TRIPUDIUM - TRIticum Photosynthesis Under Drought and fluctuating Irradiance: Use of Mutants phenotyping to approach crop photosynthetic regulation

Decreased crop plant productivity under drought stress is related to the shortage of water in soil, which results in impairment of photosynthesis, including negative effects on the thylakoid membrane function. A reported effect is an altered ratio between photosystem I and II (PSI and PSII), which is probably relieved by adjustments of the LHCII antenna system to balance excitation and electron transport. Fine tuning of excitation and electron flow is expected to be vital especially under natural conditions characterized by light intensity fluctuations. The effects of fluctuating light, currently addressed by basic photosynthetic research, are ignored in crop plants exposed to stress. Since chlorophyll-deficient wheat mutant lines show variable degrees of LHCII antenna depletion, they are a suitable experimental material to test the hypothesis of an antenna involvement in effective photosystem regulation under drought stress. Based on extensive consultations with Prof. Marian Brestic, leader of the Slovak PlantScreen Phenotyping Unit (SPPU) at the Slovak University of Nitra (SUA), this research project exploits the availability of three + three chlorophyll-deficient mutant lines of Triticum aestivum L. and T. durum L., for which an extensive dataset has recently been compiled regarding fundamental photosynthetic properties. In particular, an increased risk of PSI photoinhibition was revealed in the mutants, caused by an over-reduced PSI acceptor side. During an 8-week-long access to the SPPU, plants belonging to the 8 wheat lines will be cultivated under 4 combinations of 2 variables: well watering vs drought stress; steady light vs fluctuations of high light. The plan covers a period of 7 weeks experimentation. The first two weeks will be used to acclimate plants in SPPU under two regimes of watering and to set up the treatments with fluctuating light, besides doing preliminary tests with the SPPU equipment. Then, for 5 weeks the automated plant phenotyping will be done daily (RGB scans, chlorophyll fluorescence imaging, hyperspectral imaging). Some additional handheld measurements of photosynthetic parameters will be done at variable time intervals. Expected results are a better understanding of PSI/PSII/antenna interplay under drought stress and fluctuating light, an improved efficiency of stress-tolerance screening in crops under a controlled environment, and phenotyping datasets to be made freely available to the scientific community.