Studies have indicated that endogenous concentrations of plant hormones are regulated very locally within plants. To understand the mechanisms underlying hormone-mediated physiological processes, it is indispensable to know the exact hormone concentrations at cellular levels. In the present study, we established a system to determine levels of ABA and jasmonoyl-isoleucine (JA-Ile) from single cells. Samples taken from a cell of Vicia faba leaves using nano-electrospray ionization (ESI) tips under a microscope were directly introduced into mass spectrometers by infusion and subjected to tandem mass spectrometry (MS/MS) analysis. Stable isotope-labeled [D(6)]ABA or [(13)C(6)]JA-Ile was used as an internal standard to compensate ionization efficiencies, which determine the amount of ions introduced into mass spectrometers. We detected ABA and JA-Ile from single cells of water- and wound-stressed leaves, whereas they were almost undetectable in non-stressed single cells. The levels of ABA and JA-Ile found in the single-cell analysis were compared with levels found by analysis of purified extracts with liquid chromatography-tandem mass spectrometry (LC-MS/MS). These results demonstrated that stress-induced accumulation of ABA and JA-Ile could be monitored from living single cells.
Keywords: Abscisic acid (ABA); Jasmonoyl-isoleucine (JA-Ile); Mass spectrometry; Single cell; Vicia faba; Water and wound stresses.
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