Interaction between La3+ and MP-11 in the physiological solution

Effects of rare earth and acid rain pollution on plant chloroplast ATP synthase and element contents at different growth stages

Combined rare earth and acid rain pollution has become a new environmental problem, seriously affecting plant survival. The effects of these two kinds of pollutants on plant photosynthesis have been reported, but the micro mechanisms are not very clear. In this research, we studied the effects of lanthanum [La(III), 0.08, 1.20 and 2.40 mM] and acid rain (pH value = 2.5, 3.5 and 4.5) on the ATPase activity and gene transcription level and the functional element contents in rice leaf chloroplasts. The results showed that the combined 0.08 mM La(III) and pH 4.5 acid rain increased the ATPase activity and gene transcription level as well as contents of some functional elements. But other combined treatments of acid rain and La(III) reduced the ATPase activity and gene transcription level as well as functional element contents. The change magnitude of the above indexes at rice booting stage was greater than that in seedling stage or grain filling stage. These results reveal that effects of La(III) and acid rain on ATPase activity and functional element contents in rice leaf chloroplasts are related to the combination of La(III) dose and acid rain intensity and the plant growth stage. In addition, the changes in the ATPase activity were related to ATPase gene transcription level. This study would provide a reference for understanding the microcosmic mechanism of rare earth and acid rain pollution on plant photosynthesis and contribute to evaluate the possible environmental risks associated with combined La(III) and acid rain pollution.

ONE SENTENCE SUMMARY

The effects of La(III) and acid rain on activity and gene transcription level of rice chloroplast ATPase and contents of functional elements were different at different growth stages.

Insight into mechanism of lanthanum (III) induced damage to plant photosynthesis

A great deal of literature is available regarding the environmental and ecological effects of rare earth element pollution on plants. These studies have shown that excess lanthanum (La) (III) in the environment can inhibit plant growth and even cause plant death. Moreover, inhibition of plant photosynthesis is known to be one of the physiological bases of these damages. However, the mechanism responsible for these effects is still unclear. In this study, the mechanism of La(III)-induced damage to plant photosynthesis was clarified from the viewpoint of the chloroplast ultrastructure, the contents of chloroplast mineral elements and chlorophyll, the transcription of chloroplast ATPase subunits and chloroplast Mg(2+)-ATPase activity, in which rice was selected as a study object. Following treatment with low level of La(III), the chloroplast ultrastructure of rice was not changed, and the contents of chloroplast mineral elements (Mg, P, K, Ca, Mn, Fe, Ni, Cu, and Zn) increased, but the chlorophyll content did not change significantly. Moreover, the transcription of chloroplast ATPase subunits, chloroplast Mg(2+)-ATPase activity, the net photosynthetic rate and growth indices increased. Following treatment with high levels of La(III), the chloroplast ultrastructure was damaged, chloroplast mineral elements (except Cu and Zn) and chlorophyll contents decreased, and the transcription of chloroplast ATPase subunits, chloroplast Mg(2+)-ATPase activity, the net photosynthetic rate and growth indices decreased. Based on these results, a possible mechanism of La(III)-induced damage to plant photosynthesis was proposed to provide a reference for scientific evaluation of the potential ecological risk of rare earth elements in the environment.

Roles of horseradish peroxidase in response to terbium stress

The pollution of the environment by rare earth elements (REEs) causes deleterious effects on plants. Peroxidase plays important roles in plant response to various environmental stresses. Here, to further understand the overall roles of peroxidase in response to REE stress, the effects of the REE terbium ion (Tb(3+)) on the peroxidase activity and H2O2 and lignin contents in the leaves and roots of horseradish during different growth stages were simultaneously investigated. The results showed that after 24 and 48 h of Tb(3+) treatment, the peroxidase activity in horseradish leaves decreased, while the H2O2 and lignin contents increased. After a long-term (8 and 16 days) treatment with Tb(3+), these effects were also observed in the roots. The analysis of the changes in peroxidase activity and H2O2 and lignin contents revealed that peroxidase plays important roles in not only reactive oxygen species scavenging but also cell wall lignification in horseradish under Tb(3+) stress. These roles were closely related to the dose of Tb(3+), duration of stress, and growth stages of horseradish.

Engineered hydrochar composites for phosphorus removal/recovery: Lanthanum doped hydrochar prepared by hydrothermal carbonization of lanthanum pretreated rice straw

Engineered hydrochar composites (EHC) were synthesized by hydrothermal carbonization (HTC) of lanthanum pretreated rice straw. The as-prepared composite with about 30% lanthanum content showed greater P removal potential than La(OH)3, indicating the synergistic effect of hydrochar and lanthanum in P removal. The adsorption results showed that EHC showed great P adsorption capacities (>50mgPg(-1)) in the pH range of 2.5-10.5, and the presence of competing anions had little negative effects on P adsorption on EHC. The equilibrium time for P adsorption on EHC was considerably reduced under acid condition (12h) compared to alkaline condition (48h). The maximum adsorption capacity was 61.57mgPg(-1) according to Langmuir isotherms. These results suggested that EHC was highly effective in P adsorption in a wide range of pH and the presence of competing anions, thus EHC could be a promising adsorbent for phosphorus removal/recovery from wastewater.

