Abstract
Relatively few studies have been focused so far on magnesium–isotope fractionation during plant growth, element uptake from soil, root-to-leaves transport and during chlorophylls biosynthesis. In this work, maize and garden cress were hydroponically grown in identical conditions in order to examine if the carbon fixation pathway (C4, C3, respectively) might have impact on Mg-isotope fractionation in chlorophyll-a. The pigment was purified from plants extracts by preparative reversed phase chromatography, and its identity was confirmed by high-resolution mass spectrometry. The green parts of plants and chlorophyll-a fractions were acid-digested and submitted to ion chromatography coupled through desolvation system to multiple collector inductively coupled plasma-mass spectrometry. Clear preference for heavy Mg-isotopes was found in maize green parts (∆26Mgplant-nutrient 0.65, 0.74 for two biological replicates, respectively) and in chlorophyll-a (∆26Mgchlorophyll-plant 1.51, 2.19). In garden cress, heavy isotopes were depleted in green parts (∆26Mgplant-nutrient (−0.87)–(−0.92)) and the preference for heavy isotopes in chlorophyll-a was less marked relative to maize (∆26Mgchlorophyll-plant 0.55–0.52). The observed effect might be ascribed to overall higher production of energy in form of adenosine triphosphate (ATP), required for carbon fixation in C4 compared to C3, which could reduce kinetic barrier and make equilibrium fractionation prevailing during magnesium incorporation to protoporphyrin ring.
Highlights
The phenomenon of mass-dependent stable isotope fractionation is well documented for variety of elements in both, abiotic and biotic systems [1]
The main idea of this study was to examine Mg-isotope fractionation in chlorophyll-a extracted from two plants with different carbon fixation systems
Mg-isotope fractionation was measured in green parts of the plants harvested from two biological replicates, applying five technical replicates (20 analytical runs by ion chromatography (IC)-MC ICP-MS) after the same digestion procedure
Summary
The phenomenon of mass-dependent stable isotope fractionation is well documented for variety of elements in both, abiotic and biotic systems [1]. Molecules 2020, 25, 1644 inductively coupled plasma-mass spectrometry (MC ICP-MS) is accepted as a gold standard in providing reliable isotope fractionation data for metals of geochemical and biological relevance [6,7]. This technique offers efficient ionization, high mass resolution and high-precision measurements with relatively low sample requirement and high throughput. In the instrumental set-up, column effluent was passed through a self-regenerating suppressor for the replacement of mobile phase anion(s) by OH– and, only the column fraction containing metal of interest entered the plasma This was achieved within the six-port injection valve, where column effluent before and after analyte elution was discarded while bracketing solution was directed to MC ICP-MS [8]
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