Botanisches Institut II der Universität Würzburg, Würzburg, Germany.
Planta. 1971 Mar;100(1):76-86. doi: 10.1007/BF00386887.
Large areas of the lower epidermis of full-grown leaves of Polypodium vulgare (and Valerianella locusta) are normally separated from the mesophyll by an extensive subepidermal airspace. Epidermal stripes were prepared for experiments to simulate these conditions in order to investigate stomatal reactions. They were placed with their inner surface in contact with an airspace of uniformly high humidity. The outer surface was treated with air of varying degrees of humidity. The stomatal reactions were observed by microscope and the opening of the guard cells determined photographically.Treatment of the outer side of the epidermis with dry air led to a rapid closing of the stomata, whilst moist air caused opening. This induction of opening and closing movements could be repeated up to 15 times with the same stoma by changing the degree of humidity. Neighbouring groups of stomata showed different apertures according to their individual humidity conditions. The degree of aperture of the stomata depended on the water potential of the ambient air and also on the humidity conditions in the subepidermal airspace.The cause of this stomatal behaviour could lie in the "peristomatal transpiration". In this way, the guard cells are able to function as "humidity sensors" which "measure" the difference in water potential inside and outside the leaf. Their aperture thus is controlled by their individual transpiration conditions. This controlling mechanism could be very important for the water economy of plants. They would appear to be able to reduce their transpiration through an increase in diffusion resistance of the stomata during decreasing humidity in the ambient air, without changing the water status of the whole leaf.
凤尾蕨（和节节麦）成熟叶片的下表皮的大部分区域通常通过广泛的表皮下空气间隙与叶肉分离。为了模拟这些条件进行实验，制备了表皮条纹。将它们的内表面与均匀高湿度的气隙接触。用不同湿度的空气处理外表面。通过显微镜观察气孔反应，并通过照相确定保卫细胞的开度。用干燥空气处理表皮外侧会导致气孔迅速关闭，而潮湿空气会导致气孔张开。通过改变湿度，可以对同一气孔重复进行多达 15 次的开闭运动诱导。根据其各自的湿度条件，相邻的气孔群显示出不同的开度。气孔的开度取决于环境空气的水势，也取决于表皮下空气间隙中的湿度条件。这种气孔行为的原因可能在于“周皮蒸腾”。通过这种方式，保卫细胞可以作为“湿度传感器”，“测量”叶片内外水势的差异。因此，它们的开度受其各自蒸腾条件的控制。这种控制机制对于植物的水分利用效率可能非常重要。它们似乎能够通过增加气孔在环境空气中湿度降低时的扩散阻力来减少蒸腾，而不改变整个叶片的水分状况。
