Abstract
Aromatic rice (Oryza sativa) fetches a premium price due to the pleasant aroma. The major aroma compound 2-acetyl-1-pyrroline (2AP) has been found to be enhanced under stress. This condition can be considered to study the genes, precursors, enzymes, and metabolites involved in elevated levels of 2AP biosynthesis. In the present study, 100 mM salt treatment was given to two aromatic rice cultivars Ambemohar-157 (A-157) and Basmati-370 (B-370) at the vegetative stage (VS3). After salt treatment, in the leaves, 2AP contents were elevated by 2.2 and 1.8 fold in A-157 and B-370, respectively. Under these elevated 2AP conditions, the precursor amino acids (glutamate, putrescine, ornithine, and proline), their related genes, enzymes, and metabolites (methylglyoxal and γ-aminobutyric acid (GABA) related to 2AP biosynthesis were analyzed. In addition, agronomic characters were also studied. It was observed that the proline content was enhanced in both the cultivars by 29% (A-157) and 40% (B-370) as compared to control. The Δ1-pyrroline-5-carboxylate synthetase (P5CS) enzyme activity was increased in salt-treated plants leaf tissue by 31% (A-157) and 40% (B-370) compared to control. The P5CS gene expression was enhanced by A-157 (1.8 fold) and B-370 (2.2 fold) compared to control, putrescine content in A-157 and B-370 decreased by 2.5 and 2.7 fold respectively as compared to control. The ornithine decarboxylase (ODC) activity was enhanced in A-157 (12%) and B-370 (35%) over control. Further, ODC gene expression was enhanced in both the cultivars A-157 (1.5 fold) and B-370 (1.3 fold). The diamino oxidase (DAO) enzyme activity was increased by 28% (A-157) and 35% (B-370) respectively over control. The GABA content marginally increased over control in both the cultivars namely, A-157 (1.9%) and B-370 (9.5%). The methylglyoxal levels were enhanced by 1.4 fold in A-157 and 1.6 fold in B-370. Interestingly, the enhancement in 2AP in the vegetative stage also helped to accumulate it in mature grains (twofold in A-157 and 1.5 fold in B-370) without test weight penalty. The study indicated that the ornithine and proline together along with methylglyoxal contribute towards the enhancement of 2AP under salt stress.
Highlights
By ornithine decarboxylase (ODC) to produce 2AP
From the previous reports, it’s clear that if the aromatic rice is treated with salt stress during the vegetative phase, it enhances 2AP in the leaves as well as in the grains, but the enzymatic and molecular mechanisms related to 2AP enhancement and the related gene expression have rarely been studied[20]
In the present study, 100 mM salt treatment was given to two aromatic rice cultivars Ambemohar-157 (A-157) and Basmati-370 (B-370) at the vegetative stage ( VS3)
Summary
By ornithine decarboxylase (ODC) to produce 2AP. Another possible pathway to synthesize 2AP is through methylglyoxal non-enzymatic reaction directly with Δ1-pyrroline-5-carboxylate (P5C)[9,11]. In the leaves of aromatic rice, salinity elevated 2AP concentration[13]. Poonlaphdecha et al.[18] studied the effect of salinity at different growth phases in aromatic rice and revealed that during the vegetative and reproductive phase, it enhances 2AP but significantly reduces the crop yield. From the previous reports, it’s clear that if the aromatic rice is treated with salt stress during the vegetative phase, it enhances 2AP in the leaves as well as in the grains, but the enzymatic and molecular mechanisms related to 2AP enhancement and the related gene expression have rarely been studied[20]. In the leaves, 2AP contents were elevated by 2.2 and 1.8 fold in A-157 and B-370, respectively Under these elevated 2AP conditions, the precursor amino acids (glutamate, putrescine, ornithine, and proline), their related genes, enzymes, and metabolites (methylglyoxal and γ-aminobutyric acid (GABA)) related to 2AP biosynthesis were analyzed
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