Iron homeostasis in the annual and perennial stem zones of <i>Arabis alpina</i>

Plants store nutrients, including the micronutrient iron, in bioavailable forms to support growth in subsequent seasons. The perennial lifestyle is preponderant in nature. Arabis alpina is a perennial model organism with a particular architecture of branches having proximal perennial (PZ) and distal annual (AZ) stem zones with distinct anatomy and physiology. PZ undergoes secondary growth and stores carbon-rich macromolecules. Here, we investigated iron homeostasis in PZ versus AZ. We localized iron in stem internodes of PZ and AZ using Perls staining and ferritin immunodetection in the wild-type Pajares (Paj) and perpetual flowering 1 mutant. We mined transcriptome data of the developing PZ and AZ. Iron accumulated at various development stages in PZ and AZ. Iron levels in PZ were ca. two-fold higher than in AZ, irrespective of flowering. Iron was predominantly located within plastid-bound ferritin. Gene expression patterns supported the significance of ferritin and demonstrated enrichment of transcripts related to iron homeostasis within stems. Distinct patterns of expression among iron homeostasis genes were observed in relation to iron content in PZ and AZ, indicating tissue-specific regulatory mechanisms governing iron accumulation. Secondary growth in PZ plays a role in iron storage in the perennial A. alpina, while AZ may transiently store iron for seed production. Future research will address different iron homeostasis signalling pathways in AZ and PZ.