Fig. 7

Mass spectra of Chl a extracted from non-labeled and ¹³C-labeled Arabidopsis plants. FTICR-MS showing three types of quasi-molecular ions of Chl a, [M]⁺, [M + H]⁺ and [M + K]⁺, in a non-labeled (a) and a ¹³C-labeled (c) sample. Deviations from the expected mass (Δ) are given in ppm. TQ-MS showing two types of quasi-molecular ions, [M + H]⁺ and [M + K]⁺, in the same non-labeled (b) and ¹³C-labeled (d) samples as in a and c. The [M]⁺ peak was hardly detected and thus not considered in the analysis of TQ-MS data. Mass peaks of ¹³C-labeled [M + H]⁺ and non-labeled [M + K]⁺ were overlapping at m/z 931–933 in d. The contribution of non-labeled [M + K]⁺ in this m/z region was estimated from the intensity of non-labeled [M + H]⁺ peaks and the ratio between [M + H]⁺ and [M + K]⁺ peaks found in b (1:0.26). For Chl, natural abundance of Mg isotopes (²⁴Mg 79%, ²⁵Mg 10% and ²⁶Mg 11%) was taken into account to calculate their contributions to each mass peak. The estimated peak intensity of ²⁴Mg-Chl as [M + H]⁺ was then considered representative of Chl a in the analysis of TQ-MS data. Peak assignment of these data is summarized in Additional file 2: Tables S11–S14