Impact of abiotic stress and micronutrient supplementation on the 2-acetyl-1-pyrroline content in KDML105 rice (Oryza sativa L.)

This study investigated the effects of abiotic stress and mineral supplementation on 2-acetyl-1-pyrroline (2-AP) content in Thai jasmine rice (Oryza sativa L. cv. 'Khao Dawk Mali 105'; KDML105). Rice aroma quality fundamentally influences the market value of aromatic rice. Therefore, enhancing the aromatic compound, 2-acetyl-1-pyrroline (2-AP) could improve rice aroma quality. In this study, KDML105 rice plants at the reproductive stage were used to investigate the effects of abiotic stress (drought, salinity and combined salt-drought stress) and mineral supplementation (Ca, Cu, Mg, Fe, and Zn) on 2-AP content compared to the control plants which were not treated with abiotic stress and exogenous minerals supplementation. The results found that proline levels in plants which were treated with salt stress or combined salt-drought stress accumulated higher leaf proline content (7.7-fold and 9.7-fold increases) compared to those of control plants (30.15 µg/g FW). Although the proline content increased, there were no significant differences in 2-AP levels of the plants. In contrast, the proline content of plants subjected to minerals did not increase while the 2-AP content increased compared to the control plants (3.37 ppm), particularly in plants supplemented with Ca and Cu (6.10 and 5.26 ppm, respectively). These findings indicated that mineral supplements did not stimulate proline production. However, it could induce or suppress other compounds in 2-AP synthesis pathway, resulting in high 2-AP accumulation. This was probably due to the downregulation of the betaine aldehyde dehydrogenase 2 gene (BADH2). Not only gene regulations in the pathway, but also external factors, such as the drying process after harvesting, affect 2-AP content. The results revealed that the solar-dried grain method caused higher 2-AP content compared to hot-air-dried and undried grains. Thus, targeted mineral supplementation and appropriate post-harvest processes are involved in enhancing aromatic quality in jasmine rice. In addition, supplemented plants with Ca significantly enhanced FRAP activity accompanied by remarkable increases in both total phenolic and total flavonoid contents.