A new technology of modulated Chl a fluorescence image: In vivo measurement of the PSII maximum photochemical efficiency and its heterogeneity within leaves

doi:10.17521/cjpe.2016.0001

Abstract

Abstract:

The spatial photosynthetic heterogeneity within leaves is an important prerequisite for the studies on the photosynthetic model, the mechanism(s) of photoinhibition and light protection, etc. However, currently the in vivo measurement of the spatial photosynthetic heterogeneity within leaves is difficult. The present study improved the device assembled by Vogelmann & Evans (2002), thereby acquired the photosystem II (PSII) maximum photochemical efficiency (F_v/F_m) images within leaves. Finally, these images were processed and data of F_v/F_m and its spatial variations could be obtained, with the aid of MATLAB software. Based on the innovative technique, an investigation of the effects of strong light on the F_v/F_m and its spatial heterogeneity within leaves has been carried out. It was found that F_v/F_m within leaves was not homogonous. Strong light led to a general decrease of F_v/F_m (PSII photoinhibition) across leaf section, and the palisade tissue close to the epidermis layer had high tolerance to photoinhibition. Compared with control, short-term photoinhibition caused a larger spatial variation of F_v/F_m within leaves, which may be related to the chloroplast-avoidance response induced by high-fluence. On the contrary, long-term light inhibition led to a smaller spatial variation of F_v/F_m within leaves, indicating such mechanism is no longer effective. Compared to other types of chlorophyll fluoremeter, the device in the present study can in vivo obtain the panoramic picture of F_v/F_m within leaves, providing a powerful tool for the studies on the mechanism(s) attributed to the spatial heterogeneity of photosynthetic capacity of leaf, which is critical for the understanding on several hot spots in the research field of photosynthesis.

http://jtp.cnki.net/bilingual/detail/html/ZWSB201609009

Key words: Spinacia oleracea, chlorophyll fluorescence image, photoinhibition

Da-Yong FAN, Zeng-Juan FU, Zong-Qiang XIE, Rong-Gui LI, Shu-Min ZHANG. A new technology of modulated Chl a fluorescence image: In vivo measurement of the PSII maximum photochemical efficiency and its heterogeneity within leaves[J]. Chin J Plant Ecol, 2016, 40(9): 942-951.

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URL: https://www.plant-ecology.com/EN/10.17521/cjpe.2016.0001

https://www.plant-ecology.com/EN/Y2016/V40/I9/942

Figures/Tables 10

Table 1 The comparison of current fluorometers which can measure maximum photochemical efficiency (Fv/Fm)

参数 Index	型号 Type
参数 Index	PAM101-102-103¹⁾	IMAGING-PAM	PEA	本仪器 This set-up
信号采集方式 Signal acquisition mode	调制-锁相放大 Lock-in amplifier	CCD连续采集 CCD continuous collection	光电连续采集 Photoelectric continuous collection	CCD连续采集 CCD continuous collection
荧光数据形式 Fluorescence data format	点式 Point	图像 Image	点式 Point	图像 Image
测量光光强 The measuring light intensity	20-30²⁾	10-1 000	3 000	1 000³⁾
测量光脉冲宽度 The measuring light pulse width	2 μs⁴⁾	1.8 ms	2 s	160 μs
测量光周期 The measuring cycle duration	600 μs⁵⁾	125-1 000 ms	NA	3.3 ms
测量光脉冲宽度在OJIP的位置 The position of the measuring light pulse in OJIP curve	O段 At O stage	接近J段 Close to J stage	NA	接近O段 Close to O stage
测量光占空比 The measuring light duty cycle	1/300	1.8/(125-1000)	NA	1/30
饱和光光强 Saturating light intensity (μmol·m^-2·s^-1)	>3 000	800-1 200	3 000	1 000
测量光光强是否与饱和光光强一致 Is the measuring light intensity consistent with the saturating light intensity?	否 No	否⁶⁾ No⁶⁾	是 Yes	是 Yes
可否得到叶水平面荧光异质性 Can the fluorescence image on the leaf surface be obtained?	否 No	可以 Yes	否 No	可以⁷⁾ Yes⁷⁾
可否得到叶横截面荧光异质性 Can the fluorescence across leaf section be obtained?	否 No	否⁸⁾ No⁸⁾	否 No	可以⁹⁾ Yes⁹⁾
测量光和饱和光的均匀性 The uniformity of measuring and saturating light source	均匀 Uniform	一定范围内均匀 Uniform within a specific range	均匀 Uniform	均匀¹⁰⁾ Uniform¹⁰⁾

Fig. 3 Effect of the current set-up of modulated measuring light on maximum photochemical efficiency (Fv/Fm) values (mean ± SD).

Fig. 1 Block diagram of the experimental set-up of measurement of chlorophyll fluorescence yield within leaves. 1, leaf clip; 2, leaf pad; 3, leaf disk; 4, microscope objective; 5, incident modulated measuring light (for the determination of Fo) and saturate light (for the determination of Fm); 6, blue laser LED; 7, chopper (when turned on, modulated measuring light is created, for the determination of Fo; when turned off, continuous strong light is created, for the determination of Fm); 8, constant current source; 9, beam splitter; 10, chl a fluorescence; 11, short-wave cut-off filter (RG9); 12, charge coupled device (CCD); 13, computer. Fo, minimum fluorescence yield in dark-adapted state; Fm, maximum fluorescence yield in dark- adapted state

Fig. 2 Spectrum of 1 W high power blue laser diode. Measured by a fiber optic spectrometer AvaSpec-ULS2048×64 (Avantes, Apeldoorn, the Netherlands).

Fig. 4 The false color images of maximum photochemical efficiency (Fv/Fm) across leaf section after photoinhibition. A, free-hand section showing the thickness of leaf. B, 0 h. C, 1 h. D, 3 h.

Fig. 5 Maximum photochemical efficiency (Fv/Fm) heterogeneity across leaf section of control leaf.

Fig. 6 Maximum photochemical efficiency (Fv/Fm) heterogeneity across leaf section of leaf with 1 hour photoinhibition.

Fig. 7 Maximum photochemical efficiency (Fv/Fm) heterogeneity across leaf section of leaf with 3 h photoinhibition.

Fig. 8 Maximum photochemical efficiency (Fv/Fm) curves across leaf section of the control and photoinhibited leaves.

Fig. 9 Maximum photochemical efficiency (Fv/Fm) variability (S.D.) along the cross section of control and photoinhibited leaves.

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