BackgroundFragrant rice, including Thai jasmine and Indian basmati varieties, is highly valued by consumers globally. 2-acetyl-1-proline (2-AP) is the major compound responsible for the aromatic character of fragrant rice. Previously, environmental factors such as water management and salinity have been proven to influence 2-AP levels in fragrant rice; assessing the effect of additional environmental factors on 2-AP concentration is therefore eminent. The level of solar radiation (solar intensity; SI) to which a crop is exposed can affect growth, yield and grain quality, and other photosynthetic and physiological characteristics. In this study the effect of shading (i.e. the reduction of SI) on yield, quality, and 2-AP concentration in two elite Chinese fragrant rice varieties, ‘Yuxiangyouzhan’ and ‘Nongxiang 18’, has been investigated. Furthermore, accumulation of the plant stress response molecules proline and gamma-aminobutyric acid, which have also been implicated in pathways leading to 2-AP production, was assessed to study shading effects on these compounds in fragrant rice, and to further possibly determine fluxes in biochemical pathways leading to 2-AP accumulation.ResultsThis study has revealed significant changes in the yield and quality characters under shading treatment. Additionally, 2-AP and GABA content in grains was significantly increased for all shading treatments in both varieties. In addition to 2-AP, ten other volatile compounds were studied; results indicated that shading treatments could have a selective effect on the metabolism of these volatile compounds.ConclusionsIn this study, we have demonstrated that shading during grain filling has significant effects on yield and quality traits in rice, and leads to the accumulation of GABA and 2-AP. We discuss the implications of these findings in terms of pathways leading to 2-AP and GABA production in fragrant rice, which have not been fully elucidated. The shading effect on ten additional volatile compounds is also discussed. Finally we discuss possible effects of variation in solar intensity resulting from anthropogenic emissions on fragrant rice production.

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BackgroundPlant growth regulators play important roles in plant growth and development, but little is known about roles of plant growth regulators in yield, grain qualities and antioxidant enzyme activities in super hybrid rice. In this study, gibberellic acid(GA3), paclobutrazol (PBZ), 6-Benzylaminopurine(6-BA) treatments and distilled water (control) were sprayed to two hybrid rice cultivars (Peizataifeng and Huayou 86) at the heading stage in the field experiments in both early and late season in 2007. Treatments were arranged in a split-plot design with four replications. Cultivars treatments with two newly developed super hybrid rice Peizataifeng and Huayou86 were the main plots and plant growth regulators treatments were the subplots. Subplot treatments included (1) plots sprayed with distilled water(CK), (2) plots sprayed with 20 mg L-1 GA3 prepared using 95% ethanol as surfactant(GA3), (3) plots sprayed with 50 mg L-1 PBZ(PBZ), (4) plots sprayed with 30 mg L-1 6-BA(6-BA).ResultsSpraying PBZ with 50 mg L-1 or 6-BA with 30 mg L-1 at the heading stage could increase the number of spikelets per panicle, seed setting rate and grain yields in Peizataifeng and Huayou86 in both seasons. PBZ treatment also significantly improved head rice rate and amylose content in Peizataifeng and Huayou86 in early season. Furthermore, it was observed that spraying PBZ or 6-BA could increase super oxide dismutase (SOD) and peroxidase (POD) activities, decrease accumulation of malendialdehyde (MDA) in flag leaves at the late growth stage.ConclusionsApplication of PBZ or 6-BA partially alleviated the detrimental effects of rice senescence by modulating the activity of enzymatic antioxidants, and improving antioxidant system, which helped in sustaining plant growth. Therefore, spraying PBZ with 50 mg L-1 or 6-BA with 30 mg L-1 at the heading stage could increase grain yields and improve grain qualities in the two super hybrid rice.Electronic supplementary materialThe online version of this article (doi:10.1186/1939-8433-6-9) contains supplementary material, which is available to authorized users.