Table_1_Physiological and Proteomic Analysis of Different Molecular Mechanisms of Sugar Beet Response to Acidic and Alkaline pH Environment.DOCX

Soil pH is a major constraint to crop plant growth and production. Limited data are available on sugar beet growth status under different pH conditions. In this study, we analyzed the growth status and phenotype of sugar beet under pH 5, pH 7.5, and pH 9.5. It was found that the growth of sugar beet was best at pH 9.5 and worst at pH 5. The activities of superoxide dismutase (SOD) and peroxidase (POD) in leaves and roots increased as pH decreased from 9.5 to 5. Moreover, compared with pH 9.5, the levels of soluble sugar and proline in leaves increased significantly at pH 5. To explore the mechanisms of sugar beet response to different soil pH environments, we hypothesized that proteins play an important role in plant response to acidic and alkaline pH environment. Thus, the proteome changes in sugar beet modulated by pH treatment were accessed by TMT-based quantitative proteomic analysis. A total of three groups of differentially expressed proteins (DEPs) (pH 5 vs. pH 7.5, pH 9.5 vs. pH7.5 and pH 5 vs. pH 9.5) were identified in the leaves and roots of sugar beet. Several key proteins related to the difference of sugar beet response to acid (pH 5) and alkaline (pH 9.5) and involved in response to acid stress were detected and discussed. Moreover, based on proteomics results, QRT-PCR analysis confirmed that expression levels of three N transporters (NTR1, NRT2.1, and NRT2.5) in roots were relatively high under alkaline conditions (pH 9.5) compared with pH 5 or pH 7.5. The total nitrogen content of pH 9.5 in sugar beet was significantly higher than that of pH 7.5 and pH 5. These studies increase our understanding of the molecular mechanism of sugar beet response to different pH environments.

土壤pH（soil pH）是制约作物生长与产量的关键限制因素。目前针对不同pH条件下甜菜生长状态的相关研究数据较为匮乏。本研究针对pH 5、pH 7.5及pH 9.5三种条件下甜菜的生长状态与表型特征展开分析。结果显示，甜菜在pH 9.5条件下生长状态最佳，而在pH 5条件下生长最差。叶片与根系中超氧化物歧化酶（superoxide dismutase, SOD）和过氧化物酶（peroxidase, POD）的活性随pH值从9.5降至5的过程逐步升高。此外，与pH 9.5条件相比，pH 5条件下甜菜叶片内可溶性糖与脯氨酸的含量显著升高。为探究甜菜响应不同土壤pH环境的分子机制，本研究提出假设：蛋白质在植物应对酸性与碱性pH环境的过程中发挥重要调控作用。因此，本研究采用基于TMT的定量蛋白质组学分析方法，对pH处理调控下甜菜的蛋白质组变化进行了评估。本研究在甜菜叶片与根系中，共鉴定得到三组差异表达蛋白质（differentially expressed proteins, DEPs），分别为pH 5 vs. pH 7.5、pH 9.5 vs. pH7.5以及pH 5 vs. pH 9.5。研究还检测并探讨了若干与甜菜响应酸性（pH 5）、碱性（pH 9.5）环境差异相关，且参与酸胁迫应答过程的关键蛋白质。此外，基于蛋白质组学分析结果，实时定量反转录PCR（quantitative reverse transcription PCR, QRT-PCR）验证结果显示，与pH 5或pH 7.5条件相比，碱性环境（pH 9.5）下甜菜根系内3种氮转运蛋白（NTR1、NRT2.1及NRT2.5）的表达水平相对更高。甜菜在pH 9.5条件下的总氮含量显著高于pH 7.5与pH 5条件下的总氮含量。本研究有助于加深学界对甜菜响应不同pH环境的分子机制的理解。