Stress-induced delay of the I-P rise of the fast chlorophyll a fluorescence transient in tomato

Abstract

Fast chlorophyll a fluorescence induction curve (OJIP) provides a powerful tool for rapidly assessing the photosynthetic performance of plants. However, the application of this technology in tomato plants is scarce. Here, OJIP curve was used to evaluate the photosynthetic performance of tomato plants under chilling and drought stress, and interpretation of the obtained OJIP curves was improved. The results showed that the performance index (PI-abs) and the amplitude of I-P phase of greenhouse-grown tomato plants decreased rapidly with the decline of ambient temperatures and fluctuated with the changes in temperature during the autumn-winter transition. However, photosystem II efficacy (Fv/Fm) showed slow response. In the chambers, net photosynthetic rate (PN) and photochemical efficiency were inhibited by short-term chilling stress. The amplitudes of O-J phase and I-P phase were slightly affected by chilling stress. Interestingly, the appearance of I points of OJIP curves was delayed by chilling stress. Consequently, the corrected amplitudes of I-P phase were found to be significantly inhibited by chilling. Moreover, the corrected amplitudes of I-P phase correlated well with PN and PI-abs, during chilling and subsequent recovery. Mutation of PGR5, which is involved in cyclic electron flow, resulted in declines of photosynthetic parameters including the corrected amplitudes of I-P phase under control and chilling conditions. Under drought stress, the corrected amplitudes of I-P phase and operational photochemical efficiency [Y(II)] also progressively declined in parallel. However, Fv/Fm remained stable even when plants showed a wilting phenotype. Our results indicate that the delay of I point by stress should be considered when using the amplitude of I-P phase to reflect the status of photosynthetic apparatus in response to stress.