Nanometer accuracy statistical interferometric technique in monitoring the short-term effects of exogenous plant hormones, auxin and gibberellic acid, on rice plants

Statistical interferometric technique (SIT) is a highly sensitive, high speed non-contact, and non-destructive optical technique developed by our group capable of measuring instantaeoues sub-nanometer displacements. SIT applied to plant leaf elongation revealed nanometric intrinsic fluctuaitons (NIF) that are robust and sensitive to variations in the environment making NIF as a measure of healthiness of the plants. In this study, exogenous plant hormones, auxin (2,4-dichlorophenoxyacetic acid-2,4-D), and gibberellic acid (GA₃), along with an auxin transport inhibitor 2,3,5-triiodobenzoic acid-TIBA, that affect plant growth were used to investigate their effects on NIF. Rice (Oriza sativa) seedlings were used, and their roots were exposed to 1, 2, and 4 µM 2,4-D, and the auxin transport inhibitor, TIBA, of 10, and 20 µM for 22 h and GA₃ solution of different concentrations of 10, 40, and 100 µM for 5 h. Results showed significant increment in NIF for 1 µM and reduction for 4 µM 2,4-D while applicaiton of both 10, and 20 µM TIBA led to reduction in NIF. On the other hand, significant increment in NIF for 40 µM, and a significant reduction at a higher concentration of 100 µM for 5 hours of GA₃ were also observed in comparison to those of control. Our results indicate that NIF as revealed by SIT could show both the positive and negative effects depending on the concentration of exogenous hormones, and transport inhibitors. Results suggest that SIT could be a valuable tool being sensitive enough to speedily assess the effects of plant growth hormones.