## 3 Discussion  
We reported that GABA accumulation in germinated rice was detected at 12 h duration, and the highest content was about 1.4-fold that obtained from the rice germinated for 24 h compared with 0 h (Figure 1). The accumulation of GABA after the highest value at a 24-h germination duration rapidly decreased, and the lowest content occurring at 96 h was 2.5-fold lower than that at 24 h. As previously reported, [PERSON] and [PERSON] [26] found for that almost 21 rice varieties, including the upland rice varieties, the highest GABA accumulation was obtained from rice germinated for 24 h. A slight difference was observed from a study of Indica and Japonica rice, in which the highest GABA accumulations were detected at 36 h for both rice genotypes. At the peak of GABA accumulation, Indica rice seems to have a higher GABA accumulation than Japonica rice, while the glutamate decarboxylase activity (GAD) of both rice genotypes appeared in the highest value at 24 h [19]. The accumulation of GABA and 2 AP in plants is synthesized via l-proline metabolism, and acts as active BADH2 catalyzing the conversion of Gabald to GABA, while the inactive BADH2 cyclisation of Gabald forms \(\Delta^{1}\)-pyrroline and finally the addition of an acetyl group forms 2 AP [6; 7]. In plants, other pathways for GABA accumulation may occur via the GABA shunt [9]. Our results show that the 2 AP content of the non-irradiated rice (0 Gy) was 23-fold lower than the highest 2 AP content of the irradiated rice (20 Gy). On the other hand, the GABA content of the non-irradiated rice (0 Gy) was 2.6-fold higher than the lowest GABA content of the irradiated rice (300 Gy). Moreover, the 2 AP content of the irradiated rice increased with all gamma doses compared with the non-irradiated rice, while the GABA content of the irradiated rice decreased with all gamma doses compared with the non-irradiated rice. Recently, we reported the effect of gamma irradiation on the 2 AP content and plant growth of Thai black glutinous rice. The present data indicated that the 2 AP content of the irradiated rice shoots were higher than those of the rice shoots of non-irradiated rice. Also, the 2 AP content of the rice grains was stimulated by gamma irradiation, and at high gamma doses the 2 AP content was higher than that of the low gamma doses [25]. A previous researcher reported that high gamma doses cause DNA damage, inhibition of cell cycle, base deletions and base substitution, decrease of soluble protein, decrease of photosynthetic pigments and inhibition of plant growth [21; 24; 25; 27; 28; 29]. These effects by gamma irradiation have hypothesized the inhibition of GABA accumulation in both pathways (l-proline metabolism and GABA shunt), while the inhibition of the GABA content via l-proline metabolism may activate the synthesis of 2 AP content. This suggests that the accumulation of both GABA and 2 AP occurs via l-proline metabolism. Furthermore, our results showed larger changes in 2 AP contents than in GABA contents between non-irradiated and irradiated rice; this result may be because GABA is synthesized via two pathways and while 2 AP is synthesized only via l-proline metabolism. Our study shows that the volatile compounds of irradiated rice decreased with the increase of the gamma dose (Tables 1 and 2). A previous researcher reported that the increase of the gamma dose caused a decrease of biochemical compounds [29]; this may explain the decrease in volatile compounds in our study. The volatile compounds 2 AP and octanal have been abundantly reported in fragrant rice [3; 4; 5; 30]. Our results show that these compounds were detected for all gamma doses, and the 2 AP content of the irradiated rice was at a higher level than that of the non-irradiated rice, also the level of Octanal in the irradiated rice seemed to be higher than that of the non-irradiated rice (Tables 1 and 2). Concerning Octanal, this compound is related to sweet and odor-active compounds [31].