Strigolactones (SLs) have recently been found to regulate shoot branching, but the functions of SLs at other stages of development and the regulation of SL-related gene expression are mostly unknown in Arabidopsis. In this study, we performed real-time reverse transcription-PCR (RT-PCR) and microarray analysis using wild-type plants and SL-deficient/insensitive mutants to understand the molecular mechanisms underlying SL biosynthesis and signaling. We found that there is responsiveness to SL in the gene expression of Arabidopsis seedlings, which includes feedback regulation of two carotenoid cleavage dioxygenase genes. Microarray analysis revealed that exogenously applied SL regulated the expression of several genes, including light signaling-related genes and auxin-inducible genes. We also found that MORE AXILLARY GROWTH (MAX)2 plays an important role in the expression of SL-regulated genes. Our data support previous studies indicating that SL might function at the seedling stage. Analysis of SL-responsive and MAX2 downstream gene candidates provides new opportunities to broaden our understanding of SL signaling.

SummaryA variety of insect species induce galls on host plants. Several studies have implicated phytohormones in insect-induced gall formation. However, it has not been determined whether insects can synthesize phytohormones. It has also never been established that phytohormones function in gall tissues.Liquid chromatography and tandem mass spectrometry (LC/MS/MS) were used to analyse concentrations of endogenous cytokinins and the active auxin IAA in the gall-inducing sawfly (Pontania sp.) and its host plant, Salix japonica. Feeding experiments demonstrated the ability of sawfly larvae to synthesize IAA from tryptophan. Gene expression analysis was used to characterize hormonal signalling in galls.Sawfly larvae contain high concentrations of IAA and t-zeatin, and produce IAA from tryptophan. The glands of adult sawflies, the contents of which are injected into leaves upon oviposition and are involved in the initial stages of gall formation, contain an extraordinarily high concentration of t-zeatin riboside. Transcript levels of some auxin-and cytokinin-responsive genes are significantly higher in gall tissue than in leaves.The abnormally high concentration of t-zeatin riboside in the glands strongly suggests that the sawfly can synthesize cytokinins as well as IAA. Gene expression profiles indicate high levels of auxin and cytokinin activities in growing galls.

The glycosylated forms of abscisic acid (ABA) have been identified from many plant species and are known to be the forms of ABA-catabolism, although their (physiological) roles have not yet been elucidated. ABA-glucosyltransferase (-GTase) is thought to play a key role in the glycosylation of ABA. We isolated an ABA-inducible GTase gene from UDP-GTase homologs obtained from adzuki bean (Vigna angularis) seedlings. The deduced amino acid sequence (accession no. AB065190) showed 30% to 44% identity with the known UDP-GTase homologs. The recombinant protein with a glutathione S-transferase-tag was expressed in Escherichia coli and showed enzymatic activity in an ABA-specific manner. The enzymatic activity was detected over a wide pH range from 5.0 to 9.0, the optimum range being between pH 6.0 and 7.3, in a citrate and Tris-HCl buffer. The product from racemic ABA and UDP-d-glucose was identified to be ABA-GE by gas chromatography/mass spectrometry. The recombinant GTase (rAOG) converted 2-trans-(ϩ)-ABA better than (ϩ)-S-ABA and (Ϫ)-R-ABA. Although trans-cinnamic acid was slightly converted to its conjugate by the GTase, (Ϫ)-PA was not at all. The mRNA level was increased by ABA application or by water stress and wounding. We suggest that the gene encodes an ABA-specific GTase and that its expression is regulated by environmental stress.Abscisic acid (ABA) is a plant hormone that regulates plant growth, development, seed maturation or dormancy, and germination (Fincher, 1989;McCarty, 1995;Leung and Giraudat, 1998) and that mediates such stress responses as environmental stress adaptation to salinity, low temperature, UV irradiation, and water deficiency, including the procedure for rapid stomatal closure by ion efflux from guard cells (Chandler and Robertson, 1994;Ingram and Bartels, 1996;Albinsky et al., 1999). In these phenomena, ABA induces or regulates corresponding gene expression in the biochemical and physiological processes (Leung and Giraudat, 1998;Rock, 2000;Sö derman et al., 2000). The ABA level is simultaneously regulated by catabolism and/or biosynthesis in these processes (Bray, 1997;Zeevaart, 1999). Stress not only stimulates ABA biosynthesis to increase its level, but also promotes ABA catabolism to increase phaseic acid (PA), dihydrophaseic acid (DPA), etc. (Zeevaart, 1980(Zeevaart, , 1983Creelman et al., 1987). Various findings from structure-activity relationships have demonstrated that the activities of ABA were markedly decreased or even lost when its side chain was modified (Walton, 1983). In general, active ABA can be rapidly metabolized to some inactive structures in higher plants through two main routes (Zeevaart and Creelman, 1988;Zeevaart, 1999;Barthe et al., 2000): One is the hydroxylation pathway, and the other is conjugation (Fig. 1). The former route involves active ABA first being converted to 8Ј-hydroxy ABA (HOABA) and then further metabolized to other inactive structures such as hydroxymethyl glutaryl (HMG)-HOABA, methyl ester (Me)HMG-HOABA, PA, DPA, etc. The latter is the simple c...

