Low induction of non-photochemical quenching and high photochemical efficiency in the annual desert plant Anastatica hierochuntica

Non-photochemical quenching (NPQ) plays a major role in photoprotection. Anastatica hierochuntica is an annual desert plant found in hot deserts. We compared A. hierochuntica to three other different species: Arabidopsis thaliana, Eutrema salsugineum and Helianthus annuus, which have different NPQ and photosynthetic capacities. Anastatica hierochuntica plants had very different induction kinetics of NPQ and, to a lesser extent, of photosystem II electron transport rate (PSII ETR), in comparison to all other plants species in the experiments. The major components of the unusual photosynthetic and photoprotective response in A. hierochuntica were: (1) Low NPQ at the beginning of the light period, at various light intensities and CO₂ concentrations. The described low NPQ cannot be explained by low leaf absorbance or by low energy distribution to PSII, but was related to the de-epoxidation state of xanthophylls. (2) Relatively high PSII ETR at various CO₂ concentrations in correlation with low NPQ. PSII ETR responded positively to the increase of CO₂ concentrations. At low CO₂ concentrations PSII ETR was mostly O₂ dependent. At moderate and high CO₂ concentrations the high PSII ETR in A. hierochuntica was accompanied by relatively high CO₂ assimilation rates. We suggest that A. hierochuntica have an uncommon NPQ and PSII ETR response. These responses in A. hierochuntica might represent an adaptation to the short growing season of an annual desert plant.