lower GA concentrations compared with shoots, making GA a suitable hormone for mediating this growth redistribution. In this study, the effect of progressive drought on GA content was determined in the base of the 4th leaf and root tips of wheat seedlings, containing the growing regions, as well as in the remaining leaf and root tissues. In addition, the contents of other selected hormones known to be involved in stress responses were determined. Transcriptome analysis was performed on equivalent tissues and drought-associated differential expression was determined for hormone-related genes. RESULTS: After 5 days of applying progressive drought to 10-day old seedlings, the length of leaf 4 was reduced by 31% compared with watered seedlings and this was associated with significant decreases in the concentrations of bioactive GA1 and GA4 in the leaf base, as well as of their catabolites and precursors. Root length was unaffected by drought, while GA concentrations were slightly, but significantly higher in the tips of droughted roots compared with watered plants. Transcripts for the GA-inactivating gene TaGA2ox4 were elevated in the droughted leaf, while those for several GA-biosynthesis genes were reduced by drought, but mainly in the non-growing region. In response to drought the concentrations of abscisic acid, cis-zeatin and its riboside increased in all tissues, indole-acetic acid was unchanged, while trans-zeatin and riboside, jasmonate and salicylic acid concentrations were reduced. CONCLUSIONS: Reduced leaf elongation and maintained root growth in wheat seedlings subjected to progressive drought were associated with attenuated and increased GA content, respectively, in the growing regions. Despite increased TaGA2ox4 expression, lower GA levels in the leaf base of droughted plants were due to reduced biosynthesis rather than increased catabolism. In contrast to GA, the other hormones analysed responded to drought similarly in the leaf and roots, indicating organ-specific differential regulation of GA metabolism in response to drought.

• Keywords
• Drought, gene expression, gibberellins, plant hormones, wheat,
• MeSH
• Gibberellins metabolism   MeSH
• Hormones metabolism   MeSH
• Plant Roots metabolism   MeSH
• Plant Leaves metabolism   MeSH
• Droughts MeSH
• Triticum * metabolism   MeSH
• Seedlings * metabolism   MeSH
• Water metabolism   MeSH
• Zeatin MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Gibberellins MeSH
• Hormones MeSH
• Water MeSH
• Zeatin MeSH

UNLABELLED: Cytokinins (CKs) are involved in several developmental stages in the life-cycle of plants. The CK content in plants and their respective organs are susceptible to changes under different environmental conditions. In the current study, we profiled the CK content in the above and underground organs of three legumes (Lessertia frutescens, Mucuna pruriens and Pisum sativum) grown in soils collected from four locations (Ashburton, Bergville, Hluhluwe and Izingolweni) in KwaZulu-Natal province, South Africa. The quantified CK contents in the three legumes were categorized on the basis of their side chains (isoprenoid, aromatic and furfural) and modifications (e.g. free bases and glucosides). Legume and soil types as well as their interaction significantly influenced the concentrations of CKs. Lessertia frutescens, Mucuna pruriens and Pisum sativum had CK content that ranged from 124-653, 170-670 and 69-595 pmol/g DW, respectively. Substantial quantity (> 600 pmol/g DW) of CK were observed in plants grown in Bergville (above-ground part of Lessertia frutescens) and Izingolweni (underground part of Mucuna pruriens) soils. A total of 28 CK derivatives observed in the legumes comprised of isoprenoid (22), aromatic (5) and furfural (1) side-chain CKs. However, the 16 CK derivatives in Mucuna pruriens were isoprenoid-type based on the side-chain. Generally, a higher ratio of cis-zeatin (cZ) relative to the trans-zeatin (tZ) was evident in the above-ground part of Lessertia frutescens and Pisum sativum for the four soil treatments. In terms of functional and physiological importance of the CKs, the free bases (active form) and ribosides (translocation form) were the most abundant CK in Lessertia frutescens and Pisum sativum. However, N-glucoside, a deactivation/detoxicification product was the most dominant CK in Mucuna pruriens from Hluhluwe and Izingolweni soils. The total CKs in the underground parts of the legumes had a positive significant correlation with the total phosphorus and nitrogen content in the plant as well as the soil nitrogen. Overall, the CK profiles of the legumes were strongly influenced by the soil types. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-01021-2.

