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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]

Steviol glycosides (SGs) are natural compounds present in Stevia rebaudiana (Bertoni) Bertoni, which are approximately 200-400 times sweeter than sucrose. A biosynthetic pathway of SGs shares a biosynthetic pathway of gibberellin (GA) through a formation of ent-kaurenoic acid. Previous studies have demonstrated that SG-related genes are upregulated by exogenous GA treatment. However, the transcription level of UGT85C2, which is involved in a glycosylation step to steviol from steviolmonoside and suggests a rate-limiting step in the SGs biosynthesis, remains controversial in GA treatments. To have a detailed understanding of the relationship between SGs and GAs, a concentration gradient of exogenous GA3, GA inhibitor daminozide (DAM), and naphthaleneacetic acid (NAA) was used for treatment by the leaf infiltration method. Results showed that transcription level of UGT85C2 and the total number of stevioside and rebaudioside-A induced by GA3, DAM, or NAA treatment were significantly upregulated compared to an untreated group. These results suggest that the GA biosynthetic pathway affects the number of SGs and that hormonal crosstalk occurs between GA and auxin, which changes the number of SGs in S. rebaudiana. Controlling the GA biosynthesis could be considered to modulate the yield of SGs. [ABSTRACT FROM AUTHOR]