珊瑚树和大豆叶片叶绿素荧光的非光化学猝灭

Non photochemical Quenching of Chlorophyll Fluorescence in Soybean and Sweet Viburnum Leaves

用ＰＡＭ２０００ 型荧光仪和７５４ 型分光光度计观测了珊瑚树和大豆叶片叶绿素荧光的非光化学猝灭快、中和慢３ 个组分（ｑＮｆ，ｑＮｍ 与ｑＮｓ） 和５０５ ｎｍ 光吸收的日变化。主要结果如下：（１） 中午，珊瑚树叶片的ｑＮｓ 比ｑＮｆ 大得多，而大豆叶片的这两个参数却几乎处于同一水平。它们的ｑＮｍ 虽然也随光强变化，但与ｑＮｓ 和ｑＮｆ 相比，除早晨和傍晚以外全天的水平都是最低的。（２） 珊瑚树叶片的初始荧光水平（Ｆｏ） 中午最低，而大豆叶片的Ｆｏ 中午最高。（３） 饱和光照射引起的珊瑚树叶片５０５ ｎｍ 光吸收的增加比大豆叶片大得多。（４） 珊瑚树叶片５０５ ｎｍ 光吸收的日变化方式与ｑＮｓ 的相类似。（５） 叶黄素循环的抑制剂ＤＴＴ对珊瑚树叶片ｑＮｓ 的抑制（５７ ％ ） 比对大豆叶片ｑＮｓ 的抑制（２３ ％ ） 严重。

Diurnal variations in values of the three components, the fast phase (qN f), the middle phase (qN m ), and the slow phase (qN s), of non photochemical quenching of chlorophyll fluorescence and light absorbance at 505 nm in soybean and sweet viburnum leaves were observed by using a portable PAM 2000 fluorometer and a spectrophotometer (754 Model). The results are as follows: (1) qN f and qN s increased gradually in leaves of both species as sunlight intensity rose in the morning. At midday qN s was much higher than qN f in sweet viburnum leaf, while in soybean leaf the two parameters were at almost the same level. Among the three components of non photochemical quenching of chlorophyll fluorescence in leaves of the two species, qN m was always at a very low level in the whole day except in the early morning and late afternoon, although it also changed with light intensity (Figs.1, 2). (2) At midday the level of the original fluorescence (Fo) reached its minimum and maximum of the diurnal course for sweet viburnum and soybean leaves, respectively (Figs.1, 2). (3) Light absorbance change at 505 nm caused by illumination with a saturating light (1 300 μmol photons m -2 s -1 ) for 75 minutes was much stronger in sweet viburnum leaf than in soybean leaf (Fig.3). (4) In sweet viburnum leaf the diurnal variation pattern of light absorbance at 505 nm, expressed as A 505 / A 652 , was similar to those of both qN s and photon flux density of sunlight with a peak value at midday (Fig.4). (5) qN s was more severely inhibited by DTT(dithiothreitol), an inhibitor of the xanthophyll cycle, in sweet viburnum leaf (57%) than in soybean leaf (23%) (Fig.5). Based on the above results it is concluded that in comparison with the thermal dissipation processes related to the xanthophyll cycle, inactivation of PSⅡ reaction center, and the proton gradient across thylakoid membrane, state transition is not likely an important mechanism in protecting the photosynthetic apparatus against photodamage under natural conditions. The xanthophyll cycle dependent thermal dissipation process is the predominant protective mechanism in sweet viburnum leaf but not in soybean leaf. The slow component of non photochemical quenching of chlorophyll fluorescence (qN s) is closely linked to the xanthophyll cycle in sweet viburnum leaves.