Quantitative analysis of cytokinins in plants by high performance liquid chromatography: electronspray ionization ion trap mass spectrometry

Rapid analysis of six cytokinins in tomato plants using phenylboronic acid and ionic liquid functionalized monolithic capillary column combined with UHPLC-MS/MS

In this study, 4-vinylphenylboronic acid, ionic liquid, and dipentaerythritolhexakis(3-mercaptopropionate) were used as functional monomers to prepare monolithic column in fused-silica capillaries by thermally induced sulfhydryl-alkenyl click polymerization. Based on the properties of 4-vinylphenylboronic acid and ionic liquid, the monolithic capillary column (VPBA-SH-IL) exhibited excellent permeability and chemical stability with the ability to efficiently enrich trace amounts of cytokinins from complex substrates via B←N coordination, π-π interactions, cation-π interactions, S-π interactions and hydrophobic interactions. Under the optimal adsorption conditions, the adsorption efficiency of VPBA-SH-IL for six cytokinins could reach more than 95 %, and the adsorption capacities ranged from 0.18 to 0.99 mg·m-1. A reliable and sensitive method for the determination of six cytokinins in organs of tomato (root, stem, leaf and fruit) was established by using the monolithic capillary column as in-tube solid-phase microextraction coupled with UHPLC-MS/MS. The developed method showed a wide linear range (0.010-10.0 μg·L-1) and low limits of detection (1.6-3.3 ng·L-1). The recoveries of the six cytokinins in spiked samples ranged from 80.6 % to 108 % with the relative standard deviations of 2.4-8.7 % (n = 5). The VPBA-SH-IL shows good potential for extraction and analysis of trace cytokinins in complex matrices such as plants, which is of great significance in exploring the mechanism of plant growth and development.

Transcriptomic and Metabolomic Analysis of Soybean Nodule Number Improvements with the Use of Water-Soluble Humic Materials

Water-soluble humic materials (WSHMs) can enhance the nodule numbers of soybean plants. In this study, targeted metabolomics and transcriptomics were used to understand this mechanism. Results showed that 500 mg/L WSHM increased the adsorption and colonization of rhizobia in soybean roots. High-performance liquid chromatography and targeted metabolomics showed that WSHMs could regulate the content and distribution of endogenous hormones of soybean plants at the initial stage of soybean nodulation. Transcriptomic analysis showed a total of 2406 differentially expressed genes (DEGs) by the 25th day, accounting for 4.89% of total annotation genes (49159). These DEGs were found to contribute primarily to the MAPK signaling pathway, glycolysis/gluconeogenesis, and plant hormone signal transduction according to the -log 10 (Padjust) value in the KEGG pathway. Subsequently, DEGs related to these hormones were selected for verification using quantity-PCR. The WSHM increased the number of nodules by regulating the expression of endogenous hormones in soybean plants.

Integrated multi-omics analysis uncovers roles of mdm-miR164b-MdORE1 in strigolactone-mediated inhibition of adventitious root formation in apple

Apple is one of the most important fruit crops in temperate regions and largely relies on cutting propagation. Adventitious root formation is crucial for the success of cutting propagation. Strigolactones have been reported to function in rooting of woody plants. In this study, we determined that strigolactones have inhibitory effects on adventitious root formation in apple. Transcriptome analysis identified 12 051 differentially expressed genes over the course of adventitious root initiation, with functions related to organogenesis, cell wall biogenesis or plant development. Further analysis indicated that strigolactones might inhibit adventitious root formation through repressing two core hub genes, MdLAC3 and MdORE1. Combining small RNA and degradome sequencing, as well as dual-luciferase sensor assays, we identified and validated three negatively correlated miRNA-mRNA pairs, including mdm-miR397-MdLAC3 and mdm-miR164a/b-MdORE1. Overexpression of mdm-miR164b and silencing MdORE1 exhibited enhanced adventitious root formation in tobacco and apple, respectively. Finally, we verified the role of mdm-miR164b-MdORE1 in strigolactone-mediated repression of rooting ability. Overall, the identified comprehensive regulatory network in apple not only provides insight into strigolactone-mediated adventitious root formation in other woody plants, but also points to a potential strategy for genetic improvement of rooting capacity in woody plants.

