The same result was recorded in the D-Pantothenic acid sodium treated Saprolegnia spores. The decrease in the mitochondrial density was directly proportional with the exposure time, when different time points were used. The reduction and disorganization in spore/hyphal mitochondria following boric acid treatment is supporting the hypothesis that mitochondrial toxicity might be one of its primary modes of action. Mitochondrial membrane potential is critical for maintaining many mitochondrial processes including ATP synthesis and the control of ROS generation; its disturbance could diminish energy production. Thus, changes in DYm were also followed using the fluorescent dye. Hyphae from non-treated controls showed intense fluorescence as TMRE dye accumulates in active mitochondria due to their relative negative charge. On the other side, boric acid treated hyphae showed a drop in the fluorescence intensity as the inactive mitochondria with decreased membrane potential fail to sequester TMRE. Reactive oxygen species are important signaling molecules normally present in cells, however, their accumulation under pathological conditions leads to oxidative stress. Therefore, ROS with DYm can be used as an indicator of the cell physiological status and the function of the mitochondria. This might explain the high accumulation of ROS in some of the treated hyphae with a lower mitochondrial activity than the non-treated ones. Regarding the nucleus, no obvious changes were observed on the nuclear morphology of the treated spores examined by TEM. The nuclear mitosis has been described before in Saprolegnia spp., thus, the Tulathromycin B effect of the boric acid on the nuclear division was followed using the nucleic acid specific dye DAPI. Spores kept in water were able to develop germlings that elongated. Almost all the organelle-containing cytoplasm in the cyst body was able to relocate to the developed germlings as described before and the nucleus was able to divide. In contrast, the nuclei of the treated spores failed to divide when they were examined with the CLSM. This effect of the boric acid on the nuclear division might be correlated to a reduction in DNA synthesis as suggested by Ku et al., apparently due to the absence of sufficient energy related to the impairment of normal mitochondrial function. The metabolic activity and proliferation of treated spores were also investigated using an MTS assay. This assay relies on the metabolism of the MTS reagent into formazan by dehydrogenase enzymes. It thereby gives an indication on the functional state and integrity of the mitochondria. The significant reduction of the MTS reagent in the non-treated water control group following 24 h incubation indicates their high mitochondrial metabolic and proliferation activity. In contrast, the boric acid treated group has almost similar results as the positive control group treated with bronopol. The integrity of the membrane of treated Saprolegnia spores was interpreted by using a propidium iodide stain. The fact that the treated spores did not take up the dye nor germinate is suggesting that boric acid does not have a direct effect on treated spore membranes at the tested concentration which also suggests that BA could cause slow loss of viability. All in all our study is explaining the toxic activity of boric acid on Saprolegnia by its effect on mitochondrial function and the inhibition of the general metabolism. Future investigations for the possibility of combining boric acid with potential anti-Saprolegnia candidates targeting cellular components other than mitochondria should be considered. Recent studies show that stem/progenitor cells may regenerate cardiac tissue directly by inducing neovasculogenesis and cardiogenesis.