It accounts for 50 % of soluble leaf protein ( 20-30 % of total leaf nitrogen ) and 30 % of soluble leaf protein in plants ( 5-9 % of total leaf nitrogen ) . It accounts for 50 % of soluble leaf protein in plants ( 20-30 % of total leaf nitrogen ) and 30 % of soluble leaf protein in plants ( 5-9 % of total leaf nitrogen ) .