Manganese (Mn) is essential for various plant processes, including lignin biosynthesis,
cell wall formation, and enzyme activities, among others the function of the water
splitting complex in photosystem II of the thylakoid membranes of chloroplasts. Although
Mn homeostasis plays a pivotal role in plant cells, the regulation of Mn distribution
at the cellular level is still poorly understood. Mn transporters in the plant membranes,
among others NATURAL RESISTANCE-ASSOCIATED MACROPHAGE PROTEIN 1 (NRAMP1) channel the
Mn content of the cell towards the site of incorporation to enzyme proteins. Localization
of NRAMP1 is regulated by PH DOMAIN CONTAINING 1 (PH1), determining the trafficking
of NRAMP1. Unlike PH1, the role of PH2 in Mn transport remained unclear. Applying
Arabidopsis thaliana ph1ph2 double mutant lacking functional PH1 and PH2 proteins,
we aimed to explore whether PH2 influences NRAMP1 localization and, consequently,
Mn allocation in plant cells, and whether PH proteins are responsible for pleiotropic
effects in Mn distribution. On cryosectioned, lyophilized samples we employed particle
induced X-ray fluorescence microscopy (µPIXE) and low-energy X-ray fluorescence (LEXRF)
microspectroscopy to map Mn distribution at tissue and cell levels, respectively.
Comparing wild type and ph1ph2 lines grown under Mn containing and Mn deprived conditions,
ph1ph2 line indicated a perturbed plastidial Mn accumulation resulted in a failures
to respond the altered Mn nutrition. Along with the altered Mn distribution, we also
observed minor shifts in the Fe distribution within the cells, with a noticeable shift
towards the plastids.
This work was supported by the grant K-146865 of NKFIH, Hungary, and by the Bilateral
Research Agreement of Centre National de la Recherche Scientifique and Hungarian Academy
of Sciences (HAS). Á.S. was supported by the János Bolyai Scholarship of HAS (BO-00113-23-8).
Instrument center access was financed under ReMade@ARI PID 34653 (financed as part
of HORIZON-INFRA-2021-SERV-01, agreement No. 101058414, 10039728 and 22.0018). We
acknowledge Elettra-Sincrotrone, Trieste, Italy for the beam time access (20245567).
