Table_1_Level of Sulfite Oxidase Activity Affects Sulfur and Carbon Metabolism in Arabidopsis.DOCX

Molybdenum cofactor containing sulfite oxidase (SO) enzyme is an important player in protecting plants against exogenous toxic sulfite. It was also demonstrated that SO activity is essential to cope with rising dark-induced endogenous sulfite levels and maintain optimal carbon and sulfur metabolism in tomato plants exposed to extended dark stress. The response of SO and sulfite reductase to direct exposure of low and high levels of sulfate and carbon was rarely shown. By employing Arabidopsis wild-type, sulfite reductase, and SO-modulated plants supplied with excess or limited carbon or sulfur supply, the current study demonstrates the important role of SO in carbon and sulfur metabolism. Application of low and excess sucrose, or sulfate levels, led to lower biomass accumulation rates, followed by enhanced sulfite accumulation in SO impaired mutant compared with wild-type. SO-impairment resulted in the channeling of sulfite to the sulfate reduction pathway, resulting in an overflow of organic S accumulation. In addition, sulfite enhancement was followed by oxidative stress contributing as well to the lower biomass accumulation in SO-modulated plants. These results indicate that the role of SO is not limited to protection against elevated sulfite toxicity but to maintaining optimal carbon and sulfur metabolism in Arabidopsis plants.

含钼辅因子的亚硫酸盐氧化酶（sulfite oxidase, SO）是植物抵御外源性有毒亚硫酸盐的关键防御因子。已有研究表明，在经历长期暗胁迫的番茄植株中，SO活性对于清除暗诱导产生的内源性亚硫酸盐积累、维持最优碳硫代谢水平至关重要。目前针对SO与亚硫酸盐还原酶（sulfite reductase）对不同浓度硫酸盐及碳源的直接暴露响应的研究仍较为匮乏。本研究以野生型拟南芥（Arabidopsis）、亚硫酸盐还原酶及SO调控植株为实验材料，通过设置过量或限量的碳、硫供应条件，证实了SO在拟南芥碳硫代谢中的核心作用。与野生型植株相比，SO功能受损突变体在施加低浓度或过量蔗糖（sucrose）、硫酸盐（sulfate）后，生物量积累（biomass accumulation）速率显著降低，且伴随亚硫酸盐水平升高。SO功能受损会导致亚硫酸盐流向硫酸盐还原通路，进而造成有机硫过度积累。此外，亚硫酸盐水平升高会诱发氧化应激（oxidative stress），进一步加剧SO调控植株的生物量积累下降。上述结果表明，SO的生物学功能不仅局限于抵御升高的亚硫酸盐毒性，还可维持拟南芥体内最优的碳硫代谢平衡。