Hormonal profiles in dormant turions of 22 aquatic plant species: do they reflect functional or taxonomic traits?

BACKGROUND AND AIMS

Turions are vegetative, dormant overwintering organs formed in aquatic plants in response to unfavourable ecological conditions. Contents of cytokinin (CK) and auxin metabolites and ABA as main growth and development regulators were compared in innately dormant autumnal turions of 22 aquatic plant species of different functional ecological or taxonomic groups with those in non-dormant winter apices in three aquatic species and with those in spring turions of four species after their overwintering.

METHODS

The hormones were analysed in miniature turion samples using ultraperformance liquid chromatography coupled with triple quadrupole mass spectrometry.

KEY RESULTS

In innately dormant turions, the total contents of each of the four main CK types, biologically active forms and total CKs differed by two-three orders of magnitude across 22 species; the proportion of the active CK forms was 0.18-67 %. Similarly, the content of four auxin forms was extremely variable and the IAA proportion as the active form was 0.014-99 %. The ABA content varied from almost zero to 54 µmol kg-1 dry weight and after overwintering, it usually significantly decreased. Hormone profiles depended most of all functional traits studied on the place of turion sprouting (surface vs. bottom) and suggest that this trait is crucial for turion ecophysiology.

CONCLUSIONS

The key role of ABA in regulating turion dormancy was confirmed. However, the highly variable pattern of the ABA content in innately dormant and in overwintered turions indicate that the hormonal mechanism regulating the innate dormancy and its breaking in turions are not united within aquatic plants.

OsNAC103, an NAC transcription factor negatively regulates plant height in rice

MAIN CONCLUSION

OsNAC103 negatively regulates rice plant height by influencing the cell cycle and crosstalk of phytohormones. Plant height is an important characteristic of rice farming and is directly related to agricultural yield. Although there has been great progress in research on plant growth regulation, numerous genes remain to be elucidated. NAC transcription factors are widespread in plants and have a vital function in plant growth. Here, we observed that the overexpression of OsNAC103 resulted in a dwarf phenotype, whereas RNA interference (RNAi) plants and osnac103 mutants showed no significant difference. Further investigation revealed that the cell length did not change, indicating that the dwarfing of plants was caused by a decrease in cell number due to cell cycle arrest. The content of the bioactive cytokinin N6-Δ2-isopentenyladenine (iP) decreased as a result of the cytokinin synthesis gene being downregulated and the enhanced degradation of cytokinin oxidase. OsNAC103 overexpression also inhibited cell cycle progression and regulated the activity of the cell cyclin OsCYCP2;1 to arrest the cell cycle. We propose that OsNAC103 may further influence rice development and gibberellin-cytokinin crosstalk by regulating the Oryza sativa homeobox 71 (OSH71). Collectively, these results offer novel perspectives on the role of OsNAC103 in controlling plant architecture.

Comparative transcriptome analysis of high- and low-embryogenic Hevea brasiliensis genotypes reveals involvement of phytohormones in somatic embryogenesis

BACKGROUND

Rubber plant (Hevea brasiliensis) is one of the major sources of latex. Somatic embryogenesis (SE) is a promising alterative to its propagation by grafting and seed. Phytohormones have been shown to influence SE in different plant species. However, limited knowledge is available on the role of phytohormones in SE in Hevea. The anther cultures of two Hevea genotypes (Yunyan 73477-YT and Reken 628-RT) with contrasting SE rate were established and four stages i.e., anthers (h), anther induced callus (y), callus differentiation state (f), and somatic embryos (p) were studied. UPLC-ESI-MS/MS and transcriptome analyses were used to study phytohormone accumulation and related expression changes in biosynthesis and signaling genes.

RESULTS

YT showed higher callus induction rate than RT. Of the two genotypes, only YT exhibited successful SE. Auxins, cytokinins (CKs), abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), gibberellins (GAs), and ethylene (ETH) were detected in the two genotypes. Indole-3-acetic acid (IAA), CKs, ABA, and ETH had notable differences in the studied stages of the two genotypes. The differentially expressed genes identified in treatment comparisons were majorly enriched in MAPK and phytohormone signaling, biosynthesis of secondary metabolites, and metabolic pathways. The expression changes in IAA, CK, ABA, and ETH biosynthesis and signaling genes confirmed the differential accumulation of respective phytohormones in the two genotypes.

CONCLUSION

These results suggest potential roles of phytohormones in SE in Hevea.

Comparative transcriptome analysis of juniper branches infected by Gymnosporangium spp. highlights their different infection strategies associated with cytokinins

BACKGROUND

Gymnosporangium asiaticum and G. yamadae can share Juniperus chinensis as the telial host, but the symptoms are completely different. The infection of G. yamadae causes the enlargement of the phloem and cortex of young branches as a gall, but not for G. asiaticum, suggesting that different molecular interaction mechanisms exist the two Gymnosporangium species with junipers.

RESULTS

Comparative transcriptome analysis was performed to investigate genes regulation of juniper in responses to the infections of G. asiaticum and G. yamadae at different stages. Functional enrichment analysis showed that genes related to transport, catabolism and transcription pathways were up-regulated, while genes related to energy metabolism and photosynthesis were down-regulated in juniper branch tissues after infection with G. asiaticum and G. yamadae. The transcript profiling of G. yamadae-induced gall tissues revealed that more genes involved in photosynthesis, sugar metabolism, plant hormones and defense-related pathways were up-regulated in the vigorous development stage of gall compared to the initial stage, and were eventually repressed overall. Furthermore, the concentration of cytokinins (CKs) in the galls tissue and the telia of G. yamadae was significantly higher than in healthy branch tissues of juniper. As well, tRNA-isopentenyltransferase (tRNA-IPT) was identified in G. yamadae with highly expression levels during the gall development stages.

CONCLUSIONS

In general, our study provided new insights into the host-specific mechanisms by which G. asiaticum and G. yamadae differentially utilize CKs and specific adaptations on juniper during their co-evolution.

On the human health benefits of microalgal phytohormones: An explorative in silico analysis

Phytohormones represent a group of secondary metabolites with different chemical structures, in which belong auxins, cytokinins, gibberellins, or brassinosteroids. In higher plants, they cover active roles in growth or defense function, while their potential benefits for human health protection were noted for some phytohormones and little explored for many others. In this study, we developed a target fishing strategy on fifty-three selected naturally occurring phytohormones covering different families towards proteins involved in key cellular functions related to human metabolism and health protection/disease. This in silico analysis strategy aims to screen the potential human health-driven bioactivity of more than fifty phytohormones through the analysis of their interactions with specific targets. From this analysis, twenty-eight human targets were recovered. Some targets e.g., the proteins mitochondrial glutamate dehydrogenase (GLUD1) or nerve growth factor (NGF) bound many phytohormones, highlighting their involvement in amino acid metabolism and/or in the maintenance or survival of neurons. Conversely, some phytohormones specifically interacted with some proteins, e.g., SPRY domain-containing SOCS box protein 2 (SPSB2) or Inosine-5'-monophosphate dehydrogenase 1 (IMPDH1), both involved in human immune response. They were then investigated with a molecular docking analysis approach. Our bioprospecting study indicated that many phytohormones may endow human health benefits, with potential functional role in multiple cellular processes including immune response and cell cycle progression.