In plants, gibberellin (GA)-responding mutants have been used as tools to identify the genes that control specific steps in the GA-biosynthetic pathway. They have also been used to determine which native GAs are active per se, i.e., further metabolism is not necessary for bioactivity. We present metabolic evidence that the Dl gene of maize (Zea mays L.) controls the three biosynthetic steps: GA20 to GA1, GA20 to GA5, and GA5 to GA3. We also present evidence that three gibberellins, GA1, GA5, and GA3, have per se activity in stimulating shoot elongation in maize. The metabolic evidence comes from the injection of [17-13C,3H]GA20 and [17-13C,3H] GA5 into seedlings of dl and controls (normal and d5), followed by isolation and identification of the 13C-labeled metabolites by full-scan GC-MS and Kovats retention index.For the controls, GA20 was metabolized to GA1, GA3, and GA5; GA5 was metabolized to GA3. For the dl mutant, GA20 was not metabolized to GA1, GA3, or to GA5, and GA5 was not metabolized to GA3. The bioassay evidence is based on dosage response curves using dl seedlings for assay. GA1, GA3, and GA5 had similar bioactivities, and they were 10-times more active than GA20.linear and there is no evidence for a metabolic grid with the other pathways, as has been shown for cell-free preparations obtained from seeds of bean, cucumber, and pea (for review, see ref.3).The biological significance of the metabolic studies in maize comes from the use of GA mutants that exhibit a dwarf phenotype, yet respond by normal growth to applied GAs. Thus, the relative responses of the mutants to specific GAs together with information on the role of the genes in controlling specific steps in the pathway have led to the conclusion that only a limited number of GAs in the pathway are active per se, i.e., they do not require further metabolism to be bioactive (for reviews, see refs. 10-12).The purpose of the present study was to examine the metabolic steps, GA20 to GA5, GA5 to GA3 and GA20 to GA1 in relation to the dl mutation (blockage after GA20). To this end, [17-13C,3H]GA2o and [17-13C,3H]GAs were fed to dl seedlings and to controls (normal and d5 seedlings) and the metabolites from the feeds were analyzed by full-scan GC-MS. In addition, the bioactivities of GA20, GA1, GA5, and GA3 were determined using dl seedlings for assay.The gibberellins (GAs) are tetracarbocyclic diterpenes that occur naturally in higher plants (1). There is continued interest in the biosynthetic origin of the GAs since some of them are known to act as native regulators controlling a range of growth responses, including seed germination, floral development, and shoot elongation (for reviews, see refs. 2 and 3).All GAs are biosynthesized from trans-geranylgeranyl diphosphate (GGDP) via ent-copalyl diphosphate (CDP) and the tetracyclic hydrocarbon, ent-kaurene. ent-Kaurene is sequentially oxidized to ent-7a-hydroxykaurenoic acid, which is then rearranged to GA12-aldehyde and oxidized to GA12. At least three pathways diverge from GA12-aldehyde and ...

