| Summary: | 碩士 === 中興大學 === 生命科學系所 === 95 === One major fragrant compound found in many aromatic rice varieties is 2-acetyl-1-pyrroline (2-AP). Proline is known to provide nitrogen skeleton in jasmine rice KDML 105. Biosynthesis of proline is catalyzed by Δ1-pyrroline-5-carboxylate synthetase (P5CS) or Orn-d-aminotransferase using glutamate or ornithine as precursor and producing 1-pyrroline-5-carboxylate (P5C). P5C is reduced to proline via P5C reductase. Proline is catabolized to P5C via FAD- or NADP-dependent proline dehydrogenase (PDH) and P5C is further oxidized to glutamate via P5C dehydrogenase. The main focus of this thesis is to analyze the accumulation of proline and the activities of key enzymes in proline metabolism to the production of 2-AP in TNG 67 and SA0420 under different nitrogen and water status.
The amount of proline accumulated in SA0420 was 1.2-fold of TNG 67 at different growth stages. The activity of P5CS in SA0420 was 2-fold of TNG 67 and the activity of PDH in SA0420 was 0.8-fold of TNG 67. Therefore, the increase of proline accumulation in SA0420 is the result of increase synthesis and decrease degradation. There is no significant difference in the activity of OAT. Application of increase amounts of nitrogen fertilizer at seed-bearing stage increased the activity of P5CS in SA0420, but did not affect the proline content and the activity of PDH. Water-deficit treatments caused 1.2-fold increase of P5CS and 0.5-fold decrease of PDH in SA0420. Although the activities of key enzyme changed, the level of proline did not change in SA0420 under water-deficit treatments suggesting proline or P5C is metabolized through other metabolic pathways or translocated to other parts of plant.
A positive correlation was found between the activity of P5CS and 2-AP content. Huand et al (2007) found 6.5% P5C automatically converted into 2-AP in the presence of triose at room temperature, suggesting P5C is the precursor for 2-AP. Precursor feeding experiments showed that 5-fold increase in production of 2-AP when seedlings was fed by 14C-glutamate, while 2-fold increase when fed with 14C-proline, suggesting glutamate is the major precursor for 2-AP in SA0420.
In conclusion, elevated activity of P5CS in SA0420 leads to production of P5C and the excess P5C is converted to 2-AP in order to decrease the toxicity of this highly oxidative compound.
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