He Jie, Qin Lin
National Institute of Education, Nanyang Technological University, Singapore, Singapore.
Front Plant Sci. 2021 Jun 4;12:686910. doi: 10.3389/fpls.2021.686910. eCollection 2021.
(common ice plant), as a nutritious ready-to-eat salad in Singapore, has become popular in recent years. However, basic data about the impacts of NO supply on its NO accumulation and nutritional quality are lacking. In this study, all plants were first grown indoor hydroponically in 10% artificial seawater (ASW) with modified full-strength Netherlands Standard Composition nutrient solution for 11 days, before transferring them to different reduced NO solutions. All plants grew well and healthy after 7 days of treatment. However, plants grown with 3/4 N and 1/2 N were bigger with higher shoot and root fresh weight (FW), greater leaf number, and total leaf area (TLA) than those grown with full nitrogen (N), 1/4 N, and 0 N. grown with full N, 3/4 N, and 1/4 N had similar specific leaf area (SLA), while 0 N plants had significantly lower SLA. All plants had similar leaf succulence (LS). However, leaf water content (LWC) was lower, while leaf dry matter accumulation (LDMC) was higher in 0 N plants after 7 days of treatment. Compared with plants grown with full N, shoot NO concentrations in 3/4 N, 1/2 N, and 1/4 N plants were constant or slightly increased during the treatments. For 0 N plants, shoot NO concentration decreased significantly during the treatment compared with other plants. Shoot NO accumulation was associated with nitrate reductase activity (NRA). For instance, after 7 days of treatment, shoot NO concentration and NRA on a FW basis in 0 N plants were, respectively, 45 and 31% of full N plants. After transferring full N to 0 N for 7 days, all had higher chlorophyll (Chl) content coupled with higher electron transport rate (ETR) and higher effective quantum yield of PSII, while full N plants had higher non-photochemical quenching (NPQ). The 0N plants had much higher concentrations of proline, total soluble sugar (TSS), and total ascorbic acid (ASC) than other plants. In conclusion, totally withdrawing NO from the growth media prior to harvest could be one of the strategies to reduce shoot NO concentration. Reduced NO supply further enhanced nutritional values as concentrations of proline, TSS, and ASC were enhanced markedly in plants after transferring them from full N to 0 N.
（冰叶日中花）作为一种营养丰富的即食沙拉，近年来在新加坡颇受欢迎。然而，关于氮供应对其氮积累和营养品质影响的基础数据尚缺。在本研究中，所有植株首先在含有改良的全强度荷兰标准成分营养液的10%人工海水中水培种植11天，之后将它们转移至不同的低氮溶液中。处理7天后，所有植株生长良好且健康。然而，与在全氮（N）、1/4 N和0 N条件下生长的植株相比，在3/4 N和1/2 N条件下生长的植株更大，地上部和根系鲜重（FW）更高，叶片数量更多，总叶面积（TLA）更大。在全氮、3/4 N和1/4 N条件下生长的植株具有相似的比叶面积（SLA），而0 N条件下的植株SLA显著更低。所有植株的叶片肉质化程度（LS）相似。然而，处理7天后，0 N条件下植株的叶片含水量（LWC）更低，而叶片干物质积累量（LDMC）更高。与在全氮条件下生长的植株相比，在3/4 N、1/2 N和1/4 N条件下生长的植株地上部氮浓度在处理期间保持恒定或略有增加。对于0 N条件下的植株，与其他植株相比，处理期间地上部氮浓度显著降低。地上部氮积累与硝酸还原酶活性（NRA）相关。例如，处理7天后，0 N条件下植株地上部基于鲜重的氮浓度和NRA分别为全氮条件下植株的45%和31%。在从全氮转移至0 N 7天后，所有植株叶绿素（Chl）含量更高，同时电子传递速率（ETR）更高，PSII的有效量子产率更高，而全氮条件下的植株非光化学猝灭（NPQ）更高。0 N条件下的植株脯氨酸、总可溶性糖（TSS）和总抗坏血酸（ASC）的浓度比其他植株高得多。总之，在收获前从生长介质中完全去除氮可能是降低地上部氮浓度的策略之一。低氮供应进一步提高了营养价值，因为将植株从全氮转移至0 N后，脯氨酸、TSS和ASC的浓度显著增加。