Molecular and physiological characterization of the effects of auxin-enriched rootstock on grafting

Grafting is a highly useful technique, and its success largely depends on graft union formation. In this study, we found that root-specific expression of the auxin biosynthetic gene iaaM in tobacco, when used as rootstock, resulted in more rapid callus formation and faster graft healing. However, overexpression of the auxin-inactivating iaaL gene in rootstocks delayed graft healing. We observed increased endogenous auxin levels and auxin-responsive DR5::GUS expression in scions of WT/iaaM grafts compared with those found in WT/WT grafts, which suggested that auxin is transported upward from rootstock to scion tissues. A transcriptome analysis showed that auxin enhanced graft union formation through increases in the expression of genes involved in graft healing in both rootstock and scion tissues. We also observed that the ethylene biosynthetic gene ACS1 and the ethylene-responsive gene ERF5 were upregulated in both scions and rootstocks of the WT/iaaM grafts. Furthermore, exogenous applications of the ethylene precursor ACC to the junction of WT/WT grafts promoted graft union formation, whereas application of the ethylene biosynthesis inhibitor AVG delayed graft healing in WT/WT grafts, and the observed delay was less pronounced in the WT/iaaM grafts. These results demonstrated that elevated auxin levels in the iaaM rootstock in combination with the increased auxin levels in scions caused by upward transport/diffusion enhanced graft union formation and that ethylene was partially responsible for the effects of auxin on grafting. Our findings showed that grafting success can be enhanced by increasing the auxin levels in rootstocks using transgenic or gene-editing techniques.

Differential Subcellular Distribution of Cytokinins: How Does Membrane Transport Fit into the Big Picture?

Cytokinins are a class of phytohormones, signalling molecules specific to plants. They act as regulators of diverse physiological processes in complex signalling pathways. It is necessary for plants to continuously regulate cytokinin distribution among different organs, tissues, cells, and compartments. Such regulatory mechanisms include cytokinin biosynthesis, metabolic conversions and degradation, as well as cytokinin membrane transport. In our review, we aim to provide a thorough picture of the latter. We begin by summarizing cytokinin structures and physicochemical properties. Then, we revise the elementary thermodynamic and kinetic aspects of cytokinin membrane transport. Next, we review which membrane-bound carrier proteins and protein families recognize cytokinins as their substrates. Namely, we discuss the families of "equilibrative nucleoside transporters" and "purine permeases", which translocate diverse purine-related compounds, and proteins AtPUP14, AtABCG14, AtAZG1, and AtAZG2, which are specific to cytokinins. We also address long-distance cytokinin transport. Putting all these pieces together, we finally discuss cytokinin distribution as a net result of these processes, diverse in their physicochemical nature but acting together to promote plant fitness.

Characterization of the cytokinin sensor TCSv2 in arabidopsis and tomato

BACKGROUND

Hormones are crucial to plant life and development. Being able to follow the plants hormonal response to various stimuli and throughout developmental processes is an important and increasingly widespread tool. The phytohormone cytokinin (CK) has crucial roles in the regulation of plant growth and development.

RESULTS

Here we describe a version of the CK sensor Two Component signaling Sensor (TCS), referred to as TCSv2. TCSv2 has a different arrangement of binding motifs when compared to previous TCS versions, resulting in increased sensitivity in some examined tissues. Here, we examine the CK responsiveness and distribution pattern of TCSv2 in arabidopsis and tomato.

CONCLUSIONS

The increased sensitivity and reported expression pattern of TCSv2 make it an ideal TCS version to study CK response in particular hosts, such as tomato, and particular tissues, such as leaves and flowers.

