Abstract
The effect of temperature shift on Polyporus umbellatus sclerotial development was investigated. Micromorphology of the sclerotia was observed by using scanning electron microscopy (SEM). The cytochemical localization of H2O2 expressed as CeCl3 deposition at the subcellular level was observed by using transmission electron microscopy (TEM). Nox gene expression in sclerotia and mycelia was detected by quantitative real-time PCR (qRT-PCR) analysis. In addition, superoxide dismutase (SOD) and catalase (CAT) specific activities increased during sclerotial development and decreased after the antioxidant diphenyleneiodonium (DPI) was used. Results indicated that the temperature shift treatment induced P. umbellatus sclerotial formation. Compared with the mycelia, the Nox gene was respectively upregulated by 10.577-, 30.984- and 25.469-fold in the sclerotia of SI, SD and SM stages respectively. During the sclerotial formation, H2O2 accumulation was observed in the cell walls or around the organelle membranes of the mycelial cells. The antioxidant DPI decreased the generation of H2O2 in mycelial cells. The specific activity of SOD and CAT levels was decreased significantly by DPI. The activity of the two antioxidant enzymes in the mycelia increased much more during sclerotial formation (p < 0.05). Oxidative stress was closely associated with sclerotial development in P. umbellatus induced by temperature shift treatment.
Highlights
Polyporus umbellatus (Pers.) Fr. is one of the traditional medicinal mushrooms, of whose sclerotia exhibiting diverse pharmacological effects [1]
After being cultivated for about 30 days at 8 °C, P. umbellatus mycelia began to inflate into spherical, oval or irregular shapes, accompanied by interwoven hyphae in certain spots of the mycelium, which indicated the appearance of sclerotial initiation (SI) (Figure 1b)
As our study showed, compared with the mycelia cultivated in the control group, the superoxide dismutase (SOD) and the CAT specific activities of the mycelia cultured in the temperature shift group increased during the period of sclerotial initiation stage and reduced a little afterwards, and maintained a high level throughout the sclerotial development process (Figures 5 and 6)
Summary
Polyporus umbellatus (Pers.) Fr. is one of the traditional medicinal mushrooms, of whose sclerotia exhibiting diverse pharmacological effects [1]. Due to a decreased abundance in natural sources, researchers have made great efforts to produce sclerotia in the laboratory. Sclerotia are compact bodies of aggregated hyphae which can survive for long periods under unfavorable conditions such as starvation, coldness, nutrition depletion, etc. Environmental factors can affect fungal growth and sclerotial formation. It has been reported that the carbon source and growth medium initial pH affect the sclerotial formation of P. umbellatus [3]. We found that exposure to low temperatures increased the levels of reactive oxygen species (ROS) and rendered
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