*2.6. MALDI-TOF/TOF Mass Spectrometry*

The solutions containing the tryptic peptides were desalted and concentrated to a final volume of 4 μL with Zip-Tip C18 (Millipore Corporation, Billerica, MA, USA), according to the manufacturer's protocol, then dispersed into an α-cyano-4-hydroxycinnamic acid (4- HCCA) matrix, prepared by dissolving 4-HCCA in 50% acetonitrile/0.05% trifluoroacetic acid and spotted on a MALDI plate. The analysis was performed through a model 4800 MALDI-TOF/TOFTM MS analyzer (Applied Biosystems, Foster City, CA, USA). Peptide mass spectra were acquired in reflectron mode (500–4000 m/z range) and analyzed with the help of mMass v5.5 open-source software (http://www.mmass.org/ (accessed on 2 February 2021)). A peak list was created for each feature, and then manually controlled for the presence of signal from the matrix complex, human keratin peptides and trypsin. The main parameters were set as follows: digestion enzyme trypsin with one missed cleavage, mass type monoisotopic, 100 ppm peptide tolerance, methionine oxidation

and cysteine carbamidomethylation were set to enzymatic cleavage as fixed and variable modifications respectively.

Peptide mass fingerprinting analysis was performed with the software Mascot (http://www.matrixscience.com (accessed on 2 February 2021)) and proteins were identified with the Swiss-Prot data base of *A. thaliana* (thale cress). The information about gene loci was found in the UniProt and in TAIR database (https://www.arabidopsis. org/ (accessed on 2 February 2021)) for the corresponding *A. thaliana* proteins names and description.