GhNAC83 inhibits corm dormancy release by regulating ABA signaling and cytokinin biosynthesis in Gladiolus hybridus

Corm dormancy is an important trait for breeding in many bulb flowers, including the most cultivated Gladiolus hybridus. Gladiolus corms are modified underground stems that function as storage organs and remain dormant to survive adverse environmental conditions. Unlike seed dormancy, not much is known about corm dormancy. Here, we characterize the mechanism of corm dormancy release (CDR) in Gladiolus. We identified an important ABA (abscisic acid) signaling regulator, GhPP2C1 (protein phosphatase 2C1), by transcriptome analysis of CDR. GhPP2C1 expression increased during CDR, and silencing of GhPP2C1 expression in dormant cormels delayed CDR. Furthermore, we show that GhPP2C1 expression is directly regulated by GhNAC83, which was identified by yeast one-hybrid library screening. In planta assays show that GhNAC83 is a negative regulator of GhPP2C1, and silencing of GhNAC83 promoted CDR. As expected, silencing of GhNAC83 decreased the ABA level, but also dramatically increased cytokinin (CK; zeatin) content in cormels. Binding assays demonstrate that GhNAC83 associates with the GhIPT (ISOPENTENYLTRANSFERASE) promoter and negatively regulates zeatin biosynthesis. Taken together, our results reveal that GhNAC83 promotes ABA signaling and synthesis, and inhibits CK biosynthesis pathways, thereby inhibiting CDR. These findings demonstrate that GhNAC83 regulates the ABA and CK pathways, and therefore controls corm dormancy.

Identification and expression analysis of strigolactone biosynthetic and signaling genes reveal strigolactones are involved in fruit development of the woodland strawberry (Fragaria vesca)

BACKGROUND

The development and ripening of fresh fruits is an important trait for agricultural production and fundamental research. Almost all plant hormones participate in this process. Strigolactones (SLs) are a new class of plant hormones that regulate plant organ development and stress tolerance, but little is known about their roles in fruit development.

RESULTS

In this study, we identified SL biosynthetic and signaling genes in woodland strawberry, a typical non-climacteric fruit, and analyzed the expression patterns of these genes in different plant tissues and developing fruits. One D27, two MAX1, and one LBO gene were identified as involved in SL biosynthesis, and one D14, one D3, and two D53 genes as related to SL signaling. The proteins encoded by these genes had similar motifs as SL biosynthetic and signaling proteins in rice and Arabidopsis. The genes had different expression levels in the root, stem, leaf, and petiole of woodland strawberry. In addition, the expression of most SL biosynthetic genes was high in developing carpel, anther, and style, while that of SL signaling genes was high in carpel and style, but low in anther, suggesting active SL biosynthesis and signaling in the developing carpel and style. Notably, the expression of SL biosynthetic and signaling genes was significantly increased in the receptacle after pollination and decreased during receptacle development. Moreover, low or no expression of these genes was detected in ripening fruits.

CONCLUSIONS

Our results suggest that SLs play a role in the early stages of woodland strawberry fruit development. Our findings provide insight into the function of SLs and will facilitate further study of the regulation by SLs of fresh fruit development.

