Plant cells form a highly dynamic microtubule network organized into different arrays that are essential for many important cellular activities. A key feature of microtubules is their dynamic behaviour in which individual microtubules stochastically switch between periods of growth and disassembly. This feature contributes substantially to the rapid reorganization of the microtubule system in response to environmental and developmental stimuli. In this review we highlight recent developments on the dynamic behaviour of microtubules in plant cells and discuss some of the mechanisms responsible for the regulation of microtubule turnover. We also include an outline of the contribution of the dynamics toward the overall arrangement of the plant microtubule network. Special attention is given to the spatiotemporal changes in the microtubule configuration and dynamics during the establishment of the relationships between plants and other organisms.
Plants in the genus Arabidopsis are facultative LD plants that flower much earlier under LD conditions than SD regimens, with the photoperiod (or LD) pathway contributing to floral acceleration. LHY and CCA1 genes, among other factors, have central roles in the circadian clock of Arabidopsis, which plays a key role in measuring day length. GI gene mediates the circadian clock and floral activator genes, CO and FT, to control photoperiodic flowering. GI is required to set the peak phase of CO expression at the end of the light period under LD conditions, so that the CO protein is stabilized and activated by light to increase FT expression. However, recent studies have demonstrated that the role of SDs is not solely to switch off CO activity. For example, GI interacts with SPY, a negative regulator of the GA signal. The flowering times of gi mutants were still significantly later under SD conditions than LD regimes, which suggests that GI has a potential role in accelerating the start of flowering, even under SDs. Over-expression of either FT or TSF genes caused early flowering, and the acceleration of flowering was enhanced under SDs, suggesting that SDs have an additional role to that in the LHY/CCA1-GI-CO-FT pathway. In this short review, we discuss the hidden roles of SDs in controlling flowering based on recent studies of the molecular genetics of flowering time in Arabidopsis.
Current GM crops may not appeal to Africa because of relevance, proprietary issues, and a negative reaction towards GM foods in Europe. Nonetheless, Bt cotton may hold a promise if fair access to the technology is ensured and biosafety structures are put in place. However, Africans may continue raising the biosafety flag in order to avoid being cornered by unfair trade rules. Africans should not overstretch biosafety and socio-economic concerns to the extent of putting barriers against biotechnology adoption than the circumstances on the ground merit. African countries should build domestic capacity through formation of linkages with advanced research institutes and international organizations to make use of biotechnology. However, constraints to coordinating the existent but fragmented domestic capacity across organizational barriers ought to be overcome. In Africa, presence of vocal scientists that articulate the merits of biotechnology and experience with the private sector are positive signals and a strong political clout of the Ministry of Environment a negative signal for a GM-friendly national policy. A transparent dialogue among stakeholders should result in a shared vision required to balance GM regulation with the need to adopt available technologies and develop technological capability. Biotechnology-proficient countries may need to understand the concerns of the poor and may put the trade magic behind to reassure Africans to see biotechnology through biosafety lenses only.
We have cloned gibberellin (GA) 3β-hydroxylase cDNA, (HvGA3ox), a homolog of the rice gene OsGA3ox from germinating barley seeds. HvGA3ox cDNA was expressed in Escherichia coli as a fusion protein capable of oxidizing GA9 to GA4 and GA20 to GA1. Deduced amino acid sequence analysis showed that HvGA3ox was identical to HvGA3ox2, which shares a high homology with the OsGA3ox2 isoform that plays an important role for induction of α-amylase in germinating rice seeds. Northern blot analysis showed that HvGA3ox2 gene was expressed only in germinating seeds, not in other organs. Typical feedback regulation was not observed in seedling treated with either biologically active GA (GA3) or uniconazole, an inhibitor of GA biosynthesis. HvGA3ox2 mRNA was detected from 12 h after imbibition just before expression of α-amylase gene, Amy1. In situ hybridization of germinating seeds revealed that HvGA3ox2 mRNA was localized in the epithelium up to at least 3 days after imbibition. Our results suggest that GA biosynthesis in epithelium is important for expression of α-amylase in germinating barley seeds, and that HvGA3ox2 encodes the key enzyme of this event.