Bulb growth potential is independent of leaf longevity for the spring ephemeral Erythronium americanum Ker-Gawl

Growth in most spring ephemerals is decreased under warmer temperatures. Although photosynthetic activities are improved at warmer temperatures, leaves senesce earlier, which prevents the bulb from reaching a larger size. A longer leaf life duration during a warm spring, therefore, may improve bulb mass. We tested this hypothesis by modulating leaf life span of Erythronium americanum through the application of Promalin® (PRO; cytokinins and gibberellins) that prolonged or silver thiosulfate (STS) that reduced leaf duration. Gas exchange and chlorophyll fluorescence were measured along with leaf and bulb carbohydrate concentrations. Plants were also pulse labelled with 13CO2 to monitor sugar transport to the bulb. Lower photosynthetic rates and shorter leaf life span of STS plants reduced the amount of carbon that they assimilated during the season, resulting in a smaller bulb compared with control plants. PRO plants maintained their photosynthetic rates for a longer period than control plants, yet final bulb biomass did not differ between them. We conclude that seasonal growth for E. americanum is not limited by leaf life duration under warm growing conditions, but rather by limited sink growth capacity. Under global warming, spring geophytes might be at risk of being reduced in size and, eventually, reproducing less frequently.

Protective effect of plant compounds in pesticides toxicity

INTRODUCTION

The relationship between pesticide exposure and the occurrence of many chronic diseases, including cancer, is confirmed by literature data.

METHODS

In this review, through the analysis of more than 70 papers, we explore an increase in oxidative stress level caused by exposure to environmental pollutants and the protective effects of plant-origin antioxidants.

RESULTS AND DISCUSSION

One of the molecular mechanisms, by which pesticides affect living organisms is the induction of oxidative stress. However, recently many plant-based dietary ingredients with antioxidant properties have been considered as a chemopreventive substances due to their ability to remove free radicals. Such a food component must meet several conditions: eliminate free radicals, be easily absorbed and function at an appropriate physiological level. Its main function is to maintain the redox balance and minimize the cellular damage caused by ROS. Therefore, it should be active in aqueous solutions and membrane domains. These properties are characteristic for phenolic compounds and selected plant hormones. Phenolic compounds have proven antioxidant properties, while increasing number of compounds from the group of plant hormones with a very diverse chemical structure turn out to act as antioxidants, being potential food ingredients that can eliminate negative effects of pesticides.

The S40 family members delay leaf senescence by promoting cytokinin synthesis

Leaf senescence is regulated by both endogenous hormones and environmental stimuli in a programmed and concerted way. The members of the S40 family have been reported to play roles in leaf senescence. Here we identified an S40 family member, CiS40-11, from Caragana intermedia. Phylogenetic analysis revealed that the CiS40-11 protein had the highest identity with AtS40-5 (AT1G11700) and AtS40-6 (AT1G61930) of Arabidopsis thaliana. CiS40-11 was highly expressed in leaves and was down-regulated after dark treatment. The subcellular localization analysis showed that CiS40-11 was a cytoplasm-nucleus dual-localized protein. Leaf senescence was delayed in both the CiS40-11 overexpressed A. thaliana and its transiently expressed C. intermedia. Transcriptomic analysis and endogenous hormones assay revealed that CiS40-11 inhibited leaf senescence via promoting the biosynthesis of cytokinins by blocking AtMYB2 expression in the CiS40-11 overexpression lines. Furthermore, overexpression of either AtS40-5 or AtS40-6 showed similar phenotype as the CiS40-11 overexpressing lines, while in the ats40-5a or ats40-6a mutants, the AtMYB2 expression was increased and their leaves exhibited a premature senescence phenotype. These results provide a new molecular mechanism of the S40 family in leaf senescence regulation of plants.

The source, level, and balance of nitrogen during the somatic embryogenesis process drive cellular differentiation

Since the discovery of somatic embryogenesis (SE), it has been evident that nitrogen (N) metabolism is essential during morphogenesis and cell differentiation. Usually, N is supplied to cultures in vitro in three forms, ammonium (NH₄⁺), nitrate (NO₃^-), and amino N from amino acids (AAs). Although most plants prefer NO₃^- to NH₄⁺, NH₄⁺ is the primary form route to be assimilated. The balance of NO₃^- and NH₄⁺ determines if the morphological differentiation process will produce embryos. That the N reduction of NO₃^- is needed for both embryo initiation and maturation is well-established in several models, such as carrot, tobacco, and rose. It is clear that N is indispensable for SE, but the mechanism that triggers the signal for embryo formation remains unknown. Here, we discuss recent studies that suggest an optimal endogenous concentration of auxin and cytokinin is closely related to N supply to plant tissue. From a molecular and biochemical perspective, we explain N's role in embryo formation, hypothesizing possible mechanisms that allow cellular differentiation by changing the nitrogen source.

Cypripedium subtropicum embryo development and cytokinin requirements for asymbiotic germination

BACKGROUND

Cypripedium subtropicum is a unique, endangered lady's slipper orchid with evergreen leaves on non-dormant shoots that is native to southwestern China. This study documents the major developmental events in C. subtropicum seed development from fertilization to seed maturity, determines the optimum period for seed collection, and examines the cytokinin requirements for asymbiotic germination and protocorm survival.

RESULTS

Structural studies revealed that embryo development proceeded after successful fertilization at 60 days after pollination (DAP). At 105 DAP, a globular embryo with the shrinking inner seed coat was observed, and seeds collected at this time point exhibited optimal germination. After 120 DAP, most seeds had a mature embryo within the capsule, and within the cells of the embryo proper, numerous proteins/lipid bodies were present as the main storage products. In addition, the inner seed coat had compressed into a thin layer that tightly enclosed the embryo, while the outer seed coat had progressively elongated, resulting in a hair-like appearance of the mature seed. Histochemical staining using Nile red and toluidine blue O (TBO) indicated that the lignified inner and outer seed coats may lead to coat-imposed dormancy. Seeds collected at this stage germinated poorly. Analyses of cytokinin preferences and optimal concentrations for germination and protocorm survival showed that both 6-(γ,γ-dimethylallylamino) purine (2iP) and 6-benzylaminopurine (BA) enhanced germination compared with the control, although higher concentrations of BA (4 and 8 μM) suppressed germination. The protocorm survival rate improved with increasing 2iP concentration.

CONCLUSIONS

This study provides a reproducible procedure for culturing immature seeds of C. subtropicum based on a defined time schedule of seed development. In addition, the cytokinin 2iP was shown to improve germination and protocorm survival. This study provides a scientific basis for seedling establishment through asymbiotic seed culture for further reintroduction efforts.

Quantification of six types of cytokinins: Integration of an ultra-performance liquid chromatographic-electrospray tandem mass spectrometric method with antibody based immunoaffinity columns equally recognizing cytokinins in free base and nucleoside forms

Cytokinins (CTKs) exist in various types in plants. The accurate quantification of free base and nucleoside types of cytokinins are helpful for better understanding their physiological role. In the present study, antibodies against trans-zeatin riboside (tZR) and N⁶-isopentenyladenine riboside (iPR) antibodies with equal recognition to free base and nucleoside cytokinins were developed. The cross-reactivity of tZR mAb 3G101G7 with tZR, trans-zeatin (tZ), dihydrozeatin riboside (DHZR), dihydrozeatin (DHZ), iPR, and N⁶-isopentenyladenine (iP) was 100.0%, 95.7%, 19.1%, 18.0%, 1.1%, and 0.7%, and that of iPR mAb 5C82F1 with above-mentioned 6 types of cytokinins was 1.5%, 1.4%, 5.7%, 3.1%, 100.0% and 92.6%, respectively. The obtained antibodies were used to prepare two immunoaffinity columns (IAC). The elution efficiencies of tZR 3G101G7-IAC for tZ and tZR, DHZ and DHZR and of iPR 5C82F1-IAC for iP and iPR were almost no difference with the same loading amount on their corresponding IACs. Subsequently, six types of cytokinins in mepiquat chloride (MC)-treated cotton (Gossypium hirsutum L.) roots were determined by IACs combined with ultra-performance liquid chromatography-electrospray tandem mass spectrometry (UPLC-ESI-MS/MS). The contents of tZR, iPR and DHZR were increased by 9.3∼38.5%, 6.6∼23.5%, and 30.1∼110.0%, respectively, whereas those of tZ and iP were reduced by 5.3∼20.0% and 27.7∼32.1%, respectively. The decreased tZ and iP levels led to the ratio of auxin-to-active cytokinins increase to promote lateral root initiation in MC-treated cotton seeding. Integration of the IACs equally recognizing cytokinins in their free base and nucleoside forms with UPLC-ESI-MS/MS can accurately quantify different cytokinins in plant tissues.

