Aromatic rice has a high market value due to its special fragrance and the most important compound in the grains of aromatic rice is 2-acetyl-1-pyrroline (2-AP). In an effort to improve the 2-AP content and the yield of aromatic rice, two known rice cultivars, Yungao and Yundi, were cultivated across two seasons, and two irrigation and nitrogen management practices were investigated. The results showed that the treatment management practice (TNW) treatment improved panicle number per hill, seed setting rate, and 1000 grain weight and grain yield for both cultivars in early and late season. Significant improvement in grain yield was only observed in Yundi in both seasons. Moreover, the 2-AP content in grains was increased for both cultivars in both seasons during grain filling period. Significant increase in 2-AP in grains was observed for Yungao at maturity in both seasons, at 7 d AH in early season and at 14 d AH in late season whilst for Yundi at 7 d AH, 14 d AH and 21 d AH in early season, and at 14 d AH in late season. Furthermore, 2-AP content in leaves and grains was decrease during grain filling period while proline content in grains was enhanced during grain filling period. Significant relationships were also observed between 2-AP and proline contents in the leaves/grains of both rice cultivars.
Changes of the content of starch, amylose and the activities of 3 key enzymes involved in starch synthetic metabolism in developing rice grains under four different temperature in phytotrons during grain filling stage of two aromatic rice varieties were studied. The results showed that compared with that under the lower temperature (21°C and 23°C), the content of starch and amylose and the activities of SBE and GBSS under higher temperatures (26°Cand 30°C) were generally higher at the beginning of the grain filling stage and obviously lower during the middle and late grain filling stage, with the exception of the activity SSS which were always higher under lower temperature. The relationship between the changes of activities of SSS, SBE and the variation of starch accumulating rate was very close and so did the relationship between GBSS activity and the amylose content. The lower activities of SSS, SBE and GBSS during the middle and late grain filling stage may be the key physiological factors which lead to the poorer progress quality and appearance quality of aromatic rice under high temperature.
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