Abstract
BackgroundIt is becoming clear that ozone affects not only grain yield but also grain quality in rice. However, the biochemical mechanisms responsible for ozone-induced changes in appearance quality or components are poorly understood. We analyzed appearance quality and starch composition in the rice cultivars “Koshihikari” (japonica) and “Kasalath” (indica) grown under elevated ozone conditions.ResultsElevated ozone significantly increased the proportion of immature (mainly chalky) kernels in “Koshihikari” but not in “Kasalath”. Scanning electron microscopy of transverse sections of kernels showed that endosperm starch granules of “Koshihikari” ripened under elevated ozone were loosely packed with large spaces and contained irregular rounded granules. Amylose content was increased in “Koshihikari” kernels with ozone exposure, but was unchanged in “Kasalath” kernels. Distribution analysis of amylopectin chain length showed that ozone induces a decrease of long-side chains and alterations of short side-chains in “Koshihikari” kernels. Furthermore, Starch Synthase (SS) IIIa transcript levels in “Koshihikari” caryopses were decreased by elevated ozone.ConclusionsThe japonica cultivar “Koshihikari” showed significant deterioration in appearance quality of kernels caused by abnormal starch accumulation due to exposure to ozone. The alteration patterns of amylose and amylopectin in ozone-exposed rice kernels are similar to those in rice kernels harvested from SSIIIa-deficient mutants. These findings suggest that the increase of chalky kernels in ozone-treated “Koshihikari” is partly attributable to the repressed expression of SSIIIa involved in amylopectin side-chain elongation with ozone exposure. Elevated ozone reduced appearance quality in “Koshihikari” although it did not impair starch properties contributing to the eating quality of cooked rice.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-016-0079-4) contains supplementary material, which is available to authorized users.
Highlights
It is becoming clear that ozone affects grain yield and grain quality in rice
Effect of Ozone on Grain Yield and Quality in Two Rice Cultivars Grain yields were lowered to 4.2 and 5.2 % in “Koshihikari” and “Kasalath”, respectively, in plants grown under elevated ozone from that in plants grown under ambient air, the difference was not statistically significant (Table 1)
Expression Levels of Genes Involved in Starch Synthase in Ozone-Exposed Rice Cultivars Given that the content of long chains of amylopectin with degree of polymerization (DP) > 30 was reduced in “Koshihikari” kernels under elevated ozone levels from those in kernels grown under ambient air, we evaluated the expression in rice caryopses of the STARCH SYNTHASE (SS) IIIa gene, which plays an important role in generating long chains of amylopectin, and of other genes involved in starch synthesis (SSI and GRANULE BOUND (GB) SSI) (Fig. 5 and Additional file 2)
Summary
It is becoming clear that ozone affects grain yield and grain quality in rice. The biochemical mechanisms responsible for ozone-induced changes in appearance quality or components are poorly understood. It is becoming clear that ozone influences grain yield and grain quality of rice by increasing protein and reducing starch concentrations and absolute amounts of nutrient elements (Frei et al 2012; Huang et al 2012; Zheng et al 2013). The biochemical mechanisms responsible for ozone-induced changes in the components or appearance quality of rice kernels are poorly understood. Impairment of rice grain quality by elevation of tropospheric ozone concentration is of greater concern than a decline in rice yield, especially in East Asia
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