Deriving fluorometer-specific values of relative PSI fluorescence intensity from quenching of F 0 fluorescence in leaves of Arabidopsis thaliana and Zea mays

The effect of stepwise increments of red light intensities on pulse-amplitude modulated (PAM) chlorophyll (Chl) fluorescence from leaves of A. thaliana and Z. mays was investigated. Minimum and maximum fluorescence were measured before illumination (F 0 and F M, respectively) and at the end of each light step (\( F^{\prime}_{0} \) and \( F^{\prime}_{\text{M}} \), respectively). Calculated \( F^{\prime}_{0} \) values derived from F 0, F M and \( F^{\prime}_{\text{M}} \) fluorescence according to Oxborough and Baker (1997) were lower than the corresponding measured \( F^{\prime}_{0} \) values. Based on the concept that calculated \( F^{\prime}_{0} \) values are under-estimated because the underlying theory ignores PSI fluorescence, a method was devised to gain relative PSI fluorescence intensities from differences between calculated and measured \( F^{\prime}_{0} \). This method yields fluorometer-specific PSI data as its input data (F 0, F M, \( F^{\prime}_{0} \) and \( F^{\prime}_{\text{M}} \)) depend solely on the spectral properties of the fluorometer used. Under the present conditions, the PSI contribution to F 0 fluorescence was 0.24 in A. thaliana and it was independent on the light acclimation status; the corresponding value was 0.50 in Z. mays. Correction for PSI fluorescence affected Z. mays most: the linear relationship between PSI and PSII photochemical yields was clearly shifted toward the one-to-one proportionality line and maximum electron transport was increased by 50 %. Further, correction for PSI fluorescence increased the PSII reaction center-specific parameter, 1/F 0 − 1/F M, up to 50 % in A. thaliana and up to 400 % in Z. mays.