Regulation of transplasmalemma electron transport in oat mesophyll cells by sphingoid bases and blue light

Illumination/Darkness-Induced Changes in Leaf Surface Potential Linked With Kinetics of Ion Fluxes

A highly reproducible plant electrical signal-light-induced bioelectrogenesis (LIB) was obtained by means of periodic illumination/darkness stimulation of broad bean (Vicia faba L.) leaves. By stimulating the same position of the same leaf with different concentrations of NaCl, we observed that the amplitude and waveform of the LIB was correlated with the intensity of stimulation. This method allowed us to link dynamic ion fluxes induced by periodic illumination/darkness to salt stress. The self-referencing ion electrode technique was used to explore the ionic mechanisms of the LIB. Fluxes of H+, Ca2+, K+, and Cl- showed periodic changes under periodic illumination/darkness before and after 50 mM NaCl stimulation. Gray relational analysis was used to analyze correlations between each of these ions and LIB. The results showed that different ions are involved in surface potential changes at different stages under periodic illumination/darkness. The gray relational grade reflected the contribution of each ion to the change in surface potential at a certain time period. The ion fluxes data obtained under periodic illumination/darkness stimulation will contribute to the future development of a dynamic model for interpretation of electrophysiological events in plant cells.

Foliar application of selenium for protection against the first stages of mycotoxin infection of crop plant leaves

BACKGROUND

The aim of this study was to investigate whether the application of selenium (Se) ions directly to the leaf surface can protect plants against infection by the fungal toxin zearalenone (ZEA). The experiments were performed for the most common and agronomically important crops such as wheat, oat, and barley (both tolerant and sensitive varieties) because mycotoxin accumulation in plants is the cause of many diseases in animals and people.

RESULTS

ZEA at a concentration of 10 µmol L^-1 either alone or in combination with Se (5 µmol L^-1 Na₂ SeO₄ ) was applied to the second leaf of seedlings. Visualization of leaf temperature profiles by infrared thermography demonstrated a decrease in temperature at the location of ZEA infection that was more noticeable in sensitive genotypes. The presence of Se significantly suppressed changes at the site of ZEA application in all tested plants, especially the tolerant genotypes. Microscopic observations confirmed that foliar administration of ZEA resulted in its penetration to deeper localized cells and that damage induced by ZEA (mainly to chloroplasts) decreased after Se application. Analyses of antioxidant enzymes demonstrated the involvement of Se in antioxidation mechanisms, in particular by activating SOD and CAT under ZEA-induced stress conditions.

CONCLUSION

The foliar application of Se to seedling leaves may be a non-invasive method of protecting crops against the first steps of ZEA infection. © 2018 Society of Chemical Industry.

Plant sphingolipids: decoding the enigma of the Sphinx

Sphingolipids are a ubiquitous class of lipids present in a variety of organisms including eukaryotes and bacteria. In the last two decades, research has focused on characterizing the individual species of this complex family of lipids, which has led to a new field of research called 'sphingolipidomics'. There are at least 500 (and perhaps thousands of) different molecular species of sphingolipids in cells, and in Arabidopsis alone it has been reported that there are at least 168 different sphingolipids. Plant sphingolipids can be divided into four classes: glycosyl inositol phosphoceramides (GIPCs), glycosylceramides, ceramides, and free long-chain bases (LCBs). Numerous enzymes involved in plant sphingolipid metabolism have now been cloned and characterized, and, in general, there is broad conservation in the way in which sphingolipids are metabolized in animals, yeast and plants. Here, we review the diversity of sphingolipids reported in the literature, some of the recent advances in our understanding of sphingolipid metabolism in plants, and the physiological roles that sphingolipids and sphingolipid metabolites play in plant physiology.

Dihydroxylation of 2-vinylaziridine: efficient synthesis ofd-ribo-phytosphingosine

An efficient and highly stereoselective synthesis of D-ribo-(2S,3S,4R)-phytosphingosine was accomplished in 62% overall yield starting from commercially available (2S)-hydroxymethylaziridine via osmium-catalyzed asymmetric dihydroxylation as a key step.

A post-genomic approach to understanding sphingolipid metabolism in Arabidopsis thaliana

AIMS

To highlight the importance of sphingolipids and their metabolites in plant biology.

SCOPE

The completion of the arabidopsis genome provides a platform for the identification and functional characterization of genes involved in sphingolipid biosynthesis. Using the yeast Saccharomyces cerevisiae as an experimental model, this review annotates arabidopsis open reading frames likely to be involved in sphingolipid metabolism. A number of these open reading frames have already been subject to functional characterization, though the majority still awaits investigation. Plant-specific aspects of sphingolipid biology (such as enhanced long chain base heterogeneity) are considered in the context of the emerging roles for these lipids in plant form and function.

CONCLUSIONS

Arabidopsis provides an excellent genetic and post-genomic model for the characterization of the roles of sphingolipids in higher plants.

