The Hebrew University of Jerusalem, Department of Agricultural Botany, Rehovot 76100, Israel.
Plant Physiol. 1986 Mar;80(3):778-81. doi: 10.1104/pp.80.3.778.
On a clear day, leaf laminas of Lavatera cretica tracked the solar position throughout the day. The laminar azimuth did not diverge from the solar azimuth by more than 12 degrees from sunrise to sunset. Tracking of the solar elevation started 1 to 2 hours after sunrise and ceased 1 to 2 hours before sunset. On an overcast day, the laminas reoriented horizontally. After sunset, following a clear day, the laminas performed a nocturnal reorientation, with three well defined phases. During the initial phase the laminas relaxed their strained sunset-facing orientation to one perpendicular to their petioles. This equilibrium configuration was maintained throughout the following phase, which was apparently concerned with time-measuring. During the final phase, the laminas reoriented, before sunrise, to a position facing the direction of the anticipated sunrise. This directional information is phototropic and was retained for 3 to 4 diurnal cycles, probably in the pulvinus itself, which is the site of the response. Laminas of plants transferred from sunlight either to darkness, or to a simulated natural photoperiod under overhead illumination, were facing the originally anticipated direction of sunrise at the time of each of the three to four subsequent sunrises (after which they reverted to the dark orientation in darkness, or to the horizontal one with overhead illumination). Cotyledonary laminas required directional information for the nocturnal reorientation during 3 or 4 cycles of simulated sunrise to sunset transitions.
在晴天，Lavatera cretica 的叶片薄片全天跟踪太阳位置。从日出到日落，叶片方位与太阳方位的偏差不超过 12 度。太阳高度角的跟踪从日出后 1 到 2 小时开始，在日落前 1 到 2 小时停止。在阴天，薄片水平重新定向。在晴天日落之后，薄片会进行夜间重新定向，有三个明显的阶段。在初始阶段，薄片放松其在日落方向上的紧张状态，变为垂直于叶柄。这个平衡状态在随后的阶段中一直保持，显然与计时有关。在最后阶段，薄片在日出前重新定向，面向预期的日出方向。这个方向信息是向光性的，并且在 3 到 4 个昼夜周期中被保留，可能在响应的部位——叶枕中。从阳光转移到黑暗或在头顶照明下模拟自然光周期的植物叶片在随后的 3 到 4 个日出中的每个日出时都面向最初预期的日出方向（之后，它们在黑暗中恢复到黑暗定向，或在头顶照明下恢复到水平定向）。子叶薄片在模拟日出到日落转变的 3 或 4 个周期中需要方向信息进行夜间重新定向。