• Keywords
• Biomass, Fabaceae, Nitrogen fixation, Nodulation, Phytohormones, Rhizobia,
• Publication type
• Journal Article MeSH

The spatial location and timing of plant developmental events are largely regulated by the well balanced effects of auxin and cytokinin phytohormone interplay. Together with transport, localized metabolism regulates the concentration gradients of their bioactive forms, ultimately eliciting growth responses. In order to explore the dynamics of auxin and cytokinin metabolism during early seedling growth in Theobroma cacao (cacao), we have performed auxin and cytokinin metabolite profiling in hypocotyls and root developmental sections at different times by using ultra-high-performance liquid chromatography-electrospray tandem mass spectrometry (UHPLC-MS/MS). Our work provides quantitative characterization of auxin and cytokinin metabolites throughout early root and hypocotyl development and identifies common and distinctive features of auxin and cytokinin metabolism during cacao seedling development.

• Keywords
• Theobroma cacao, auxin, cytokinin, phytohormone metabolism, root development,
• Publication type
• Journal Article MeSH

In the complex process of homeostasis of phytohormones cytokinins (CKs), O-glucosylation catalyzed by specific O-glucosyltransferases represents one of important mechanisms of their reversible inactivation. The CK O-glucosyltransferases belong to a highly divergent and polyphyletic multigene superfamily of glycosyltransferases, of which subfamily 1 containing UDP-glycosyltransferases (UGTs) is the largest in the plant kingdom. It contains recently discovered O and P subfamilies present in higher plant species but not in Arabidopsis thaliana. The cis-zeatin O-glucosyltransferase (cisZOG) genes belong to the O subfamily encoding a stereo-specific O-glucosylation of cis-zeatin-type CKs. We studied different homologous genes, their domains and motifs, and performed a phylogenetic reconstruction to elucidate the plant evolution of the cisZOG gene. We found that the cisZOG homologs do not form a clear separate clade, indicating that diversification of the cisZOG gene took place after the diversification of the main angiosperm families, probably within genera or closely related groups. We confirmed that the gene(s) from group O is(are) not present in A. thaliana and is(are) also missing in the family Brassicaceae. However, cisZOG or its metabolites are found among Brassicaceae clade, indicating that remaining genes from other groups (UGT73-group D and UGT85-group G) are able, at least in part, to substitute the function of group O lost during evolution. This study is the first detailed evolutionary evaluation of relationships among different plant ZOGs within angiosperms.

• MeSH
• Brassicaceae genetics   MeSH
• Cytokinins genetics   MeSH
• Glucosyltransferases genetics   MeSH
• Magnoliopsida * genetics   metabolism   MeSH
• Gene Expression Regulation, Plant * MeSH
• Plant Proteins genetics   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Cytokinins MeSH
• Glucosyltransferases MeSH
• Plant Proteins MeSH

Cold acclimation, the necessary prerequisite for promotion of freezing tolerance, is affected by both low temperature and enhanced far-red/red light (FR/R) ratio. The impact of FR supplementation to white light, created by artificial LED light sources, on the hormone levels, metabolism, and expression of the key hormone metabolism-related genes was determined in winter barley at moderate (15 °C) and low (5 °C) temperature. FR-enhanced freezing tolerance at 15 °C was associated with promotion of abscisic acid (ABA) levels, and accompanied by a moderate increase in indole-3-acetic acid (IAA) and cis-zeatin levels. The most prominent impact on the plants' freezing tolerance was found after FR pre-treatment at 15 °C (for 10 days) followed by cold treatment at FR supplementation (7 days). The response of ABA was diminished in comparison with white light treatment, probably due to the elevation of stress tolerance during FR pre-treatment. Jasmonic acid (JA) and salicylic acid (SA) were transiently reduced. When the plants were exposed directly to a combination of cold (5 °C) and FR supplementation, ABA increase was higher than in white light, and was associated with enhanced elevation of JA and, in the longer term (after 7 days), with IAA and cis-zeatin increase, which indicates a stronger stress response and better acclimation. Cold hardening was more efficient when FR light was applied in the early developmental stage of the barley plants (three-leaf stage, 18 days), rather than in later stages (28-days). The dynamics of the phytohormone changes are well supported by the expression profiles of the key hormone metabolism-related genes. This series of treatments serves as evidence for the close relationship between plant hormones, light quality, and low temperature at the beginning of cold acclimation. Besides the timing of the FR treatments, plant age also represents a key factor during light spectrum-dependent cold acclimation.