Interplay of phytohormones facilitate sorghum tolerance to aphids

Interactions among phytohormones are essential for providing tolerance of sorghum plants to aphids. Plant's encounter with insect herbivores trigger defense signaling networks that fine-tune plant resistance to insect pests. Although it is well established that phytohormones contribute to antixenotic- and antibiotic-mediated resistance to insect pests, their role in conditioning plant tolerance, the most durable and promising category of host plant resistance, is largely unknown. Here, we screened a panel of sorghum (Sorghum bicolor) inbred lines to identify and characterize sorghum tolerance to sugarcane aphids (SCA; Melanaphis sacchari Zehntner), a relatively new and devastating pest of sorghum in the United States. Our results suggest that the sorghum genotype SC35, the aphid-tolerant line identified among the sorghum genotypes, displayed minimal plant biomass loss and a robust photosynthetic machinery, despite supporting higher aphid population. Phytohormone analysis revealed significantly higher basal levels of 12-oxo-phytodienoic acid, a precursor in the jasmonic acid biosynthesis pathway, in the sorghum SCA-tolerant SC35 plants. Salicylic acid accumulation appeared as a generalized plant response to aphids in sorghum plants, however, SCA feeding-induced salicylic acid levels were unaltered in the sorghum tolerant genotype. Conversely, basal levels of abscisic acid and aphid feeding-induced cytokinins were accumulated in the SCA-tolerant sorghum genotype. Our findings imply that the aphid-tolerant sorghum genotype tightly controls the relationship among phytohormones, as well as provide significant insights into the underlying mechanisms that contribute to plant tolerance to sap-sucking aphids.

Review: Isoprenoid and aromatic cytokinins in shoot branching

Shoot branching is an important event of plant development that defines growth and reproduction. The BRANCHED1 gene (BRC1/TB1/FC1) is crucial for this process. Within the phytohormones, cytokinins directly activate axillary buds to promote shoot branching. In addition, strigolactones and auxins inhibit bud outgrowth. This review addresses the involvement of aromatic and isoprenoid cytokinins in shoot branching. And how auxins and strigolactones contribute to regulating this process also. The results obtained by others and our working group with lemongrass (Cymbopogon citratus) show that cytokinins affect both shoot and root apical meristem development, consistent with other plant species. However, many questions remain about how cytokinins and strigolactones antagonistically regulate BRC1 gene expression. Additionally, many details of the interaction among cytokinins, auxins, and strigolactones need to be clarified. We will gain a more comprehensive scheme of bud outgrowth with these details.

Hormonal control of cell identity and growth in the shoot apical meristem

How cells acquire their identities and grow coordinately within a tissue is a fundamental question to understand plant development. In angiosperms, the shoot apical meristem (SAM) is a multicellular tissue containing a stem cell niche, which activity allows for a dynamic equilibrium between maintenance of stem cells and production of differentiated cells that are incorporated in new aerial tissues and lateral organs produced in the SAM. Plant hormones are small-molecule signals controlling many aspects of plant development and physiology. Several hormones are essential regulators of SAM activities. This review highlights current advances that are starting to decipher the complex mechanisms underlying the hormonal control of cell identity and growth in the SAM.

Bacillus as a source of phytohormones for use in agriculture

Microbial plant biostimulants (MPBs) are capable of improving the productivity and quality of crops by activating plant physiological and molecular processes, representing an efficient tool in sustainable agriculture. Through phytohormone production, MPBs are capable of regulating plant physiological processes, increasing the productivity and quality of crops, in addition to being an efficient alternative in the industrial production of phytohormones. Bacillus is a bacterial genus with various species on the market being used as biopesticides, due to their ability to produce antimicrobial, nematicidal and insecticidal compounds. The capability of Bacillus species to protect plants against pests and/or pathogens also entails the triggering or increase of plant defense responses. Furthermore, a relevant number of species from the genus Bacillus provoke plant growth promotion by different mechanisms such as increasing the tolerance of their host plants under abiotic stress conditions or improving plant nutrition. In several cases, the plant response is mediated by the bacterial production of phytohormones. In the present work, all studies from recent decades where the production of phytohormones by Bacillus species are reported, highlighting their role in host plants and the mechanisms by which they are capable of increasing plant growth, promoting their development, and improving their response to different stresses. KEY POINTS: • Different Bacillus-species are known as agricultural biopesticides. • Bacillus role as biostimulants is being increasingly addressed. • Bacillus represents a good source of phytohormones of agricultural interest.

Regulation of rose petal dehydration tolerance and senescence by RhNAP transcription factor via the modulation of cytokinin catabolism

Petals and leaves share common evolutionary origins but have different phenotypic characteristics, such as the absence of stomata in the petals of most angiosperm species. Plant NAC transcription factor, NAP, is involved in ABA responses and regulates senescence-associated genes, and especially those that affect stomatal movement. However, the regulatory mechanisms and significance of NAP action in senescing astomatous petals is unclear. A major limiting factor is failure of flower opening and accelerated senescence. Our goal is to understand the finely regulatory mechanism of dehydration tolerance and aging in rose flowers. We functionally characterized RhNAP, an AtNAP-like transcription factor gene that is induced by dehydration and aging in astomatous rose petals. Cytokinins (CKs) are known to delay petal senescence and we found that a cytokinin oxidase/dehydrogenase gene 6 (RhCKX6) shares similar expression patterns with RhNAP. Silencing of RhNAP or RhCKX6 expression in rose petals by virus induced gene silencing markedly reduced petal dehydration tolerance and delayed petal senescence. Endogenous CK levels in RhNAP- or RhCKX6-silenced petals were significantly higher than those of the control. Moreover, RhCKX6 expression was reduced in RhNAP-silenced petals. This suggests that the expression of RhCKX6 is regulated by RhNAP. Yeast one-hybrid experiments and electrophoresis mobility shift assays showed that RhNAP binds to the RhCKX6 promoter in heterologous in vivo system and in vitro, respectively. Furthermore, the expression of putative signal transduction and downstream genes of ABA-signaling pathways were also reduced due to the repression of PP2C homolog genes by RhNAP in rose petals. Taken together, our study indicates that the RhNAP/RhCKX6 interaction represents a regulatory step enhancing dehydration tolerance in young rose petals and accelerating senescence in mature petals in a stomata-independent manner.

Beyond transport: cytokinin ribosides are translocated and active in regulating the development and environmental responses of plants

Riboside type cytokinins are key components in cytokinin metabolism, transport, and sensitivity, making them important functional signals in plant growth and development and environmental stress responses. Cytokinin (CKs) are phytohormones that regulate multiple processes in plants and are critical for agronomy, as they are involved in seed filling and plant responses to biotic and abiotic stress. Among the over 30 identified CKs, there is uncertainty about the roles of many of the individual CK structural forms. Cytokinin free bases (CKFBs), have been studied in great detail, but, by comparison, roles of riboside-type CKs (CKRs) in CK metabolism and associated signaling pathways and their distal impacts on plant physiology remain largely unknown. Here, recent findings on CKR abundance, transport and localization, are summarized, and their importance in planta is discussed. The history of CKR analyses is reviewed, in the context of the determination of CK metabolic pathways, and research on CKR affinity for CK receptors, all of which yield essential insights into their functions. Recent studies suggest that CKR forms are a lot more than a group of transport CKs and, beyond this, they play important roles in plant development and responses to environmental stress. In this context, this review discusses the involvement of CKRs in plant development, and highlight the less anticipated functions of CKRs in abiotic stress tolerance. Based on this, possible mechanisms for CKR modes of action are proposed and experimental approaches to further uncover their roles and future biotechnological applications are suggested.

