肌醇鹽和Cl-流調控花粉管的生長和細胞的體積      氯離子外流通過肌醇3,4,5,6-四磷酸鹽調控花粉管的生長和細胞的體積

圖注： 上圖1：Cl-振蕩與花粉管生長速率一致。 上圖2：肌醇3,4,5,6-四磷酸鹽擾亂花粉管尖端的Cl-外流。負值代表外流。 花粉管生長是生物系統中自發組織的一個重要實例。在這些自發系統中，通過交互反饋通路傳遞信號，從而控制并調整分子及生化參數使之最適于生長和發揮作用。花粉作為一種研究植物細胞發育、生長以及生物生理學的模式材料，發現花粉管的振蕩生長與Ca2+、H+、K+三種陽離子振蕩內流有關。 在哺乳動物分泌細胞中，Cl-通道作為重要的調節者調控分泌活動并維持細胞體積。已經證明肌醇3,4,5,6-四磷酸鹽負調控Ca2+激活Cl-通道。不同的肌醇磷酸鹽作用于花粉管時，肌醇3,4,5,6-四磷酸鹽的作用最強。 Feijó等研究人員應用非損傷微測技術探索了肌醇3,4,5,6-四磷酸鹽和Cl-流之間的潛在關系。研究發現，在煙草和百合花粉管尖端出現振蕩的Cl-外流，從距尖端12μm開始沿著花粉管出現持續內流。氯通道阻斷劑DIDS（4,4’-diisothiocyanatostilbene-2,2‘-disulfonic acid）和5-硝基-2-(3-苯丙氨基)-苯甲酸（5-nitro-2-(3-phenylpropylamino)benzoic acid）分別在80μM和20μM時能夠完全抑制煙草花粉管生長，誘導細胞體積增大，擾亂尖端Cl-外流。另外，肌醇3,4,5,6-四磷酸鹽編碼的信號不利于花粉管生長，并可誘導細胞體積增大，擾亂正常的Cl-振蕩外流。相關分析表明Cl-外流的周期在時間上與生長周期吻合，且生長周期中Cl-外流與囊泡運動有關。 這一研究對于認識調控花粉管平衡和生長網絡中的Cl-動力學非常重要。 關鍵詞：花粉管（pollen tube）;Cl-流（Chloride flux）;肌醇3,4,5,6-四磷酸鹽（inositol 3,4,5,6-tetra kisphosphate） 參考文獻：Laura Zonia, et al. The Plant Cell, 2002, 14: 2233-2249 全文下載：http://www.xuyue.net/xylt/viewthread.php  【轉載請注明出處】

------------------------------

Abstract：

Oscillatory growth of pollen tubes has been correlated with oscillatory influxes of the cations Ca²⁺, H⁺, and K^+. Using an ion-specific vibrating probe, a new circuit was identified that involves oscillatory efflux of the anion Cl^- at the apex and steady influx along the tube starting at 12μm distal to the tip. This spatial coupling of influx and efflux sites predicts that a vectorial flux of Cl^- ion traverses the apical region. The Cl- channel blockers 4,4’-diisothiocyanatostilbene-2,2’-disulfonic acid (DIDS) and 5-nitro-2-(3-phenylpropylamino)benzoic acid completely inhibited tobacco pollen tube growth at 80 and 20μM, respectively. Cl^- channel blockers also induced increases in apical cell volume. The apical 50μm of untreated pollen tubes had a mean cell volume of 3905±75μm³. DIDS at 80μM caused a rapid and lethal cell volume increase to 6206±171μm³, which is at the point of cell bursting at the apex. DIDS was further demonstrated to disrupt Cl- efflux from the apex, indicating that Cl^- flux correlates with pollen tube growth and cell volume status. The signal encoded by inositol 3,4,5,6-tetrakisphosphate [Ins(3,4,5,6)P₄] antagonized pollen tube growth, induced cell volume increases, and disrupted Cl^- efflux. Ins(3,4,5,6)P₄ decreased the mean growth rate by 85%, increased the cell volume to 5997±148μm3, and disrupted normal Cl^- efflux oscillations. These effects were specific for Ins(3,4,5,6)P₄ and were not mimicked by either Ins(1,3,4,5)P₄ or Ins(1,3,4,5,6)P₅. Growth correlation analysis demonstrated that cycles of Cl^- efflux were coupled to and temporally in phase with cycles of growth. A role for Cl^- flux in the dynamic cellular events during growth is assessed. Differential interference contrast microscopy and kymographic analysis of individual growth cycles revealed that vesicles can advance transiently to within 2 to 4μm of the apex during the phase of maximally increasing Cl^- efflux, which temporally overlaps the phase of cell elongation during the growth cycle. In summary, these investigations indicate that Cl^- ion dynamics are an important component in the network of events that regulate pollen tube homeostasis and growth.