Microtubule mechanics: a little flexibility goes a long way

Microtubules are the least flexible of the cytoskeletal filaments, yet they are occasionally seen to be severely buckled in cells. A recent analysis suggests these buckles are evidence of high contractile forces throughout the cytoplasm, and that the other elements of the cytoskeleton laterally reinforce microtubules to help prevent their collapse.     

The nucleosome: a little variation goes a long way.

Changes in the overall structure of chromatin are essential for the proper regulation of cellular processes, including gene activation and silencing, DNA repair, chromosome segregation during mitosis and meiosis, X chromosome inactivation in female mammals, and chromatin compaction during apoptosis. Such alterations of the chromatin template occur through at least 3 interrelated mechanisms: post-translational modifications of histones, ATP-dependent chromatin remodeling, and the incorporation (or replacement) of specialized histone variants into chromatin. Of these mechanisms, the exchange of variants into and out of chromatin is the least well understood. However, the exchange of conventional histones for variant histones has distinct and profound consequences within the cell. This review focuses on the growing number of mammalian histone variants, their particular biological functions and unique features, and how they may affect the structure of the nucleosome. We propose that a given nucleosome might not consist of heterotypic variants, but rather, that only specific histone variants come together to form a homotypic nucleosome, a hypothesis that we refer to as the nucleosome code. Such nucleosomes might in turn participate in marking specific chromatin domains that may contribute to epigenetic inheritance.     

A little goes a long way: CLE peptides mediate phloem initiation

<正>The root system of a tree can often extend many-fold the diameter of the tree; it provides physical support,dissolved minerals and water but relies on a constant supply of nutrients from photosynthetically active tissues in aboveground organs. The phloem is responsible for such transport and the success of a plant relies heavily on the integrity of the phloem in its root system.Cell-to-cell communication is critical for the cell divisions and differentiation that generate phloem from Com m entary     

Nitric oxide as an antioxidant.

Benzoate monohydroxy compounds, and in particular salicylate, were produced during interaction of ferrous complexes with hydrogen peroxide (Fenton reaction) in a N2 environment. These reactions were inhibited when Fe complexes were flushed, prior to the addition in the model system, by nitric oxide. Methionine oxidation to ethylene by Fenton reagents was also inhibited by nitric oxide. Myoglobin in several forms such as metmyoglobin, oxymyoglobin, and nitric oxide-myoglobin were interacted with an equimolar concentration of hydrogen peroxide. Spectra changes in the visible region and the changes in membrane (microsomes) lipid peroxidation by the accumulation of thiobarbituric acid-reactive substances (TBA-RS) were determined. The results showed that metmyoglobin and oxymyoglobin were activated by H2O2 to ferryl myoglobin, which initiates membrane lipid peroxidation; but not nitric oxide-myoglobin, which, during interaction with H2O2, did not form ferryl but metmyoglobin which only poorly affected lipid peroxidation. It is assumed that nitric oxide, liganded to ferrous complexes, acts to prevent the prooxidative reaction of these complexes with H2O2.     

Nitric oxide chemistry and cellular signaling

Nitric oxide (NO) has been shown to mediate a number of different physiological functions within every major organ system. This wide variety of functional roles is made all the more remarkable when one considers that NO is a simple diatomic molecule. However, despite the simplicity of the molecule, NO possesses a wide range of chemical reactivity and multiple potential reactive targets. It is the variability of NO reactivity, which leads to its capability to control such a vast range of biological functions. In essence the functionality of NO is controlled by its chemical reactivity. In order to understand this possibility further it is necessary to consider the biologically relevant reactions of nitric oxide.     

Nitric oxide as a bioregulator of apoptosis

Nitric oxide (NO), synthesized from l-arginine by NO synthases, is a small, diffusible, highly reactive molecule with dichotomous regulatory roles under physiological and pathological conditions. NO can promote apoptosis (proapoptosis) in some cells, whereas it inhibits apoptosis (antiapoptosis) in other cells. This complexity is a consequence of the rate of NO production and the interaction with biological molecules such as iron, thiols, proteins, and reactive oxygen species. Long-lasting production of NO acts as a proapoptotic modulator by activating caspase family proteases through the release of mitochondrial cytochrome c into the cytosol, upregulation of p53 expression, activation of JNK/SAPK, and altering the expression of apoptosis-associated proteins including Bcl-2 family proteins. However, low or physiological concentrations of NO prevent cells from apoptosis induced by trophic factor withdrawal, Fas, TNFalpha, and lipopolysaccharide. The antiapoptotic mechanism can be understood via expression of protective genes such as heat shock proteins, Bcl-2 as well as direct inhibition of the apoptotic caspase family proteases by S-nitrosylation of the cysteine thiol. Our current understanding of the mechanisms by which NO exerts both pro- and antiapoptotic actions is discussed in this review article.     