Signaling network regulating plant branching: Recent advances and new challenges

Auxin alone or supplemented with cytokinins and strigolactones were long considered as the main player(s) in the control of apical dominance (AD) and correlative inhibition of the lateral bud outgrowth, the processes that shape the plant phenotype. However, past decade data indicate a more sophisticated pathways of AD regulation, with the involvement of mobile carbohydrates which perform both signal and trophic functions. Here we provide a critical comprehensive overview of the current status of the AD problem. This includes insight into intimate mechanisms regulating directed auxin transport in axillary buds with participation of phytohormones and sugars. Also roles of auxin, cytokinin and sugars in the dormancy or sustained growth of the lateral meristems were assigned. This review not only provides the latest data on implicated phytohormone crosstalk and its relationship with the signaling of sugars and abscisic acid, new AD players, but also focuses on the emerging biochemical mechanisms, at first positive feedback loops involving both sugars and hormones, that ensure the sustained bud growth. Data show that sugars act in concert with cytokinins but antagonistically to strigolactone signaling. A complex bud growth regulating network is demonstrated and unresolved issues regarding the hormone-carbohydrate regulation of AD are highlighted.

Simultaneous quantitation of cytokinin bases and their glycoconjugates with stable isotope labelling ultrahigh performance liquid chromatography mass spectrometry

Cytokinins (CKs) are one class of important phytohormones widely investigated in most aspects of plant life. Similar to other phytohormones, CKs and their glycoconjugates are hydrophilic. Their ionization efficiencies for mass spectrometry (MS) detection are rather poor, whereas their retention and separation on reverse phase liquid chromatography (RPLC) are often unsatisfying. Chemical isotope labelling LC-MS analysis methods have been developed for most other phytohormones, enhancing their LC separations and quantitative sensitivity. However, there are currently no reports for chemical-labelled CKs. Here, we report a new chemical isotope labelling LC-MS analytical method for one-pot derivatization of CK bases and their glycoconjugates, based on differential benzylation labelling of the adenine skeleton of CKs with benzyl bromide and its deuterium isotope-labelled reagent. Benzylation alters the hydrophilicity of CKs and their glycoconjugates, improving their retention and separation on RPLC. The developed method demonstrated enhanced sensitivity, as the CKs and their glycoconjugates could be analysed with LODs within the range of 0.62-25.9 pg/mL. The method also demonstrated good intra- and inter-day precisions with standard deviations in the range of 1.9%-13.0%, and acceptable accuracy with recoveries in the range of 84.0%-119.9%. The developed method was employed on the quantitation of CKs in the fresh roots of Astragalus membranaceus collected from both fertilized and unfertilized fields. The significant impact that fertilizers had on endogenous CKs metabolism was observed. As such, monitoring endogenous CKs and their metabolites might be promising to control fertilizer abuse.

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.

Prospection of cyanobacteria producing bioactive substances and their application as potential phytostimulating agents

• Using cyanobacteria extracts at low doses reduces the toxicity risk in cucumber seeds.

• Optimal doses of cytokinins and salicylic acid benefit the early plant growth stages.

• Cyanobacterial siderophores favor plant growth during the seedling phase.

• Strain Nostoc SAB-M612 stood out for their stimulant ability in cucumber seedlings.

This work clarifies some of the substances involved with the biostimulant effect shown by 28 cyanobacteria isolated from different aquatic environments. The production of salicylic acid, cytokinins, siderophores and phosphate solubilization were analyzed in vitro, as well as the phytostimulant/phytotoxic effect on watercress seeds at two different extract concentrations (0.5 and 0.2 mg mL⁻¹). The most prominent plant growth promoting cyanobacteria were verified in vivo at two different doses (0.5 and 0.1 mg mL⁻¹). 21.4 % and 7.1 % of the tested strains produced siderophores or phosphate solubilization, respectively. The production of salicylic acid was stood out for the strains Calothrix SAB-B797, Nostoc SAB-B1300 and Nostoc SAB-M612, while Nostoc SAB-M251 and Trichormus SAB-M304 were noticeable regard to cytokinin production. The highest values of germination occurred when the extracts were applied in low dose (0.5 mg mL⁻¹). Nostoc SAB-M612 provoked the stimulation of aerial and radicular growth in cucumber seedlings.

Plant-Associated Microbes Alter Root Growth by Modulating Root Apical Meristem

Rhizobacteria are known to produce a variety of signal molecules which may modify plant growth by interfering with phytohormone balance. Among the microbial signals are phytohormones, known to contribute to plant endogenous pool of phytohormones. The current chapter describes different methods to study the regulation of gene expression in root apical meristem in response to rhizobacterial inoculation. We describe protocol for the detection of in planta modulation of CKs and IAA by rhizobacteria and their impact on root growth, dissecting the underlying plant signaling pathway by RNA sequencing.

New biological trends on cell and callus growth and azadirachtin production in Azadirachta indica

Azadirachtin is an important secondary metabolite from Azadirachta indica used as a natural biopesticide. This study is the first comprehensive report concerning the influence of plant growth regulators on callus induction, cell suspension growth, and azadirachtin accumulation and production in cell suspension cultures of A. indica. We investigated the effect of plant growth regulators including different types of auxins and cytokinins and their combinations on callus induction, cell suspension growth, and azadirachtin accumulation and production. The highest percentage of callusing (100%) obtained at different combinations of plant growth regulators on MS medium supplemented with 1 mg/L picloram and 2 mg/L kinetin and the highest fresh weight of callus (264.50 mg) was observed in MS medium containing 1.5 mg/L NAA and 3 mg/L kinetin. In cell suspension cultures, the maximum cell density, SCV, and PCV were 2.44 × 10⁶ cells per mL, 97.95%, and 81.46%, respectively, obtained in the MS medium containing 1.5 mg/L 2,4-D and 3 mg/L zeatin riboside. The highest average growth rate (0.25 days) was on MS medium containing 1.5 mg/L NAA and 3 mg/L zeatin riboside. The MS medium supplemented with 1 mg/L picloram and 2 mg/L kinetin produced the highest amount of fresh cell weight (493.02 g/L), dry cell weight (77.27 g/L), azadirachtin accumulation (3.69 mg/gDW), and azadirachtin production (285.64 mg/L). The results showed that all measured indices had positive correlation with together except FCW and DCW with azadirachtin accumulation.

Identification and characterization of the first cytokinin glycosyltransferase from rice

BACKGROUND

Cytokinins are one of the five major hormones families in plants and are important for their normal growth and environmental adaptability. In plants, cytokinins are mostly present as glycosides in plants, and their glycosylation modifications are catalyzed by family 1 glycosyltransferases. Current research on cytokinin glycosylation has focused on the biochemical identification of enzymes and the analysis of metabolites in Arabidopsis. There are few studies that examine how cytokinin glycosylation affects its synthesis and accumulation in plants. It is particularly important to understand these processes in food crops such as rice (Oryza sativa); however, to date, cytokinin glycosyltransferase genes in rice have not been reported.

RESULTS

In this study, we identified eight rice genes that were functionally homologous to an Arabidopsis cytokinin glycosyltransferase gene. These genes were cloned and expressed in a prokaryotic system to obtain their purified proteins. Through enzymatic analysis and liquid chromatography-mass spectrometry, a single rice glycosyltransferase, Os6, was identified that glycosylated cytokinin in vitro. Os6 was overexpressed in Arabidopsis, and the extraction of cytokinin glycosides showed that Os6 is functionally active in planta.

