High speed and high precision optical interferometric technique to investigate instantaneous growth related changes of plant leaves

Instantaneous growth related changes of leaves of Radish, Soybean and rice plants were investigated with a high-speed and ultra-high accuracy optical interferometer. The interferometer, called statistical interferometer, SIT (Statistical Interferometric Technique) is a real-time, non-contact, and robust one and has a subnanometric accuracy and can measure leaf elongation changes every 500 ms. SIT revealed the existence of nanometric fluctuations in the elongation of leaves. Control experiments with dead and mature leaves did indeed establish the existence of null or smaller standard deviations in the fluctuations in contrast to the large deviations obtained for young and healthier leaves. Moreover, the standard deviations of the fluctuations were found to be sensitive to environment of ozone(O3), a secondary atmospheric pollutant. Long term O3 exposure with Radish and Soybean leaves led to a decrease in the standard deviations of nanometric fluctuations with increase in O3 concentrations which correlated with a decrease of gas exchange measures. Under short term O3 exposures for 3 h with two Japanese rice cultivars, cv. Koshihikari and cv. Fusaotome that are known to have varying O3 tolerance made the nanometric fluctuations to decrease in comparison to gas exchange measures which showed no variation. The fluctuations could also differentiate the cultivar's sensitivity to O3 with cv. Koshihikari showing a drastic reduction in comparison to cv. Fusaotome. The results suggest that the nanometric fluctuations may possibly relate to the life maintaining physiological state of the plant and thus may act as an indicator of the vitality of the plant.