Masayuki Katsumi

A single treatment of rice seedlings with 5-azacytidine induces heritable dwarfism and undermethylation of genomic DNA.

SummaryA single exposure of germinated rice seeds (Oryza sativa) to either of the DNA demethylating agents 5-azacytidine (azaC) or 5-azadeoxycytidine (azadC) induced dwarf plants. At maturity, seeds treated with azaC exhibited normal morphological characteristics in comparison with untreated controls except that their height (total stem length) was reduced by about 15%. The M1 progeny, obtained by self-fertilization of an azaC-induced dwarf plant, segregated into dwarf (35%) and apparently tall types (65%). The M2 progenies, obtained by self-fertilization of dwarf M1 plants, were also dwarf, while those from tall M1 plants were only tall. Genomic DNA isolated from mature leaves of azaC-treated seeds showed about a 16% reduction in the 5-methylcytosine (m5C) content in comparison with DNA from untreated samples. A similar reduction in the m5C content was also observed in the M1 and M2 progenies. Thus, both undermethylation and dwarfism induced by azaC treatment were heritable. The results suggest that azaC induced demethylation of genomic DNA, which caused an altered pattern of gene expression and consequently a reduction in plant stem length.

Rice gibberellin-insensitive gene homolog, OsGAI, encodes a nuclear-localized protein capable of gene activation at transcriptional level.

This paper reports isolation and properties of a rice gene, OsGAI, a putative homolog of the GAI of Arabidopsis thaliana. OsGAI encodes a polypeptide of 625 amino acids, which shows 53-55% identity to GAI and RGA from A. thaliana, and 85% identity to wheat rht-D1a and maize d8. Genomic DNA blot analysis indicated the OsGAI to be a single-copy gene in the rice genome. RNA blot hybridization showed that OsGAI transcripts increased within 6h upon GA(3) but not ABA application. This GA-induced increment in OsGAI transcripts did not require de novo protein synthesis. High levels of OsGAI transcripts were detected in nodes, internodes, leaf sheaths and ears of adult plants and leaf sheaths of young seedlings, where GA enhances cell elongation and division. Transiently expressed OsGAI-GFP fusion protein located to the nucleus in onion epidermal cells. Transactivation assays clearly indicated that OsGAI protein is a transcriptional activator or a coactivator.

EFFECTS OF GIBBERELLIN AND ABSCISIC ACID ON THE CORTICAL MICROTUBULE ORIENTATION IN HYPOCOTYL CELLS OF LIGHT-GROWN CUCUMBER SEEDLINGS

Effects of gibberellin (GA4) and abscisic acid (ABA) on the orientation of cortical microtubules (MTs) in the epidermal and cortex cells of light-grown cucumber (Cucumis sativus L. cv Aonagajibai) hypocotyls were examined by immunofluorescence microscopy. MTs were observed in the 0-1 mm region (region A) and 3-4 mm region (region D) below the cotyledonary node. GA4 promoted and ABA inhibited hypocotyl elongation. In the control, the predominant pattern of MT arrangement in the tangential surface of epidermal cells (Ep-t) was oblique in region A and oblique/longitudinal in region D, while in the radial surface of epidermal cells (Ep-r), the MT arrangement was mostly transverse in both regions. The MT arrangement in the radial surface of cortex cells (C-r) was all transverse in both regions. GA4 increased transversely oriented MTs and decreased obliquely and longitudinally oriented MTs, whereas ABA increased obliquely and longitudinally oriented MTs and decreased transversely oriented MTs in Ep-t and Ep-r in both regions. ABA counteracted GA4-induced effects on MT orientation as well as elongation. The frequency of the occurrence of transverse MTs in Ep-t but not in Ep-r and C-r was found to be highly correlated to the growth rate of the hypocotyl, suggesting that the epidermis is the essential tissue that limits the growth of the hypocotyl.

Biological activities of gibberellins and their glucosides in Pharbitis nil

Abstract Growth-promoting effects of gibberellins and their glucosides isolated from immature seeds of Japanese morning glory ( Pharbitis nil ) were compared in six bioassay systems. GA 3 glucoside exhibited much less activity than GA 3 in the dwarf rice (under aseptic conditions), dwarf maize ( d 1 , d 2 and d 5 ), cucumber and dwarf pea assays. GA 8 , GA 26 , GA 27 and GA 29 showed low activities in all the bioassay systems, while their glucosides were even less active. Thus gibberellin glucosides do not appear to be active in growth regulation.

Triiodobenzoic acid, an auxin polar transport inhibitor, suppresses somatic embryo formation and postembryonic shoot/root development in Eleutherococcus senticosus.

