Section of Genetics, Cell Biology and Development, Department of Biology, University of Patras, 26100-Patra, Greece.
Mycologia. 2003 Mar-Apr;95(2):308-16.
Certain phytopathogenic fungi differentiate by forming sclerotia by an unclear biochemical mechanism. We have proposed that sclerotial differentiation might be regulated by fungal antioxidant defense. Part of this defense might be ascorbic acid, which in its reduced form is a well-known antioxidant. This natural antioxidant was studied in Sclerotium rolfsii in relation to oxidative-growth conditions, developmental stages and strain-differentiating ability. The transition of a sclerotial strain from the undifferentiated to the differentiated stage was accompanied by a sharp shift in the ratio of reduced/oxidized ascorbate toward the oxidized form. Ascorbate profiles and lipid peroxidation levels were different between the sclerotial strain grown under high- and low-oxidative stress conditions, as well as between a nonsclerotial S. rolfsii strain grown under high-oxidative stress conditions. In addition, the ratio of reduced/oxidized ascorbate in the nonsclerotial strain remained unchanged throughout growth. Lipid peroxidation under high-oxidative stress conditions in sclerotial S. rolfsii colonies one day before differentiation was 3.6-fold higher than in same-day colonies of this strain grown under low-oxidative stress conditions and 2.5-fold higher than in similar-day colonies of the nonsclerotial strain grown under high-oxidative stress conditions. Exogenous ascorbate caused a concentration-dependent reduction of lipid peroxidation and a proportional inhibition of the degree of sclerotial differentiation in the sclerotial strain grown under high-oxidative stress conditions by lowering its lipid peroxidation before differentiation to levels similar to the strain grown under low-oxidative stress conditions and to the nonsclerotial strain. Ascorbic acid might be produced by the sclerotial strain to reduce oxidative stress, although less efficiently than the nondifferenting strain. The data of this study support our theory that oxidative stress might be the triggering factor of sclerotial differentiation in phytopathogenic fungi.
某些植物病原真菌通过一种不明的生化机制形成菌核来进行分化。我们提出菌核分化可能受到真菌抗氧化防御的调节。这种防御的一部分可能是抗坏血酸，其还原形式是一种众所周知的抗氧化剂。在 Sclerotium rolfsii 中，我们研究了这种天然抗氧化剂与氧化生长条件、发育阶段和菌株分化能力的关系。从未分化到分化阶段的菌核菌株的转变伴随着还原/氧化抗坏血酸比向氧化形式的急剧转变。在高氧化应激和低氧化应激条件下生长的菌核菌株以及在高氧化应激条件下生长的非菌核 S. rolfsii 菌株之间，抗坏血酸图谱和脂质过氧化水平不同。此外，非菌核菌株的还原/氧化抗坏血酸比在整个生长过程中保持不变。分化前一天高氧化应激条件下菌核 S. rolfsii 菌落中的脂质过氧化水平比低氧化应激条件下相同日龄菌株的脂质过氧化水平高 3.6 倍，比高氧化应激条件下相同日龄非菌核菌株的脂质过氧化水平高 2.5 倍。外源性抗坏血酸可导致脂质过氧化的浓度依赖性降低，并通过在高氧化应激条件下生长的菌核菌株降低分化前的脂质过氧化水平，使其达到与低氧化应激条件下生长的菌株相似的水平，从而使菌核菌株的分化程度呈比例抑制。菌核菌株可能产生抗坏血酸以减轻氧化应激，尽管效率低于未分化的菌株。本研究的数据支持我们的理论，即氧化应激可能是植物病原真菌菌核分化的触发因素。
