Application of rhodamine B thiolactone to fluorescence imaging of Hg2+ in Arabidopsis thaliana

Exposure to mercury causes severe damage to plants, animals and even humans. Concern over mercury toxicity has encouraged the development of efficient, sensitive, and selective methods for the in vivo detection of mercury. Although a variety of studies have been published describing fluorescence imaging of mercury in animal cells and tissues, no in vivo monitoring has been developed for plant systems until now. In this paper, we report the semi-quantitative fluorescence imaging of Hg2+ ions in a common model plant Arabidopsis thaliana (A. thaliana), with rhodamine B thiolactone (RBS) as a novel Hg2+ probe. The experimental results show that RBS is plant cell wall and cell membrane permeable, and the probe responds selectively to Hg2+ ions instead of the other species in plant systems. Real-time monitoring of Hg2+ absorption in roots of A. thaliana by RBS shows that saturation of Hg2+ uptake could occur in a short period of 3 days at most. The transportation and accumulation of Hg2+ ions in roots of A. thaliana have also been studied, revealing that most of Hg2+ ions reside in root cap and meristematic zone, and only a small amount of Hg2+ ions can reach the maturation zone. This indicates that the interaction of Hg2+ ions with any Hg2+-philic species including proteins in these regions may be responsible for plant poisoning and even death.