PIL5 represses floral transition in Arabidopsis under long day conditions

PHYTOCHROME INTERACING FACTOR 3 LIKE 5 (PIL5), also named PHYTOCHROME INTERACTING FACTOR 1 (PIF1) is an important b-HLH transcription factor in Arabidopsis thaliana. Here we show that mutant of pil5-1 displays early flowering phenotype. We demonstrate that the expressions of the major flowering promoter genes [FLOWERING LOCUS T (FT), SUPPRESOR OF OVEREXPRESSION OF CO 1 (SOC1), and LEAFY (LFY)] are upregulated in the mutant of pil5-1. There is a significant increase of the mRNA of PIL5 in the mutants of co2-1, ft-10, soc1-2, and lfy-4. These changes provide the molecular evidence that PIL5 interacts with the flowering regulators to control flowering time. Moreover, it is shown in our results that PIL5 mutation mediates the increased contents of gibberellic acid (GA). Which is further supported by the qRT-PCR analysis, an increased transcriptome level of the GA biosynthesis genes (GA3ox1, GA3ox2, GA20ox1, GA20ox2, and GA20ox3) has been observed in the pil5-1 mutants as compared to the wild type. Collectively, PIL5 is involved in floral transition interacting with flowering integrators and GA.

Putative zeatin O-glucosyltransferase OscZOG1 regulates root and shoot development and formation of agronomic traits in rice

As a ubiquitous reaction, glucosylation controls the bioactivity of cytokinins in plant growth and development. Here we show that genetic manipulation of zeatin-O-glucosylation regulates the formation of important agronomic traits in rice by manipulating the expression of OscZOG1 gene, encoding a putative zeatin O-glucosyltransferase. We found that OscZOG1 was preferentially expressed in shoot and root meristematic tissues and nascent organs. The growth of lateral roots was stimulated in the overexpression lines, but inhibited in RNA interference lines. In shoots, knockdown of OscZOG1 expression by RNA interference significantly improved tillering, panicle branching, grain number per panicle and seed size, which are important agronomic traits for grain yield. In contrast, constitutive expression of OscZOG1 leads to negative effects on the formation of the grain-yielding traits with a marked increase in the accumulation levels of cis-zeatin O-glucoside (cZOG) in the transgenic rice plants. In this study, our findings demonstrate the feasibility of improving the critical yield-determinant agronomic traits, including tiller number, panicle branches, total grain number per panicle and grain weight by downregulating the expression level of OscZOG1. Our results suggest that modulating the levels of cytokinin glucosylation can function as a fine-tuning switch in regulating the formation of agronomic traits in rice.

GA4 and IAA were involved in the morphogenesis and development of flowers in Agapanthus praecox ssp. orientalis

The transition from vegetative to reproductive growth represents a major phase change in angiosperms. Hormones play important roles in this process. In this study, gibberellic acid (GA), cytokinins (CKs), indoleacetic acid (IAA), and abscisic acid (ABA) were analyzed during the flowering in Agapanthus praecox ssp. orientalis. Eleven types of endogenous gibberellins in addition to GA1 were detected in various organs. GA9 was detected with the highest concentrations, followed by GA5, GA8, and GA19. However, GA4 was the main bioactive GA that was involved in the regulation of flowering. Eight types of endogenous cytokinins were detected in A. praecox ssp. orientalis, and zeatin, zeatin riboside, zeatin-O-glucoside, and N(6)-isopentenyladenosine-5-monophosphate were present at higher levels throughout the study, of which zeatin plays an important role in the development of various organs. IAA increased by 581% in the shoot tips from the vegetative to inflorescence bud stages and had the most significant changes during flowering. Phytohormone immunolocalization analysis suggested that IAA involved in differentiation and development of each floral organs, GA and zeatin play important roles in floret primordia differentiation and ovule development. Using exogenous plant growth regulators proved that GA signaling regulate the scape elongation and stimulate early-flowering, and IAA signaling is involved in the pedicel and corolla elongation and delay flowering slightly.

