Ion Permeabilities in Mouse Sperm Reveal an External Trigger for SLO3-Dependent Hyperpolarization

Unlike most cells of the body which function in an ionic environment controlled within narrow limits, spermatozoa must function in a less controlled external environment. In order to better understand how sperm control their membrane potential in different ionic conditions, we measured mouse sperm membrane potentials under a variety of conditions and at different external K⁺ concentrations, both before and after capacitation. Experiments were undertaken using both wild-type, and mutant mouse sperm from the knock-out strain of the sperm-specific, pH-sensitive, SLO3 K⁺ channel. Membrane voltage data were fit to the Goldman-Hodgkin-Katz equation. Our study revealed a significant membrane permeability to both K⁺ and Cl⁻ before capacitation, as well as Na⁺. The permeability to both K⁺ and Cl⁻ has the effect of preventing large changes in membrane potential when the extracellular concentration of either ion is changed. Such a mechanism may protect against undesired shifts in membrane potential in changing ionic environments. We found that a significant portion of resting membrane potassium permeability in wild-type sperm was contributed by SLO3 K⁺ channels. We also found that further activation of SLO3 channels was the essential mechanism producing membrane hyperpolarization under two separate conditions, 1) elevation of external pH prior to capacitation and 2) capacitating conditions. Both conditions produced a significant membrane hyperpolarization in wild-type which was absent in SLO3 mutant sperm. Hyperpolarization in both conditions may result from activation of SLO3 channels by raising intracellular pH; however, demonstrating that SLO3-dependent hyperpolarization is achieved by an alkaline environment alone shows that SLO3 channel activation might occur independently of other events associated with capacitation. For example sperm may undergo stages of membrane hyperpolarization when reaching alkaline regions of the female genital tract. Significantly, other events associated with sperm capacitation, occur in SLO3 mutant sperm and thus proceed independently of hyperpolarization.     

Differential inactivation of plant lauric acid omega- and in-chain-hydroxylases by terminally unsaturated fatty acids

The microsomal fraction from Vicia sativa L. cv. Septimane contains a cytochrome P-450-dependent lauric acid omega-hydroxylase that is inactivated in a time-dependent, pseudo-first-order manner when the microsomes are incubated with 11-dodecynoic acid. The rate constant for the inactivation is approximately 4.3-4.8 X 10(-3) s-1. In contrast, the olefinic analog 11-dodecenoic acid is primarily a time-independent inhibitor of the omega-hydroxylase. 1-Aminobenzotriazole, 3-phenoxy-1-propyne, and 3-(2,4-dichlorophenoxy)-1-propyne, mechanism-based inactivators of cinnamic acid 4-hydroxylase, and 9-decenoic acid, a mechanism-based inactivator of the lauric acid in-chain hydroxylase, are at best poor inactivators of the omega-hydroxylase. Conversely, cinnamic acid 4-hydroxylase is only slightly affected by concentrations of 11-dodecynoic acid that completely inactivate the omega-hydroxylase. 11-Dodecynoic acid is thus a potent, relatively specific, inactivator of the V. sativa lauric acid omega-hydroxylase.     

An assessment of red list data for the Pezizomycotina (Ascomycota): Umbria (Italy) as a test case

Abstract

A Red List of all 108 Pezizomycotina (Ascomycota) species recorded in Umbria Region (central Italy) is provided. According to the IUCN categories and criteria, 60.18% of the assessed species are classified as threatened, whereas 12.96% are Near Threatened (NT), 1.86% are Least Concerned (LC) and a noteworthy amount of 25% are Data Deficient (DD). As a consequence of the downlisting applied to the majority of the assessed taxa, according to the guidelines for application of IUCN red list criteria at Regional level, only 1.54% of the threatened species is Critically Endangered (CR), while 46.15% are Endangered (EN) and 52.31% are Vulnerable (VU). Given that the present work represents the first complete regional red list of Pezizomycotina in Italy, and that a national, as well as a European red list do not exist to date, it could be considered as a case study for other Italian Regions as well as for other European countries, aiming at the compilation of a national and European red list of this fungal group mostly overlooked in conservation strategies.     

