Hsieh En-Jung, Liao Siao-Wei, Chang Ching-Yuan, Tseng Chu-Han, Wang Shan-Li, Grillet Louis
College of Agriculture and Bioresources, Department of Agricultural Chemistry, National Taiwan University, Building No. 2, Rm. 209A No. 1, Sec. 4, Roosevelt Rd, Taipei, 10617, Taiwan.
Bot Stud. 2023 Aug 25;64(1):24. doi: 10.1186/s40529-023-00396-7.
Iron deficiency is the leading cause of anemia worldwide, particularly in countries with predominant plant-based diets. Plants constitute the main source of dietary iron. Increasing their iron concentration could reduce the occurrence of anemia. The water spinach Ipomoea aquatica is consumed as a vegetable throughout Asia and tolerates high iron concentrations making it an attractive candidate for iron biofortification. L-DOPA is an allelopathic molecule secreted by some legumes. L-DOPA can trigger the expression of Fe deficiency-inducible genes, and could potentially be used as a biostimulant to increase Fe concentration.
L-DOPA significantly affected root growth of water spinach, and triggered a massive accumulation of Fe in roots. Both effects were exacerbated when L-DOPA was dissolved in KOH, which is surprising given that L-DOPA is less stable at high pH. To check whether a higher pH could indeed increase the bioactivity of L-DOPA, we used Arabidopsis thaliana, which grows at lower pH than water spinach, and subjected the plants to L-DOPA treatments at pH 5.5 and pH 6.0, which are both within the optimal range for Arabidopsis nutrition. At pH 6.0, the root growth of Arabidopsis was more strongly inhibited than at pH 5.5. We found that at higher pH, L-DOPA oxidizes to form a melanin precipitate.
We concluded that the oxidation of L-DOPA that we observed upon solubilization in KOH, or in nutrient solutions at slightly higher pH produces melanin-related molecules that are more potent than L-DOPA itself to trigger the primary root growth inhibition, Fe uptake and root Fe accumulation in water spinach and Arabidopsis.
缺铁是全球贫血的主要原因，尤其是在以植物性饮食为主的国家。植物是膳食铁的主要来源。提高其铁含量可以减少贫血的发生。空心菜（蕹菜）在亚洲各地作为蔬菜食用，并且能够耐受高铁浓度，使其成为铁生物强化的有吸引力的候选植物。L-多巴是一些豆科植物分泌的化感分子。L-多巴可以触发缺铁诱导基因的表达，并有可能用作生物刺激剂来增加铁含量。
L-多巴显著影响空心菜的根系生长，并引发铁在根部的大量积累。当L-多巴溶解在氢氧化钾中时，这两种效应都会加剧，鉴于L-多巴在高pH值下不太稳定，这一结果令人惊讶。为了检验较高的pH值是否确实能提高L-多巴的生物活性，我们使用了拟南芥，其生长的pH值低于空心菜，并在pH 5.5和pH 6.0下对植物进行L-多巴处理，这两个pH值都在拟南芥营养的最佳范围内。在pH 6.0时，拟南芥的根系生长比在pH 5.5时受到更强的抑制。我们发现，在较高的pH值下，L-多巴氧化形成黑色素沉淀。
我们得出结论，在溶解于氢氧化钾或略高pH值的营养液中时，我们观察到的L-多巴氧化产生了与黑色素相关的分子，这些分子比L-多巴本身更能有效地抑制空心菜和拟南芥的初生根生长、促进铁吸收以及使根部铁积累。
