The precursors Proto IX and Mg-Proto IX were quantified using Plant ProtoIX/Mg-Proto IX ELISA Kit (HS354-Pt, Hengyuan, Shanghai, China). ATPase and MgCh activities were assessed using the Plant ATPase (HB328X-Pt, Hengyuan, Shanghai, China) and MgCh ELISA Kit (HB144X-Pt, Hengyuan, Shanghai, China).