Mass spectrometry （MS） has been used to quantify endogenous levels of plant metabolites.　However, standard analyses, for example, with gas-chromatography MS or liquid-chromatography MS require a relatively large amount of plant materials.　Therefore, it has been difficult to know exactly the levels of target molecules at specific tissues or cells by the methods.　On the other hand, imaging MS and single-cell MS are potentially suitable techniques for visualizing local distribution of various chemical compounds in plants at tissue and single cell levels, although they are not yet commonly used in plant science studies.　The four feature articles in this volume describe the current status of research using imaging MS and single-cell MS.

Some studies suggested that abscisic acid （ABA）, and the jasmonic acid related-compound, 12-oxo-phytodienoic acid （OPDA）, play crucial roles in seed development, dormancy, and germination.　However, a lack of suitable technique for visualizing ABA and OPDA has restricted the investigation of their biological mechanisms in the immature seeds.　Mass spectrometry imaging （MSI） is a powerful tool for visualization of metabolites in biological tissue.　Here, I discuss the MSI workflow using matrix-assisted laser desorption/ionization （MALDI） and desorption electrospray ionization （DESI）.　Next, I introduce our recent studies on the visualization of ABA and OPDA in immature Phaseolus vulgaris L. seeds by DESI-MSI and derivatization with Girard’s reagent T in MALDI-MSI analyses.　I end with a discussion on the future prospects of the application of MSI for the plant hormones analysis.

Plant hormones can act in synergistic and antagonistic ways in response to biotic and abiotic stresses and in plant growth and development.　Thus, a technique is needed to determine the distributions and concentrations of several plant hormones simultaneously.　A relatively new technology, mass spectrometry imaging （MSI）, enables acquisition of direct mapping and imaging of biomolecules that are present in tissue sections.　MSI enables the simultaneous detection of multiple analytes on a single section of plant tissue, even in the absence of target-specific markers, such as antibodies.　Recently, MSI has been used to localize multi-plant hormones that are small molecules （m/z < 500）.　Here, we illustrate a technology of multiple-hormone imaging using MSI and discuss the potential for investigating the roles of hormone signaling in plant development and stress responses.

We have developed “Live Single-cell Mass Spectrometry” technique for a direct analysis of endogenous compounds in a single living cell.　The technique comprises a sampling from a living animal cell captured under video-microscopic observation, a nano-electrospray ionization of the sampled cell or cytosols and a high-resolution mass spectrometry.　The technique with stable isotope-labeled reagents realizes quantitatively to trace the metabolic processes of endogenous compounds as well as xenobiotics in a live cell.　In this paper, we demonstrate localization analysis of histidine metabolites in single living RBL-2H3 cells and to trace histidine metabolism using stable isotope labeling.　This method has enabled us to analyze not only location of metabolic pathways but also metabolic processes of interest molecules, and it can be used in various organelle metabolomics in a single live cell.　Currently, the technique is further improved and evolved to be a robotic cell manipulator with a confocal bio-imaging system so that a single cell or cytosol from a single live cell is automatically sampled based on a captured 3D bioimage.

The progress of single-cell omics approaches has been remarkable these days.　Metabolomics is not an exception to that progress.　MALDI-MS enables to measure samples with high spatial resolution.　At the same time, Live-single-cell MS （Single-cell MS） was also developed to detect metabolome data from the single-cell content.　We measured many terpenoid indole alkaloids （TIAs） in various cell types with single-cell MS.　It has been considered from gene expression analysis that TIAs are produced through internal phloem associated parenchyma cells, epidermal cells, and idioblast cells in Catharanthus roseus.　However, single-cell metabolome analysis revealed that many intermediates localize in idioblast cells against past expectations.　These results suggest that plants have a complex and compartmentalized secondary metabolism.　Here, we will show the results of single-cell MS and future subjects for single-cell approaches.

Parasitic plants obtain nutrients and water from their angiosperm hosts via the infecting organ called haustorium.　Striga spp. are devastating parasitic weeds that parasitize important crops, such as maize, rice and sorghum, and therefore cause significant yield losses that are estimated as billion dollars annually.　Recent completion of Striga asiatica genome sequence provided us insights into evolution of parasitic plants.　Whole genome duplication in the Striga lineage and co-option of lateral root development programs may have brought innovation of haustorium formation.　The KAI2 genes encoding strigolactone receptors were locally duplicated in the Striga genome.　Furthermore, the large genome segments were horizontally transferred to Striga genome from their Poaceae hosts.　This article summarizes the Striga genome evolution together with recently-sequenced holoparasitic Cuscuta genomes.

Strgigolactones （SLs） were initially characterized as host-derived chemical signals that induce seed germination of root parasitic plants.　They were then recharacterized as symbiotic signals for arbuscular mycorrhizal fungi that supply inorganic nutrients such as phosphate to the host plants.　In 2008, it was demonstrated that SLs act as plant hormones that regulate shoot branching.　After the discovery of the hormonal function of SLs, there have been much progress in the SL research field.　In this review we will introduce the latest knowledge on the SL perception and its signaling mechanism.　DWARF14 （D14）, which was characterized to be the SL receptor, is belonging to the α/β-hydrolase superfamily, and actually it can hydrolyze the SL molecules.　Thus, there have been discussions about the relationships between the hydrolase activity and the signal transducing function of D14.　We introduce several signaling models reported so far with a focus on this point.

Surfactants that contain both hydrophobic groups and hydrophilic groups in chemical structures play unique performances in various industrial fields.　It is well known that surfactants show an important role in improving the performances of pesticide formulations and in mediating their environmental effects.　In this review, I give an overview of surfactants in plant protection not only as additives of pesticide formulations but also as tank-mix adjuvants, insecticides, fungicides etc.

Many climate models predict that water stress will increasingly challenge agricultural yields and exacerbate projected food deficits.　To maintain a stable food supply, the improvement of water use in wheat crop production is essential to overcome water resource deficiencies.　The phytohormone abscisic acid （ABA） has critical roles for drought stress tolerance and the control of transpiration from leaves.　In this report, we introduce that enhancing the response of ABA signaling using an ABA receptor can confer drought stress tolerance and increase water use efficiency （i.e., the ratio of CO2 assimilation to transpiration）.　We developed an ABA-receptor-overexpressing wheat （TaPYLox） that exhibited significantly lower total lifetime water consumption and increased biomass and grain production per liter of water consumption.　Improved water use efficiency in TaPYLox was attributed to the increased photosynthetic activity in the leaves.　TaPYLox also alleviated the decline of seed productivity and grain quality under reduced water conditions.　Our findings provide a general strategy for increasing water productivity that should be portable to other crops due to the high conservation of the ABA signaling pathway.

In 2010, it was revealed some high-yield rice varieties were susceptible to benzobicyclon （BBC）, herbicide for weed control in rice paddy fields.　BBC belongs to β-triketone herbicides （bTHs） and inhibits 4-hydroxyphenylpyruvate dioxygenase （HPPD） of weed.　We identified a causative gene from rice.　This gene, HIS1 （HPPD INHIBITOR SENSITIVE 1）, that confers resistance to BBC and other β-triketone herbicides.　We showed that HIS1 encodes an Fe（II）/2-oxoglutarate-dependent oxygenase that detoxifies bTHs by catalyzing their hydroxylation.　Genealogy analysis revealed that BBC-sensitive rice variants inherited a dysfunctional his1 allele from an indica rice variety.　Forced expression of HIS1 in some plants other than rice conferred resistance not only to BBC but also to four additional β-triketone herbicides.　HIS1 may prove useful for breeding herbicide-resistant crops for both molecular and traditional breeding programs.