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AbstractSorghum [Sorghum bicolor (L.) Moench] is one of the major fodder crops. Sufficient nitrogen (N) supply is essential for a good yield and forage quality. However, N excess may cause nitrate accumulation in the plant, which can be toxic to ruminant livestock animals. Silicon (Si) application reportedly enhances the utilization of N and reduces the nitrate content in plants. However, our knowledge regarding the interaction between Si and N in sorghum is still limited. Hence, this study investigated the possibility of nitrate content reduction by Si application in sorghum. We analyzed the nitrate content in the shoots of 6-week-old hydroponically grown plants with or without Si application. The analysis was also conducted with plants at the heading stage (13-week-old) receiving higher N supply. The dry matter production was not affected by Si application in either experiment. The assimilated N was slightly decreased by Si application in 6-week-old plants, but not in plants at the heading stage. The nitrate content was reduced by Si application in both experiments. The effect of Si application on the N metabolism was confirmed by a modulated expression of the genes for N transport and assimilation, in which an upregulation of the cytokinin signal transduction pathway might be involved. The in vitro digestibility was not significantly affected by Si application. These findings suggest that Si application benefits fodder sorghum production by reducing nitrate content without compromising the biomass yield and quality, although further study with plants grown under more practical conditions is necessary. [ABSTRACT FROM AUTHOR]

Sorghum [Sorghum bicolor (L.) Moench] has been receiving attention as a feedstock for biomass energy. Since nitrogen (N) significantly affects the plant biomass production, diagnosing the N status of sorghum during its growth would be significant. Therefore, in this study, we analyzed the changes in several physiological parameters of sorghum in response to N limitation, with the aim of identifying candidates of N status biomarkers in this species. Parameters responding early and sensitively to N deficiency were searched in hydroponically cultured seedlings, and their applicability to field conditions was examined. We found that the leaf chlorophyll content measured as a soil-plant analysis development (SPAD) value was promising as a candidate N status biomarker, as it showed responses consistent with N regimes in field conditions in multiple genotypes. A gene expression analysis was capable of detecting N deficiency sensitively at an early stage, although its application to practical situations requires further investigation to identify a suitable sets of marker genes. [ABSTRACT FROM AUTHOR]