NO在極性生長中的功能

NO調節花粉管生長過程中胞內外Ca2+的變化和細胞壁構建

一氧化氮（NO） 在植物的生長發育過程中具有非常重要的作用。近日，中科院植物所林金星研究組深入研究了裸子植物白皮松花粉管生長過程中，NO對Ca2+、微絲骨架、囊泡轉運和細胞壁構建的調節作用。 NO作為重要的信號分子，參與調控花粉管極性生長。通過應用顯微注射、非損傷微測、免疫熒光標記等技術發現NO釋放劑促進花粉萌發和花粉管伸長，并且具有濃度效應，而抑制劑則抑制花粉萌發和花粉管生長，同時使花粉管頂端膨大，喪失極性；NO釋放劑促進胞外Ca2+內流，頂端Ca2+濃度梯度增加，NO抑制劑抑制胞外Ca2+內流，頂端Ca2+濃度梯度降低。 此外，NO釋放劑促進囊泡運輸，使花粉管頂端微絲束解聚，NO抑制劑具有相反的作用，同時NO使花粉管頂端酯化果膠增加而酸性果膠降低。 在白皮松花粉管中，NO促進胞外Ca2+內流，從而維持胞內Ca2+濃度梯度，進而影響花粉管頂端微絲骨架的組裝，促進囊泡運輸，使花粉管頂端酯化果膠累積，最終促進花粉管的正常生長。通過Ca2+流和細胞學實驗結果，全面地認識了NO在花粉管中極性生長中的功能。 右圖:使用熒光標記技術和非損傷微測技術得到的花粉管尖端Ca2+在NO釋放劑和抑制劑處理后的Ca2+含量以及Ca2+流的變化圖(右圖)。正值為外流，負值為內流。

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.