Effect of 5-aminolevulinic acid (ALA) on photosynthetic rate, hydrogen peroxide content, antioxidant level and active oxygen-scavenging enzymes in spinach (Spinacia oleracea L.)

The effects of 5 - aminolevulinic acid (ALA), a key precursor in the biosyn thesis of porphyrins, in a low level (0, 0.18, 0.60 or 1.80mM) on the photo synthetic rate, hydrogen peroxide contents, antioxidant substrates, and act ive oxygen - scavenging enzymes were investigated in the 3rd leaves of spin ach (Spinacia oleracea). 1. Photosynthetic rates of leaves that were treated with different concentr ations of ALA, increased significantly in day 3, and remained so for 6 days . 2. Hydrogen peroxide (H2O2) contents in leaves increased from day 6 to 9. T he increase seems to be correlated with the promotion of the photosynthetic rate. 3. Oxidized ascorbate (DHA)/reduced ascorbate (ASC) ratio in treated leaves tended to remain constant, whereas reduced glutathione (GSH)/oxidized glut athione (GSSG) ratio increased. 4. Catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (G R) activities increased by day 3 after the ALA treatment. Superoxide dismut ase (SOD) activity did not vary after ALA treatment.