Specific features of light energy conversion in biological photo-elements

The study aims to analyze the influence of structural changes in thylakoid membranes, induced by foliar fertilization, on energy transfer in the photosynthetic system using fluorescence spectroscopy methods. Control and experimental plant groups were established for the research. Structural analysis was performed using transmission electron microscopy (TEM), which provided images of ultra-thin leaf sections followed by quantitative assessment of the morphometric parameters of chloroplast grana. Micrograph processing and statistical analysis were carried out using artificial intelligence-based software (GRANA). The functional state of the photosystems was evaluated based on chlorophyll fluorescence spectra were obtained using a spectrofluorometer in a 90-degree geometry mode upon excitation with light at a wavelength of 425 nm. Results. It was found that the application of foliar fertilization leads to a statistically significant structural reorganization of the thylakoid membranes. The experimental samples showed a reduction in the median grana area by ~ 38 % and their perimeter by ~ 16 %, indicating denser and more ordered packing. Simultaneously, fluorescence spectroscopy revealed a narrowing of the peak half-width corresponding to photosystem II by 1.8 nm (8%) in the treated plants. This change indicates a reduction in the energetic heterogeneity of the antenna complexes and an increase in the efficiency of excitation energy transfer. Conclusion. Based on the comprehensive studies, it was concluded that the primary mechanism of action of foliar fertilizers is the optimization of the thylakoid membrane nanostructure, which, within the concept of photonic crystals, creates more favorable conditions for light energy conversion. An increase in the regularity of the ultrastructural organization was demonstrated. The obtained results confirm the potential of using fluorescence spectroscopy as a rapid, non-invasive method for diagnosing the physiological state of plants in closed space systems.