Deciphering small noncoding RNAs during the transition from dormant embryo to germinated embryo in Larches (Larix leptolepis)

Small RNAs (sRNAs), as a key component of molecular biology, play essential roles in plant development, hormone signaling, and stress response. However, little is known about the relationships among sRNAs, hormone signaling, and dormancy regulation in gymnosperm embryos. To investigate the roles of sRNAs in embryo dormancy maintenance and release in Larix leptolepis, we deciphered the endogenous “sRNAome” in dormant and germinated embryos. High-throughput sequencing of sRNA libraries showed that dormant embryos exhibited a length bias toward 24-nt while germinated embryos showed a bias toward 21-nt lengths. This might be associated with distinct levels of RNA-dependent RNA polymerase2 (RDR2) and/or RDR6, which is regulated by hormones. Proportions of miRNAs to nonredundant and redundant sRNAs were higher in germinated embryos than in dormant embryos, while the ratio of unknown sRNAs was higher in dormant embryos than in germinated embryos. We identified a total of 160 conserved miRNAs from 38 families, 3 novel miRNAs, and 16 plausible miRNA candidates, of which many were upregulated in germinated embryos relative to dormant embryos. These findings indicate that larches and possibly other gymnosperms have complex mechanisms of gene regulation involving miRNAs and other sRNAs operating transcriptionally and posttranscriptionally during embryo dormancy and germination. We propose that abscisic acid modulates embryo dormancy and germination at least in part through regulation of the expression level of sRNA-biogenesis genes, thus changing the sRNA components.

Adenine phosphoribosyl transferase 1 is a key enzyme catalyzing cytokinin conversion from nucleobases to nucleotides in Arabidopsis

In plants, the cytokinin metabolic processes, including cytokinin biosynthesis, interconversion, inactivation, and degradation, play critical roles in the regulation of cytokinin homeostasis and plant development. Purine metabolic enzymes have been implied to catalyze the cytokinin interconversion in previous works. In this study, we report that Adenine Phosphoribosyl Transferase 1 (APT1) is the causal gene of the high-dose cytokinin-resistant mutants. APT1 catalyzes the cytokinin conversion from free bases to nucleotides, and is functionally predominant among the five members of the Arabidopsis Adenine Phosphoribosyl Transferase family. Loss of APT1 activity in plants leads to excess accumulation of cytokinin bases, thus evoking myriad cytokinin-regulated responses, such as delayed leaf senescence, anthocyanin accumulation, and downstream gene expression. Thus, our study defines APT1 as a key metabolic enzyme participating in the cytokinin inactivation by phosphoribosylation.

Sense-, antisense- and RNAi-4CL1 regulate soluble phenolic acids, cell wall components and growth in transgenic Populus tomentosa Carr

Regulation of lignin biosynthesis affects plant growth and wood properties. Transgenic downregulation of 4-coumarate:coenzyme A ligase (4CL, EC 6.2.1.12) may reduce lignin content in cell walls, which could improve the qualities of pulp in papermaking and increase the efficiency of bioenergy applications. To determine the effects of Ptc4CL1 on lignin biosynthesis and plant growth, Populus tomentosa Carr. was transformed using sense-, antisense-, and RNAi-4CL1 genes. The growth properties, gene expression, enzyme activity, lignin content and composition and content of soluble phenolic acids were investigated in 1-year-old field-grown transgenic poplar trees. Transgenic up- and down-regulation of 4CL1 altered lignin content and composition in transgenic poplars, but there were no negative effects on the growth of transgenic plants. In addition, the severe changes in auxin observed in transgenic lines led to significantly enhanced growth performance. Furthermore, lignin content was tightly correlated with the alteration of 4CL1 enzymatic activity, which was correlated with 4CL1 gene expression. A significant increase in S units in lignin with a slight increase in sinapic acid was observed in 4CL1 down-regulated transgenic poplars. These results suggest that 4CL1 is a traffic control gene in monolignol biosynthesis and confirm that 4CL1 activity has been implicated with sinapoyl activation. Finally, our data demonstrate that there is cross-correlation among 4CL1 gene expression, 4CL1 enzyme activity, soluble phenolic acid, lignin monomer biosynthesis, and lignin content.

