Plant Biophysics/
Biochemistry Research Laboratory

Fig. 1  Single-cell analytical method, called ‘picolitre pressure-probe electrospray-ionization mass spectrometry
(picoPPESI-MS)’ (Nakashima et al., 2016)

By combining a cell pressure probe with Orbitrap mass spectrometer, we have developed a powerful single-cell analytical method, called ‘picolitre pressure-probe electrospray-ionization mass spectrometry (picoPPESI-MS)’(Nakashima et al., 2016).  

Fig. 2  The picoPPESI-MS system in the laboratory.

This technique allows us to conduct the various experiments in intact plants and ionize the metabolites in the picoliter cell sap directly collected from the target cells by the means of pressure probe.  And subsequently, metabolome analysis can be performed in real-time without the need of any pretreatment prior to the MS analysis (Nakashima et al., 2016).  It should be emphasized that this analytical method was designed to be performed in the picoliter fluids collected from the target cells, knowing the physiological status, such as turgor in the ‘living’ cells (Nakashima et al., 2016).  This method also allows to determine the volume of sap with a transparent capillary tip, if necessary (Nakata et al., 2022).

In our laboratory, matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF-MS) is also introduced.  Similarly, the combinations of pressure probe and MALDI mass spectrometry techniques can be used for studying molecular biology at cell level in intact plants (Gholipour et al., 2010).  

Regarding mass spectrometry research, we have been cooperating with Prof. R. Erra-Balsells of the University of Buenos Aires, which has produced three Nobel laureates in Physiology/Medicine and Chemistry related to sugar chemistry and sugar metabolisms and has the academic cooperation agreement with Ehime University.  Prof. Dr. Erra-Balsells specializes in mass spectrometry, photochemistry, and sugar chemistry. She visits this laboratory for four months every year, and teaches basic chemistry and mass spectrometry techniques for graduate research study.

We use these single-cell metabolomics to study various physiological disorders in plants, such as heat-induced rice chalky formation (Fig. 3).

Fig. 3  Typical heat-induced chalky rice, called ‘white-back rice’.

We also developed a carbon tracer analysis in plants using Orbitrap mass analyzer using the steady carbon isotope (Wada et al., 2014, 2017). Currently, we are further improving picoPPESI-MS and related analytical methods.