Study of essential element accumulation in the leaves of a Cu-tolerant plant Elsholtzia splendens after Cu treatment by imaging laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used for the quantitative imaging of Cu and other essential elements (such as K, Mg, Mn, P, S and B) in the leaves of a Cu-tolerant plant Elsholtzia splendens treated with the enriched 65Cu isotope tracer (isotope abundance of 89.2%). The leaves (newly formed, fully grown and oldest) were scanned directly with a focused Nd:YAG laser in the laser ablation chamber. The ablated material was transported with argon as carrier gas to a quadrupole-based ICP-MS (ICP-QMS), and the ion intensities of 65Cu+, 39K+, 24Mg+, 55Mn+, 31P+, 34S+ and 11B+ were measured by ICP-QMS to study the accumulation of Cu and other elements of interest. Standard reference material NIST SRM 1515 Apple Leaves doped with known concentrations of analytes (from 0.1 to 2000 mg L−1) was measured together with the samples by LA-ICP-MS and was used for the quantification of the analytical data. Notable accumulation of Cu in the newly formed leaves was clearly identified by imaging LA-ICP-MS. The increased isotope ratios of 65Cu/63Cu measured by LA-ICP-MS demonstrated the path of Cu uptake and accumulation via the petiole and main veins in the leaves. Cu stress-induced accumulation of K, Mg, Mn, P and S in the newly formed leaves was observed, while B was not significantly affected. In the present study, the concentrations of K, Mg, Mn, P and S were not obviously changed in the fully grown leaves after short-term treatment. Along with the treatment, a visible decrease of K and P was found in the oldest leaves, while other elements were not influenced by Cu stress.