Setaria parviflora and Paspalum urvillei are iron hyperaccumulating species. In order to understand how they are iron resistant, this study evaluated the adjustments in photosynthetic apparatus, metabolic pathways, and antioxidant response after exposure to iron excess. Two assays were carried out with different purposes. S. parviflora and P. urvillei were grown in Hoagland & Arnon nutrient solution containing 0.009, 1, 2, 4 and 7 mM Fe-EDTA to evaluate which Fe concentration causes accumulation of this element above the toxicity threshold. In addition, leaf samples were collected from plants growing in 0.009 and 7 mM iron-EDTA solution on the 6°, 10°, 14° and 18° day of growth in order to evaluate the adjustments in terms of primary metabolite concentrations and the antioxidant capacity. Only the 7 mM iron-EDTA treatment caused a toxic iron accumulation in the shoot of both species. P. urvillei had decreased photosynthetic rate only upon exposure to 7 mM iron-EDTA, in addition, adjustments in the electron transport rate through photosystem II and oxidation state of quinones were observed. Meanwhile, S. parviflora presented a gradual reduction in photosynthetic rate, although with higher non-photochemical quenching of fluorescence values. P. urvillei showed inhibition of tricarboxylic acid cycle. Based on the activity of antioxidant enzymes, S. parviflora showed higher ascorbate peroxidase, peroxidase values, and lipid peroxidation. We additionally identified that malate can also function to neutralize the free-reactive Fe and may contribute to the tolerance mechanism in P. urvillei. Therefore, these species have the ability to accumulate high concentrations of iron within a few days using effective and different adjustments in photosynthetic, antioxidant and carbon metabolism to cope with iron excess.

中文翻译：

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了解铁超蓄积草中的光合和代谢调节

Setaria parviflora和Paspalum urvillei是铁超富集物种。为了了解它们如何抗铁，本研究评估了暴露于铁过量后光合装置，代谢途径和抗氧化剂反应的调节。出于不同目的进行了两种测定。S. parviflora和P. urvillei在含有0.009、1、2、4和7 mM Fe-EDTA的Hoagland＆Arnon营养液中生长，以评估哪种Fe浓度导致该元素的积累超过毒性阈值。此外，还从生长在第6、10、14和18天的0.009和7 mM铁-EDTA溶液中生长的植物中收集叶片样品，以便评估主要代谢产物浓度和抗氧化剂的调节容量。只有7 mM铁-EDTA处理导致两种物种的枝条中有毒的铁积累。仅在暴露于7 mM铁-EDTA的情况下，P。urvillei的光合作用速率降低，此外，还观察到通过光系统II的电子传输速率和醌的氧化态的调节。同时，S。parviflora尽管具有更高的非光化学猝灭性荧光值，但光合速率却逐渐降低。P. urvillei表现出对三羧酸循环的抑制作用。基于抗氧化酶的活性，S。parviflora显示出较高的抗坏血酸过氧化物酶，过氧化物酶值和脂质过氧化作用。我们还确定了苹果酸还可以起到中和游离反应性Fe的作用，并且可能有助于P. urvillei的耐受机制。因此，这些物种利用光合作用，抗氧化剂和碳代谢的有效和不同的调整来解决铁过量的问题，从而能够在几天内积累高浓度的铁。