Using statistical interferometry technique (SIT), a highly sensitive interferometry technique developed in our laboratory, we reported about the existence of nanometric intrinsic fluctuations (NIF) in a variety of plants. SIT permits noncontact, noninvasive, and fast detection of plant growth fluctuations in subnanometer scale. We propose the application of NIF to investigate the effect of heavy metal, cadmium, on growth dynamics of Chinese chive (Allium tuberosum). NIFs of leaves were observed for 3 days under four different concentrations of CdCl2: 0, 0.001, 0.01, and 0.1 mM. Results showed significant reduction of NIFs within 4 h for all Cd concentrations, and there was a further decrease with the exposure time of Cd under 0.1 and 0.01 mM. In addition, under 0.001 mM, a significant recovery could be observed after a rapid reduction in the first 4 h. As a comparison, measured antioxidative enzymes increased with increasing Cd concentration. However, no significant increase could be seen within the initial 4 h under a smaller concentration of 0.001 mM as seen for NIFs. The results imply that NIF can be used as an indicator for heavy metal stress on plants as well as it can be more sensitive to detect the influence of smaller Cd amounts on plants at an early stage.
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