Influence of exogenous 5-aminolevulinic acid on chlorophyll synthesis and related gene expression in oilseed rape de-etiolated cotyledons under water-deficit stress

Abstract

5-aminolevulinic acid (ALA) is an essential precursor for the biosynthesis of tetrapyrrols such as heme and chlorophyll (Chl). Previous studies have focused mainly on promotive effects of exogenous ALA on plant growth, while regulatory mechanisms affecting Chl biosynthesis have been only partially discussed. In the present study, the ameliorative role of exogenous ALA was investigated on Chl and endogenous ALA biosynthesis in six-day-old etiolated oilseed rape (Brassica napus L.) cotyledons during the de-etiolated stage. We showed that exogenously applied ALA of a low dosage enhanced Chl and ALA accumulation in cotyledons, while 600 μM ALA treatment inhibited the accumulation of Chl and ALA severely. However, the gene expression levels of glutamyl-tRNA reductase (HEMA) and glutamate-1-semialdehyde aminotransferase (GSA) were not affected under either low or high ALA concentrations. Furthermore, water deficit induced by polyethylene glycol 6000 (PEG) suppressed the Chl and ALA accumulation in cotyledons, while the inhibition was partially alleviated in cotyledons pretreated with ALA. The decrease in Chl biosynthesis induced by PEG stress was assumed to be related to downregulation of HEMA and Mg-chelatase ChlH (ChlH), and upregulation of ferrochelatase (FC) genes. Moreover, exogenously applied ALA did not show any effect on the expression of Chl synthesis-related genes under PEG treatment. These results showed a difference in suppressing ALA synthesis due to the high concentration of ALA and PEG treatment. Exogenously applied ALA did not affect the expression of HEMA and GSA, thus exogenous ALA regulated Chl synthesis not via the regulation of transcriptional level in ALA biosynthesis. However, the inhibition in Chl and endogenous ALA accumulation by PEG treatment may be attributed to downregulation of HEMA and ChlH, and upregulation of FC.

5-Aminolevulinic acid (ALA) biosynthetic and metabolic pathways and its role in higher plants: a review

“…Indicating that the improvement of photosynthesis by ALA in plants was not only related to PSII, but also to PSI and electron transfer chain. In addition, the application of ALA results in increases in the content of endogenous ALA. As elucidated in the research of oilseed rape, exogenous ALA enhanced the tetrapyrrol biosynthesis pathway and the content of chlorophyll (Liu et al 2016). The relative expression of upstream gene of ALA, GluTS, was upregulated by exogenous ALA (30 mg/L) and contents of intermediates (Proto IX, Mg-Proto IX and Pchlide) were increased in B. napus L. under 200 mM NaCl stress (Xiong et al 2018).…”

Effect of Low Temperature on Chlorophyll Biosynthesis and Chloroplast Biogenesis of Rice Seedlings during Greening

“…Thus, our results suggested the protective role of exogenous ALA and contribute to further illustrate its mechanism. Nevertheless, exogenous ALA increased chlorophyll accumulation in etiolated oilseed rape, but failed to enhance its cold tolerance [61]. Application of exogenous ALA is an exciting field to explore, and might be beneficial for increasing chlorophyll content and improving cold resistance of rice seedlings.…”

PP2A and microtubules function in 5‐aminolevulinic acid‐mediated H2O2 signaling in Arabidopsis guard cells

“…5‐aminolevulinic acid (ALA) is a key precursor in tetrapyrrole biosynthesis in all organisms, such as chlorophyll and heme in plants. It has been recognized as a vital plant growth regulator due to its various roles in several key physiological processes such as promoting plant growth and conferring abiotic stress tolerance in plants (Liu et al , Xu et al , Niu et al , Sun et al , Akram et al , Liu et al , Wu et al ). Increasing attention has been paid to ALA because of its environmental‐friendly characteristic and great application potential in agriculture (Wang et al , Akram and Ashraf ) and horticulture (Feng et al , An et al , Zheng et al , An et al , Zheng et al ).…”