Uptake and translocation of strontium in hydroponically grown maize plants, and subsequent effects on tissue ion content, growth and chlorophyll a/b ratio: comparison with Ca effects

Strontium is an element which can be found in the environment in a large range of concentrations, as a result of natural mineral degradation or consecutively to polluting anthropic activities. The transfer of such a contaminant from the environment to plants is a first step leading to contamination of the food pathway. Therefore the main objective of our work was to investigate the Sr(2+) transfer from the environment to the plants via root uptake, and to characterize some of the physiological effects induced by this element in maize plants. Hydroponically grown plants were exposed to SrCl(2) in different experimental conditions. Data reported here show that, depending on the external [Sr(2+)] tested, the uptake of Sr(2+) by Zea mays L cv. "Liberal" roots resulted from at least two saturating- (in the range 0.04-25 mM), and one non-saturating (for [Sr(2+)] up to 100 mM) transport components. The Sr(2+) uptake by roots and the translocation of Sr(2+) from root to shoot were increased when external Sr(2+) concentration was increased from 0.1 mM to 10 mM. However the relative efficiency of the "solution-to-plant root" transfer was higher for low external [Sr(2+)], whereas the relationship between the relative "root-to-shoot" transfer and the external [Sr(2+)] was more complex as it depended in particular on the incubation duration. Once taken up by the roots, part of the Sr(2+) was translocated to the leaves where it affected the chlorophyll a/b ratio mainly by decreasing the chlorophyll a content. Sr(2+) was also found to decrease the Mg and Ca contents of plant tissues. Sr(2+) effect on plant growth depended on the organ age and Sr(2+) concentration. At first sight, both Sr(2+) and Ca(2+) could be considered to exert quite similar overall effects in maize plants. This was in particular the case on shoot water and Chl b contents, and shoot DW. However, at similar concentration, Sr(2+) was generally less efficient at stimulating or more efficient at inhibiting the physiological processes studied, than Ca(2+). In particular, both ions induced significantly different effects on seedling radicle elongation, root length, DW and Mg content, and shoot Mg content. Taken together present data evidence that the amount of Sr(2+) transferred from environment to plants was sufficient to affect some physiological processes in maize plants. Most of the Sr(2+)-induced effects were different from those induced by Ca(2+) in a similar range of concentration, which suggests that Sr(2+) could not simply be considered to mimic Ca(2+). (C) 2010 Elsevier B.V. All rights reserved.