Nitric oxide and Fenton/Haber-Weiss chemistry: nitric oxide is a potent antioxidant at physiological concentrations

We have examined the action of nitric oxide (NO) on the ability of Fenton's reagent (ferrous iron and hydrogen peroxide), to oxidize a number of organic optical probes. We found that NO is able to arrest the oxidation of organic compounds at concentrations of NO found in brain, in vivo. We present evidence that Fenton's reagent proceeds via a ferryl intermediate ([Fe[double bond]O]2+), before the generation of hydroxyl radical *OH. NO reacts rapidly with this ferryl, blocking the production of *OH. We propose that NO has an important role in protecting biological tissues, and the brain in particular, from Fenton chemistry.     

Sex pheromone biosynthesis,storage and release in a female moth: making a little go a long way

Moth pheromone research has pioneered much of our understanding of long-distance chemical communication. Two important characteristics of this communication have, however, remained largely unaddressed: the release of small quantities of pheromone by most moth species, despite potential advantages of releasing greater amounts, and the intermittency of release in some species, limiting the time of mate attraction. We addressed the proximate mechanisms underlying these characteristics by manipulating biosynthesis, storage and release of pheromone in females of the noctuid moth Chloridea virescens. We found that (i) mass release is determined by pheromone mass on the gland surface; (ii) amounts synthesized are limited by pheromone biosynthesis activating neuropeptide concentration, not precursor availability; (iii) some gland structural feature limits mass release rate; (iv) intermittent calling enables release at a mass rate greater than biosynthetic rate; and (v) at typical mass release rates, the periodicity of pheromone availability on the gland surface roughly matches the periodicity (intermittency) of calling. We conclude that mass release in C. virescens and possibly many other species is low because of constraints on biosynthesis, storage and gland structure. Further, it appears the behaviour of intermittent calling in C. virescens may have evolved as a co-adaptation with pheromone availability, allowing females to release pheromone intermittently at higher mass rates than the biosynthesis rate.     

Nitric oxide as a regulator of inflammatory processes

Nitric oxide (NO) plays an important role in mediating many aspects of inflammatory responses. NO is an effector molecule of cellular injury, and can act as an anti-oxidant. It can modulate the release of various inflammatory mediators from a wide range of cells participating in inflammatory responses (e.g., leukocytes, macrophages, mast cells, endothelial cells, and platelets). It can modulate blood flow, adhesion of leukocytes to the vascular endothelium and the activity of numerous enzymes, all of which can have an impact on inflammatory responses. In recent years, NO-releasing drugs have been developed, usually as derivatives of other drugs, which exhibit very powerful anti-inflammatory effects.     

Nitric oxide acts as an antioxidant and delays methyl jasmonate-induced senescence of rice leaves

In the present study, we evaluate the protective effect of nitric oxide (NO) against senescence of rice leaves promoted by methyl jasmonate (MJ). Senescence of rice leaves was determined by the decrease of protein content. MJ treatment resulted in (1) induction of leaf senescence, (2) increase in H₂O₂ and malondialdehyde (MDA) contents, (3) decrease in reduced form glutathione (GSH) and ascorbic acid (AsA) contents, and (4) increase in antioxidative enzyme activities (ascorbate peroxidase, glutathione reductase, peroxidase and catalase). All these MJ effects were reduced by free radical scavengers such as sodium benzoate and GSH. NO donors [N-tert-butyl-α-phenylnitrone (PBN), sodium nitroprusside, 3-morpholinosydonimine, and AsA+NaNO₂] were effective in reducing MJ-induced leaf senescence. PBN prevented MJ-induced increase in the contents of H₂O₂ and MDA, decrease in the contents of GSH and AsA, and increase in the activities of antioxidative enzymes. The protective effect of PBN on MJ-promoted senescence, MJ-increased H₂O₂ content and lipid peroxidation, MJ-decreased GSH and AsA, and MJ-increased antioxidative enzyme activities was reversed by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, a NO-specific scavenger, suggesting that the protective effect of PBN is attributable to NO released. Reduction of MJ-induced senescence by NO in rice leaves is most likely mediated through its ability to scavenge active oxygen species including H₂O₂     

Nitric oxide as a signal in plants.

Molecular, genetic and biochemical studies have identified key players in the signaling pathways regulating growth and development, as well as defense responses in plants. Recently, nitric oxide (NO) - the versatile and powerful effector of animal redox-regulated signaling and immune responses - was shown to mediate plant defense responses against pathogens. Interestingly, several key components involved in NO-mediated signaling in animals also appear to be operative in plants.     

植物中的一氧化氮信号分子

综述了NO分子在植物中的生物合成、主要生理功能以及在耐受生物胁迫和非生物胁迫响应中的作用,以及植物对NO信号转导过程中cGMP途径和其他途径的关系。