一氧化氮（NO）在硝酸盐调节玉米根伸长中的作用

植物根系大小和形态是决定植物吸氮能力的重要因素，而植物根系生长发育与土壤中营养元素的分布及其有效性密切相关，尤其是硝酸盐。然而目前关于硝酸盐调节植物根系生长的生理机制仍不清楚。一氧化氮（NO）是一种重要的气体信号分子，参与植物体内多种生理生化过程，包括调节根的生长发育。本研究以玉米自交系478为材料，采用营养液培养法，探讨了NO在硝酸盐调节玉米根系生长中的作用。主要结果和结论如下： 玉米幼苗在不同硝酸盐水平下生长7天后，主根伸长随着硝酸盐浓度的升高而下降;与0.01 mM硝酸盐处理下的玉米主根伸长相比，0.1 mM和1 mM硝酸盐处理对玉米主根伸长分别抑制了30%和36%。随着硝酸盐浓度的增加，玉米主根根尖过氧化氢（H2O2）含量表现出降低的趋势，而抗氧化酶，如超氧化物歧化酶（SOD）、过氧化氢酶（CAT）、过氧化物酶（POD）的活性则表现出增加的趋势。外源供应过氧化氢对低浓度硝酸盐（0.01 mM）和高浓度硝酸盐（10 mM）处理下的玉米根伸长都没有影响，这表明了根尖过氧化氢含量的下降不是高浓度硝酸盐抑制玉米主根伸长的原因。 NO供体硝普钠（SNP）能够缓解高浓度硝酸盐对玉米主根伸长的抑制，而对低浓度硝酸盐处理下的主根伸长没有影响，而且NO清除剂亚甲基兰（MB）和NO合成酶抑制剂Nω-硝基-L-精氨酸（L-NNA）显著抑制了低浓度硝酸盐处理下的玉米主根伸长，而对高浓度硝酸盐处理下的玉米主根伸长没有影响。用NO特异性荧光染料4,5-二氨基乙酰乙酸荧光素(DAF-2DA)检测结果表明：高浓度硝酸盐显著降低玉米根尖NO含量。而玉米根中的硝酸还原酶活性随硝酸盐浓度的增加而增加。以上结果说明，高浓度硝酸盐抑制玉米主根伸长可能是与根尖NO合成酶的下调所导致的内源NO含量的降低有关。 另外，外源生长素（IAA）能缓解高浓度硝酸盐对玉米主根伸长的抑制，同时，也增加了高浓度硝酸盐处理下玉米根中内源NO含量，而对低浓度硝酸盐处理下的玉米根中内源NO没有影响。因此推测，根尖生长素的下降导致内源NO含量的降低可能是高浓度硝酸盐抑制玉米主根伸长的原因。

Arc Root Attachment on the Anode Surface of Arc Plasma Torch Observed with a Novel Method

The arc-root attachment on the anode surface of a dc non-transferred arc plasma torch has been successfully observed using a novel approach. A specially designed copper mirror with a boron nitride film coated on its surface central-region is employed to avoid the effect of intensive light emitted from the arc column upon the observation of weakly luminous arc root. It is found that the arc-root attachment is diffusive on the anode surface of the argon plasma torch, while constricted arc roots often occur when hydrogen or nitrogen is added into argon as the plasma-forming gas.

Arc Root Motions In An Argon-Hydrogen Direct-Current Plasma Torch At Reduced Pressure

Arc root motions in generating dc argon-hydrogen plasma at reduced pressure are optically observed using a high-speed video camera. The time resolved angular position of the arc root attachment point is measured and analysed. The arc root movement is characterized as a chaotic and jumping motion along the circular direction on the anode surface.

Arc Root Motion In An Argon-Hydrogen Dc Plasma Torch

Arc root motion on the anode surface of a dc non-transferred plasma torch was observed. Adding hydrogen changes the arc root attachment from a diffused type to a constricted type, and the arc root of Ar-H-2 plasma suddenly,jumps from one spot to another irregularly. Images of the arc root motions taken by a high-speed video camera are presented.

Comparative observation of Ar, Ar-H-2 and Ar-N-2 DC arc plasma jets and their arc root behaviour at reduced pressure

Results observed experimentally are presented, about the DC arc plasma jets and their arc-root behaviour generated at reduced gas pressure without or with an applied magnetic field. Pure argon, argon-hydrogen or argon- nitrogen mixture was used as the plasma-forming gas. A specially designed copper mirror was used for a better observation of the arc-root behaviour on the anode surface of the DC non-transferred arc plasma torch. It was found that in the cases without an applied magnetic field, the laminar plasma jets were stable and approximately axisymmetrical. The arc-root attachment on the anode surface was completely diffusive when argon was used as the plasma-forming gas, while the arc-root attachment often became constrictive when hydrogen or nitrogen was added into the argon. As an external magnetic field was applied, the arc root tended to rotate along the anode surface of the non-transferred arc plasma torch.

Comparative Observation of DC Arc Plasma Jets and Their Arc Root Behaviors at Reduced Pressure

Experimentally observed, results are presented for the DCarcplasmajets and theirarc-rootbehaviors generated atreduced gas pressure and without or with an' applied magnetic field. Pure argon, argon -hydrogen or argon-nitrogen mixture is used as the plasma-forming gas. A specially designed copper mirror is constructed and used for better observing the arc-root behavior on the anode surface of the DC non-transferred arcplasma torch. It is shown that for the cases without applied magnetic field, the laminar plasmajets are stable and approximately axisymmetrical. The arc-root attachment on the anode surface is completely diffusive when argon is used as the plasma-forming gas, while the arc-root attachment often becomes constrictive when hydrogen or nitrogen is added into the argon. When an external magnetic field is applied, the arcroot tends to rotate along the anode surface of the non-transferred arcplasma torch.

Development of arc root attachment in the nozzle of 1 kW N2 and H2-N2 arcjet thrusters

Arc root behavior affects the energy transfer and nozzle erosion in an arcjet thruster. To investigate the development of arc root attachment in 1 kW class N2 and H2-N2 arcjet thrusters from the time of ignition to the stably working condition, a kinetic series of end-on view images of the nozzle obtained by a high-speed video camera was analyzed. The addition of hydrogen leads to higher arc voltage levels and the determining factor for the mode of arc root attachment was found to be the nozzle temperature. At lower nozzle temperatures, constricted type attachment with unstable motions of the arc root was observed, while a fully diffused and stable arc root was observed at elevated nozzle temperatures.