Paraheliotropism in Robinia pseudoacacia plants: an efficient mean to cope with photoinhibition

The contribute of paraheliotropism in PSII photoprotection at high light and temperature was assessed by gas exchange and chlorophyll fluorescence. Measurements were performed at 10:00, 12:00, 15:00 and 18:00 on blocked leaves (BL) and on control unblocked leaves (UL) of R. pseudoacacia. In BL at midday as well as at 15:00 and 18:00, An, gCO2, ΦPSII, IPO and F’q/F’v declined compared to 10:00 whereas Ci/Ca ratio and qN increased significantly. Differently from BL, UL maintained an higher An, IPO and ΦPSII as well as a lower qN throughout the day. At 18:00, An, gCO2, ΦPSII and F’q/F’v of BL recovered as compared to 15:00 even if the values remained lower than 10:00 and UL. Moreover, conversely to UL, a significant decrease of Fv/Fm was observed in the evening. Data suggest that in R. pseudoacacia leaf movements represent an efficient strategy to face the photoinhibition at no cost for plant in terms of An reduction.