運用改良式膨壓探針探討捕蠅草膨壓動態與多尺度形變之關聯性

Abstract

研究快速植物運動的生物力學機制長期以來是一項挑戰，主要原因在於其運動時間尺度遠快於單純水力傳輸所能解釋的範圍。以捕蠅草為例，膨壓被認為與捕蟲葉片的閉合密切相關，但由於缺乏在活體組織中的直接量測證據，無法確認膨壓是閉合的直接驅動力，或僅負責建立預應力 (prestress) 的準備狀態。我們利用改良式膨壓探針，直接量測補蠅草葉片中肋腹側與背側的膨壓動態，並比較完全水合、脫水與復水條件下的壓力特徵。此外，結合掃描式電子顯微鏡分析組織的結構方向性，進一步探討絕對膨壓與腹背壓力比值在運動過程中的關聯性。結果顯示，陷阱閉合並非由局部膨壓上升所驅動，而是腹背兩側膨壓同時下降，且腹背壓力比值在開放與閉合狀態間呈現反轉，此現象僅出現在具閉合能力的陷阱中。結構分析進一步顯示，腹背表皮層在細胞排列上的差異，為等向性膨壓轉換為方向性形變提供了結構基礎。綜上所述，膨壓並非捕蠅草閉合的直接驅動力，而是建立可供細胞壁快速釋放彈性的預應力力學狀態；組織層級的結構各向異性則決定了能量轉換的方向性。水合狀態透過調控預應力的可用性與分配，形成決定捕蠅草快速閉合的臨界條件。

The biomechanics of rapid plant movements often exceed the speeds achievable through simple hydraulics. In the Venus flytrap, the exact mechanical role of turgor pressure has remained debated due to a lack of direct in vivo measurements. This study clarifies these dynamics using a modified injection-type pressure probe to monitor adaxial and abaxial midrib turgor under varying hydration conditions. Our results demonstrate that trap closure is not driven by increasing localized pressure; instead, snapping is consistently accompanied by a marked turgor decrease on both sides. While pressure remains constant across tissue layers, a stable inversion of the adaxial-to-abaxial pressure ratio is essential for functional closure. Scanning electron microscopy reveals pronounced structural anisotropy, with perpendicular to each other cellular alignments between the upper and lower epidermis. This architecture provides the template for converting isotropic turgor into directional deformation. We conclude that turgor pressure functions primarily as a physiological source of prestress, enabling elastic energy storage. Hydration status directly determines the functional capacity of the snapping mechanism.