Xue Wang

Effects of Rare Earth Elements and REE-Binding Proteins on Physiological Responses in Plants

Rare earth elements (REEs), which include 17 elements in the periodic table, share chemical properties related to a similar external electronic configuration. REEs enriched fertilizers have been used in China since the 1980s. REEs could enter the cell and cell organelles, influence plant growth, and mainly be bound with the biological macromolecules. REE-binding proteins have been found in some plants. In addition, the chlorophyll activities and photosynthetic rate can be regulated by REEs. REEs could promote the protective function of cell membrane and enhance the plant resistance capability to stress produced by environmental factors, and affect the plant physiological mechanism by regulating the Ca²⁺ level in the plant cells. The focus of present review is to describe how REEs and REE-binding proteins participate in the physiological responses in plants.

Effects of Lanthanum on the Change of Calcium Level in the Root Cells of Rice

Rare-earth elements (REEs) have been widely used in agriculture for the growth of crops in China since the 1980s. As a secondary messenger, calcium ion (Ca2+) participates in physiological and biochemical reactions in plants via cellular or intercellular signal transduction networks. The aim of this study was to investigate the effects of trivalent lanthanum (La3+) on the change of Ca2+ in the root cells of rice (Oryza sativa L. cv. Shengdao 16) with laser-scanning confocal microscopy. The results indicated that Ca2+ level in the root cells was affected by the concentrations of La3+. The level of Ca2+ slightly decreased in the root of rice treated with 0.2 mmol L–1 La3+, and Ca2+ oscillation was induced in the root of rice treated with 1.0 mmol L–1 La3+. However, Ca2+ level increased in the root of rice treated with 2.0 mmol L–1 La3+. In addition, the results indicated that Ca2+ level in the rice roots slightly decreased after Ca2+ inhibitors verapamil (VP), ruthenium red (RR), trifluperazine (TFP), and ethylene glycol tetraacetic acid (EGTA) were added. Moreover, the effects of 2.0 mmol L–1 La3+ on Ca2+ level in the root cells of rice were investigated after Ca2+ was inhibited with VP, TFP, RR, and EGTA. Inhibited with VP, TFP, RR, and EGTA, Ca2+ level slightly decreased or was not affected in the rice roots treated with 2.0 mmol L–1 La3+. The results showed that La3+ participated in the signal transduction networks via calmodulin (CaM) and that La3+ might enter into the root cells via the membrane and intracellular Ca2+ channels.

Lanthanum regulates the reactive oxygen species in the roots of rice seedlings

In this study, the effects of La3+ on the reactive oxygen species (ROS) and antioxidant metabolism were studied in the roots of rice (Oryza sativa L. cv Shengdao 16) exposed to increasing concentrations of La3+ (0.05, 0.1, 0.5, 1.0, and 1.5 mM). The level of hydrogen peroxide, superoxide anion, and malondialdehyde was increased by 0.5, 1.0 and 1.5 mM La3+, and the activity of catalase and peroxidase was increased by 0.05 and 0.1 mM La3+. However, La3+ treatments stimulated superoxide dismutase activity in the roots of rice seedlings at all tested concentrations. In addition, the probe 2′,7′-dichlorofluorescein diacetate (H2DCF-DA) was used to investigate the instantaneous change of ROS in the root cells with the laser-scanning confocal microscopy. The result indicated that ROS level was declined after treated with 0.05 mM La3+. The results showed that the appropriate concentration of La3+ decreased the level of ROS, and hormetic effects on the antioxidant metabolism were found in the roots of rice exposed to 0.05, 0.1, 0.5, 1.0, and 1.5 mM La3+.

Analysis of reactive oxygen species in the guard cell of wheat stoma with confocal microscope

Recently, the laser‐scanning confocal microscope has become a routine technique and indispensable tool for cell biological studies. Previous studies indicated that reactive oxygen species (ROS) were generated in tobacco epidermal cells with confocal microscope. In the present studies, the probe 2′,7′‐dichlorof luorescein diacetate (H2DCF‐DA) was used to research the change of ROS in the guard cell of wheat stoma, and catalase (CAT) was used to demonstrate that ROS had been labeled. The laser‐scanning mode of confocal microscope was XYT, and the time interval between two sections was 1.6351 s. Sixty optical sections were acquired with the laser‐scanning confocal microscope, and CAT (60,000 U mg−1) was added after four optical sections were scanned. Furthermore, the region of interest (ROI) was circled and the fluorescence intensity of ROS was quantified with Leica Confocal Software. The quantitative data were exported and the trend chart was made with software Excell. The results indicated that ROS were produced intracellularly in stomatal guard cells, and the quantified fluorescence intensity of ROS was declined with CAT added. It is a good method to research the instantaneous change of ROS in plant cells with confocal microscope and fluorescence probe H2DCF‐DA. Microsc. Res. Tech., 2011.