Phosphorus toxicity disrupts Rubisco activation and reactive oxygen
species defence systems by phytic acid accumulation in leaves
Abstract
Phosphorus (P) is an essential mineral nutrient for plants.
Nevertheless, excessive P accumulation in leaf mesophyll cells causes
necrotic symptoms in land plants; this phenomenon is termed P toxicity.
However, the detailed mechanisms underlying P toxicity in plants have
not yet been elucidated. This study aimed to investigate the molecular
mechanism of P toxicity in rice. We found that under excessive inorganic
P (Pi) application, Rubisco activation decreased and photosynthesis was
inhibited, leading to lipid peroxidation. Although the defence systems
against reactive oxygen species (ROS) accumulation were activated under
excessive Pi application conditions, the Cu/Zn-type superoxide dismutase
activities were inhibited. A metabolic analysis revealed that excessive
Pi application led to an increase in the cytosolic sugar phosphate
concentration and the activation of phytic acid synthesis. These
conditions induced mRNA expression of genes that are activated under
metal-deficient conditions, although metals did accumulate. These
results suggest that P toxicity is triggered by the attenuation of both
photosynthesis and metal availability within cells mediated by phytic
acid accumulation. Here, we discuss the whole phenomenon of P toxicity,
beginning from the accumulation of Pi within cells to death in land
plants.