Phosphorus toxicity disrupts Rubisco activation and reactive oxygen
species defense systems by phytic acid accumulation in leaves
Phosphorus (P) is one of the essential mineral nutrients for plants.
Nevertheless, large amounts of accumulated P easily wither whole plants,
and this phenomenon is termed as P toxicity. For improving P-use
efficiency, to overcome P toxicity is necessary for plant growth.
However, the detailed mechanisms underlying P toxicity in plants have
not yet been elucidated. In this study, we aimed to investigate the
molecular mechanism of P toxicity in rice. We found that, under
excessive inorganic-P (Pi) application conditions, Rubisco activation
decreased and photosynthesis was inhibited, leading to
lipid-peroxidation. Although the defense systems against reactive oxygen
species accumulation were activated under excessive Pi application
conditions, the Cu/Zn-type superoxide dismutase activity was inhibited.
A metabolic analysis revealed that excess Pi application led to an
increase in the cytosolic sugar-phosphate content, and activation of
phytic acid synthesis. These conditions induced mRNA expressions of the
genes that are activated under metal-deficiency conditions, although
metals were rather accumulated. These results suggested 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 plants.