CONCLUSIONS

The identification and characterization of the first cytokinin glycosyltransferase from rice is important for future studies on the cytokinin metabolic pathway in rice. An improved understanding of rice cytokinin glycosyltransferases may facilitate genetic improvements in rice quality.

Yeasts producing zeatin

The present paper describes the first screening study of the ability of natural yeast strains to synthesize in culture the plant-related cytokine hormone zeatin, which was carried out using HPLC-MS/MS. A collection of 76 wild strains of 36 yeast species (23 genera) isolated from a variety of natural substrates was tested for the production of zeatin using HPLC-MS/MS. Zeatin was detected in more than a half (55%) of studied strains and was more frequently observed among basidiomycetous than ascomycetous species. The amount of zeatin accumulated during the experiment varied among species and strains. Highest zeatin values were recorded for basidiomycete Sporobolomyces roseus and ascomycete Taphrina sp. that produced up to 8,850.0 ng and 5,166.4 ng of zeatin per g of dry biomass, respectively. On average, the ability to produce zeatin was more pronounced among species isolated from the arctic-alpine zone than among strains from tropical and temperate climates. Our study also demonstrated that epiphytic strains and pigmented yeast species, typically for phyllosphere, are able to more often produce a plant hormone zeatin than other yeasts.

Effect of constitutive expression of Arabidopsis CLAVATA3 on cell growth and possible role of cytokinins in leaf size control in transgenic tobacco plants

We generated transgenic tobacco plants (Nicotiana tabacum L.) with overexpression of the Arabidopsis thaliana CLAVATA3 (CLV3) gene which is known to be a negative regulator of cell division. Surprisingly, most of the 35S::CLV3 transgenic plants showed no phenotypic differences with the wild type plants. However, there were considerable changes in the morphological parameters between 35S::CLV3 overexpressors and wild type plants. As expected, the number of meristematic cells in the shoot apical meristem was reduced in 35S::CLV3 plants as compared to the wild type plants. Moreover, overexpression of CLV3 exerted morphological changes not only to shoot apical meristem but also to leaves and flowers. Thus, transgenic plants were characterized by reduced number of epidermal and mesophyll cells as well as stomatal pores in mature leaves. However, there was a compensatory increase in leaf cell size of 35S::CLV3 plants that contributed to maintenance of organ size within the normal range. We observed that expression of cell expansion-promoted genes, expansin NtEXPA4 and endo-xyloglucan transferase NtEXGT, were elevated in mature leaves. In contrast, there was a decrease in the transcript level of the cell division-related AINTEGUMENTA-like (NtANTL) gene in 35S::CLV3 transgenic plants. In addition, we detected an increase in cytokinin level without any changes in the contents of IAA and ABA in 35S::CLV3 overexpressors. Interestingly, cytokinin treatment was shown to stimulate the expression of NtEXPA4 and NtEXGT genes in 35S::CLV3 transgenic plants. We propose that observed compensatory cell expansion in leaves of 35S::CLV3 transgenic plants may be due, at least in part, to a possible link between cytokinin signalling and cell expansion-related genes.

Enhancement of phenolic and flavonoids compounds, antioxidant and cytotoxic effects in regenerated red cabbage by application of Zeatin

This study evaluated the roles of zeatin (2 mg/L) on direct organogenesis, phytochemical compounds, antioxidant activity, and cytotoxic activity in regenerated shoots of red cabbage. The results revealed that the extract of explant treated by 2 mg/L zeatin gives the highest content of total phenolics (5.18 mg gallic acid equivalent/g dry weight) and flavonoids (1.52 mg rutin equivalent/g dry weight). Moreover, HPLC and GC-MS analyses indicated that various bioactive compounds in red cabbage are significantly enhanced with increasing zeatin concentration. Besides that, antioxidant activity test showed that in vitro shooting culture using 2 mg/L zeatin displayed higher antioxidant activity in all assays (DPPH, FRAP and ABTS) compared to control with respective values of 68.12%, 73.28%, and 54.1%, respectively. Finally, the cytotoxic properties illustrated that the extracts of red cabbage explant treated by 2 mg/L zeatin exhibited the strongest cytotoxic effect towards cancer cells compared to control.

Effects of kinetin on plant growth and chloroplast ultrastructure of two Pteris species under arsenate stress

Cytokinins (CTKs) are effective in alleviating abiotic stresses on plants, but little information is available regarding the effects of CTKs on arsenic (As) accumulation and changes of chloroplast ultrastructure in plants with different As-accumulating ability. Here a hydroponic experiment was designed to evaluate the effects of different concentration of kinetin (KT, 0-40 mg/L) on growth and chloroplast ultrastructure of As hyperaccumulator Pteris cretica var. nervosa and non-hyperaccumulator Pteris ensiformis treated by 5 mg/L arsenate for 14 days. The growth parameters, As accumulation, contents of photosynthetic pigments and chloroplast ultrastructure were examined. The results showed that KT promoted the growth of two plants, and significantly increased As accumulation and translocation in P. cretica var. nervosa and P. ensiformis at 5 and 20 mg/L, respectively. Additionally, the contents of chlorophyll a and carotenoid in two plants showed no significant difference at 20 mg/L KT compared to the control. Chloroplast ultrastructure of P. cretica var. nervosa was integral with KT application. Comparatively, the swollen chloroplasts were increased, plasmolysis appeared, and chloroplast grana slice layers and stroma lamellas were clearly separated or distorted at 5 mg/L KT in P. ensiformis. The length and width of chloroplasts in P. cretica var. nervosa were significantly increased with KT addition compared to the control. However, the length of chloroplasts in P. ensiformis was significantly decreased but their width showed no significant change. Furthermore, the deterioration of chloroplast ultrastructure in P. ensiformis was ameliorated by 40 mg/L KT. These results suggested that KT increased As accumulation and was beneficial to maintain the photosynthetic pigments for a good growth of plants. Therefore, KT could maintain and reorganize the ultrastructure integrality of As-stressed chloroplasts to some extent for the two plants, especially at high concentration.

Induction of Somatic Embryogenesis in Jatropha curcas

Jatropha curcas has been a promising crop for biofuel production for the last decade. However, the lack of resistant materials to diseases and improved quality of the oil produced by the seeds has restricted the use of this promising crop. The genetic modifications in the fatty acid pathway, as well as the introduction of resistance to different diseases, would change the fate of Jatropha. To achieve these goals, we need to have a very efficient regeneration system. Here, we report a very useful protocol to induce somatic embryogenesis from leaves of Jatropha using cytokinin as the only growth regulator.

Tomato (Solanum lycopersicum) SlIPT4, encoding an isopentenyltransferase, is involved in leaf senescence and lycopene biosynthesis during fruit ripening

BACKGROUND

Lycopene is an important carotenoid pigment in red fruits and vegetables, especially in tomato. Although lycopene biosynthesis and catabolism have been found to be regulated by multiple factors including phytohormones, little is known about their regulatory mechanism. Cytokinins are crucial to various aspects of plant growth. Isopentenyltransferases (IPTs) catalyze the initial rate-limiting step of cytokinins biosynthesis, however, their roles in fruit ripening remain unclear.

RESULTS

Here, the functions of SlIPT4, encoding an isopentenyltransferase, were characterized via RNAi-mediated gene silencing in tomato. As we expected, silencing of SlIPT4 expression resulted in accelerated leaf senescence. However, down-expression of SlIPT4 generated never-red orange fruits, corresponding with a dramatic reduction of lycopene. Among lycopene biosynthesis-related genes, the fact of remarkable decrease of ZISO transcript and upregulation of other genes, revealed that SlIPT4 regulates positively lycopene biosynthesis via directly affecting ZISO expression, and also supported the existence of regulatory loops in lycopene biosynthesis pathway. Meanwhile, the accumulation of abscisic acid (ABA) was reduced and the transcripts PSY1 were increased in SlIPT4-RNAi fruits, supporting the feedback regulation between ABA and lycopene biosynthesis.

