## 4 Discussion  
The current study investigates the application of biospeckle OCT to monitor the dynamic changes during seed germination and under the presence of AMD. The structure of a seed changes dynamically during germination. Thus, in practice, OCT, a technique that visualizes structures, should be capable of monitoring structural changes. However, because the structural changes are random, generating random changes in OCT intensity, we proposed to use biospeckle OCT for investigating seed germination under AMD.  
Furthermore, the germination could be affected by many factors such as humidity, light levels, and environmental stress. AMD, one such environmental stress, can affect the metabolic rate, organelle morphology, and locomotion rate of seeds and plants [32]. During germination, the structure of the seed changed dynamically, and this was dependent on the pH of the medium used for germination.  
AMD has the effect of changing the pH of the medium and, thus, becomes an environmental stress, introducing physiological changes during seed germination. We expect such physiological changes would lead to changes in scatterers or organelles within the seed.  
As possible scatterers, there are several internal microstructures such as mitochondria, Golgi bodies, and possibly chloroplasts within the seed. The movement of such structures from cell growth, cell division, and cytoplasmic flow, could contribute to the slow-to-rapid changes that would lead to changes in the intensity of the random interference patterns; in other words, changes in biospeckles observed in the bOCT images. Therefore, external environmental stress can affect those movements [35; 36; 37], leading to the difference in bOCT images of the seeds treated with AMD at different concentrations.  
[PERSON] et al. [38] studied the effect of different pH levels (3.0-6.0) on germination and seedling growth of groundnuts. They found that a low pH did not affect seed germination but significantly reduced seedling survival and growth. The results on seedling growth are consistent with our findings. However, low-pH AMD accelerated the germination of kaikware seeds in this study. There are two possible reasons: Low pH accelerates the softening of the hard seed coat of kaikware, allowing water to enter the endosperm more quickly. The water enters and softens the seed coat, and oxygen penetrates more easily, enhancing the embryo's respiration, making it easy for the embryo to break through the seed coat [39]. In addition, other studies have shown that FeSO\({}_{4}\) can promote seed germination [40; 41].  
The elements Fe and S contained in AMD are essential elements for plants, but the results of bOCT at 48 h and biomass after 7 days showed that the plants under AMD  
Figure 9: Fresh weight, dry weight, and water content of Kaiware daikon under different treatments (different letters, a b c, represent statistical differences between treatments; the error bar represents standard deviation; Fisher-LSD multiple comparison; \(p<0.05\) level; number N = 6).  
treatment were in poor condition. [PERSON] et al. [42] studied the effect of different pH nutrient solutions on ginger, cassava, maize, wheat, French beans, and tomatoes. The results showed that the damaging effects of low pH on the root system were observed in all species. At pH 3.3, roots of all species were shortened, thickened, relatively few in number, turned brown or dark gray in color, and the lateral root growth was severely inhibited. The roots are an essential part of nutrient transport, and poor root growth will affect the growth of shoots. This is consistent with the findings of the present study that the negative effect of AMD on seedlings is higher levels of AMD or lower pH affecting macro growth. Our studies with bOCT also suggest low pH can have a significant effect on the earlier stages of germination, thus possibly shortening overall duration requirements for the case of kaiware daikon species.