黑色素前驅物控制阿拉伯芥鐵的吸收

Abstract

不論對於動物或是植物而言，鐵都是十分重要的金屬元素。缺鐵性貧血 (Iron Deficiency Anemia, IDA)是世界上很普遍的健康問題，造成IDA的其中一個重要原因是世界主要農作物中缺乏鐵。本研究目的旨在利用生物刺激素 (biostimulant) 提升植物吸收鐵的能力以及植物種子中的鐵含量，做為增加作物鐵吸收的前期試驗。本實驗研究的生物刺激素為黑色素的前驅物左旋多巴 ( L-3,4-dihydroxyphenylalanine, L-DOPA)。經過水耕試驗，可以發現L-DOPA雖然具有植物相剋物質 (allelopathic compound) 的特性，卻能有效的提升阿拉伯芥根部吸收鐵的能力，並且能力提升隨著施用濃度而上升。不過，完全氧化的L-DOPA在水耕環境中並不能促進根部鐵吸收。另一方面，土耕試驗結果顯示，澆灌3 mM的 L-DOPA時阿拉伯芥種子中的鐵含量可以達到控制組的三倍之多。此外，黑色素生成路徑中除了L-DOPA的其他的前驅物(皆為indolic compounds)也能夠影響阿拉伯芥的鐵吸收能力，其影響如下述：當適量供應這些indolic compounds且環境中的鐵充足時，阿拉伯芥的鐵吸收能力增加；反之在鐵缺乏時，阿拉伯芥的鐵吸收能力則會遭到抑制。這些結果顯示，黑色素生合成路徑上之各類化合物能顯著的影響阿拉伯芥體內鐵的動態平衡，於提升作物鐵含量之應用上具成為生物刺激素的發展潛力。

Fe is an important metallic element for both animals and plants. Fe deficiency anemia (IDA) is a common health problem worldwide, and one of the fundamental causes is the lack of Fe in the world's major crops. The purpose of this study is to use a biostimulant to enhance the ability of plants to absorb Fe and increase the Fe content in plant seeds as a preliminary test for increasing crop Fe absorption. The biostimulant studied in this thesis is L-3,4-dihydroxyphenylalanine (L-DOPA), the precursor of melanin. Through hydroponic experiments, it was found that although L-DOPA has allelopathic properties, it can effectively enhance the capability of Arabidopsis roots to absorb Fe, and the capability to absorb Fe increases with the concentration applied. However, fully oxidized L-DOPA cannot promote root Fe absorption in hydroponic environments. On the other hand, soil-based experiments showed that watering with 3 mM of L-DOPA increase the Fe content in Arabidopsis seeds to more than three folds that of the control group. In addition, other precursors of melanin in the melanin biosynthetic pathway (two of which are indolic compounds) can also affect the Fe absorption ability of Arabidopsis. When these indolic compounds are supplied in moderation with sufficient Fe in the environment, the Fe absorption ability of Arabidopsis increases; otherwise when Fe is lacked, the Fe absorption ability is inhibited. These results suggest that various compounds in the melanin biosynthetic pathway can significantly affect the homeostasis of Fe in Arabidopsis and have the potential to become a biostimulant for increasing crop Fe content.