The Role of Light-Harvesting Complex II Organization in the Efficiency of Light-Dependent Reactions in the Photosynthetic Apparatus of Pisum sativum L.

In this study, the functions of the photosynthetic machinery were evaluated using chlorophyll <i>a</i> fluorescence technique (PAM and JIP test) in pea plants (<i>Pisum sativum</i> L. cv Borec) and its LHC II oligomerization variants (mutants <i>Costata 2</i>/<i>133</i> and <i>Coeruleovireus 2</i>/<i>16</i>). The oligomeric forms of LHCII increased in the following order: <i>Costata 2</i>/<i>133</i> < Borec wt < <i>Coeruleovireus 2</i>/<i>16</i>. Data revealed that the mutant with higher LHCII oligomerization (<i>Coeruleovireus 2</i>/<i>16</i>) at low light intensity (LL, 150 µmol photons/m²·s) exhibited the following: (i) decreased energy dissipation and increased electron transport efficiency; (ii) higher reaction center density; (iii) increased amounts of the open reaction centers (qp) and their excitation efficiency (Φexc); and (iv) influenced the reoxidation of Q_A^-, alleviating its interaction with plastoquinone. These effects enhanced photosynthetic performance related to PSII photochemistry (PI_ABS) and overall photosynthetic efficiency (PItotal). High light intensity (HL, 500 µmol photons/m²·s) caused a reduction in open reaction centers (qp), excitation efficiency (Φexc), photochemical energy conversion of PSII (Φ_PSII), maximum efficiency of PSII photochemistry in light (Fv'/Fm'), and linear electron transport via PSII, with more pronounced effects observed in membranes with a lower degree of LHCII oligomerization (<i>Costata 2</i>/<i>133</i>). This study provides novel experimental evidence for the pivotal role of the LHCII structural organization in determining the efficiency of light-dependent reactions of photosynthesis.