Sclerotial Formation of Polyporus umbellatus by Low Temperature Treatment under Artificial Conditions

Abstract

Background Polyporus umbellatus sclerotia have been used as a diuretic agent in China for over two thousand years. A shortage of the natural P. umbellatus has prompted researchers to induce sclerotial formation in the laboratory.Methodology/Principal Finding P. umbellatus cultivation in a sawdust-based substrate was investigated to evaluate the effect of low temperature conditions on sclerotial formation. A phenol-sulfuric acid method was employed to determine the polysaccharide content of wild P. umbellatus sclerotia and mycelia and sclerotia grown in low-temperature treatments. In addition, reactive oxygen species (ROS) content, expressed as the fluorescence intensity of mycelia during sclerotial differentiation was determined. Analysis of ROS generation and sclerotial formation in mycelia after treatment with the antioxidants such as diphenyleneiodonium chloride (DPI), apocynin (Apo), or vitamin C were studied. Furthermore, macroscopic and microscopic characteristics of sclerotial differentiation were observed. Sclerotia were not induced by continuous cultivation at 25°C. The polysaccharide content of the artificial sclerotia is 78% of that of wild sclerotia. In the low-temperature treatment group, the fluorescent intensity of ROS was higher than that of the room temperature (25°C) group which did not induce sclerotial formation all through the cultivation. The antioxidants DPI and Apo reduced ROS levels and did not induce sclerotial formation. Although the concentration-dependent effects of vitamin C (5–15 mg mL−1) also reduced ROS generation and inhibited sclerotial formation, using a low concentration of vitamin C (1 mg mL−1) successfully induced sclerotial differentiation and increased ROS production.Conclusions/SignificanceExposure to low temperatures induced P. umbellatus sclerotial morphogenesis during cultivation. Low temperature treatment enhanced ROS in mycelia, which may be important in triggering sclerotial differentiation in P. umbellatus. Moreover, the application of antioxidants impaired ROS generation and inhibited sclerotial formation. Our findings may help to provide new insights into the biological mechanisms underlying sclerotial morphogenesis in P. umbellatus.

Oxalic acid and sclerotial differentiation of Polyporus umbellatus

“…During P. umbellatus sclerotial formation, the fungus relies on antioxidant mechanisms to neutralize the excessive reactive oxygen species26. On one hand, the sclerotial exudate consists of fatty acids, ammonia, proteins and various enzymes, including the antioxidant enzymes peroxidase and catalase31.…”

“…4, panel A) under the same cultivation conditions. This is probably because the P. umbellatus mycelia formed sclerotia to adapt to the hyperoxidant conditions by increasing the oxalic acid concentration and avoiding the oxidative stress state2638. It is generally reasonable to assume that oxalic acid serves as an antioxidant during sclerotial differentiation.…”

“…Previously, oxalate crystals were observed during the cultivation of sclerotia under artificial conditions using scanning electronic microscopy (SEM)26, begging the question: what roles does the endogenous oxalic acid play during P. umbellatus mycelial growth and sclerotial formation? This question sparked our interest in determining the endogenous oxalic acid levels in different cultivation mediums, mycelia, sclerotia and the sclerotial exudate of P. umbellatus .…”

Hypovirulence of Sclerotium rolfsii Caused by Associated RNA Mycovirus

“…The formation and development of sclerotia are associated with a series of signaling genes, such as reports in S. sclerotiorum that the microbial opsin homolog gene sop1 was involved in sclerotial development and virulence of this fungus (Lyu et al, 2015). Previous studies have shown that sclerotial development in some fungi was associated with and affected by a series of physical, chemical or nutritional factors, such as low temperatures, oxidative stress and low PH (Chet and Henis, 1975; Choi et al, 2002; Xing et al, 2013). In addition, the cAMP and the mitogen-activated protein kinase (MAPK) signal pathways are involved in sclerotial development of S. sclerotiorum (Rollins and Dickman, 1998; Chen et al, 2004), and this process also requires calcineurin in an oxalic-acid-independent manner (Harel et al, 2006).…”

Guangdong Herbal Tea Attenuates Restraint Stress-provoked Liver and Kidney Damage in Mice via Activation of the Nrf2/ARE Signaling Pathway

“…The triterpenoid concentration was detected with ursolic acid as the standard product by vanillin colorimetry at 546nm [37]. The polysaccharide content was measured using the phenol-sulfuric acid method at 490nm based on a standard curve for glucose [38].…”