Meyer Philipp, Förster Nadja, Huyskens-Keil Susanne, Ulrichs Christian, Geilfus Christoph-Martin
Faculty of Life Sciences Division of Controlled Environment Horticulture Humboldt-Universität zu Berlin Berlin Germany.
Faculty of Life Sciences Division Urban Plant Ecophysiology Humboldt-Universität zu Berlin Berlin Germany.
Plant Environ Interact. 2021 Feb 4;2(1):36-44. doi: 10.1002/pei3.10039. eCollection 2021 Feb.
Onset of salinity induces the pH of the leaf apoplast of Pak choi transiently to increase over a period of 2 to 3 hr. This pH event causes protein abundances in leaves to increase. Among them are enzymes that are key for the phenylpropanoid pathway. To answer the questions whether this short-term salt stress also influences contents of the underlying phenylpropanoids and for clarifying as to whether the apoplastic pH transient plays a role for such a putative effect, Pak choi plants were treated with 37.5 mM CaCl against a non-stressed control. A third experimental group, where the leaf apoplast of plants treated with 37.5 mM CaCl, was clamped in the acidic range by means of infiltration of 5 mM citric acid/sodium citrate (pH 3.6), enabled validation of pH-dependent effects. Microscopy-based live cell imaging was used to quantify leaf apoplastic pH in planta. Phenolics were quantified shortly after the formation of the leaf apoplastic pH transient by means of HPLC-DAD-ESI-MS. Results showed that different phenolic compounds were modulated at 150 and 200 min after the onset of chloride salinity. A pH-independent reduction in phenolic acid abundance as well as an accumulation of phenolic acid:malate conjugates was quantified after 200 min of salt stress. However, at 150 min after the onset of salt stress, flavonoids were significantly reduced by salinity in a pH-dependent manner. These results provided a strong indication that the pH of the apoplast is a relevant component for the short-term metabolic response to chloride salinity.
盐分胁迫开始后，在2至3小时内，小白菜叶片质外体的pH值会短暂升高。这种pH值变化会导致叶片中蛋白质丰度增加。其中包括苯丙烷类途径的关键酶。为了回答这种短期盐胁迫是否也会影响潜在苯丙烷类化合物的含量，以及质外体pH值的短暂变化是否在这种假定的影响中起作用，将小白菜植株用37.5 mM氯化钙处理，以无胁迫的植株作为对照。第三个实验组，用5 mM柠檬酸/柠檬酸钠（pH 3.6）浸润，将用37.5 mM氯化钙处理的植株的叶片质外体pH值维持在酸性范围，以此验证pH依赖性效应。基于显微镜的活细胞成像用于定量植物体内叶片质外体的pH值。通过HPLC-DAD-ESI-MS在叶片质外体pH值短暂变化形成后不久对酚类物质进行定量。结果表明，在氯化物盐胁迫开始后的150和200分钟，不同的酚类化合物受到调节。在盐胁迫200分钟后，定量分析了酚酸丰度的pH非依赖性降低以及酚酸-苹果酸共轭物的积累。然而，在盐胁迫开始后的150分钟，黄酮类化合物因盐分胁迫而以pH依赖性方式显著减少。这些结果有力地表明，质外体的pH值是对氯化物盐胁迫短期代谢反应中的一个相关组成部分。