CONCLUSION

The study revealed the crucial roles of SlIPT4 in leaf senescence and the regulatory network of lycopene biosynthesis in tomato, providing a new light on the lycopene biosynthesis and fruit ripening.

Identification and expression analysis of cytokinin metabolic genes IPTs, CYP735A and CKXs in the biofuel plant Jatropha curcas

The seed oil of Jatropha curcas is considered a potential bioenergy source that could replace fossil fuels. However, the seed yield of Jatropha is low and has yet to be improved. We previously reported that exogenous cytokinin treatment increased the seed yield of Jatropha. Cytokinin levels are directly regulated by isopentenyl transferase (IPT), cytochrome P450 monooxygenase, family 735, subfamily A (CYP735A), and cytokinin oxidase/dehydrogenase (CKX). In this study, we cloned six IPT genes, one JcCYP735A gene, and seven JcCKX genes. The expression patterns of these 14 genes in various organs were determined using real-time quantitative PCR. JcIPT1 was primarily expressed in roots and seeds, JcIPT2 was expressed in roots, apical meristems, and mature leaves, JcIPT3 was expressed in stems and mature leaves, JcIPT5 was expressed in roots and mature leaves, JcIPT6 was expressed in seeds at 10 days after pollination, and JcIPT9 was expressed in mature leaves. JcCYP735A was mainly expressed in roots, flower buds, and seeds. The seven JcCKX genes also showed different expression patterns in different organs of Jatropha. In addition, CK levels were detected in flower buds and seeds at different stages of development. The concentration of N⁶-(Δ²-isopentenyl)-adenine (iP), iP-riboside, and trans-zeatin (tZ) increased with flower development, and the concentration of iP decreased with seed development, while that of tZ increased. We further analyzed the function of JcCYP735A using the CRISPR-Cas9 system, and found that the concentrations of tZ and tZ-riboside decreased significantly in the Jccyp735a mutants, which showed severely retarded growth. These findings will be helpful for further studies of the functions of cytokinin metabolic genes and understanding the roles of cytokinins in Jatropha growth and development.

Magnesium and organic biostimulant integrative application induces physiological and biochemical changes in sunflower plants and its harvested progeny on sandy soil

Magnesium (Mg) often leaches down in sandy soils due to high mobility and its foliar application proves to be beneficial. Organic biostimulants also prove to be helpful to affect plant physio-biochemistry and antioxidative defense system. The present study evaluated the beneficial effects of seed soaking in maize grain extract (MGE; 3%) in integration with or without foliar Mg (1 mM) in comparison to control (no treatment) on growth, yield performance, seed oil and fatty acid profile including physiological and biochemical basis of Hysun-336 sunflower hybrid grown on a sandy soil under greenhouse conditions. The integrative treatment (seed soaking in MGE + foliar spray with Mg) elevated growth traits, plant water status and membrane stability index, and reduced electrolyte leakage. Improved leaf contents of chlorophylls, carotenoids, total soluble sugars and proline, activities of non-enzymatic and enzymatic antioxidants were also observed. In addition, enhanced uptake of N, P, K including Mg and endogenous levels of plant hormones IAA, GA₃ and zeatin were recorded with the integrative treatment. Seed yield and oil contents including oleic (mono-unsaturated) and linoleic (poly-unsaturated) fatty acids also increased; however, a decrease in other saturated, mono-unsaturated and poly-unsaturated fatty acids was noticed. Improved seed and seedling vigor traits were also observed in progeny of sunflower that harvested from the integrative treatment. In summary, improved plant performance by the integrative treatment may be attributed to improved activities of antioxidants contributing to improved plant water content, nutrient uptake and endogenous hormonal levels in sunflower plants grown under sandy soil conditions.

Cytokinin activity of N6-benzyladenine derivatives assayed by interaction with the receptors in planta, in vitro, and in silico

Biological effects of hormones in both plants and animals are based on high-affinity interaction with cognate receptors resulting in their activation. The signal of cytokinins, classical plant hormones, is perceived in Arabidopsis by three homologous membrane receptors: AHK2, AHK3, and CRE1/AHK4. To study the cytokinin-receptor interaction, we used 25 derivatives of potent cytokinin N⁶-benzyladenine (BA) with substituents in the purine heterocycle and/or in the side chain. The study was focused primarily on individual cytokinin receptors from Arabidopsis. The main in planta assay system was based on Arabidopsis double mutants retaining only one isoform of cytokinin receptors and harboring cytokinin-sensitive reporter gene. Classical cytokinin biotest with Amaranthus seedlings was used as an additional biotest. In parallel, the binding of ligands to individual cytokinin receptors was assessed in the in vitro test system. Quantitative comparison of results of different assays confirmed the partial similarity of ligand-binding properties of receptor isoforms. Substituents at positions 8 and 9 of adenine moiety, elongated linker up to 4 methylene units, and replacement of N⁶ by sulfur or oxygen have resulted in the suppression of cytokinin activity of the derivative toward all receptors. Introduction of a halogen into position 2 of adenine moiety, on the contrary, often increased the ligand activity, especially toward AHK3. Features both common and distinctive of cytokinin receptors in Arabidopsis and Amaranthus were revealed, highlighting species specificity of the cytokinin perception apparatus. Correlations between the extent to which a compound binds to a receptor in vitro and its ability to activate the same receptor in planta were evaluated for each AHK protein. Interaction patterns between individual receptors and ligands were rationalized by structure analysis and molecular docking in sensory modules of AHK receptors. The best correlation between docking scores and specific binding was observed for AHK3. In addition, receptor-specific ligands have been discovered with unique properties to predominantly activate or block distinct cytokinin receptors. These ligands are promising for practical application and as molecular tools in the study of the cytokinin perception by plant cells.

Boron deficiency inhibits root growth by controlling meristem activity under cytokinin regulation

Significant advances have been made in the last years trying to identify regulatory pathways that control plant responses to boron (B) deficiency. Still, there is a lack of a deep understanding of how they act regulating growth and development under B limiting conditions. Here, we analyzed the impact of B deficit on cell division leading to root apical meristem (RAM) disorganization. Our results reveal that inhibition of cell proliferation under the regulatory control of cytokinins (CKs) is an early event contributing to root growth arrest under B deficiency. An early recovery of QC46:GUS expression after transferring B-deficient seedlings to control conditions revealed a role of B in the maintenance of QC identity whose loss under deficiency occurred at later stages of the stress. Additionally, the D-type cyclin CYCD3 overexpressor and triple mutant cycd3;1-3 were used to evaluate the effect on mitosis inhibition at the G1-S boundary. Overall, this study supports the hypothesis that meristem activity is inhibited by B deficiency at early stages of the stress as it does cell elongation. Likewise, distinct regulatory mechanisms seem to take place depending on the severity of the stress. The results presented here are key to better understand early signaling responses under B deficiency.

