Do Antimonite and Silicon Share the Same Root Uptake Pathway by Lsi1 in Sorghum bicolor L. Moench?

A study was conducted to further develop our understanding of antimony (Sb) uptake in plants. Unlike other metal(loid)s, such as silicon (Si), the mechanisms of Sb uptake are not well understood. However, SbIII is thought to enter the cell via aquaglyceroporins. We investigated if the channel protein Lsi1, which aids in Si uptake, also plays a role in Sb uptake. Seedlings of WT sorghum, with normal silicon accumulation, and its mutant (sblsi1), with low silicon accumulation, were grown in Hoagland solution for 22 days in the growth chamber under controlled conditions. Control, Sb (10 mg Sb L-1), Si (1mM) and Sb + Si (10 mg Sb L-1 + 1 mM Si) were the treatments. After 22 days, root and shoot biomass, the concentration of elements in root and shoot tissues, lipid peroxidation and ascorbate levels, and relative expression of Lsi1 were determined. When mutant plants were exposed to Sb, they showed almost no toxicity symptoms compared to WT plants, indicating that Sb was not toxic to mutant plants. On the other hand, WT plants had decreased root and shoot biomass, increased MDA content and increased Sb uptake compared to mutant plants. In the presence of Sb, we also found that SbLsi1 was downregulated in the roots of WT plants. The results of this experiment support the role of Lsi1 in Sb uptake in sorghum plants.

Multiple effects of silicon on alleviation of nickel toxicity in young maize roots.

Although beneficial metalloid silicon (Si) has been shown to alleviate the toxicity of various heavy metals, there is a lack of knowledge about the role of Si in possible alleviation of phytotoxicity caused by excess of essential nickel (Ni). In the present study we investigated the growth and biomass production, reactive oxygen species (ROS) formation and activities of selected antioxidants, as well as combined effect of Ni and Si on the integrity of cell membranes and electrolyte leakage in young maize roots treated for 24, 48 and 72 h with excess of Ni and/or Si. By histochemical methods we also visualized Ni distribution in root tissues and compared the uptake of Ni and Si with the development of root apoplasmic barriers. Ni enhanced the root lignification and suberization and shifted the development of apoplasmic barriers towards the root tip. Similarly, localization of Ni correlated with lignin and suberin deposition in root endodermis, further supporting the barrier role of this tissue in Ni uptake. Si reversed the negative impact of Ni on root anatomy. Additionally, improved cell membrane integrity, and enhanced ascorbate-based antioxidant system might be the mechanisms how Si partially mitigates the deleterious effects of Ni excess in maize plants.

Contrasting the roles of the I-II loop gating brake in CaV3.1 and CaV3.3 calcium channels.

Low-voltage-activated CaV3 channels are distinguished among other voltage-activated calcium channels by the most negative voltage activation threshold. The voltage dependence of current activation is virtually identical in all three CaV3 channels while the current kinetics of the CaV3.3 current is one order slower than that of the CaV3.1 and CaV3.2 channels. We have analyzed the voltage dependence and kinetics of charge (Q) movement in human recombinant CaV3.3 and CaV3.1 channels. The voltage dependence of voltage sensor activation (Qon-V) of the CaV3.3 channel was significantly shifted with respect to that of the CaV3.1 channel by +18.6 mV and the kinetic of Qon activation in the CaV3.3 channel was significantly slower than that of the CaV3.1 channel. Removal of the gating brake in the intracellular loop connecting repeats I and II in the CaV3.3 channel in the ID12 mutant channel shifted the Qon-V relation to a value even more negative than that for the CaV3.1 channel. The kinetic of Qon activation was not significantly different between ID12 and CaV3.1 channels. Deletion of the gating brake in the CaV3.1 channel resulted in a GD12 channel with the voltage dependence of the gating current activation significantly shifted toward more negative potentials. The Qon kinetic was not significantly altered. ID12 and GD12 mutants did not differ significantly in voltage dependence nor in the kinetic of voltage sensor activation. In conclusion, the putative gating brake in the intracellular loop connecting repeats I and II controls the gating current of the CaV3 channels. We suggest that activation of the voltage sensor in domain I is limiting both the voltage dependence and the kinetics of CaV3 channel activation.

