The rice slender mutant (slr1-1) is caused by a single recessive mutation and results in a constitutive gibberellin (GA) response phenotype. The mutant elongates as if saturated with GAs. In this mutant, (1) elongation was unaffected by an inhibitor of GA biosynthesis, (2) GA-inducible alpha-amylase was produced by the aleurone layers without gibberellic acid application, and (3) endogenous GA content was lower than in the wild-type plant. These results indicate that the product of the SLR1 gene is an intermediate of the GA signal transduction pathway. SLR1 maps to OsGAI in rice and has significant homology with height-regulating genes, such as RHT-1Da in wheat, D8 in maize, and GAI and RGA in Arabidopsis. The GAI gene family is likely to encode transcriptional factors belonging to the GRAS gene superfamily. DNA sequence analysis revealed that the slr1-1 mutation is a single basepair deletion of the nuclear localization signal domain, resulting in a frameshift mutation that abolishes protein production. Furthermore, introduction of a 6-kb genomic DNA fragment containing the wild-type SLR1 gene into the slr1-1 mutant restored GA sensitivity to normal. These results indicate that the slr1-1 mutant is caused by a loss-of-function mutation of the SLR1 gene, which is an ortholog of GAI, RGA, RHT, and D8. We also succeeded in producing GA-insensitive dwarf rice by transforming wild-type rice with a modified SLR1 gene construct that has a 17-amino acid deletion affecting the DELLA region. Thus, we demonstrate opposite GA response phenotypes depending on the type of mutations in SLR1.

The rice slender mutant ( slr1-1 ) is caused by a single recessive mutation and results in a constitutive gibberellin (GA) response phenotype. The mutant elongates as if saturated with GAs. In this mutant, (1) elongation was unaffected by an inhibitor of GA biosynthesis, (2) GA-inducible ␣ -amylase was produced by the aleurone layers without gibberellic acid application, and (3) endogenous GA content was lower than in the wild-type plant. These results indicate that the product of the SLR1 gene is an intermediate of the GA signal transduction pathway. SLR1 maps to OsGAI in rice and has significant homology with height-regulating genes, such as RHT-1Da in wheat, D8 in maize, and GAI and RGA in Arabidopsis. The GAI gene family is likely to encode transcriptional factors belonging to the GRAS gene superfamily. DNA sequence analysis revealed that the slr1-1 mutation is a single basepair deletion of the nuclear localization signal domain, resulting in a frameshift mutation that abolishes protein production. Furthermore, introduction of a 6-kb genomic DNA fragment containing the wild-type SLR1 gene into the slr1-1 mutant restored GA sensitivity to normal. These results indicate that the slr1-1 mutant is caused by a loss-of-function mutation of the SLR1 gene, which is an ortholog of GAI , RGA , RHT , and D8 . We also succeeded in producing GA-insensitive dwarf rice by transforming wild-type rice with a modified SLR1 gene construct that has a 17-amino acid deletion affecting the DELLA region. Thus, we demonstrate opposite GA response phenotypes depending on the type of mutations in SLR1 .

Long day (LD) exposure of rosette plants causes rapid stem/petiole elongation, a more vertical growth habit, and flowering; all changes are suggestive of a role for the gibberellin (GA) plant growth regulators. For Arabidopsis (Arabidopsis thaliana) L. (Heynh), we show that enhancement of petiole elongation by a far-red (FR)-rich LD is mimicked by a brief (10 min) end-of-day (EOD) FR exposure in short day (SD). The EOD response shows red (R)/FR photoreversibility and is not affected in a phytochrome (PHY) A mutant so it is mediated by PHYB and related PHYs. FR photoconversion of PHYB to an inactive form activates a signaling pathway, leading to increased GA biosynthesis. Of 10 GA biosynthetic genes, expression of the 20-oxidase, AtGA20ox2, responded most to FR (up to a 40-fold increase within 3 h). AtGA20ox1 also responded but to a lesser extent. Stimulation of petiole elongation by EOD FR is reduced in a transgenic AtGA20ox2 hairpin gene silencing line. By contrast, it was only in SD that a T-DNA insertional mutant of AtGA20ox1 (ga5-3) showed reduced response. Circadian entrainment to a daytime pattern provides an explanation for the SD expression of AtGA20ox1. Conversely, the strong EOD/LD FR responses of AtGA20ox2 may reflect its independence of circadian regulation. While FR acting via PHYB increases expression of AtGA20ox2, other GA biosynthetic genes are known to respond to R rather than FR light and/or to other PHYs. Thus, there must be different signal transduction pathways, one at least showing a positive response to active PHYB and another showing a negative response.

Six phenolic antioxidative compounds [5-caffeoylquinic acid (chlorogenic acid), 3,5-dicaffeoylquinic acid, quercetin 3-galactoside, quercetin 3-glucoside, quercetin 3-(6-malonylglucoside), and quercetin 3-(6-malonylgalactoside) (tentative)] were identified from the leaves of Corchorus olitorius L. (moroheiya) by NMR and FAB-MS. The contents of these phenolic compounds, ascorbic acid, and alpha-tocopherol in C. olitorius leaves were determined, and their antioxidative activities were measured using the radical generator-initiated peroxidation of linoleic acid. The results obtained showed that 5-caffeoylquinic acid was a predominant phenolic antioxidant in C. olitorius leaves.

Gibberellin (GA) 20-oxidase (GA20ox) is a key enzyme that normally catalyzes the penultimate steps in GA biosynthesis. One of the GA20ox genes in rice (Oryza sativa L.), OsGA20ox2 ( SD1 ), is well known as the "Green Revolution gene", and loss-of function mutation in this locus causes semi-dwarfism. Another GA20ox gene, OsGA20ox1, has also been identified, but its contribution to plant stature has remained unclear because no suitable mutants have been available. We isolated a mutant, B142, tagged with a T-DNA containing three CaMV 35S promoters, which showed a tall, GA-overproduction phenotype. The final stature of the B142 mutant reflects internode overgrowth and is approximately twice that of its wild-type parent. This mutant responds to application of both GA3 and a GA biosynthesis inhibitor, indicating that it is a novel tall mutant of rice distinct from GA signaling mutants such as slr1 . The integrated T-DNAs, which contain three CaMV 35S promoters, are located upstream of the OsGA20ox1 open reading frame (ORF) in the B142 mutant genome. Analysis of mRNA and the endogenous GAs reveal that biologically active GA level is increased by up-regulation of the OsGA20ox1 gene in B142. Introduction of OsGA20ox1 cDNA driven by 35S promoter into the wild type phenocopies the morphological characteristics of B142. These results indicate that the elongated phenotype of the B142 mutant is caused by up-regulation of the OsGA20ox1 gene. Moreover, the final stature of rice was reduced by specific suppression of the OsGA20ox1 gene expression. This result indicates that not only OsGA20ox2 but also OsGA20ox1 affects plant stature.