Noboru Murofushi

Involvement of jasmonic acid in elicitor-induced phytoalexin production in suspension-cultured rice cells

It has been suggested that jasmonic acid (JA) could be an integral part of a general signal transduction system regulating inducible defense genes in plants. It was reported that treatment with an elicitor (N-acetylchitoheptaose) induced production of phytoalexin in suspension-cultured rice (Oryza sativa L.) cells. In this study, the role of JA in the induction of phytoalexin production by N-acetylchitoheptaose was investigated. Exogenously applied ([plus or minus])-JA (10–4 M) clearly induced the production of momilactone A, a major phytoalexin, in suspension-cultured rice cells. On the other hand, in rice cells treated with N-acetylchitoheptaose, endogenous JA was rapidly and transiently accumulated prior to accumulation of momilactone A. Treatment with ibuprofen, an inhibitor of JA biosynthesis, reduced production of momilactone A in the cells treated with N-acetylchitoheptaose, but the addition of ([plus or minus])-JA increased production of momilactone A to levels higher than those in the elicited rice cells. These results strongly suggest that JA functions as a signal transducer in the induction of biosynthesis of momilactone A by N-acetylchitoheptaose in suspension-cultured rice cells.

Light effects on endogenous levels of gibberellins in photoblastic lettuce seeds

Gibberellin A1 (GA1), 3-epi-GA1 GA17, GA19, GA20, and GA77 were identified by Kovats retention indices and full-scan mass spectra from gas chromatography-mass spectrometry analysis of a purified extract of mature seeds of photoblastic lettuce (Lactuca sativa L. cv. Grand Rapids). Non-13-hydroxylated GAs such as GA4 and GA9 were not detected even by highly sensitive radioimmunoassay. These results show that the major biosynthetic pathway of GAs in lettuce seeds is the early-13-hydroxylation pathway leading to GA1, which is suggested to be physiologically active in lettuce seed germination. Quantification of endogenous GAs in the lettuce seeds by gas chromatography-selected ion monitoring using deuterated GAs as internal standards indicated that the endogenous level of GA1 increased to a level about three times that of dark control 6 h after a brief red light irradiation, and that far-red light given after red light suppressed the effect of red light. The contents of GA20 and GA19 were not affected by the red light irradiation. Evidence is also presented that 3-epi-GA1 is a native GA in the lettuce seeds.

Identification of gibberellins in the rice plant and quantitative changes of gibberellin A19 throughout its life cycle

The major endogenous gibberellin (GA) in shoots, roots and ears of the rice plant, Oryza sativa L. japonica cv. Nihonbare, was identified as GA19 by combined gas liquid chromatography-mass spectrometry (GC-MS) and GC-selected ion current monitoring (GC-SICM). Another GA present in these tissues in small quantity was tentatively identified as GA1 by GC-SICM, and GA4 may be present in the seeds (kernels) of 3rd-leaf-stage seedlings. Using GC-SICM, the GA19 content was quantified throughout the life cycle of rice plants. It was found to reach high levels (ca. 10–15 μg/kg fresh weight) in 3rd-leaf seedlings, at panicle initiation (shoots), and during heading and anthesis (ears). The levels of GA19 in Oryza sativa indica cv. T-136 underwent changes closely similar to those found in Nihonbare. The growth-promoting activity in rice of exogenous GA19 is generally considerably less than that of GA1. It therefore seems possible that GA19 functions as a “pool GA”. The level of active GAs such as GA1 may be regulated by the rate of biosynthesis of GA19 or its metabolic conversions.

New lead compounds for brassinosteroid biosynthesis inhibitors

The first brassinosteroid biosynthesis inhibitor is reported. Among newly synthesized triazole derivatives, 4-(4-chlorophenyl)-2-phenyl-3-(1,2,4-triazoyl)butan-2-ol (6) was found to inhibit the growth of cress seedlings, and this inhibition was recovered by the treatment of brassinolide, suggesting that compound 6 primarily inhibits brassinosteroid biosynthesis.

Metabolism of gibberellins in early immature bean seeds

Abstract The endogenous free gibberellins in two different stages of immature Phaseolus vulgaris seeds were investigated and GA 17 , GA 20 , GA 29 , a

Metabolism of gibberellins in maturing and germinating bean seed

Abstract Tritium-labeled gibberellins (GA 1 , GA 4 , GA 5 , GA 8 and GA 20 ) were fed to immature bean seeds 18 days after anthesis and their metabolic pathways were investigated. The results suggest that GA 4 and GA 20 are both converted to GA 1 , and the latter and GA 5 into GA 8 . Conversions to corresponding glucosides and glucosyl esters also occurred. On germination, GA 1 was rapidly converted into GA 8 glucoside, and a slight decrease in radioactivity of GA 1 glucosyl ester was observed.

Biosynthesis of brassinolide from teasterone via typhasterol and castasterone in cultured cells of Catharanthus roseus

The biosynthesis of brassinolide (BL) in crown gall and nontransformed cells of Catharanthus roseus in which BL, castasterone (CS), typhasterol (TY), and teasterone (TE) are endogenous was investigated using deuterated TY and TE as substrates. The metabolites were analyzed by gas chromatography-mass spectrometry (GC-MS) and/or GC-selected ion monitoring (SIM). It was found that these cells converted TY to CS and BL, as well as TE to TY and CS. Because the pathway from CS to BL in the cells has already been confirmed, a biosynthetic sequence of TE → TY → CS → BL was established. Reversible conversion between TE and TY was observed.

Conversion of 24-methylcholesterol to 6-oxo-24-methylcholestanol, a putative intermediate of the biosynthesis of brassinosteroids, in cultured cells of Catharanthus roseus

Precursor administration experiments with 2H-labeled 6-oxocampestanol, 6-deoxocastasterone and 6alpha-hydroxycastasterone in cultured cells of Catharanthus roseus were performed and the metabolites were analyzed by GC-MS. [2H6]Cathasterone was identified as a metabolite of [2H6]6-oxocampestanol, whereas [2H6]6alpha-hydroxycastasterone and [2H6]castasterone were identified as metabolites of [2H6]6-deoxocastasterone, and [2H6]castasterone was identified as a metabolite of [2H6]6alpha-hydroxycastasterone, indicating that 6-deoxocastasterone is converted to castasterone via 6alpha-hydroxycastasterone. In addition, 6-deoxocathasterone, a putative biosynthetic intermediate in the late C6-oxidation pathway, was identified as an endogenous brassinosteroid. These studies provide further evidence supporting our proposed biosynthetic pathways for brassinolide.

Biosynthesis of brassinolide from castasterone in cultured cells of Catharanthus roseus

Feeding experiments with tritium- and deuterium-labeled castasterone (CS) were conducted with three cell lines of Catharanthus roseus, including crown gall cells and nontransformed cells. In all three cell lines, the conversion of CS to brassinolide (BL) was observed and unequivocally confirmed by gas chromatography/mass spectrometry (GC/MS). This is the first conclusive evidence that CS is the biosynthetic precursor of BL.

The methyl ester of a new gibberellin, GA73: the principal antheridiogen.dta in Lygodium japonicum

The principal antheridiogen in the fern Lygodium japonicum was isolated and characterized as the methyl ester of a new gibberellin, GA73 (9,11-didehydro-GA9). In L. japonicum, GA73 methyl ester exhibited high activity in inducing antheridial formation at 10-15 M and dark spore germination at 10-12 M and in inhibiting archegonial formation at 10−12 M.