Department of Biochemistry and Genetics, The Connecticut Agricultural Experiment Station, New Haven, Connecticut 06504.
Plant Physiol. 1991 May;96(1):172-7. doi: 10.1104/pp.96.1.172.
The responses of minimal and maximal fluorescence yields of chlorophyll a to irradiance of actinic white light were determined by pulse modulated fluorimetry in leaf discs from tobacco, Nicotiana tabacum, at 1.6, 20.5, and 42.0% (v/v) O(2). Steady-state maximal fluorescence yield (F(m)', measured during a saturating light pulse) declined with increasing irradiance at all O(2) levels. In contrast, the steady-state minimal fluorescence yield (F(o)', measured during a brief dark interval) increased with irradiance relative to that recorded for the fully dark-adapted leaf (F(o)) or that observed after 5 minutes of darkness (F(o) (*)). The relative magnitude of this increase was somewhat greater and extended to higher irradiances at the elevated O(2) levels compared with 1.6% O(2). Suppression of F(o)' was only observed consistently at saturating irradiance. The results are interpreted in terms of the occurrence of photosystem II units possessing exceedingly slow turnover times (i.e. "inactive" units). Inactive units play an important role, along with thermal deactivation of excited chlorophyll, in determining the response of in vivo fluorescence yield to changes in irradiance. Also, a significant interactive effect of O(2) concentration and the presence or absence of far red light on oxidation of photosystem II acceptors in the dark was noted.
在 1.6%、20.5%和 42.0%（v/v）O2 下，通过脉冲调制荧光法测定了烟草叶片中叶绿素 a 的最小和最大荧光产额对光强的响应。在所有 O2 水平下，稳态最大荧光产额（F(m)’，在饱和光脉冲期间测量）随光强的增加而降低。相比之下，稳态最小荧光产额（F(o)’，在短暂的黑暗间隔期间测量）相对于完全黑暗适应叶片（F(o)）或黑暗 5 分钟后（F(o)（*））记录的荧光产额随光强增加。与 1.6%O2 相比，在较高 O2 水平下，这种增加的幅度稍大，并且扩展到更高的光强。只有在饱和辐照度下才会观察到 F(o)’的抑制。结果从光合系统 II 单位具有极慢周转率（即“不活跃”单位）的角度进行了解释。不活跃的单位与激发态叶绿素的热失活一起，在确定体内荧光产额对辐照度变化的响应方面起着重要作用。此外，还注意到 O2 浓度和远红光的存在或不存在对黑暗中光合系统 II 受体氧化的显著交互作用。
