[Application of polarization fluorescence to the study on the effects of oxidative stress on wheat chloroplast]

In the present paper wheat flag leaves were collected during the tasseling period, and then 1 mmol x L(-1) hydrogen peroxide was added to induce oxidative stress on leaves. In comparison, the detached leaves were also kept under drought or darkness condition for 24 h for the same purpose. Following the preparation of chloroplasts, polarization fluorescence spectroscopic method was utilized to measure fluorescence emission spectra and fluorescence excitation spectra of chloroplasts in the case of VV, VH, HV and HH, where V and H is representative of vertical polarization and horizontal polarization, respectively. Gaussian deconvolution was done on emission spectra, and the fitting data revealed that no matter whether Chla or Chlb molecules were excited upon excitation at 436 nm or 475 nm, the ratio of fluorescence peak area at 684 nm and 720 nm, i. e. A684/ A720, tends to increase slightly after oxidative stress. In addition, some useful information was available from polarization excitation spectra, where it was observed that the treatment of oxidative stress gave rise to higher ratio of excitation peak intensity between 436 nm and 475 nm (E436/E475), indicating that Chla made more contribution to PSII fluorescence emission than Chlb did. Simultaneously, the ratio of 475 nm and 600 nm (E475/E600), representing the energy transfer efficiency from Car to Chlb, was also found to be higher after the detached leaves were treated. In addition, both fluorescence polarization and viscosity were calculated in this paper, and the data showed that oxidative stress should be responsible for higher fluorescence polarization at 680 nm and higher viscosity in microenviroment. The above-mentioned phenomenon is consistent with the lipid peroxidation of unsaturated fatty acids. It also provides a simple and feasible method to study oxidative stress.