Abstract
Zinc (as an essential phytonutrient) and cadmium (as a toxic but readily bioavailable nonessential metal for plants) share similar routes for crossing plant biomembranes, although with a substantially different potential for translocation into above-ground tissues. The in situ distribution of these metals in plant cells and tissues (particularly intensively-dividing and fast-growing areas) is poorly understood. In this study, 17-day-old radish (Raphanus sativus L.) plants grown in nutrient solution were subjected to short-term (24 h) equimolar contamination (2.2 µM of each 70Zn and Cd) to investigate their accumulation and distribution in the shoot apex (leaf primordia) and edible fleshy hypocotyl tissues. After 24-h exposure, radish hypocotyl had similar concentration (in µg/g dry weight) of 70Zn (12.1 ± 1.1) and total Cd (12.9 ± 0.8), with relatively limited translocation of both metals to shoots (concentrations lower by 2.5-fold for 70Zn and 4.8-fold for Cd) as determined by inductively-coupled plasma mass spectrometry (ICP-MS). The in situ Zn/Cd distribution maps created by high-resolution secondary ion mass spectrometry (NanoSIMS, Cameca, Gennevilliers, France) imaging corresponded well with the ICP-MS data, confirming a similar pattern and uniform distribution of 70Zn and Cd across the examined areas. Both applied techniques can be powerful tools for quantification (ICP-MS) and localisation and visualisation (NanoSIMS) of some ultra-trace isotopes in the intensively-dividing cells and fast-growing tissues of non-metalophytes even after short-term metal exposure. The results emphasise the importance of the quality of (agro)ecosystem resources (growing media, metal-contaminated soils/waters) in the public health risk, given that, even under low contamination and short-term exposure, some of the most toxic metallic ions (e.g., Cd) can relatively rapidly enter the human food chain.
Highlights
Understanding of trace metal homeostasis and phyto-physiological processes has expanded considerably in recent decades and is being used in phytoremediation technologies (e.g., [1]), bio-fortification of food
Given that trace metals can accumulate in edible tissues and/or primary nutrient deposition sites, consumption of vegetables (especially fresh that are nutritive highly valued) is one of the main entry routes of certain trace metals (Cd, Zn, Hg) into humans [4,5,6,7]
To the best of our knowledge, this is the first report of detailed localisation of low concentrations of and 64 Zn/70 Zn in the shoot apex and hypocotyl of radish exposed to relatively low concentrations of metallic ions over a short period of time
Summary
Understanding of trace metal homeostasis and phyto-physiological processes has expanded considerably in recent decades and is being used in phytoremediation technologies (i.e., clean-up of metal-contaminated land by plants) (e.g., [1]), bio-fortification of food Vascular tissues (i.e., xylem and phloem) are crucial for transport, distribution and deposition of essential and non-essential trace metal elements (e.g., [11]) from roots to shoots [12]. Mapping of Cd and Zn at the nano-scale in metal-sensitive (yet edible) plant parts and/or in tissues with low metal concentration (e.g., shoots) might be challenging because of potentially low signal (i.e., metal concentration down to several mg/kg) To overcome these difficulties, researchers used relatively long-term studies (e.g., few months) and/or unusually high concentrations of metals (e.g., [1,24,25]) that might cause phytotoxicity, diminishing the environmental and physiological relevance of results obtained. Zn/Cd distribution in the xylem area of hypocotyl (organ widely consumed by humans) as well as fast-growing shoot apices using NanoSIMS
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
