Cadmium (Cd) is toxic to crown roots (CR), which are essential for maintaining normal growth and development in rice seedlings. Nitric oxide (NO) is an important signaling molecule that plays a pivotal role in plant root organogenesis. Here, the effects of Cd on endogenous NO content and root growth conditions were studied in rice seedlings. Results showed that similar to the NO scavenger, cPTIO, Cd significantly decreased endogenous NO content and CR number in rice seedlings, and these decreases were recoverable with the application of sodium nitroprusside (SNP, a NO donor). Microscopic analysis of root collars revealed that treatment with Cd and cPTIO inhibited CR primordia initiation. In contrast, although SNP partially recovered Cd-caused inhibition of CR elongation, treatment with cPTIO had no effect on CR elongation. L: -NMMA, a widely used nitric oxide synthase (NOS) inhibitor, decreased endogenous NO content and CR number significantly, while tungstate, a nitrate reductase (NR) inhibitor, had no effect on endogenous NO content and CR number. Moreover, enzyme activity assays indicated that treatment with SNP inhibited NOS activity significantly, but had no effect on NR activity. All these results support the conclusions that a critical endogenous NO concentration is indispensable for rice CR primordia initiation rather than elongation, NOS is the main source for endogenous NO generation, and Cd decreases CR number by inhibiting NOS activity and thus decreasing endogenous NO content in rice seedlings.

We report a nonlinear electrothermal-loaded accelerometer for microgravity measurement, achieving quasi-zero stiffness nearby its static equilibrium position. The high mechanical sensitivity is attributed to the compression of the spring, in addition to the geometric parameters matched with quasi-zero stiffness characteristic. To make the spring compressed effectively, a V-shape electrothermal actuator was adopted in the design. The FEA results in multiphysics clearly show the different performance of the accelerometer when it is at applied voltage or not, verifying that the electrothermal-loaded mechanism has an effective influence on the sensitivity of accelerometer. At the applied voltage of 22.3 V, the natural frequency of the accelerometer decreases from 501.95 Hz to 8.24 Hz, while the other two higher mode frequencies remain above 500 Hz. In addition, this mechanism realizes a quasi-zero stiffness approximately of 0.007 N m −1 within a linear working range of ±400 µg and the stiffness becomes larger beyond this range protecting the device being overloaded.

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