Direct interaction between terbium ion and peroxidase in horseradish at different pH values

Rare earth elements (REEs) entering plant cells can directly interact with peroxidase in plants, which is the structural basis for the decrease in the activity of peroxidase. Different cellular compartments have different pH values. However, little information is available regarding the direct interaction between REEs and peroxidase in plants at different pH values. Here, we investigated the charge distribution on the surface of horseradish peroxidase (HRP) molecule as well as the interaction of terbium ion (Tb(3+), one type of REEs) and HRP at different pH values. Using the molecular dynamics simulation, we found that when the pH value was from 4.0 to 8.0, a large amount of negative charges were intensively distributed on the surface of HRP molecule, and thus, we speculated that Tb(3+) with positive charges might directly interact with HRP at pH 4.0-8.0. Subsequently, using ultraviolet-visible spectroscopy, we demonstrated that Tb(3+) could directly interact with HRP in the simulated physiological solution at pH 7.0 and did not interact with HRP in other solutions at pH 5.0, pH 6.0 and pH 8.0. In conclusion, we showed that the direct interaction between Tb(3+) and HRP molecule depended on the pH value of cellular compartments.

Amperometric glucose biosensor based on layer-by-layer films of microperoxidase-11 and liposome-encapsulated glucose oxidase

An important step in several bioanalytical applications is the immobilization of biomolecules. Accordingly, this procedure must be carefully chosen to preserve their biological structure and fully explore their properties. For this purpose, we combined the versatility of the layer-by-layer (LbL) method for the immobilization of biomolecules with the protective behavior of liposome-encapsulated systems to fabricate a novel amperometric glucose biosensor. To obtain the biosensing unit, an LbL film of the H2O2 catalyst polypeptide microperoxidase-11 (MP-11) was assembled onto an indium-tin oxide (ITO) electrode followed by the deposition of a liposome-encapsulated glucose oxidase (GOx) layer. The biosensor response toward glucose detection showed a sensitivity of 0.91±0.09 (μA/cm2)/mM and a limit of detection (LOD) of 8.6±1.1 μM, demonstrating an improved performance compared to similar biosensors with a single phospholipid-liposome or even containing a non-encapsulated GOx layer. Finally, glucose detection was also performed in a zero-lactose milk sample to demonstrate the potential of the biosensor for food analysis.

One of the possible mechanisms for the inhibition effect of Tb(III) on peroxidase activity in horseradish (Armoracia rusticana) treated with Tb(III)

One of the possible mechanisms for the inhibition effect of Tb(III) on peroxidase activity in horseradish (Armoracia rusticana) treated with Tb(III) was investigated using some biophysical and biochemical methods. Firstly, it was found that a large amount of Tb(III) can be distributed on the cell wall, that some Tb(III) can enter into the horseradish cell, indicating that peroxidase was mainly distributed on cell wall, and thus that Tb(III) would interact with horseradish peroxidase (HRP) in the plant. In addition, peroxidase bioactivity was decreased in the presence of Tb(III). Secondly, a new peroxidase-containing Tb(III) complex (Tb-HRP) was obtained from horseradish after treatment with Tb(III); the molecular mass of Tb-HRP is near 44 kDa and the pI is about 8.80. Thirdly, the electrocatalytic activity of Tb-HRP is much lower than that of HRP obtained from horseradish without treatment with Tb(III). The decrease in the activity of Tb-HRP is due to the destruction (unfolding) of the conformation in Tb-HRP. The planarity of the heme active center in the Tb-HRP molecule was increased and the extent of exposure of Fe(III) in heme was decreased, leading to inhibition of the electron transfer. The microstructure change in Tb-HRP might be the result of the inhibition effect of Tb(III) on peroxidase activity in horseradish.

Spectroscopic studies of interactions involving horseradish peroxidase and Tb3+

The spectroscopic properties of interactions involving horseradish peroxidase (HRP) and Tb3+ in the simulated physiological solution was investigated with some electrochemical and spectroscopic methods, such as cyclic voltammetry (CV), circular dichroism (CD), X-ray photoelectron spectroscopy (XPS) and synchronous fluorescence (SF). It was found that Tb3+ can coordinate with oxygen atoms in carbonyl groups in the peptide chain of HRP, form the complex of Tb3+ and HRP (Tb-HRP), and then lead to the conformation change of HRP. The increase in the random coil content of HRP can disturb the microstructure of the heme active center of HRP, in which the planarity of the porphyrin cycle in the heme group is increased and then the exposure extent of the electrochemical active center is decreased. Thus Tb3+ can inhibit the electrochemical reaction of HRP and its electrocatalytic activity for the reduction of H2O2 at the Au/Cys/GC electrode. The changes in the microstructure of HRP obstructed the electron transfer of Fe(III) in the porphyrin cycle of the heme group, thus HRP catalytic activity is inhibited. The inhibition effect of Tb3+ on HRP catalytic activity is increased with the increasing of Tb3+ concentration. This study would provide some references for better understanding the rare earth elements and heavy metals on peroxidase toxicity in living organisms.