• Keywords
• LED lighting, barley, frost-tolerance, low R/FR ratio, phytohormones,
• MeSH
• Acclimatization physiology   MeSH
• Hordeum genetics   metabolism   radiation effects   MeSH
• Abscisic Acid metabolism   MeSH
• Indoleacetic Acids metabolism   MeSH
• Plant Leaves genetics   metabolism   radiation effects   MeSH
• Cold Temperature * MeSH
• Reverse Transcriptase Polymerase Chain Reaction MeSH
• Gene Expression Regulation, Plant radiation effects   MeSH
• Plant Growth Regulators metabolism   MeSH
• Gene Expression Profiling methods   MeSH
• Light * MeSH
• Freezing MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• indoleacetic acid MeSH Browser
• Abscisic Acid MeSH
• Indoleacetic Acids MeSH
• Plant Growth Regulators MeSH

In the context of global climate change, forest tree research should be addressed to provide genotypes with increased resilience to high temperature events. These improved plants can be obtained by heat priming during somatic embryogenesis (SE), which would produce an epigenetic-mediated transgenerational memory. Thereby, we applied 37 °C or 50 °C to maritime pine (Pinus pinaster) megagametophytes and the obtained embryogenic masses went through the subsequent SE phases to produce plants that were further subjected to heat stress conditions. A putative transcription factor WRKY11 was upregulated in priming-derived embryonal masses, and also in the regenerated P37 and P50 plants, suggesting its role in establishing an epigenetic memory in this plant species. In vitro-grown P50 plants also showed higher cytokinin content and SOD upregulation, which points to a better responsiveness to heat stress. Heat exposure of two-year-old maritime pine plants induced upregulation of HSP70 in those derived from primed embryogenic masses, that also showed better osmotic adjustment and higher increases in chlorophyll, soluble sugars and starch contents. Moreover, ϕPSII of P50 plants was less affected by heat exposure. Thus, our results suggest that priming at 50 °C at the SE induction phase is a promising strategy to improve heat resilience in maritime pine.

• Keywords
• HSP, Pinus pinaster, ROS, WRKY, heat stress, hormones, photosynthesis, priming, somatic embryogenesis, transgenerational memory,
• Publication type
• Journal Article MeSH

Cytokinins are plant hormones, derivatives of adenine with a side chain at the N6-position. They are involved in many physiological processes. While the metabolism of trans-zeatin and isopentenyladenine, which are considered to be highly active cytokinins, has been extensively studied, there are others with less obvious functions, such as cis-zeatin, dihydrozeatin, and aromatic cytokinins, which have been comparatively neglected. To help explain this duality, we present a novel hypothesis metaphorically comparing various cytokinin forms, enzymes of CK metabolism, and their signalling and transporter functions to the comics superheroes Hulk and Deadpool. Hulk is a powerful but short-lived creation, whilst Deadpool presents a more subtle and enduring force. With this dual framework in mind, this review compares different cytokinin metabolites, and their biosynthesis, translocation, and sensing to illustrate the different mechanisms behind the two CK strategies. This is put together and applied to a plant developmental scale and, beyond plants, to interactions with organisms of other kingdoms, to highlight where future study can benefit the understanding of plant fitness and productivity.

• Keywords
• Hulk/Deadpool, aromatic cytokinins, cis-zeatin, cytokinin biosynthesis, cytokinin oxidase/dehydrogenase, cytokinin signalling, cytokinin transport, cytokinins, isopentenyl transferase,
• MeSH
• Arabidopsis metabolism   MeSH
• Models, Biological MeSH
• Biological Transport MeSH
• Biological Assay MeSH
• Cytokinins metabolism   MeSH
• Plant Physiological Phenomena * MeSH
• Glycosylation MeSH
• Hydrolysis MeSH
• Kinetics MeSH
• Kinetin metabolism   MeSH
• Oxidoreductases metabolism   MeSH
• Plant Growth Regulators metabolism   MeSH
• Plants metabolism   MeSH
• Signal Transduction * MeSH
• Protein Binding MeSH
• Zeatin analogs & derivatives   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• cytokinin oxidase MeSH Browser
• Cytokinins MeSH
• dihydrozeatin MeSH Browser
• Kinetin MeSH
• Oxidoreductases MeSH
• Plant Growth Regulators MeSH
• Zeatin MeSH