Plant sterols: Diversity, biosynthesis, and physiological functions

© 2016, Pleiades Publishing, Ltd.Sterols, which are isoprenoid derivatives, are structural components of biological membranes. Special attention is now being given not only to their structure and function, but also to their regulatory roles in plants. Plant sterols have diverse composition; they exist as free sterols, sterol esters with higher fatty acids, sterol glycosides, and acylsterol glycosides, which are absent in animal cells. This diversity of types of phytosterols determines a wide spectrum of functions they play in plant life. Sterols are precursors of a group of plant hormones, the brassinosteroids, which regulate plant growth and development. Furthermore, sterols participate in transmembrane signal transduction by forming lipid microdomains. The predominant sterols in plants are β-sitosterol, campesterol, and stigmasterol. These sterols differ in the presence of a methyl or an ethyl group in the side chain at the 24th carbon atom and are named methylsterols or ethylsterols, respectively. The balance between 24-methylsterols and 24-ethylsterols is specific for individual plant species. The present review focuses on the key stages of plant sterol biosynthesis that determine the ratios between the different types of sterols, and the crosstalk between the sterol and sphingolipid pathways. The main enzymes involved in plant sterol biosynthesis are 3-hydroxy-3methylglutaryl-CoA reductase, C24-sterol methyltransferase, and C22-sterol desaturase. These enzymes are responsible for maintaining the optimal balance between sterols. Regulation of the ratios between the different types of sterols and sterols/sphingolipids can be of crucial importance in the responses of plants to stresses

Characterization of the homeologous genes of C24-sterol methyltransferase in Triticum aestivum L.

© 2016, Pleiades Publishing, Ltd.Three homeologous copies of the TaSMT1 gene for C24-sterol methyltransferase, which are located on chromosomes A, B, and D of Triticum aestivum hexaploid genome, were discovered. The bioinformatic analysis of the structure of these genes and sequencing de novo promoter sequences revealed differential expression of homeologous TaSMT1 genes in leaves and roots of wheat seedlings under normal conditions and in stress

Extracellular redox cycling and hydroxyl radical production occurs widely in lichenized Ascomycetes

© 2017 British Mycological SocietySome free-living Ascomycetes and white and brown rot Basidiomycetes can generate hydroxyl radicals using extracellular redox cycling. However, the mechanisms of hydroxyl radical production differ between white and brown rot Basidiomycetes, and are unknown for Ascomycetes. Here, we present a survey of extracellular hydroxyl radical production by a range of lichenized Ascomycetes. Results show that given a quinone and chelated ferric ions, many lichens can readily produce hydroxyl radicals, and this is accompanied by the reduction of Fe3+ to Fe2+. In white rot fungi, extracellular redox enzymes have been proposed to be involved in hydroxyl radical generation. However, a survey of a wide range of lichens suggests that in these fungi hydroxyl radical production does not directly correlate with the activity of laccases and peroxidases. Rather, radicals are probably produced by a mechanism like that proposed for brown rot fungi. Potential roles of hydroxyl radicals produced by lichens include the breakdown of lignocellulosic residues in the soil which may allow lichens to live a partially saprotrophic existence, the breakdown of toxic soil chemicals and the formation of an ‘oxidative burst’ to deter potential pathogens

Extracellular redox cycling and hydroxyl radical production occurs widely in lichenized Ascomycetes

© 2017 British Mycological Society.Some free-living Ascomycetes and white and brown rot Basidiomycetes can generate hydroxyl radicals using extracellular redox cycling. However, the mechanisms of hydroxyl radical production differ between white and brown rot Basidiomycetes, and are unknown for Ascomycetes. Here, we present a survey of extracellular hydroxyl radical production by a range of lichenized Ascomycetes. Results show that given a quinone and chelated ferric ions, many lichens can readily produce hydroxyl radicals, and this is accompanied by the reduction of Fe3+ to Fe2+. In white rot fungi, extracellular redox enzymes have been proposed to be involved in hydroxyl radical generation. However, a survey of a wide range of lichens suggests that in these fungi hydroxyl radical production does not directly correlate with the activity of laccases and peroxidases. Rather, radicals are probably produced by a mechanism like that proposed for brown rot fungi. Potential roles of hydroxyl radicals produced by lichens include the breakdown of lignocellulosic residues in the soil which may allow lichens to live a partially saprotrophic existence, the breakdown of toxic soil chemicals and the formation of an 'oxidative burst' to deter potential pathogens

Biochemical characterization of peroxidases from the moss Dicranum scoparium

© 2018 South African Association of Botanists Mosses are a convenient model to study stress responses of plants because of their remarkable stress tolerance. Peroxidase (EC 1.11.1.7) activities were tested in three moss species, namely Dicranum scoparium, Hylocomium splendens and Pleurozium schreberi growing together in the same location in a boreal forest. Peroxidase activity in D. scoparium was twice as high as in other mosses. Total peroxidase activity in unstressed D. scoparium was constitutively high; furthermore, long-term desiccation caused a significant increase in activity after 48 h of drying. Interestingly, when thalli desiccated for a week were rapidly rehydrated, peroxidase activity initially declined and then increased after 2 h rehydration. Diverse anionic and cationic isoforms were detected by native isoelectric focusing and PAGE of both crude extracts and partially purified peroxidases. The ability of peroxidases from D. scoparium to produce superoxide radical (O2•−) was confirmed using the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) reduction assay and in-gel nitroblue tetrazolium chloride (NBT) staining; specific O2•−producing isoforms were revealed using 2D electrophoresis. Given a quinone and chelated Fe3+D. scoparium could produce extracellular hydroxyl radical (•OH), and production was increased by desiccation/rehydration stress. The possible roles of peroxidases and quinone reductases in apoplastic•OH production is discussed. Our data demonstrate that D. scoparium possesses high constitutive peroxidase activity that can be further increased by desiccation stress. Among the diverse moss peroxidases, some anionic isoforms displayed both pro- and antioxidative activities. These findings suggest that the ability of peroxidases to produce and detoxify reactive oxygen species is an evolutionarily ancient characteristic, important for plant stress tolerance

Spermine Induces Autophagy in Plants: Possible Role of NO and Reactive Oxygen Species

© 2018, Pleiades Publishing, Inc. This is the first study to show that polyamine spermine, a low-molecular-weight nitrogen-containing compound, can induce autophagy in plants. This process is accompanied by an increased generation of reactive oxygen species and nitric oxide, which play a signal role and are required for triggering autophagy

Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition)

In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. For example, a key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process versus those that measure fl ux through the autophagy pathway (i.e., the complete process including the amount and rate of cargo sequestered and degraded). In particular, a block in macroautophagy that results in autophagosome accumulation must be differentiated from stimuli that increase autophagic activity, defi ned as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (inmost higher eukaryotes and some protists such as Dictyostelium ) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the fi eld understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. It is worth emphasizing here that lysosomal digestion is a stage of autophagy and evaluating its competence is a crucial part of the evaluation of autophagic flux, or complete autophagy. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. Along these lines, because of the potential for pleiotropic effects due to blocking autophagy through genetic manipulation it is imperative to delete or knock down more than one autophagy-related gene. In addition, some individual Atg proteins, or groups of proteins, are involved in other cellular pathways so not all Atg proteins can be used as a specific marker for an autophagic process. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field