PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Excitation pressure dependent development of non-radiative charge recombination pathways in wild type and F2 mutant of barley. Alexander Ivanov^*,1, Marianna Krol¹, Prafullachandra Sane¹, Dominic Rosso ¹, Autar Mattoo², Isabelle Booij-James², Norman Huner¹, ¹ Department of Biology, London, Ontario, Canada² USDA-ARS Vegetable Laboratory, Beltsville, Maryland, USA

ABSTRACT- Thylakoid protein phosphorylation plays an important role in the regulation of light harvesting processes, energy distribution and the turnover of thylakoid proteins under changing environmental conditions. Wild type (WT) and F2 barley mutant were grown at temperature/irradiance (^oC/ moles m^-2 s^-1) regimes corresponding to low (20/250, 5/50) and high (20/800, 5/250) excitation pressure of PSII. The highest level of D1 phosphorylation in WT barley plants occurred under conditions of high excitation pressure (5/250 and 20/800). This was accompanied by lower capacity for state I - state II transitions compared to plants grown under low excitation pressure (20/250 and 5/50). In contrast, F2 mutant plants did not perform any state transitions and exhibited much lower level of D1 phosphorylation under all conditions compared to WT. Thermoluminescence measurements of PSII revealed that S₂/S₃Q_B^- recombinations were shifted to lower temperatures in WT and F2 plants acclimated to high excitation pressure. This corresponded to lower activation energy of the S₂Q_B^- peak, thus narrowing the gap in the redox potentials between Q_A and Q_B electron acceptors and increasing the probability for reaction centre quenching of excess light. In addition, F2 mutant demonstrated a substantial shift of S₂Q_A^- to higher temperatures, thus again narrowing the gap between S₂Q_B^- and S₂Q_A^- compared to WT under all growth conditions. However, this effect was more pronounced under conditions of high excitation pressure. In this report we present evidence to suggest that the lack of capacity for state transitions and reduced capacity for xanthophyll cycle-dependent non-photochemical quenching (NPQ) in F2 mutant could be compensated by increased probability for reaction center quenching. The alterations in the structure of photosynthetic apparatus in F2 mutant and the role of LHCII in inducing higher probability for alternative non-radiative charge recombination pathways will be discussed.

KEY WORDS: Chlorina F2 Mutant, Excitation Pressure, Thermoluminescence, D1 Phosphorylation