Assessment of Photosynthetic Function by Analyzing Dynamic Change in Chlorophyll Fluorescence Intensity Induced by a Pulsed Pressure Reduction

我们尝试开发一种叶绿素荧光成像系统，在不接触植物体的情况下测量叶肉电导。最初，我们提出叶肉电导可以用一个相对指数来表示，该指数被定义为叶绿素荧光发射对光合作用叶片周围气压快速降低的响应时间的倒数。将附着在植株上的成熟番茄叶片固定在内部大小为100 ml的透明丙烯酸叶片室中，并适应光（蓝色LED提供）条件，以稳定光合作用。这个腔室是密封的，腔内的空气立即被一个手动泵吸走。腔内气压在3秒内由101.3 kPa降至50.7 kPa，并在10秒内保持气压在49 kPa以下。在此过程中，叶绿素荧光成像系统以13 fps的帧率连续测量叶片发出的叶绿素荧光强度。叶绿素荧光发射随气压的迅速降低响应非常迅速，在气压降低后0.05 s内叶绿素荧光强度增加。因此，我们得出结论，用这种测量系统和假设是不可能量化叶肉电导的。另一方面，我们发现开发的叶绿素荧光成像系统和测量方法可以用来测量光合速率。m叶绿素荧光强度在空气压力降低后立即增加，并在空气压力降低后约3秒达到峰值。不同CO_2浓度下测定的光合速率与峰高有较强的相关性。

We tried to develop a chlorophyll fluorescence imaging system to measure the mesophyll conductance without touching the plant body. Initially, we provided that the mesophyll conductance can be expressed with a relative index that is defined as the reciprocal of the response time of chlorophyll fluorescence emission to a rapid reduction of air pressure around the photosynthesizing leaf. A mature tomato leaf attached to the plant was fixed in the transparent acrylic leaf chamber with the inner size of 100 ml and acclimated to light (provided by blue LED) condition for stable photosynthesis. The chamber was hermetically closed and the air inside the chamber was immediately sucked Mby a manually powered pump. The air pressure inside the chamber decreased from 101.3 kPa to 50.7 kPa within 3 seconds and kept the air pressure less than 49 kPa for 10 seconds. During this procedure, the chlorophyll fluorescence intensity emitted by the leaf was continuously measured with the chlorophyll fluorescence imaging system at a frame rate of 13 fps. The response of chlorophyll fluorescence emission with the prompt reduction of air pressure was quite rapid and the chlorophyll fluorescence intensity increased within 0.05 second after the reduction of air pressure. Hence, we concluded that it is impossible to quantify the mesophyll conductance with this measurement systems and hypothesis. On the other hand, we found that the developed chlorophyll fluorescence imaging system and measuring method can be used to measure the photosynthetic rate. The Mchlorophyll fluorescence intensity increased just after the reduction of air pressure and reached to a peak at about 3 seconds after the reduction of air pressure. The height of the peak showed a strong correlation with the photosynthetic rate measured under different CO_2 concentrations.