Changes in Mannitol Content, Regulation of Genes Involved in Mannitol Metabolism, and the Protective Effect of Mannitol onVolvariella volvaceaat Low Temperature

Abstract

The mechanism of autolysis of Volvariella volvacea (V. volvacea) at low temperature has not been fully explained. As mannitol is among the most important osmotic adjustment substances in fungal resistance, this study sampled mycelia of strains V23 and VH3 treated at 0°C for 0, 2, 4, 8, and 10 h to analyze changes in intracellular mannitol content by high-performance anion chromatography with pulsed amperometric detection (HAPEC-PAD). Reverse transcription quantitative PCR (RT-qPCR) analysis was applied to assess differences in the transcript levels of genes associated with mannitol metabolism under low-temperature stress. A mannitol solution was added to cultures of V. volvacea fruiting bodies, and effects on the hypothermic resistance of these organs were explored by evaluating variations in sensory properties during cryogenic storage after harvest. The results suggested that in the initial stage of low-temperature treatment, intracellular mannitol was largely catabolized as an energy storage material and the expression of genes encoding enzymes involved in synthetic reactions was inhibited. However, low-temperature resistance was induced with further treatment, with activation of mannitol synthesis and inhibition of degradation; the cells accumulated mannitol, leading to osmoregulation. No significant elongation of V. volvacea fruiting bodies during storage at 4°C was observed, and these organs tended to shrink and collapse. The sensory quality of mannitol-treated fruiting bodies was much better than that of control fruiting bodies. Application of a mannitol solution at the cultivation stage of V. volvacea somewhat improved the low-temperature resistance of the fruiting bodies, verifying the correlation between mannitol and resistance to this stress in V. volvacea. The results of this study lay a foundation for a deeper understanding of the autolysis mechanism of V. volvacea, providing technical support for increasing the cryopreservation time of this species and extending the postharvest shelf life of its fruiting bodies. In addition, the mechanism underlying the low-temperature tolerance of the VH3 strain should be further explained at the molecular level.

A Comparative Study of Lactarius Mushrooms: Chemical Characterization, Antibacterial, Antibiofilm, Antioxidant and Cytotoxic Activity

“…First, because they affect the taste of edible mushrooms (by enhancing the sensation of sweet taste) and because the amount of sugar is an important indicator of storage and preservation conditions [ 31 , 32 ]. In addition, mannitol, the most abundant sugar in most mushrooms, plays an important role in regulating osmotic pressure in cells and removing RONS [ 33 ]. For example, Zhao et al [ 33 ] showed that under stress conditions such as low temperature, the synthesis of mannitol was inhibited at the initial stage of Volvariella volvacea growth.…”

The Response of Volvariella volvacea to Low-Temperature Stress Based on Metabonomics

“…Temperature plays a decisive role in the growth, storage and quality of V. volvacea ( Zhao et al, 2018 , 2019a ). V. volvacea is not resistant to low temperature, and its mycelia easily undergo autolysis, causing the fruiting bodies to wilt, become liquefied, turn brown, and rot.…”

Successive mycelial subculturing decreased lignocellulase activity and increased ROS accumulation in Volvariella volvacea

“…At the same time, low temperatures below 15°C can negatively impact its growth while causing chilling damage to its fruiting body, and routine storage temperatures (4°C) will cause V. volvacea cryogenic autolysis ( Bao et al, 2013 ). Therefore, V. volvacea cannot be stored at low temperatures like other edible mushrooms, which makes it strain degradation particularly serious ( Zhao et al, 2019 ). Regular subculturing is a commonly applied approach to preserve and rejuvenate various fungal species ( Ayala-Zermeno et al, 2017 ), but excessive subculturing may also induce the biosynthesis of toxins, DNA methylation and chromosome remodeling as shown in Cordyceps militaris ( Yin et al, 2017 ; Xin et al, 2019 ), thereby leading to strain degradation that hinders industrial applications.…”