Simultaneous determination of 24 or more acidic and alkaline phytohormones in femtomole quantities of plant tissues by high-performance liquid chromatography-electrospray ionization-ion trap mass spectrometry

Phytohormones act at relatively low concentrations as major regulatory factors of plant growth and development, and cross talk of phytohormones is currently of great interest throughout the plant science community. To meet this demand, a method that is capable of simultaneously analyzing diverse plant hormones is essential. This paper introduces a high-performance liquid chromatographic separation technique coupled with sensitive and selective ion trap mass spectrometry to simultaneously determine 24 or more acidic and alkaline phytohormones, including auxin, cis- and trans-abscisic acid, 11 cytokinins, and 10 gibberellins, in a single injection of sample. A binary solid-phase extraction using Oasis MCX cartridges for cations and Oasis MAX cartridges for anions was used to prepurify more than 24 acidic and alkaline phytohormones from a single plant extract. The method showed good linearity for all 24 phytohormones with R(2) values ranging from 0.9903 to 0.9997. Limits of detection for most of the phytohormones were in the femtomole range with some extending into the sub-femtomole range. This method was applied to hundreds of plant samples comprising different tissues from various plants, including herbaceous, woody climbing, and woody plants to demonstrate feasibility and to validate the methodology.

Tandem solid phase extraction followed by online trapping-hydrophilic interaction chromatography-tandem mass spectrometry for sensitive detection of endogenous cytokinins in plant tissues

INTRODUCTION

Cytokinins (CKs) are a group of plant hormones that play pivotal roles at low concentration in plant growth, development and regulatory pathways. In order to study the function, metabolism and signal transduction of CKs, high performance analytical techniques are required for determination of their endogenous levels.

OBJECTIVE

To develop a highly sensitive, selective and reliable method for identification and quantification of CKs by employing a tandem solid phase extraction (SPE)-online trapping-hydrophilic interaction chromatography (HILIC)-MS/MS method.

MATERIAL AND METHODS

The extraction was performed firstly with tandem SPE containing a C(18) cartridge and a silica@C(8) /SO(3) H cartridge. After CKs were eluted from the silica@C(8)/SO(3) H cartridge, the desorption solvent was concentrated and redissolved in H(2)O and then injected into the online trapping-HILIC-MS/MS system with (Poly(MAA-co-EGDMA)) monolith as the trapping column. Subsequently, trapping, washing, desorption, separation and detection were accomplished automatically on the system.

RESULTS

Good linearities were obtained for eight cytokinins with correlation coefficients (R(2)) > 0.9964. The limits of detection (LOD; S:N = 3) for the targets ranged from 0.042 to 1.6 pg/mL. Reproducibility of the method was evaluated with intraday and interday relative standard deviations (RSDs) less than 13.4% and the recoveries ranged from 77.3% to 116.3%. The results showed that the LOD of the analytical method were at least one order of magnitude lower compared with other previously reported methods. Furthermore, only 20 mg of plant tissues were required for the quantitative analysis of the major CKs, which is, to the best of our knowledge, the smallest amount reported so far for the determination of endogenous CKs in plant tissues.

CONCLUSION

The tandem SPE-online trapping-HILIC-MS/MS method developed in current study provides a powerful tool for the convenient and highly sensitive quantification of the major CKs in plant tissue.

Concurrent profiling of indole-3-acetic acid, abscisic acid, and cytokinins and structurally related purines by high-performance-liquid-chromatography tandem electrospray mass spectrometry

BACKGROUND

Cytokinins (CKs) are a group of plant growth regulators that are involved in several plant developmental processes. Despite the breadth of knowledge surrounding CKs and their diverse functions, much remains to be discovered about the full potential of CKs, including their relationship with the purine salvage pathway, and other phytohormones. The most widely used approach to query unknown facets of CK biology utilized functional genomics coupled with CK metabolite assays and screening of CK associated phenotypes. There are numerous different types of assays for determining CK quantity, however, none of these methods screen for the compendium of metabolites that are necessary for elucidating all roles, including purine salvage pathway enzymes in CK metabolism, and CK cross-talk with other phytohormones. Furthermore, all published analytical methods have drawbacks ranging from the required use of radiolabelled compounds, or hazardous derivatization reagents, poor sensitivity, lack of resolution between CK isomers and lengthy run times.