9-Hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid (KODA) induces flowers in Lemna paucicostata after reacting with catecholamine (Yokoyama et al. 2000; Yamaguchi et al. 2001), and changes in endogenous KODA levels during the flower-inductive phase in short-day-induced cotyledons are closely related to flower induction (Suzuki et al. 2003). Here, we examined the change of KODA level after the flower induction period. KODA showed a transient increase in immature flower buds in all the plants we examined, i.e., Pharbitis nil, Dianthus caryophyllus L., Dendranthema grandiflorum Kitam. and Eustoma russellianum Griseb. No such increase of KODA was seen in foliar buds of P. nil. These phenomena indicate that KODA may be involved in flower formation, as well as flower induction.
We established the adventitious-root cultures of Iris germanica, a monocotyledonous plant known for isoflavonoid production. Irigenin (5,7,3′-trihydroxy-6,4′,5′-trimethoxyisoflavone) and iristectorigenin A (5,7,3′-trihydroxy-6,4′-dimethoxyisoflavone) along with their 7-O-β-D-glucosides, iridin and iristectorin A, respectively, were found as the major components in adventitious roots in the liquid medium, and the total isoflavone content was about 3.6 µmol per g fresh weight in 3-week-old cultures, which was much higher than the 0.7 µmol per g dry weight in the rhizome previously reported (Ali et al. 1983 Phytochemistry 22: 2061). Abiotic stress was applied by addition of 3 mM cupric chloride (CuCl2) to the liquid medium. The isoflavone glucoside content was increased during the initial 6 h of CuCl2 treatment, which was followed by a decrease; the aglycone level continued to increase throughout the 48 h of treatment. The decrease in glucoside content was negatively correlated with the increase in aglycone content between 6 and 48 h. The total isoflavone content (glucosides+aglycones) at 6 h after the start of CuCl2 treatment was 1.4-fold the initial value, and nearly the same content was maintained for 48 h. Thus, the main effect of CuCl2 treatment appeared to be the induction of hydrolysis of isoflavone glucosides. A cDNA of chalcone synthase was cloned, and the mRNA was expressed in the culture producing isoflavones.
A new MADS-box gene, IbAGL17, was isolated from the tuberous root of sweetpotato (Ipomoea batatas (L.) Lam. cv. Kokei 14). IbAGL17 was expressed in vegetative tissues, especially root tissues; thickened pigmented root and tuberous root. On sequence alignment, IbAGL17 fell into the AGL17 subfamily composed of AGL16, AGL17, ANR1, NMHC5 and DEFH125, which share high sequence similarity. A transcript of IbAGL17 in root and petiole was found in the vascular tissues in tissue printing. These results suggest that expression pattern of IbAGL17 may lead to a higher proliferation potential of vegetative tissues and root development in sweetpotato.
Due to indiscriminate collection, the natural habitat of Hylotelephium sieboldii and H. sieboldii var. ettyuense have been significantly reduced. For ex situ conservation and efficient vegetative propagation, a micropropagation system based on adventitious shoot regeneration was developed for these two endangered species. Leaves, stems and roots of in vitro-grown plantlets, and flower buds of greenhouse-grown plants were used as explants. For H. sieboldii, adventitious shoots were most efficiently regenerated from flower bud explants on a medium containing 1 mg l−1 each of NAA and BA. Adventitious shoot regeneration from flower bud explants under this condition was also obtained in H. sieboldii var. ettyuense, but with lower efficiencies. Adventitious shoots of both species rooted and developed into plantlets on a medium containing 0.1 mg l−1 IBA. Almost all of these plantlets were successfully transplanted to the greenhouse. At least at early stage of growth, they showed no apparent morphological alterations.