Effect of cytokinins on in vitro multiplication, volatiles composition and rosmarinic acid content of Thymus leucotrichus Hal. shoots

An efficient in vitro multiplication protocol was designed to Thymus leucotrichus, a subshrub and perennial herb growing naturally in the Northwest of Turkey. Of all basal media studied, Murashige and Skoog medium was found to be superior to the others, providing higher shoot formation and the maximum shoot length. Varying concentrations of cytokinins, i.e., 6-benzyladenine, thidiazuron, 2-isopentenyladenine and kinetin were supplemented in the nutrient media to observe their effects on shoot development and biomass. Rosmarinic acid content and volatile compositions of both naturally growing plants and in vitro multiplied plantlets were also evaluated. 6-benzyladenine (1.0 mg/L) and kinetin (0.5 mg/L) were found to be optimum for shoot number and shoot elongation, respectively. Thidiazuron (1.0 mg/L) was superior for biomass production. Rosmarinic acid content of in vitro multiplied plants was found to be higher than that of wild plants, reaching a maximum with 0.5 mg/L 2-isopentenyladenine, which yielded 10.15 mg/g dry weight. The highest thymol content was obtained with 1.0 mg/L kinetin (55.82%), while thidiazuron (0.1 mg/L) increased carvacrol production (12.53%). Overall, Murashige and Skoog medium supplemented with 1.0 mg/L kinetin was determined to be the most favorable medium studied.

Identification and expression analysis of the IPT and CKX gene families during axillary bud outgrowth in apple (Malus domestica Borkh.)

Cytokinins (CKs) play a crucial role in promoting axillary bud outgrowth and targeting the control of CK metabolism can be used to enhance branching in plants. CK levels are maintained mainly by CK biosynthesis (isopentenyl transferase, IPT) and degradation (dehydrogenase, CKX) genes in plants. A systematic study of the IPT and CKX gene families in apple, however, has not been conducted. In the present study, 12 MdIPTs and 12 MdCKXs were identified in the apple genome. Systematic phylogenetic, structural, and synteny analyses were performed. Expression analysis of these genes in different tissues was also assessed. MdIPT and MdCKX genes exhibit distinct expression patterns in different tissues. The response of MdIPT, MdCKX, and MdPIN1 genes to various treatments (6-BA, decapitation and Lovastatin, an inhibitor of CKs synthesis) that impact branching were also investigated. Results indicated that most of the MdIPT and MdCKX, and MdPIN1 genes were upregulated by 6-BA and decapitation treatment, but inhibited by Lovastatin, a compound that effectively suppresses axillary bud outgrowth induced by decapitation. These findings suggest that cytokinin biosynthesis is required for the activation of bud break and the export of auxin from buds in apple tree with intact primary shoot apex or decapitated apple tree. MdCKX8 and MdCKX10, however, exhibited little response to decapitation, but were significantly up-regulated by 6-BA and Lovastatin, a finding that warrants further investigation in order to understand their function in bud-outgrowth.

Molecular marker of high glycyrrhizic acid content based on the SNPs of liquorice IPT gene

Previous studies found that cytokinins (CTKs) are able to significantly promote glycyrrhizic acid (GA) accumulation. This study analyzed the correlation between the contents of GA and CTKs in 98 one-year-old liquorice plants by the combination of high-performance liquid chromatography and enzyme-linked immunosorbent assay. The full length of the liquorice IPT gene was cloned and the Single-nucleotide polymorphisms (SNPs) of the IPT gene in the samples were obtained. The molecular marker of high GA content was found by performing correlation analysis on the SNPs of the IPT gene. Results indicated that the contents of GA and CTKs were positively correlated. The full-length sequence of the IPT gene was 1002 bps, and five SNPs were found in the 98 liquorice samples. One of five SNPs was 348 bps, exhibiting missense mutation and the rest displaying synonymous mutations. In the five SNPs, 348 bps was primarily associated SNP, whereas 821 and 848 bps were auxiliary associated SNP. The findings of this study provided insight into the molecular mechanism of GA genetic variation, serving as basis for improving the GA content in cultivated liquorice and the good varieties breeding.

High frequency plant regeneration from cotyledonary node explants of Cucumis sativus L. cultivar 'Green Long' via adventitious shoot organogenesis and assessment of genetic fidelity by RAPD-PCR technology

Influence of cytokinins, silver nitrate (AgNO₃) and auxins on plant regeneration from cucumber was investigated. The cotyledonary node explants were cultured on MS medium augmented with various concentrations (0.5-2.5 mg l^-1) of 6-benzyl amino purine (BAP) and kinetin (KIN) for shoot bud induction. BAP at 1.5 mg l^-1 was found to be the best concentration for induction of high frequency of multiple shoots (98.4%). Interestingly, maximum percent of multiple shoot regeneration (100%) as well as number of shoot buds (54.6 shoots/culture) was recorded on MS medium containing the combination of 4.5 mg l^-1 AgNO₃ and 1.5 mg l^-1 BAP. Multiple shoot bud regeneration frequency as well as the number of shoots was positively correlated with the concentrations of AgNO₃. Addition of silver nitrate in the medium not only enhanced the rate of multiple shoot bud regeneration but also elongation of shoot buds was observed. The highest percent of rooting (96.2%) was noticed on a medium containing the combination of indole 3-butyric acid (IBA), 1.5 mg l^-1 and KIN 0.5 mg l^-1. Acclimatized plantlets were successfully established in the field where the survival rate observed was 72%. The RAPD profiles of in vitro regenerated plants were found to be highly monomorphic and identical banding pattern with mother plant. DNA fingerprinting results confirmed that the tissue culture plantlets were found to be true-to-type. The present study describes efficient protocol for high frequency plant regeneration via adventitious shoot organogenesis in cucumber.

Micropropagation of Agave Species

The genus Agave originates from the American continent and grows in arid and semiarid places, being México the center of origin. Many species of the genus are a source of diverse products for human needs, such as food, medicines, fibers, and beverages, and a good source of biomass for the production of biofuels, among many others. These plants are gaining importance as climate change becomes more evident as heat is reaching temperatures above 40 °C worldwide and rains are scarce. Many species of the genus grow in places where other plant species do not survive under severe field conditions, due to their CAM pathway for fixing CO₂ where gas exchange occurs at night when stomata are open, allowing them to avoid excess loss of water. Most of the important species and varieties are usually propagated by offshoots that develop from rhizomes around the mother plant and by bulbils that develop up in the inflorescence, which are produced by the plant mostly when there is a failure in the production of seeds.Areas for commercial plantations are growing worldwide and therefore in the need of big amounts of healthy and good quality plantlets. Although many Agave species produce seeds, it takes longer for the plants to reach appropriate maturity and size for diverse purposes. Micropropagation techniques for the genus Agave offer the opportunity to produce relatively high amounts of plants year around in relatively small spaces in a laboratory. Here, a protocol for micropropagation that has proven good for several Agave species (including species from both subgenera) is presented in detail with two different kinds of explants to initiate the process: rescued zygotic embryos and small offshoots that grow around a mother plant.

The imbalance between C and N metabolism during high nitrate supply inhibits photosynthesis and overall growth in maize (Zea mays L.)

Nitrogen (N) is an important regulator of photosynthetic carbon (C) flow in plants, and an adequate balance between N and C metabolism is needed for correct plant development. However, an excessive N supply can alter this balance and cause changes in specific organic compounds associated with primary and secondary metabolism, including plant growth regulators. In previous work, we observed that high nitrate supply (15 mM) to maize plants led to a decrease in leaf expansion and overall biomass production, when compared with low nitrate supply (5 mM). Thus, the aim of this work is to study how overdoses of nitrate can affect photosynthesis and plant development. The results show that high nitrate doses greatly increased amino acid production, which led to a decrease in the concentration of 2-oxoglutarate, the main source of C skeletons for N assimilation. The concentration of 1-aminocyclopropane-1-carboxylic acid (and possibly its product, ethylene) also rose in high nitrate plants, leading to a decrease in leaf expansion, reducing the demand for photoassimilates by the growing tissues and causing the accumulation of sugars in source leaves. This accumulation of sugars, together with the decrease in 2-oxoglutarate levels and the reduction in chlorophyll concentration, decreased plant photosynthetic rates. This work provides new insights into how high nitrate concentration alters the balance between C and N metabolism, reducing photosynthetic rates and disrupting whole plant development. These findings are particularly relevant since negative effects of nitrate in contexts other than root growth have rarely been studied.

