An optical interferometric technique for assessing ozone induced damage and recovery under cumulative exposures for a Japanese rice cultivar

Exposure to ozone (O₃) causes reduction both in the growth and yield of rice (Oriza sativa L.). Commonly used Chlorophyll fluorescent measurements are not sensitive enough for short term exposure of O₃ aiming an immediate assessments. Such a conventional method typically needs exposure over a few days to detect the influence. As an alternative method, we proposed a novel non-invasive, robust, real-time, optical Statistical Interferometric Technique (SIT) to measure growth at an accuracy of 0.1 nm with a commonly consumed Japanese rice cultivar, Koshihikari. In the present study, we have conducted a repetitive O₃ exposure experiment for three days under three different concentrations of 0 nl l^-1 (control), 120 nl l^-1, and 240 nl l^-1, to investigate the damage and recovery strengths. As a measure to assess the effect and recovery from three consecutive day exposures of O₃, we measured the elongation rate (nm mm^-1 sec^-1) every 5.5 sec for 7 hours, and it revealed nanometric elongation rate fluctuations or Nanometric Intrinsic Fluctuations (NIF). Comparing the standard deviation (SD) of normalized nanometric intrinsic fluctuations (NNIF), which was normalized by that before the exposure, we found that drastic reductions under both 120 nl l^-1 and 240 nl l^-1 O₃ concentrations. Reduction percentages were large under high O₃ concentration of 240 nl l^-1 indicating the possibility of irreversible effect. However exposure to 120 nl l^-1 of O₃ showed recovery on the 2^nd and 3^rd days. While SIT did reveal immediate effect based on an observation for a few hours, the visible foliar effect could be observed only after a week. Hence, the technique could provide a way for fast assessment of effect and recovery due to cumulative exposure of O₃ and hence the tolerance as well as the vitality of plant.