# Effects of Different Planting Environments on the Fragrance of _Dalixiang_ (_Oryza sativa_ L.)
## 4 Discussion  
Previous reports have firmly established that higher altitudes play a pivotal role in enhancing the 2 AP content [9; 10; 23]. Moreover, during the heading stage, lower temperature conditions (22/16 \({}^{\circ}\)C) have been demonstrated to be far more conducive to 2 AP accumulation compared to higher temperatures (32/26 \({}^{\circ}\)C) [24]. Similarly, at the ripening stage, rice grains cultivated under cooler temperatures (25/20 \({}^{\circ}\)C) exhibit significantly elevated 2 AP levels than those grown under warmer conditions (35/30 \({}^{\circ}\)C) [25]. Research conducted by [PERSON] et al. [26] and [PERSON] et al. [27] has revealed that Guiyang features a lower average annual temperature and a higher average altitude relative to Meitan. Our study corroborates these findings, as the _Dalixiang_ rice planted in Guiyang consistently showed a higher 2 AP content (Figure 1B,C). Additionally, the existing literature indicates that elevated levels of soil organic matter, total nitrogen, and available nitrogen are highly favorable for 2 AP accumulation [13; 14; 15; 16; 17; 18; 28]. Our data further demonstrates that the soil at the Guiyang planting site is rich in ammonium nitrogen, organic matter, total nitrogen, and available nitrogen, which aligns with the significantly higher 2 AP content detected in _Dalixiang_ rice cultivated there (Table 2, Figure 1B,C). Therefore, in addition to altitude and temperature, these soil nitrogen-related components and organic matter are critical determinants of the 2 AP content in _Dalixiang_. The biosynthesis of 2 AP is primarily attributed to mutations in the _OsBadh2_ gene. Such mutations lead to the production of truncated or non-functional betaine aldehyde dehydrogenase (BADH2), thereby preventing the conversion of GABA-ald to GABA. Consequently, GAB-ald spontaneously cyclizes into Delta1-pyrroline, which ultimately forms 2 AP [29; 30]. In our study, at the Guiyang planting site, both the expression of the _OsBadh2_ gene and the activity of the BADH2 enzyme during the heading stage of _Dalixiang_ were significantly suppressed. Concurrently, there was a marked reduction in GABA content (Figures 1A and 2A,B). We thus hypothesize that the environmental conditions in Guiyang downregulate _OsBadh2_ expression during the heading stage, inhibiting GABA accumulation. This, in turn, promotes an increase in 2 AP content in the leaves, ultimately facilitating 2 AP accumulation in mature grains. MG, another direct precursor of 2 AP synthesis (apart from Delta1-pyrroline), is generated during the conversion of glyceraldehyde-3-phosphate to dihydroxyacetone phosphate, a reaction catalyzed by TPI encoded by the _OsTPI_ gene. MG primarily supplies the acetyl group required for the acetylation of Delta1-pyrroline to form 2 AP [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31]. Our findings show that _Dalixiang_ rice grown in Guiyang exhibited significantly higher levels of MG, _OsTPI_ gene expression, and TPI enzyme activity (Figures 3A, 4A and 5A). This strongly