Genetic analysis of rootstock-mediated nitrogen (N) uptake and root-to-shoot signalling at contrasting N availabilities in tomato

Selecting rootstocks for high nitrogen acquisition ability may allow decreased N fertilizer application without reducing tomato yields, minimizing environmental nitrate pollution. A commercial hybrid tomato variety was grafted on a genotyped population of 130 recombinant inbred lines (RILs) derived from Solanum pimpinellifolium, and compared with self- and non-grafted controls under contrasting nitrate availabilities (13.8 vs 1.0mM) in the nutrient solution. Grafting itself altered xylem sap composition under N-sufficient conditions, particularly Na⁺ (8.75-fold increase) concentration. N deprivation decreased shoot dry weight by 72.7% across the grafted RIL population, and one RIL rootstock allowed higher total leaf N content than the best of controls, suggesting more effective N uptake. Sixty-two significant QTLs were detected by multiple QTL mapping procedure for leaf N concentration (LNC), vegetative growth, and the xylem sap concentrations of Mn and four phytohormone groups (cytokinins, gibberellins, salicylic acid and jasmonic acid). Only three LNC QTLs could be common between nitrogen treatments. Clustering of rootstock QTLs controlling LNC, leaf dry weight and xylem sap salicylic acid concentration in chromosome 9 suggests a genetic relationship between this rootstock phytohormone and N uptake efficiency. Some functional candidate genes found within 2 Mbp intervals of LNC and hormone QTLs are discussed.

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.

The "STAY-GREEN" trait and phytohormone signaling networks in plants under heat stress

The increasing demand for food and the heavy yield losses in primary crops due to global warming mean that there is an urgent need to improve food security. Therefore, understanding how plants respond to heat stress and its consequences, such as drought and increased soil salinity, has received much attention in plant science community. Plants exhibit stress tolerance, escape or avoidance via adaptation and acclimatization mechanisms. These mechanisms rely on a high degree of plasticity in their cellular metabolism, in which phytohormones play an important role. "STAY-GREEN" is a crucial trait for genetic improvement of several crops, which allows plants to keep their leaves on the active photosynthetic level under stress conditions. Understanding the physiological and molecular mechanisms concomitant with "STAY-GREEN" trait or delayed leaf senescence, as well as those regulating photosynthetic capability of plants under heat stress, with a certain focus on the hormonal pathways, may be a key to break the plateau of productivity associated with adaptation to high temperature. This review will discuss the recent findings that advance our understanding of the mechanisms controlling leaf senescence and hormone signaling cascades under heat stress.

Enhanced production of berberine in In vitro regenerated cell of Tinospora cordifolia and its analysis through LCMS QToF

Tinospora cordifolia is a prioritized medicinal plant and having an immense medicinal importance especially in Indian medicinal system. But this plant needs a regeneration protocol for its rapid propagation. An efficient regeneration protocol was developed for T. cordifolia using nodal explants. High frequency of multiple shoot formation was induced when the nodal segments were cultured on MS medium supplemented with BAP (1.0 mg L⁻¹) and 2-iP (0.5 mg L⁻¹). The highest mean number of shoots per nodal explant (7.9 ± 0.45) with highest shoot length (9.3 ± 0.48 cm) and 86% response were achieved on this media and hormonal concentration. The optimum rooting was obtained on ½ strength of MS medium augmented with IBA (0.5 mg L⁻¹) with 8.3 ± 0.46 cm root length and 89% response. Micropropagated plantlets were found to be identical with the mother plant when clonal fidelity of these plantlets were analyzed with inter simple sequence repeat (ISSR) marker. The berberine content was analyzed through LCMS QToF and the highest amount was found in in vitro callus (19.8 µg/gm) followed by stem (9.3 µg/gm) and leaves of field-grown plants (8.4 µg/gm). Further, presence of berberine was confirmed by ESI–MS spectra with protonated molecular ions ([M + H]⁺) at m/z 336. Furthermore, MS–MS fragmentation pattern confirmed for the presence of berberine in both the samples. Both the spectra (standard and samples) showed common peaks for berberine in the form of protonated molecular ions ([M + H]⁺) at m/z 320, m/z 304, m/z 292, m/z 278 in MS/MS mode. The study revealed that developed protocol is potent for rapid mass propagation of this plant species with high accumulation of important secondary metabolite berberine.

Plant hormone cytokinins control cell cycle progression and plastid replication in apicomplexan parasites

Cytokinins are plant hormones that are involved in regulation of cell proliferation, cell cycle progression, and cell and plastid development. Here, we show that the apicomplexan parasites Toxoplasma gondii and Plasmodium berghei, an opportunistic human pathogen and a rodent malaria agent, respectively, produce cytokinins via a biosynthetic pathway similar to that in plants. Cytokinins regulate the growth and cell cycle progression of T. gondii by mediating expression of the cyclin gene TgCYC4. A natural form of cytokinin, trans-zeatin (t-zeatin), upregulated expression of this cyclin, while a synthetic cytokinin, thidiazuron, downregulated its expression. Immunofluorescence microscopy and quantitative PCR analysis showed that t-zeatin increased the genome-copy number of apicoplast, which are non-photosynthetic plastid, in the parasite, while thidiazuron led to their disappearance. Thidiazuron inhibited growth of T. gondii and Plasmodium falciparum, a human malaria parasite, suggesting that thidiazuron has therapeutic potential as an inhibitor of apicomplexan parasites.

Analyzing Cytokinin Responses During Plant-Nematode Interactions

Cyst nematodes are obligate biotrophs that induce the formation of a hypertrophied and hypermetabolic syncytial-feeding site in roots of the host plants. Cytokinin signaling is activated at the site of infection and contributes significantly to the formation of syncytium. Here, we describe a protocol for visualizing cytokinin signaling activation in Arabidopsis upon infection with cyst nematode Heterodera schachtii using promoter reporter lines, TCSn:GFP and ARR5:GUS.

Quantification of Cytokinin Levels and Responses in Abiotic Stresses

Since their discovery in the 1950s, it has been established that cytokinins (CKs) play important regulatory roles in various physiological processes in plants. Only recently have CKs been also implicated in the response of plants to biotic and abiotic stresses. During the last years, several analytical methods have been developed to determine CK concentrations in plant tissues. Here we present a simple and robust method for CK extraction, purification and analysis in plant tissues, using ultrahigh-performance liquid chromatography coupled to high resolution mass spectrometry (U-HPLC-HRMS). The main advantage of this methodology is the simplicity of the purification protocol and the possibility to extend it to the analysis of other plant hormones and derivatives.

Modulating the Levels of Plant Hormone Cytokinins at the Host-Pathogen Interface

Cytokinins are adenine and non-adenine derived heterogeneous class of regulatory molecules that participate in almost every aspect of plant biology. They also affect plant defense responses as well as help microbial pathogens to establish pathogenesis. The functional approaches that ensure desired and subtle modulations in the levels of plant cytokinins are highly instrumental in assessing their functions in plant immunity. Here, we describe a detailed working protocol regarding the enhanced production of cytokinins from plants that harbor isopentenyltransferase (IPT) enzyme gene under the control of 4xJERE (jasmonic acid and elicitor-responsive element) pathogen-inducible promoter. Our devised expression system is a context-dependent solution when it comes to investigating host-pathogen interactions under the modulated conditions of plant cytokinins.

Assessment of Cytokinin-Induced Immunity Through Quantification of Hyaloperonospora arabidopsidis Infection in Arabidopsis thaliana

Cytokinins have been shown to regulate plant immunity. Application of high levels of cytokinin to plants leads to decreased susceptibility to pathogens. In this chapter, we describe a fast and accurate protocol for assessment of cytokinin-induced immunity in Arabidopsis plants against an oomycete plant pathogen.