Application of Fluorescence Analysis Technology in the Study of Crop Response to Cadmium Stress

To reveal the application of fluorescence analysis technology on study of crop response to cadmium stress, the changes in cadmium concentration, chlorophyll fluorescence parameters, and fluorescence response curves of soybean seedlings under cadmium stress were analysed, and the relationship between chlorophyll fluorescence parameters and cadmium concentration in leaves was further assessed. The results showed that, with increased cadmium stress time, the concentration of cadmium in leaves increased gradually, reaching its maximum after 9 days of cadmium stress. After 1 day of cadmium stress, the PS II reaction centre of soybean could dissipate excessive excitation energy by increasing non-photochemical quenching (NPQ) and decreasing actual efficiency of PS II (Phi(PSII)) and apparent electron transport rate (ETR). Thus the physiological damages caused by energy over-excitation in PS II reaction centre were avoided and the stability of the maximal efficiency of PS II (F-v/F-m) was maintained, indicating that the dynamic photo-inhibition in soybean caused by cadmium stress then occurred. After 6 days of cadmium stress, NPQ continued to increase, but the photo-protection mechanism was insufficient to avoid the physiological damage caused by energy over-excitation. Thus, .F-v/F-m of soybean seedlings showed a trend of decrease, indicating that soybean seedlings were then affected by chronic photo-inhibition. We next performed the correlation and regression analysis between chlorophyll fluorescence parameters and cadmium concentration. F-v/F-m was non-linearly correlated with cadmium concentration (R-2 =0. 907, p<0. 05) , while Phi(PSII) (R-2 =0. 959, p<0. 01) and ETR (R-2 =0. 945, p<0. 01) were negatively correlated with cadmium concentration. In addition, NPQ and cadmium concentration was positively correlated (R-2 =0. 959, p<0. 01). These results indicated that F-v/ F-m could maintain stability under certain cadmium stress, while Phi(PSII) ETR and NPQ changed rapidly with increasing cadmium concentration. The changes in light response curves of chlorophyll fluorescence under cadmium stress were also analysed. It was found that the light response curves of Phi(PSII) and NPQ in stressed leaves showed similar trends to those observed in non-stressed leaves. However, under specific light intensity, Phi(PSII) in stressed leaves was lower than that of non-stressed leaves, while NPQ in stressed leaves was higher than that of non-stressed leaves, indicating that cadmium stress reduced the photochemistry activity of leaves, and caused more excitation energy dissipation as thermal. These studies confirmed that, fluorescence analysis technology could provide guidance for further study on the physiological mechanism of crop response to cadmium stress.