Low and High Levels of Exogenous 5-Aminolevulinic Acid Differentially Regulate Porphyrin Biosynthesis in Rice

Jingil Kim1,2   Sunyo Jung1,*   

1School of Life Sciences and Biotechnology, Kyungpook National University, Daegu 41566, Korea
2Center for Plant Aging Research, Institute for Basic Science (IBS), Daegu 42988, Korea


Rice plants were treated with either a low (50 µM, L-ALA) or a high (500 µM, H-ALA) concentration of 5-aminolevulinic acid (ALA) to find out the molecular mechanism underlying the ALA-caused modulation of porphyrin biosynthesis. Foliar application of H-ALA to rice plants developed necrotic symptom on leaves 2 days after the treatment, whereas no necrotic symptom was observed on leaves of L-ALA plants. After 2 days of ALA treatment, chlorophyll slightly increased in L-ALA plants, but decreased in H-ALA plants. While H-ALA treatment greatly decreased ALA-synthesizing capacity, L-ALA treatment did not show a significant change in ALA-synthesizing capacity. Plants treated with H-ALA exhibited a greater decline in transcript levels of HEMA1 than plants treated with L-ALA. The decrease in transcript levels of GSA did not differ between L-ALA and H-ALA plants, whereas ALAD greatly downregulated only in H-ALA plants. PPO1 was upregulated after 2 days of L-ALA treatment, but greatly downregulated with H-ALA treatment. Expression levels of CHLH, CHLD, and PORB remained or slightly decreased after 2 days of L-ALA treatment, but markedly decreased after 1 day of H-ALA treatment. This study demonstrates that a regulatory mechanism of porphyrin biosynthesis is differentially adjusted to the cellular demands in response to exogenous supply of low and high ALA concentrations.

Figures & Tables

Fig. 1.Effect of exogenous 5-aminolevulinic acid (ALA) treatment on phenotypes and photosynthetic pigments in rice plants. (A) Necrotic phenotype. Photographs were taken 2 days after ALA treatment. (B) Carotenoids. (C) Chlorophyll. (D) Chlorophyll a/b ratio. Rice plants at the three-leaf stage were sprayed with either a low (50 μM) or a high (500 μM) concentration of ALA. Cont: Control (water with 0.1% Tween-20); L-ALA: A low concentration (50 μM) of ALA treatment; H-ALA: A high concentration (500 μM) of ALA treatment; D1: 1 day after ALA treatment; D2: 2 days after ALA treatment. Treatment notations are the same as in Fig. 1. The data represent the mean±S.E. of 6 replicates. a-c: Means denoted by the same letter did not differ significantly at P<0.05 according to Duncan’s multiple range test.