BACKGROUND Chromium (Cr) exists in the environment in two chemical forms; CrIII is an essential micronutrient for glucose and lipid metabolism, whereas CrVI is toxic and a recognised carcinogen through inhalation. Numerous studies have attempted to evaluate their transfer mechanisms from soil and solution media into plants, usually with respect to the hyperaccumulation, detoxification and tolerance of the plant to CrVI. METHODS Isotopically enriched species of Cr, added as 50CrIII and 53CrVI, were used to investigate transfer from solution into the root systems of Spinacia oleracea. In addition the effect of sulphate (SO42-), as a competitor for CrVI uptake, was investigated. Separation of 50CrIII and 53CrVI was undertaken using HPLC-ICP-QQQ following isolation of root solutions using freeze/thaw centrifugation. RESULTS Irrespective of supplied CrVI concentration (250, 500 or 1000 μg L-1), the dominant species in both apoplastic (routed through cell wall and intercellular space as a passive mechanism) and symplastic (routed through cytoplasm as an active mechanism) root solutions was CrIII. There was evidence for CrVI reduction in the rhizosphere prior to uptake as an additional detoxification mechanism. Sulphate promoted uptake of CrVI through the active pathway, although increases in SO42- concentration did not yield a proportional increase in Cr symplastic solution concentration; CrIII was also the dominant species in these root solutions. CONCLUSION The results indicate that Spinacia oleracea plants can effectively reduce CrVI to CrIII and that the uptake pathways for both CrIII and CrVI are more complex than previously reported. Further work is required to understand the physiological processes that result in the reduction of CrVI prior to, and during, uptake. The efficacy of sulphate to augment existing agricultural management strategies, such as liming and organic reincorporation, also requires further investigation to establish suitable application rates and applicability to other environmental contaminants.

中文翻译：

---

使用同位素示踪剂评估根部溶液中的铬物种动态。

背景技术铬（Cr）以两种化学形式存在于环境中。CrIII是葡萄糖和脂质代谢必不可少的微量营养素，而CrVI有毒，可通过吸入被认为是致癌物。许多研究尝试评估它们从土壤和溶液介质到植物的转移机制，通常是关于植物对CrVI的过度积累，解毒和耐受性。方法采用同位素富集的Cr物种（分别为50CrIII和53CrVI）研究菠菜从溶液到根系的转移。此外，还研究了硫酸盐（SO42-）作为吸收CrVI的竞争者的作用。使用冷冻/解冻离心法分离根溶液后，使用HPLC-ICP-MS / MS分离50CrIII和53CrVI。结果不论所提供的CrVI浓度（250、500或1000μgL-1）如何，在质外生（通过细胞壁和细胞间空间作为被动机制）和共生（通过细胞质作为主动机制）中占主导地位的物种是CrIII。有证据表明，在摄入之前，根际的CrVI会降低，这是一种额外的排毒机制。硫酸盐通过活性途径促进了CrVI的吸收，尽管SO42-浓度的增加并未导致Cr共塑溶液浓度的成比例增加。CrIII也是这些根系溶液中的优势种。结论结果表明，菠菜植物可以有效地将CrVI还原为CrIII，并且CrIII和CrVI的吸收途径比以前报道的更为复杂。需要进一步的工作来了解导致摄取前和摄取过程中CrVI减少的生理过程。硫酸盐增强现有农业管理策略（如石灰和有机物再​​结合）的功效还需要进一步研究，以确定合适的施用率和对其他环境污染物的适用性。