An introduction to plant sphingolipids and a review of recent advances in understanding their metabolism and function

Sphingolipids are ubiquitous constituents of eukaryotic cells, and have been intensively investigated in mammals and yeast for decades. Aspects of sphingolipid biochemistry in plants have been explored only recently. To date, progress has been made in determining the structure and occurrence of sphingolipids in plant tissues; in characterizing the enzymatic steps involved in production and turnover of sphingolipids (and, in some cases, the genes encoding the relevant enzymes); and in identifying a variety of biological functions for sphingolipids in plants. Given that these efforts are far from complete and much remains to be learned, this review represents a status report on the burgeoning field of plant sphingolipid biochemistry. Contents Summary 677 I. Introduction 678 II. Plant sphingolipid structure 678 III. Sphingolipid metabolism in plants 683 IV. Sphingolipid functions in plants 693 V. Conclusions 696 Acknowledgements 696 References 696.

A facile synthesis of phytosphingosine from diisopropylidene-D-mannofuranose

In the present study, an efficient method with a high overall yield for preparing phytosphingosine and an analogue was developed. Starting with commercially available 2,3;5,6-di-O-isopropylidene-d-mannofuranose, a variety of lipid moieties were incorporated to obtain phytosphingosine and an analogue. Through an eight-step manipulation, phytosphingosine was obtained with an overall yield of 57%.

Involvement of plasma membrane redox activity and calcium homeostasis in the UV-B and UV-A/blue light induction of gene expression in Arabidopsis

UV and blue light are important regulators of plant gene expression and development. We investigated the signal transduction processes involved in the induction of chalcone synthase (CHS) and phenylalanine ammonia-lyase (PAL) gene expression by UV-B and UV-A/blue light in an Arabidopsis cell suspension culture. Experiments with electron transport inhibitors indicated that plasma membrane redox activity is involved in both signal transduction pathways. Calcium ionophore treatment stimulated expression of the TOUCH3 gene, and this induction was strongly antagonized by UV-A/blue and UV-B light, suggesting that both light qualities may promote calcium efflux from the cytosol. Consistent with this hypothesis, experiments with specific inhibitors indicated that UV-B and UV-A/blue light regulate calcium levels in a cytosolic pool in part via the action of specific Ca2+-ATPases. On the basis of these and previous findings, we propose that plasma membrane redox activity, initiated by photoreception, is coupled to the regulation of calcium release from an intracellular store, generating a calcium signal that is required to induce CHS expression.

Multifunctional plasma membrane redox systems

All the biological membranes contain oxidoreduction systems actively involved in their bioenergetics. Plasma membrane redox systems seem to be ubiquitous and they have been related to several important functions, including not only their role in cell bioenergetics, but also in cell defense through the generation of reactive oxygen species, in iron uptake, in the control of cell growth and proliferation and in signal transduction. In the last few years, an increasing number of mechanistic and molecular studies have deeply widened our knowledge on the function of these plasma membrane redox systems. The aim of this review is to summarize what is currently known about the components and physiological roles of these systems.

Fumonisin- and AAL-Toxin-Induced Disruption of Sphingolipid Metabolism with Accumulation of Free Sphingoid Bases

Fumonisins (FB) and AAL-toxin are sphingoid-like compounds produced by several species of fungi associated with plant diseases. In animal cells, both fumonisins produced by Fusarium moniliforme and AAL-toxin produced by Alternaria alternata f. sp. lycopersici inhibit ceramide synthesis, an early biochemical event in the animal diseases associated with consumption of F. moniliforme-contaminated corn. In duckweed (Lemna pausicostata Heglem. 6746), tomato plants (Lycopersicon esculentum Mill), and tobacco callus (Nicotiana tabacum cv Wisconsin), pure FB1 or AAL-toxin caused a marked elevation of phytosphingosine and sphinganine, sphingoid bases normally present in low concentrations. The relative increases were quite different in the three plant systems. Nonetheless, disruption of sphingolipid metabolism was clearly a common feature in plants exposed to FB1 or AAL-toxin. Resistant varieties of tomato (Asc/Asc) were much less sensitive to toxin-induced increases in free sphinganine. Because free sphingoid bases are precursors to plant "ceramides," their accumulation suggests that the primary biochemical lesion is inhibition of de novo ceramide synthesis and reacylation of free sphingoid bases. Thus, in plants the disease symptoms associated with A. alternata and F. moniliforme infection may be due to disruption of sphingolipid metabolism.

The role of plasma membrane redox activity in light effects in plants

Stimulations by light of electron transport at the plasma membrane make it possible that redox activity is involved in light-induced signal transduction chains. This is especially true in cases where component(s) of the chain are also located at the plasma membrane. Photosynthetic reactions stimulate transplasma membrane redox activity of mesophyll cells. Activity is measured as a reduction of the nonpermeating redox probe, ferricyanide. The stimulation is due to production of a cytosolic electron donor from a substance(s) transported from the chloroplast. It is unknown whether the stimulation of redox activity is a requirement for other photosynthetically stimulated processes at the plasma membrane, but a reduced intermediate may regulate proton excretion by guard cells. Blue light induces an absorbance change (LIAC) at the plasma membrane whose difference spectrum resembles certain b-type cytochromes. This transport of electrons may be due to absorption of light by a flavoprotein. The LIAC has been implicated as an early step in certain blue light-mediated morphogenic events. Unrelated to photosynthesis, blue light also stimulates electron transport at the plasma membrane to ferricyanide. The relationship between LIAC and transmembrane electron flow has not yet been determined, but blue light-regulated proton excretion and/or growth may depend on this electron flow. No conclusions can be drawn regarding any role for phytochrome because of a paucity of information concerning the effects of red light on redox activity at the plasma membrane.