No abstract

To determine the means and variations in CH4 uptake and N2O emission in the dominant soil and vegetation types to enable estimation of annual gases fluxes in the forest land of Japan, we measured monthly fluxes of both gases using a closed‐chamber technique at 26 sites throughout Japan over 2 years. No clear seasonal changes in CH4 uptake rates were observed at most sites. N2O emission was mostly low throughout the year, but was higher in summer at most sites. The annual mean rates of CH4 uptake and N2O emission (all sites combined) were 66 (2.9–175) µg CH4‐C m−2 h−1 and 1.88 (0.17–12.5) µg N2O‐N m−2 h−1, respectively. Annual changes in these fluxes over the 2 years were small. Significant differences in CH4 uptake were found among soil types (P < 0.05). The mean CH4 uptake rates (µg CH4‐C m−2 h−1) were as follows: Black soil (95 ± 39, mean ± standard deviation [SD]) > Brown forest soil (60 ± 27) ≥ other soils (20 ± 24). N2O emission rates differed significantly among vegetation types (P < 0.05). The mean N2O emission rates (µg N2O‐N m−2 h−1) were as follows: Japanese cedar (4.0 ± 2.3) ≥ Japanese cypress (2.6 ± 3.4) > hardwoods (0.8 ± 2.2) = other conifers (0.7 ± 1.4). The CH4 uptake rates in Japanese temperate forests were relatively higher than those in Europe and the USA (11–43 µg CH4‐C m−2 h−1), and the N2O emission rates in Japan were lower than those reported for temperate forests (0.23–252 µg N2O‐N m−2 h−1). Using land area data of vegetation cover and soil distribution, the amount of annual CH4 uptake and N2O emission in the Japanese forest land was estimated to be 124 Gg CH4‐C year−1 with 39% uncertainty and 3.3 Gg N2O‐N year−1 with 76% uncertainty, respectively.

Fluorescence differential display was used to isolate the gibberellin (GA)-responsive gene, CsAGP1, from cucumber (Cucumis sativus) hypocotyls. A sequence analysis of CsAGP1 indicated that the gene putatively encodes a "classical" arabinogalactan protein (AGP) in cucumber. Transgenic tobacco (Nicotiana tabacum) plants overexpressing CsAGP1 under the control of the cauliflower mosaic virus 35S promoter produced a Y(␤Glc) 3 -reactive proteoglycan in addition to AGPs present in wild-type tobacco plants. Immuno-dot blotting of the product, using anti-AGP antibodies, showed that the CsAGP1 protein had the AGP epitopes common to AGP families. The transcription level of CsAGP1 in cucumber hypocotyls increased in response not only to GA but also to indole-3-acetic acid. Although CsAGP1 is expressed in most vegetative tissues of cucumber, including the shoot apices and roots, the GA treatment resulted in an increase in the mRNA level of CsAGP1 only in the upper part of the hypocotyls. Y(␤Glc) 3 , which selectively binds AGPs, inhibited the hormone-promoted elongation of cucumber seedling hypocotyls. Transgenic plants ectopically expressing CsAGP1 showed a taller stature and earlier flowering than the wild-type plants. These observations suggest that CsAGP1 is involved in stem elongation.

Early nodulin-like proteins (ENODLs) are chimeric arabinogalactan proteins (AGPs) related to the phytocyanin family. Although they show similarities with other phytocyanins, they lack amino acid residues for copper binding. Despite the existence of other phytocyanins, information about the function of ENODLs in plants is largely lacking. In this study, we characterized ENODL genes consisting of 22 members in Arabidopsis thaliana. Structure prediction indicated that most ENODLs are glycosylphosphatidylinositol-anchored chimeric AGPs. Expression analysis by real-time reverse transcription polymerase chain reaction indicated that most ENODL genes showed spatially specific expression, mainly in the flower organs. Furthermore, we obtained and analyzed 26 homozygous T-DNA insertion lines of 15 ENODL genes, but novel biological roles were not uncovered, probably due to functional redundancy. The detailed phylogenetic and expression analyses and characterization of the available insertion lines in this study might facilitate future studies to elucidate the biological roles of ENODLs.