Biospeckle Optical Coherence Tomography (bOCT) reveals variable effects of acid mine drainage (AMD) on monocot and dicot seed germination

Acid mine drainage (AMD) is generated during the mineral extraction process. AMD contaminates farmland and rivers, so it makes sense to study the effects of AMD on crops. Since the conventional methods for studying plant responses to environmental stress are damaging and time-consuming, we propose the Biospeckle OCT (bOCT) method to evaluate the response of plants to AMD in a rapid and non-invasive way. In this study, we selected rice plant and soybean as experimental subjects. The seeds were exposed to 40 and 80 ml/L of simulated AMD solution, and the seed condition was monitored by bOCT. OCT images of the seeds were obtained at a speed of 10 frames per second for a few tens of seconds. For each pixel of the OCT structural images, the contrast across the temporal axis was calculated to give bOCT images. Meanwhile, we measured the root shoot length of rice and soybean after growing in AMD as a comparison. It was found that bOCT images clearly distinguished the changes in biological activities of seeds due to 40 and 80 ml/L of AMD treatments from those of control within much shorter time, 48 hours and 72 hours for soybean and rice, respectively, compared to the conventional method that failed to show any changes within the same time. And The seedling growing status of soybean and rice after 7 and 10 days showed the same trend as the bOCT results, respectively. This suggests that the proposed bOCT method can reveal the different responses of soybean and rice to different concentrations of AMD at a very early stage. This technique may be able to provide a reference indicator for studying plant response to environmental stress, and it is efficient and non-invasive.