Kaiser H, Kappen L
Botanisches Institut der Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany.
J Exp Bot. 2001 Jun;52(359):1303-13.
Continuous measurements of stomatal aperture simultaneously with gas exchange during periods of stomatal oscillations are reported for the first time. Measurements were performed in the field on attached leaves of undisturbed Sambucus nigra L. plants which were subjected to step-wise increases of PPFD. Oscillations only occurred when stomatal apertures were small under high water vapour mole fraction difference between leaf and atmosphere (DeltaW). They consisted of periodically repeated opening movements transiently leading to very small apertures. Measurements of the area of the stomatal complex in parallel to the determination of aperture were used to record volume changes of guard cells even if stomata were closed. Stomatal opening upon a light stimulus required an antecedent guard cell swelling before a slit occurred. After opening of the slit the guard cells again began to shrink which, with some delay, led to complete closure. Opening and closing were rhythmically repeated. The time-lag until initial opening was different for each individual stoma. This led to counteracting movements of closely adjacent stomata. The tendency to oscillate at small apertures is interpreted as being a failure of smoothly damped feedback regulation at the point of stomatal opening: Volume changes are ineffective for transpiration if stomata are still closed; however, at the point of initial opening transpiration rate rises steeply. This discontinuity together with the rather long time constants inherent in the stomatal turgor mechanism makes oscillatory overshooting responses likely if at high DeltaW the 'nominal value' of gas exchange demands a small aperture.
首次报道了在气孔振荡期间与气体交换同时进行的气孔孔径连续测量。测量是在野外对未受干扰的欧洲接骨木植株上的附着叶片进行的,这些叶片经历了光合有效辐射(PPFD)的逐步增加。只有当气孔孔径较小时,在叶片与大气之间的高水汽摩尔分数差(ΔW)下才会出现振荡。振荡由周期性重复的开放运动组成,短暂地导致非常小的孔径。在测定孔径的同时,对气孔复合体的面积进行测量,以便即使气孔关闭时也能记录保卫细胞的体积变化。光刺激下的气孔开放在裂隙出现之前需要保卫细胞先膨胀。裂隙打开后,保卫细胞再次开始收缩,这会导致气孔延迟完全关闭。开放和关闭有节奏地重复。每个单独气孔初始开放的时间滞后不同。这导致相邻气孔的运动相互抵消。在小孔径下振荡的趋势被解释为在气孔开放点平滑阻尼反馈调节的失败:如果气孔仍然关闭,体积变化对蒸腾作用无效;然而,在初始开放点,蒸腾速率会急剧上升。这种不连续性以及气孔膨压机制固有的相当长的时间常数使得如果在高ΔW下气体交换的“标称值”需要小孔径,就可能出现振荡过冲响应。