TGFß1 downregulates neurite outgrowth, expression of Ca2+ transporters, and mitochondrial dynamics of in vitro cerebellar granule cells.

Acute injury to central nervous system (CNS) triggers neurodegenerative processes that can result in serious damage or complete loss of function. After injury, production of transforming growth factor ß1 (TGFß1) increases and initiates creation of a fibrotic scar that prevents normal growth, plasticity, and recovery of damaged neurons. Administration of TGFß1 antagonists can prevent its pathological effects. To define consequences of increased TGFß1 release on calcium signaling, neuronal plasticity, excitability, and mitochondrial dynamics in CNS neurons we directly exposed a rat primary culture of cerebellar granule neurons to TGFß1. We focused on changes in expression of intracellular calcium transporters, especially inositol-1,4,5-trisphosphate receptor (IP3R) type 1, mitochondrial dynamics, and membrane excitability. TGFß1 significantly decreased the gene and protein expression of inositol-1,4,5-trisphosphate receptor type 1 and the gene expression of additional intracellular Ca transporters such as IP3R2, ryanodine receptor type 1 (RyR1), RyR2, and SERCA2. Altered calcium signaling suppressed neurite outgrowth and significantly decreased the length of the mitochondria and the frequency of mitochondrial fusion. The resting membrane potential of cerebellar granule neurons was hyperpolarized and slow after depolarization of single action potential was suppressed. LY364947, a blocker of TGFß1 receptor I, prevented these effects, and IP3 receptor blocker 2-aminoethoxydiphenyl borate (2APB) mimicked them. After CNS injury TGFß1 downregulates intracellular Ca levels and alters Ca signaling within injured neurons. We suggest that in our model TGFß1 may trigger both neurodegenerative and neuroprotective events through IP3-induced Ca signaling.

Calcium transporters and their role in the development of neuronal disease and neuronal damage.

Neurodegeneration comprises assembly of pathophysiological events that gives rise to a progressive loss of neuronal structure and function including cellular damage, diseases development or cellular death. Neurons respond by adjusting signaling pathways, from gene expression to morphological changes. In most of these processes, Ca2+ signaling plays a pivotal role. By increasing the Ca2+ concentration, the cell responds to neuronal, neurotrophic and other growth factor stimuli, however, the molecular mechanism of Ca2+-dependent neurite outgrowth and development yet requires further elucidation. Here we focus on the role of Ca2+ and selected Ca2+ transporters involved in processes of CNS neurodegeneration - inositol 1,4,5-trisphosphate (IP3Rs) and ryanodine receptors (RyRs), considering the fact that these receptors may be important "sensors" of disturbed intracellular calcium homeostasis. We propose that in vitro cellular models could serve as suitable experimental systems for the determination of the role that these receptors play in neuropathological conditions. Recognition of the principles, key players and regulatory processes may elucidate the role of Ca2+ in the regulation of neuronal proliferation, development and differentiation, growth and axon navigation in neurodegenerative and regenerative processes. This may provide a new insight and also discovery of novel therapeutic-targeting possibilities for severe neurological disorders and pathophysiological changes.

NGF-induced neurite outgrowth in PC12 cells is independent of calcium entry through L-type calcium channels.

Neuronal growth factor (NGF) induces neurodifferentiation of PC12 cells into cholinergic neurons-like cells. It was shown that intracellular Ca2+ ions participate in regulation of the differentiation of PC12 cells. We tested whether L-type calcium channels contribute to Ca2+ entry which supports neurite outgrowth accompanying NGF-activated differentiation process. Development of morphological changes did correlate with increase of functional expression of L-type calcium channels. However, inhibition of L-type calcium channels by 1 µM of isradipine did not affect significantly an NGF-activated neurite outgrowth.