Photosynthetic starch characterization using terahertz spectroscopy with a bolometer

Recent studies have demonstrated that terahertz spectroscopy can identify starch absorption peaks in solid pellets containing powdered plant samples with minimal interference of other plant matrices. Here, we applied this analytical method to assess photosynthetic capacity in plant leaves with a relatively low starch content. To monitor starch produced through photosynthesis, rice leaves were measured in the frequency range of 3.0-9.5 THz using a Fourier-transform spectrometer equipped with a bolometer. A starch over-accumulation mutant (α-glucan water dikinase1) and wild type (cv. Nipponbare) were harvested after 2 and 3 months of cultivation. In the terahertz measurements, all leaves exhibited an absorption peak at 9.0 THz attributed to starch and the peak intensities were consistent with starch contents obtained by chemical analysis. Furthermore, correlations were found between second derivative signals and starch content (R² = 0.86-0.87). However, a higher accuracy model was developed using peak height calculated using the peak top at 9.0 THz and a baseline between 8.65 and 9.35 THz (R² = 0.91). These results indicate that just three frequencies are sufficient on behalf of the full range spectra, suggesting the feasibility of a starch sensor for future applications. Therefore, terahertz technology can serve as a valuable analytical method for assessing starch accumulation and photosynthetic capacity in unpurified plant leaves.