1 盐处理对二色补血草幼苗生长和生理指标的影响
研究者用不同浓度NaCl溶液处理6叶期二色补血草幼苗并测定其生长和生理指标。结果表明低浓度NaCl（100 mM NaCl）处理促进其生长，而高浓度NaCl（300 mM NaCl）处理抑制其生长（图1a，b）。叶绿素含量与生长指标表现出相反的趋势（图1c）。主要光合指标的变化趋势和生长指标一致（图1d）。研究者对盐处理下二色补血草幼苗的生理指标进行了测定，发现盐处理明显增加了幼苗的Na+含量和Na+/K+，显著降低了K+含量（图2a，b）。可溶性蛋白和脯氨酸含量的变化与Na+含量一致（图2c，d）。有趣的是，可溶性糖（包括葡萄糖、果糖、蔗糖）含量在低浓度NaCl处理下显著降低，在高浓度NaCl处理明显增加（图2e-h）。氧化胁迫指标表明，低盐处理下，幼苗没有受到氧化胁迫或者受到很小的氧化胁迫，而高盐处理下，幼苗受到严重的氧化胁迫（图2i-l）。低盐处理下，抗氧化酶活性明显增加，而高盐胁迫下，抗氧化酶活性明显降低 （图2m-p）。以上结果说明，二色补血草是典型的盐生植物，其最优的生长条件是低盐环境，高盐胁迫下，其生长受到明显抑制。
图1. 不同浓度NaCl处理对二色补血草幼苗的（a）生长表型、（b）生长参数、（c）叶绿素含量、（d）光合参数的影响。
图2. 不同浓度NaCl处理对二色补血草幼苗无机离子含量、有机溶质含量、活性氧含量、抗氧化酶基因表达水平及抗氧化酶活性的影响
2 转录组测序分析及差异表达基因功能注释
研究者分别对100 mM NaCl（低盐） 和300 mM NaCl（高盐）处理的二色补血草叶片进行转录组测序分析，发现低盐处理下，差异表达的基因主要富集在“淀粉和蔗糖代谢”、“植物-病原物互作”以及“MAPK信号通路”等通路。高盐胁迫下，差异表达的基因主要富集在“硫代葡萄糖苷生物合成”、“光合作用-天线蛋白”和“苯丙烷生物合成”等通路。高盐胁迫和低盐处理相比，差异基于主要富集在“光合作用-天线蛋白”、“角质、木栓质和蜡质生物合成”以及“苯丙烷生物合成”等通路。以上结果表明，在低盐处理下，二色补血草通过增强捕光结构、加厚表皮屏障和提高次生代谢物的产生来抵抗盐胁迫，在高盐胁迫下，主要依赖次生代谢物的合成来抵抗氧化和渗透胁迫。
3 差异代谢分析及功能注释
研究者使用LC-ESI-MS/MS系统对盐处理下二色补血草幼苗的靶向代谢物进行分析，共鉴定出817种代谢物（图3a）。在不同浓度NaCl处理下，代谢物含量存在显著差异，低盐和高盐处理下鉴定到8类差异代谢物（图3c）。这些代谢物分别是黄酮类、脂质类、酚酸类、生物碱类、氨基酸及其衍生物类、有机酸类、木脂素和香豆素类、核苷及其衍生物类、鞣质类和其他类（图3d-f）。在低盐处理下，黄酮类、脂质类、酚酸类、生物碱类、氨基酸及其衍生物类减少，而有机酸类、木脂素类、香豆素类、核苷及其衍生物类增加（图3d）。高盐胁迫下，氨基酸及其衍生物类、脂质类、酚酸类、核苷及其衍生物类减少，而生物碱类、黄酮类、木脂素类和香豆素类增加（图3e）。和低盐处理相比，高盐胁迫下共鉴定出91种差异代谢物（图4c），在上调最显著的10种代谢物中，有4种黄酮、3种生物碱、1种酚酸、1种脂质和1种氨基酸衍生物。4种黄酮类化合物为槲皮素-3-O-（6''-O-对香豆酰）葡糖苷、槲皮素-3-O-（2''-O-对香豆酰）半乳糖苷、杨梅素-3-O-（2''-没食子酰基-4''-乙酰基）鼠李糖苷和杨梅素-3-O-（4''-乙酰基）鼠李糖苷。以上结果表明，低盐和高盐处理下代谢物含量呈现出不同的变化趋势。
图3. 代谢组及差异代谢物分析
图4. 差异代谢物表达分析
4 转录组和代谢组关联分析
研究者对转录组和代谢组进行了关联分析，对转录组和代谢组数据进行的KEGG富集分析揭示了显著富集的前25个代谢途径。其中12个代谢途径在低盐和高盐处理下都显著富集。和低盐处理相比，高盐胁迫下明显富集的代谢途径包括“植物激素信号传导”、“苯丙烷类生物合成”和“戊糖和葡糖醛酸相互转化”。关键的差异基因和代谢物主要集中在“苯丙烷类生物合成”和“类黄酮生物合成”途径中（图5）。高盐胁迫下，8种酚类代谢物（咖啡酰莽草酸、松柏醇苷、松柏醇、1-O-芥子酰基-β-D-葡萄糖、芥子酸、芥子醛、芥子醇和丁香苷）含量显著增加（图5a）。在低盐处理下，8种酚类化合物（对香豆酸、咖啡酰莽草酸、松柏醇苷、阿魏酸、芥子酸、1-O-芥子酰基-β-D-葡萄糖、芥子醛和松柏醇）含量显著增加。在低盐和高盐处理下，5种酚类化合物（咖啡酰莽草酸、松柏醇苷、松柏醇、1-O-芥子酰基-β-D-葡萄糖和芥子醛）呈现一致趋势。参与这些代谢物合成的关键基因，特别是4CL和COMT的表达模式与代谢物含量变化趋势一致。高盐胁迫下，10种类黄酮代谢物含量显著增加（图5b），其中柚皮素的含量增加了85%，柚皮素查耳酮增加了59%，松黄烷增加了42%，新橙皮苷增加了27%。然而，在低盐处理下，10种类黄酮代谢物含量明显降低，包括柚皮素、柚皮素查耳酮、松黄烷等。参与调控这些代谢物形成的关键基因HCT、CHS和FLS的表达模式与代谢物的变化趋势一致。以上结果表明， 二色补血草通过调控基因表达和代谢物合成以应对不同浓度的盐处理。
图5. 主要代谢途径
论文链接：
https://onlinelibrary.wiley.com/doi/10.1111/pbi.14534
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