The effect of auxin polar transport inhibitor on somatic embryo development and postembryonic growth in Siberian ginseng (Eleutherococcus senticosus) was examined. In the presence of 2,3,5-triiodobenzoic acid (TIBA), an auxin polar transport inhibitor, embryo formation from embryogenic cells was suppressed, while cell division was not affected. When globular embryos at different stages were transferred onto medium containing TIBA, development of axial and bilateral polarity was suppressed in a stagespecific manner. In abnormal embryos induced by TIBA, further development of shoot and root apical meristems and vascular differentiation was also suppressed. Thus, abnormal development of embryos induced by inhibition of auxin polar transport resulted in plantlets without shoots and roots.

Endogenous gibberellins in the shoots of normal- and bush-typeCucumis sativus L.

Endogenous gibberellins (GAs) in the shoots of normal- (cv. Yomaki, YO) and bush-type (cv. Spacemaster, SP) cultivars of cucumber (Cucumis sativus L.) grown under natural conditions were analyzed. From both YO and SP grown for 40 days, after sowing, a series of C-13-H GAs including GA4, GA9, GA15, GA24, GA25, GA34, and GA51 were identified by gas chromatography-mass spectrometry (GC-MS; full scan). In addition to the above GAs, GA12 and GA70 were similarly identified from both YO and SP grown for 61 days after sowing. The endogenous levels of GA4 and GA9, which are highly active in promoting cucumber hypocotyl elongation, were quantified by GC-selected ion monitoring (GC-SIM) using [2H2]GA4 and [2H4]GA9 as internal standards. No remarkable difference in terms of endogenous levels of GA4/9 was observed between YO and SP in both growth stages (40 and 61 days after sowing).

Biological activities of new gibberellins A30-A35 and A35 glucoside

Abstract The plant growth-promoting activities of new gibberellins, GA 30 , GA 30 , GA 32 , GA 33 , GA 34 , GA 35 and GA 35 glucoside were evaluated in seven bioassays. In general GA 30 , GA 30 , and GA 35 showed fairly high biological activities, whilst GA 33 , GA 34 and GA 35 glucoside were almost inactive. GA 32 was highly active, behaving similarly to GA 3 . It is suggested that the C-11β and C-12α hydroxyl groups have little influence on growth-promoting activity, although the C-12α hydroxyl group reduces activity in the cucumber hypocotyl assay.

Hormonal Control of Root Hair Growth and Development

Physiological and morphological studies on root hairs trace back to the 18th Century (see Farr 1927a,b,c). The pattern of root hair growth and development is under the influence of various factors including genetic, physiological and environmental factors (see Ridge 1995b; Peterson and Farquhar 1996). Involvement of plant hormones in the control of root hair development and elongation has been the topic of much study. Whether or not a plant hormone is required for normal progress of the developmental process of root hairs, there are at least three criteria to be considered: (1) Production of the hormone by root hairs or supply of the hormone from other sources to root hairs. For this, though it is not easy to demonstrate root hairs per se produce plant hormones, root tissues can supply them to root hairs. In addition, under natural conditions, root hairs are exposed to microorganisms which produce plant hormones (Wang et al. 1982; Pegg 1985). (2) Stimulation of the normal process by exogenous supply of the hormone and/or suppression of the process by application of inhibitors of the hormone and its recovery by the hormone. For this, supportive evidence has been reported. (3) Suppression of the process in mutants related to the hormone such as those deficient in the hormone or hormone response.

Pseudogibberellin A1 as an inhibitor of the GA3-induced growth of rice seedlings

SummaryPseudogibberellin A1 inhibited the GA3-induced growth of rice seedlings; this inhibition was completely overcome by increasing the concentration of GA3. It is concluded that pseudogibberellin A1 may act as an antigibberellin.

Light-controlled sugar-starch interconversion in epidermal chloroplasts of light-grown cucumber hypocotyl sections and its relationship to cell elongation

Sugar-starch interconversion in epidermal chloroplasts of light-grown cucumber hypocotyl sections as a regulatory mechanism of the osmotic potential of the cell was studied in relation to cell elongation. The presence of chloroplasts in epidermal cells was confirmed by electron microscopy, and also the chloroplasts were shown to act as the site of sucrose-starch interconversion. Chloroplast starch formation was induced by light, which was more distinct in the presence of sucrose (50 mM). The starch formation was microscopically detectable even at 1 hr incubation in the light with sucrose. On the other hand, no starch formation was observed in the dark both in the presence and absence of sucrose. Red light was effective, but not blue light. A photosynthetic inhibitor, 3-(4-chlorophenyl)-1:1-dimethylurea, also inhibited starch formation. Thus, epidermal chloroplast starch formation was induced under conditions where cell elongation is small and the osmotic potential (Ψ0) of the epidermal cell is high. The sugar quantity (free sugar and reducing sugar) as the osmotica of the cell was larger in the dark than in the light, whereas the quantity of starch was greater in the light than in the dark. It is assumed from these results that one of the regulatory mechanisms of the osmotic potential of the epidermal cells in sugar-starch interconversion which occurs in epidermal chloroplasts.