The anatomical basis and molecular mechanism of Arachis hypogaea nyctinastic movement

Nyctinastic movement of plants refers to the circadian rhythms of the leaves or leaflets of some plants that open during the daytime and close at night. It is the turgor movement that induces the reversible change of the volume of pulvinus motor cells. The accomplishment of this movement demands the accurate control of water and ion flux by membrane proteins and the regulation of light signals and biological clocks. The anatomical structure of Arachis hypogaea pulvinus shows that small-diameter vascular tissue is the structural foundation of nyctinastic movement. And there are a lot of plasmodesmata in the septate fibers of the pulvinus tissue, which can exchange water and ions quickly. A. hypogaea leaves began to closed slowly during the 16-20 h light period under the continuous illumination condition, which indicated that the circadian clock regulates the nyctinastic movement. Gene expression levels of ion channel protein were detected by reverse transcription-quantitative PCR. The results revealed that the anion channel AhSLAH1 is expressed explicitly in pulvinus, and AhSKOR2 is only expressed in flexor cells.