RESULTS

In this paper, a method is described for the concurrent extraction, purification and analysis of several CKs (freebases, ribosides, glucosides, nucleotides), purines (adenosine monophosphate, inosine, adenosine, and adenine), indole-3-acetic acid, and abscisic acid from hundred-milligram (mg) quantities of Arabidopsis thaliana leaf tissue. This method utilizes conventional Bieleski solvents extraction, solid phase purification, and is unique because of its diverse range of detectable analytes, and implementation of a conventional HPLC system with a fused core column that enables good sensitivity without the requirement of a UHPLC system. Using this method we were able to resolve CKs about twice as fast as our previous method. Similarly, analysis of adenosine, indole-3-acetic acid, and abscisic acid, was comparatively rapid. A further enhancement of the method was the utilization of a QTRAP 5500 mass analyzer, which improved upon several aspects of our previous analytical method carried out on a Quattro mass analyzer. Notable improvements included much superior sensitivity, and number of analytes detectable within a single run. Limits of detection ranged from 2 pM for (9G)Z to almost 750 pM for indole-3-acetic acid.

CONCLUSIONS

This method is well suited for functional genomics platforms tailored to understanding CK metabolism, CK interrelationships with purine recycling and associated hormonal cross-talk.

Classification and characterization of unknown cytokinins into essential types by in-source collision-induced dissociation electrospray ionization ion trap mass spectrometry

RATIONALE

Mass spectrometry is effective for determination of cytokinins, which are bioactive compounds with an adenine-core structure. However, it is difficult to characterize any cytokinin compound without the relevant standard or known molecular structure information. With a limited number of standards, an in-source collision-induced dissociation (CID) method for characterization and classification of unknown cytokinins was described in this study.

METHODS

Cytokinins were separated by high-performance liquid chromatography and then analyzed by electrospray ionization ion trap mass spectrometry using an in-source CID technique and multiple reaction monitoring (MRM) mode.

RESULTS

Based on the properties of multi-stage fragmentation in mass spectrometry, naturally occurring cytokinins were classified into four types (zeatin, dihydrogen zeatin, isopentenyl adenine and benzyl adenine) by losing their conjugated sugar, sugar phosphate and other substituents in the source region. Following this technique, seven unknown cytokinins were characterized from roots of maize (Zea mays) without standards and one of them was finally confirmed to be cis-zeatin-riboside.

CONCLUSIONS

An in-source CID technique combined with MRM mass spectrometry was developed to provide product ion information for identification of cytokinins and to afford guidance for the discovery of unknown cytokinins.

A mutation in the E2 subunit of the mitochondrial pyruvate dehydrogenase complex in Arabidopsis reduces plant organ size and enhances the accumulation of amino acids and intermediate products of the TCA cycle

The mitochondrial pyruvate dehydrogenase complex (mtPDC) plays a pivotal role in controlling the entry of carbon into the tricarboxylic acid (TCA) cycle for energy production. This multi-enzyme complex consists of three components: E1, E2, and E3. In Arabidopsis, there are three genes, mtE2-1, mtE2-2, and mtE2-3, which encode the putative mtPDC E2 subunit but how each of them contributes to the total mtPDC activity remains unknown. In this work, we characterized an Arabidopsis mutant, m132, that has abnormal small organs. Molecular cloning indicated that the phenotype of m132 is caused by a mutation in the mtE2-1 gene, which results in a truncation of 109 amino acids at the C-terminus of the encoded protein. In m132, mtPDC activity is only 30% of the WT and ATP production is severely impaired. The mutation in the mtE2-1 gene also leads to the over-accumulation of most intermediate products of the TCA cycle and of all the amino acids for protein synthesis. Our results suggest that, among the three mtE2 genes, mtE2-1 is a major contributor to the function of Arabidopsis mtPDC and that the functional disruption of mtE2-1 profoundly affects plant growth and development, as well as its metabolism.

