5-Aminolevulinic Acid (ALA) Alleviated Salinity Stress in Cucumber Seedlings by Enhancing Chlorophyll Synthesis Pathway

Abstract

5-Aminolevulinic acid (ALA) is a common precursor of tetrapyrroles as well as a crucial growth regulator in higher plants. ALA has been proven to be effective in improving photosynthesis and alleviating the adverse effects of various abiotic stresses in higher plants. However, little is known about the mechanism of ALA in ameliorating the photosynthesis of plant under abiotic stress. In this paper, we studied the effects of exogenous ALA on salinity-induced damages of photosynthesis in cucumber (Cucumis sativus L.) seedlings. We found that the morphology (plant height, leave area), light utilization capacity of PS II [qL, Y(II)] and gas exchange capacity (Pn, gs, Ci, and Tr) were significantly retarded under NaCl stress, but these parameters were all recovered by the foliar application of 25 mg L-1 ALA. Besides, salinity caused heme accumulation and up-regulation of gene expression of ferrochelatase (HEMH) with suppression of other genes involved in chlorophyll synthesis pathway. Exogenously application of ALA under salinity down-regulated the heme content and HEMH expression, but increased the gene expression levels of glutamyl-tRNA reductase (HEMA1), Mg-chelatase (CHLH), and protochlorophyllide oxidoreductase (POR). Moreover, the contents of intermediates involved in chlorophyll branch were increased by ALA, including protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX, protochlorophyllide (Pchlide), and chlorophyll (Chl a and Chl b) under salt stress. Ultrastructural observation of mesophyll cell showed that the damages of photosynthetic apparatus under salinity were fixed by ALA. Collectively, the chlorophyll biosynthesis pathway was enhanced by exogenous ALA to improve the tolerance of cucumber under salinity.

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

“…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). Moreover, under 50 mM NaCl stress, spraying ALA on cucumber leaves significantly reversed the depression of chlorophyll biosynthesis, up-regulated the expression level of genes related to Mg-branch, including CHLH, POR and CAO (Wu et al 2018). It indicated that the primary fluorescence of chlorophyll and the electron transfer rate of light harvesting pigment will be enhanced, and ultimately result in the promotion of photosynthesis in photosynthetical system.…”

Beneficial role of acetylcholine in chlorophyll metabolism and photosynthetic gas exchange in Nicotiana benthamiana seedlings under salinity stress

“…The salinity‐mediated decline in expression of genes (including HEMA1, CHLH and CAO ) involved in chlorophyll biosynthesis was mitigated by exogenous ACh application; particularly CHLH , which encodes the key H‐subunit of Mg‐chelatase, a crucial regulator in the Fe‐branch (Wu et al . ). In this study, we found that exogenous ACh further increased transcription levels of PAO and RCCR compared with those observed under salt stress conditions (Fig.…”

Hydrogen peroxide as a mediator of 5‐aminolevulinic acid‐induced Na+ retention in roots for improving salt tolerance of strawberries

“…ALA has been found to induce antioxidant enzyme activities (Nishihara et al , Akram and Ashraf ), as well as nonenzymatic antioxidant substances, such as ascorbate, glutathione, proline and polyphenols, which are involved in the elimination of excess ROS and the prevention of oxidative stress (Wongkantrakorn et al , Al‐Ghamdi and Elansary ). Recently, several studies have emphasized that the mechanism of ALA‐improved plant stress tolerance is associated with the promotion of tetrapyrrole metabolism (Nguyen et al , Niu and Ma , Wu et al , Xiong et al ). These are in agreement with our previous study, where Wang et al () found that the germination of pak choi seeds, promoted by ALA under salinity, depended on its conversion into tetrapyrroles.…”