Genomic information of Arabidopsis thaliana can be obtained from various public databases. Given that naming conventions often vary between databases and that the same genes can be annotated differently, we developed a web-based tool, KATANA (Kazusa Arabidopsis thaliana Annotation Abstract; http://www.kazusa.or.jp/katana/), to guide users searching for Arabidopsis genomic information to the relevant public databases from a single site. The tool contains information and annotations of genes and proteins, gene families, gene ontology (GO) terms, metabolic pathways and gene expression data from the Massively Parallel Signature Sequencing (MPSS) experiments. Given that entries in the tool are hyper-linked to those of the databases, detailed information can be accessed at the original sites. Advanced searches for metabolic pathways and GO terms can also be performed.
To investigate whether the rbcL-accD region from the chloroplast genome would be suitable for phylogenetic studies of Moraceae, we determined 2 kb of the nucleotide sequence for this region in 10 species in the family Moraceae. Genera examined included Morus, Artocarpus, Ficus, Broussonetia and Dorstenia. In the intergenic spacer and accD region, 220 variable sites and 16 indels (insertions and deletions) were found. However, rbcL-accD was highly conserved among Morus species. No difference was found among three Japanese mulberry species, M. alba cv. Minamisakari, M. bombysis cv. Kenmochi and M. latifolia cv. Kokusou 21. Only one polymorphism was found in M. nigra, which is native to West Asia. Possible transfer of the chloroplast genome between Morus species and potential use of the intergenic spacer and accD regions to study phylogenetic relationships within Moraceae are discussed.
In conjunction with Ca2+ signaling, the subcellular localization of Ca2+ channels in various plant cells has been under intense scrutiny. The present study focused on the subcellular localization of OsTPC1, a putative voltage-dependent calcium channel in rice. A newly developed antibody to the linker domain of OsTPC1 was shown to bind this protein in vitro. Immunoblotting of a plasma membrane (PM)-enriched fraction obtained by aqueous two-phase partitioning, as well as indirect immunofluorescence confocal microscopy of rice protoplasts, supported the idea that OsTPC1 is predominantly localizes in the PM, at least of suspension-cultured rice cells.
Mode of soyasaponins and betulinic acid accumulation was examined in cultured cells of Glycyrrhiza glabra L. (licorice). The time course of their accumulation was different in the cultured cells. Yeast extract promoted betulinic acid accumulation, whereas soyasaponin accumulation was suppressed. These results indicate that soyasaponin and betulinic acid production are differently regulated in cultured cells of G. glabra.
Zoysiagrass displays good adaptability to its environment, and is utilized for golf courses and athletic fields. Immature inflorescences were obtained from 5 varieties of zoysiagrass, ‘Miyako’, ‘Misato’, ‘Meyer’, ‘Yamato’ and ‘B14’. However, regenerated plants were only obtained in ‘Miyako’. A relationship between the size of the inoculated inflorescences and the callus induction frequency was observed. A high frequency of callus formation was shown in earlier developmental stages shorter than 20 mm in the length of inflorescences in ‘Miyako’. Plant regeneration was observed efficiently when the compact calli, which were formed in the callus induction medium (Linsmaier and Skoog 4 mg l−1 thiamine–HCl, 100 mg l−1 α-ketoglutaric acid, 2 mg l−1 2,4-D, 0.1 mg l−1 BA, 3% sucrose, 0.2% gelrite), were transferred to the regeneration medium (Linsmaier and Skoog 1 mg l−1 BA, 3% maltose, 0.5% gelrite ) in ‘Miyako’.
Protoplasts were isolated from embryogenic calluses of Muscari armeniacum ‘Blue Pearl’, which had been subcultured for 3 years. Protoplasts started to divide after 5–7 days of culture, and colonies consisting of 50–100 cells were produced after one month. The highest plating efficiency (10.9%) was obtained by using a medium containing 5.4 µM NAA and 4.4 µM BA, 0.5 M glucose and 2 g l−1 gellan gum. Protoplast-derived calluses produced somatic embryos at frequencies of 4.3–89.6% on media containing 0 or 0.54 µM NAA in combination with 0, 4.4, 22 or 44 µM BA, but few embryos converted into plantlets. On the other hand, over 35% of the calluses produced adventitious shoots on media containing 4.4 µM BA or 0.54 µM NAA in combination with 44 µM BA, and some of these shoots developed into plantlets following transfer to a medium without PGRs.