NO在极性生长中的功能

NO调节花粉管生长过程中胞内外Ca2+的变化和细胞壁构建

一氧化氮（NO） 在植物的生长发育过程中具有非常重要的作用。近日，中科院植物所林金星研究组深入研究了裸子植物白皮松花粉管生长过程中，NO对Ca2+、微丝骨架、囊泡转运和细胞壁构建的调节作用。 NO作为重要的信号分子，参与调控花粉管极性生长。通过应用显微注射、非损伤微测、免疫荧光标记等技术发现NO释放剂促进花粉萌发和花粉管伸长，并且具有浓度效应，而抑制剂则抑制花粉萌发和花粉管生长，同时使花粉管顶端膨大，丧失极性；NO释放剂促进胞外Ca2+内流，顶端Ca2+浓度梯度增加，NO抑制剂抑制胞外Ca2+内流，顶端Ca2+浓度梯度降低。 此外，NO释放剂促进囊泡运输，使花粉管顶端微丝束解聚，NO抑制剂具有相反的作用，同时NO使花粉管顶端酯化果胶增加而酸性果胶降低。 在白皮松花粉管中，NO促进胞外Ca2+内流，从而维持胞内Ca2+浓度梯度，进而影响花粉管顶端微丝骨架的组装，促进囊泡运输，使花粉管顶端酯化果胶累积，最终促进花粉管的正常生长。通过Ca2+流和细胞学实验结果，全面地认识了NO在花粉管中极性生长中的功能。 右图:使用荧光标记技术和非损伤微测技术得到的花粉管尖端Ca2+在NO释放剂和抑制剂处理后的Ca2+含量以及Ca2+流的变化图(右图)。正值为外流，负值为内流。

Summary
• Nitric oxide (NO) plays a key role in many physiological processes in plants, including pollen tube growth. Here, effects of NO on extracellular Ca²⁺ flux and microfilaments during cell wall construction in Pinus bungeana pollen tubes were investigated.
• Extracellular Ca²⁺ influx, the intracellular Ca²⁺ gradient, patterns of actin organization,vesicle trafficking and cell wall deposition upon treatment with the NO donor S-nitroso-N-acetylpenicillamine (SNAP), the NO synthase (NOS) inhibitor Nω-nitro-L-arginine(L-NNA) or the NO scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) were analyzed.
• SNAP enhanced pollen tube growth in a dose-dependent manner, while L-NNA and cPTIO inhibited NO production and arrested pollen tube growth. Noninvasive detection and microinjection of a Ca²⁺ indicator revealed that SNAP promoted extracellular Ca²⁺ influx and increased the steepness of the tip-focused Ca²⁺ gradient, while cPTIO and L-NNA had the opposite effect. Fluorescence labeling indicated that SNAP, cPTIO and L-NNA altered actin organization, which subsequently affected vesicle trafficking. Finally, the configuration and/or distribution of cell wall components such as pectins and callose were significantly altered in response to L-NNA. Fourier transform infrared (FTIR) microspectroscopy confirmed the changes in the chemical composition of walls.
• Our results indicate that NO affects the configuration and distribution of cell wall components in pollen tubes by altering extracellular Ca2+ influx and F-actin organization.