Accumulation of germanium (Ge) in plant tissues of grasses is not solely driven by its incorporation in phytoliths

Ge/Si ratios of plant phytoliths have been widely used to trace biogeochemical cycling of Si. However, until recently, information on how much of the Ge and Si transferred from soil to plants is actually stored in phytoliths was lacking. The aim of the present study is to (i) compare the uptake of Si and Ge in three grass species, (ii) localize Ge and Si stored in above-ground plant parts and (iii) evaluate the amounts of Ge and Si sequestrated in phytoliths and plant tissues. Mays (Zea mays), oat (Avena sativa) and reed canary grass (Phalaris arundinacea) were cultivated in the greenhouse on soil and sand to control element supply. Leaf phytoliths were extracted by dry ashing. Total elemental composition of leaves, phytoliths, stems and roots were measured by ICP-MS. For the localization of phytoliths and the determination of Ge and Si within leaf tissues and phytoliths scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was used. The amounts of Si and Ge taken up by the species corresponded with biomass formation and decreased in the order Z. mays > P. arundinacea, A. sativa. Results from LA-ICP-MS revealed that Si was mostly localized in phytoliths, while Ge was disorderly distributed within the leaf tissue. In fact, from the total amounts of Ge accumulated in leaves only 10% was present in phytoliths highlighting the role of organic matter on biogeochemical cycling of Ge and the necessity for using bulk Ge/Si instead of Ge/Si in phytoliths to trace biogeochemical cycling of Si.

     

Leaf size of woody dicots predicts ecosystem primary productivity

A key challenge in ecology is to understand the relationships between organismal traits and ecosystem processes. Here, with a novel dataset of leaf length and width for 10 480 woody dicots in China and 2374 in North America, we show that the variation in community mean leaf size is highly correlated with the variation in climate and ecosystem primary productivity, independent of plant life form. These relationships likely reflect how natural selection modifies leaf size across varying climates in conjunction with how climate influences canopy total leaf area. We find that the leaf size?primary productivity functions based on the Chinese dataset can predict productivity in North America and vice‐versa. In addition to advancing understanding of the relationship between a climate‐driven trait and ecosystem functioning, our findings suggest that leaf size can also be a promising tool in palaeoecology for scaling from fossil leaves to palaeo‐primary productivity of woody ecosystems.     

Luminescence properties of the Ln–EDTA complexes covalently linked to the chitosan biopolymers containing β‐diketonate as antenna ligands

This paper reports on the preparation, characterization, and photoluminescence properties of novel hybrid materials, in which the EDTA–Ln–L complexes (where L: H₂O, acac, bzac, dbm, and tta ligands, and Ln: Eu, Gd, and Tb) were covalently linked to the precursor medium molecular weight chitosan surface (CS) matrices or on the chitosan surfaces previously crosslinked with epichlorohydrin (CSech). The emission spectra of these materials were characterized by intraconfigurational‐4fN transitions centred on the Eu³⁺ and Tb³⁺ ions. Some broad bands from the polymeric matrix were also observed in the emission spectra, however the relative intensities of the intraconfigurational bands increased significantly for systems containing diketonate ligands when the antenna effect became more efficient. The values of the radiative rates (A_rad) were higher for crosslinked hybrid systems with epichlorohydrin, while nonradiative rates (A_nrad) presented the opposite behaviour. These data contributed to an increase in the values of emission quantum efficiency (η) for crosslinked materials. The effect of the modification process and antenna ligand on the values of intensities, intensity parameters Ω₂ e Ω₄ of the Eu³⁺ complexes were also investigated. The results showed that the crosslinked biopolymer surfaces have great potential for applications in molecular devices light converters.     

Age attenuates the T‐type CaV3.2‐RyR axis in vascular smooth muscle

Caveolae position Ca_V3.2 (T‐type Ca²⁺ channel encoded by the α‐3.2 subunit) sufficiently close to RyR (ryanodine receptors) for extracellular Ca²⁺ influx to trigger Ca²⁺ sparks and large‐conductance Ca²⁺‐activated K⁺ channel feedback in vascular smooth muscle. We hypothesize that this mechanism of Ca²⁺ spark generation is affected by age. Using smooth muscle cells (VSMCs) from mouse mesenteric arteries, we found that both Ca_v3.2 channel inhibition by Ni²⁺ (50 µM) and caveolae disruption by methyl‐ß‐cyclodextrin or genetic abolition of Eps15 homology domain‐containing protein (EHD2) inhibited Ca²⁺ sparks in cells from young (4 months) but not old (12 months) mice. In accordance, expression of Ca_v3.2 channel was higher in mesenteric arteries from young than old mice. Similar effects were observed for caveolae density. Using SMAKO Ca_v1.2^?/? mice, caffeine (RyR activator) and thapsigargin (Ca²⁺ transport ATPase inhibitor), we found that sufficient SR Ca²⁺ load is a prerequisite for the Ca_V3.2‐RyR axis to generate Ca²⁺ sparks. We identified a fraction of Ca²⁺ sparks in aged VSMCs, which is sensitive to the TRP channel blocker Gd³⁺ (100 µM), but insensitive to Ca_V1.2 and Ca_V3.2 channel blockade. Our data demonstrate that the VSMC Ca_V3.2‐RyR axis is down‐regulated by aging. This defective Ca_V3.2‐RyR coupling is counterbalanced by a Gd³⁺ sensitive Ca²⁺ pathway providing compensatory Ca²⁺ influx for triggering Ca²⁺ sparks in aged VSMCs.