A better energy allocation of absorbed light in photosystem II and less photooxidative damage contribute to acclimation of Arabidopsis thaliana young leaves to water deficit

SummaryWater deficit stress promotes excitation pressure and photooxidative damage due to an imbalance between light capture and energy use. Young leaves (YL) of Arabidopsis thaliana plants acclimate better to the onset of water deficit (OnsWD) than do mature leaves (ML). To obtain a better understanding of this differential response, we evaluated whether YL and ML of A. thaliana exposed to the OnsWD, mild water deficit (MiWD) and moderate water deficit (MoWD), show differences in their photosynthetic performance, and whether photosynthetic acclimation correlates with leaf developmental stage. Water deficit (WD) resulted in greater photooxidative damage in ML compared to YL, but the latter could not be protected under the OnsWD or MiWD, but only under MoWD. YL of A. thaliana with signs of photosynthetic acclimation under MoWD retained higher maximum quantum yield (Fv/Fm) and decreased reactive oxygen species (ROS) formation. YL under MoWD, show a reduced excitation pressure and a better balance between light capture and photochemical energy use, which contributed to their photoprotection, but only under low light intensity (LL, 130 μmol photons m−2 s−1) and not under high light (HL, 1200 μmol photons m−2 s−1). In conclusion, leaf developmental stage was correlated with photo-oxidative damage and a differential allocation of absorbed light energy in photosystem II (PSII) of Arabidopsis leaves under WD.