Analytical methods for tracing plant hormones

Plant hormones play important roles in regulating numerous aspects of plant growth, development, and response to stress. In the past decade, more analytical methods for the accurate identification and quantitative determination of trace plant hormones have been developed to better our understanding of the molecular mechanisms of plant hormones. As sample preparation is often the bottleneck in analysis of plant hormones in biological samples, this review firstly discusses sample preparation techniques after a brief introduction to the classes, roles, and methods used in the analysis of plant hormones. The analytical methods, especially chromatographic techniques and immuno-based methods, are reviewed in detail, and their corresponding advantages, limitations, applications, and prospects are also discussed. This review mainly covers reports published from 2000 to the present on methods for the analysis of plant hormones.

Rapid and sensitive hormonal profiling of complex plant samples by liquid chromatography coupled to electrospray ionization tandem mass spectrometry

BACKGROUND

Plant hormones play a pivotal role in several physiological processes during a plant's life cycle, from germination to senescence, and the determination of endogenous concentrations of hormones is essential to elucidate the role of a particular hormone in any physiological process. Availability of a sensitive and rapid method to quantify multiple classes of hormones simultaneously will greatly facilitate the investigation of signaling networks in controlling specific developmental pathways and physiological responses. Due to the presence of hormones at very low concentrations in plant tissues (10-9 M to 10-6 M) and their different chemistries, the development of a high-throughput and comprehensive method for the determination of hormones is challenging.

RESULTS

The present work reports a rapid, specific and sensitive method using ultrahigh-performance liquid chromatography coupled to electrospray ionization tandem spectrometry (UPLC/ESI-MS/MS) to analyze quantitatively the major hormones found in plant tissues within six minutes, including auxins, cytokinins, gibberellins, abscisic acid, 1-amino-cyclopropane-1-carboxyic acid (the ethylene precursor), jasmonic acid and salicylic acid. Sample preparation, extraction procedures and UPLC-MS/MS conditions were optimized for the determination of all plant hormones and are summarized in a schematic extraction diagram for the analysis of small amounts of plant material without time-consuming additional steps such as purification, sample drying or re-suspension.

CONCLUSIONS

This new method is applicable to the analysis of dynamic changes in endogenous concentrations of hormones to study plant developmental processes or plant responses to biotic and abiotic stresses in complex tissues. An example is shown in which a hormone profiling is obtained from leaves of plants exposed to salt stress in the aromatic plant, Rosmarinus officinalis.

SHORT INTERNODES-like genes regulate shoot growth and xylem proliferation in Populus

• Genes controlling plant growth and form are of considerable interest, because they affect survival and productivity traits, and are largely unknown or poorly characterized. The SHORT INTERNODES(SHI) gene is one of a 10-member SHI-RELATED SEQUENCE (SRS) gene family in Arabidopsis that includes important developmental regulators. • Using comparative sequence analysis of the SRS gene families in poplar and Arabidopsis, we identified two poplar proteins that are most similar to SHI and its closely related gene STYLISH1 (STY1). The two poplar genes are very similar in sequence and expression and are therefore probably paralogs with redundant functions. • RNAi suppression of the two Populus genes enhanced shoot and root growth, whereas the overexpression of Arabidopsis SHI in poplar reduced internode and petiole length. The suppression of the two genes increased fiber length and the proportion of xylem tissue, mainly through increased xylem cell proliferation. The transgenic modifications were also associated with significant changes in the concentrations of gibberellins and cytokinin. • We conclude that Populus SHI-RELATED SEQUENCE (SRS) genes play an important role in the regulation of vegetative growth, including wood formation, and thus could be useful tools for the modification of biomass productivity, wood quality or plant form.