Figure 9
Scheme of P toxicity in plant cells. Under normal P concentration (a),
phytic acid synthesis is maintained to produce its proper concentration
in the cytosol, preventing any negative effects of phytic acid on
physiological functions within a plant cell. Under excessive Pi
accumulation (b), an increase in the cytosolic sugar-phosphate content
activates phytic acid synthesis, and an increase in the phytic acid
concentration causes Zn insolubilization, which, in turn, decreases
Cu/Zn-SOD activities. Simultaneously, RCA content decreases depending on
the excessive accumulation of Pi, and photosynthesis is limited by a
decrease in electron sink activities, partly because of the decrease in
Rubisco activation. The decrease in electron sink activities leads to a
decrease in ATP and NADPH consumptions. Subsequently, electrons are
accumulated in PET chain, stimulating reactive oxygen species (ROS)
production. ROS accumulation is further intensified by a decrease in
Cu/Zn-SOD activity. As a result, higher ROS accumulation triggers leaf
necrosis in land plants.