Study of the senescence of rice leaves through stationary and time-resolved photoluminescence.

This work describes the relationship between the complex of photosystem I and photosystem II in the senescence process of rice leaves observed through changes in the optical response. We studied three varieties of rice plants at different aging times using time-resolved photoluminescence to measure the time decay of the emission, and stationary photoluminescence, to measure the emission wavelength. The spectra obtained with the former technique were fitted with decreasing exponential functions. Two relaxation times were obtained, one ranging between 1.0 and 1.7 ns, and the other, from 5.0 to 10.5 ns. They are associated with the electron's deexcitation of PSI and PSII, respectively, and these decay times increase as the leaf senescence process takes place. The spectra obtained with stationary photoluminescence were fitted with Voigt functions. These spectra exhibit two main peaks around 683 and 730 nm, which could be associated mainly with PSII and PSI emissions, respectively. The PSI de-excitation exhibits higher dispersive processes because chlorophyll-a molecules in it move away from each other, decreasing their concentration. Therefore, it takes longer for electrons to recombine during photosynthesis, as seen in the time-resolve response. Articulating the results of both photoluminescence techniques, the changes in the response of the photosystems of the living rice leaves during senescence are evidenced.