CLAVATA2 forms a distinct CLE‐binding receptor complex regulating Arabidopsis stem cell specification

CLAVATA1 (CLV1), CLV2, CLV3, CORYNE (CRN), BAM1 and BAM2 are key regulators that function at the shoot apical meristem (SAM) of plants to promote differentiation by limiting the size of the organizing center that maintains stem cell identity in neighboring cells. Previous results have indicated that the extracellular domain of the receptor kinase CLV1 binds to the CLV3‐derived CLE ligand. The biochemical role of the receptor‐like protein CLV2 has remained largely unknown. Although genetic analysis suggested that CLV2, together with the membrane kinase CRN, acts in parallel with CLV1, recent studies using transient expression indicated that CLV2 and CRN from a complex with CLV1. Here, we report detection of distinct CLV2‐CRN heteromultimeric and CLV1‐BAM multimeric complexes in transient expression in tobacco and in Arabidopsis meristems. Weaker interactions between the two complexes were detectable in transient expression. We also find that CLV2 alone generates a membrane‐localized CLE binding activity independent of CLV1. CLV2, CLV1 and the CLV1 homologs BAM1 and BAM2 all bind to the CLV3‐derived CLE peptide with similar kinetics, but BAM receptors show a broader range of interactions with different CLE peptides. Finally, we show that BAM and CLV1 overexpression can compensate for the loss of CLV2 function in vivo. These results suggest two parallel ligand‐binding receptor complexes controlling stem cell specification in Arabidopsis.     

高效诱导冬瓜再生植株的研究

将台湾冬瓜的种子接种于pH值为7.2的1/2MS培养基上预培养,5d左右种子即可萌发,萌发率为100%,幼苗生长正常。切取预培养15-20d的无菌幼苗的茎尖和带腋芽的茎段接种于MS 1mg/LNAA 4mg/L6-BA培养基上,10d左右在茎尖和茎段（带腋芽）切口处长出愈伤组织,30d左右在愈伤组织处分化出丛生芽,丛生芽的诱导频率接近95%,繁殖系数25.6。将小芽切下转入不加任何生长调节剂MS培养基上,培养几天后芽逐渐长大,并在芽的基部长出白色根系。选取生长健壮的试管苗经过炼苗后移栽到大田中,生长良好。     

In vitro culture of adult and juvenile bud explants of Passiflora species

Cultivar E23, an F1 hybrid of P. edulis and P. edulis f. flavicarpa is usually propagated by shoot-tip grafting. Various media were tested to evaluate the potential of E23 for in vitro propagation. Adult tissue was difficult to culture and did not respond to media containing low (<10 µM) concentrations of growth regulators. Growth of adult buds on intact stem sections was promoted by 1 week of dark incubation on MS basal medium plus 150 µM 2iP, 200 µM adenine sulphate and 17.1 µM IAA (3 mg l^–1), and further developed into shoots on MS medium plus 4.9 µM 2iP (1 mg l^–1) and 5.7 µM IAA (1 mg l^–1). By contrast, juvenile shoots of E23, and Passiflora species: edulis f. flavicarpa, edulis, alata, caerulea, mollissima, coccinea, herbertiana and suberosa grew rapidly on MS medium plus 10 µM kinetin and 5 µM IAA. Rapid multiplication was achieved on MS plus 20 µM BA, 10 µM kinetin, 5 µM IAA, and roots initiated on MS plus 5 µM IAA.Abbreviations IAA indole-3-acetic acid - 2iP N6-iso pentenyl adenine - BA N6-benzyl adenine     

In vitro study on the effect of cytokines and auxins addition to growth medium on the micropropagation and rooting of Paulownia species (Paulownia hybrid and Paulownia tomentosa)

This study represents an efficient preliminary protocol for in vitro mass production of two Paulownia species (Paulownia hybrid and Paulownia tomentosa) seedlings by using seed explant. Different concentrations of benzyladenine (BA) or Kinetin (Kin) (0.0, 2.0, 4.0, 6.0, 8.0 and 10.0 mg/L) were tested during multiplication stage. The number of shoots/explants was significantly increased with increasing either BA or Kin concentration; however, the shoot length significantly decreased. Data show that media fortified by BA (10 mg/L) combined with indole butyric acid (IBA) at 1.0 or 1.5 mg/L recorded the highest number of shoots/explant (9.13 and 9.25, respectively). After six weeks during the multiplication stage, data cleared that media fortified by benzyladenine (10 mg/L) combined with IBA at 0.5 mg/L recorded the highest shoot length (3.23 cm). The inclusion of indole butyric acid (IBA) or naphthalene acetic acid (NAA) at 1.0–1.5 mg/L to the medium significantly increased the number of roots/plantlets and the highest root length. The results indicated that IBA supplementation was more effective than NAA for in vitro rooting of both Paulownia species. The best treatment for multiplication was 10 mg/L and 8.0–10 mg/L BA for P. hybrid and P. tomentosa, respectively. Peat moss and sand (1:1, v/v) or peat moss and sand (1:2, v/v) were investigated as soil mixture during the adaptation stage. The results referred that Paulownia species plantlets were successfully survived (100 %) in soil mixture contained peat moss: sand (1:2, v/v). This mixture recorded the highest values of plantlet height and number of leaves/plantlets.     

Root biomass allocation in the world's upland forests

Because the world's forests play a major role in regulating nutrient and carbon cycles, there is much interest in estimating their biomass. Estimates of aboveground biomass based on well-established methods are relatively abundant; estimates of root biomass based on standard methods are much less common. The goal of this work was to determine if a reliable method to estimate root biomass density for forests could be developed based on existing data from the literature. The forestry literature containing root biomass measurements was reviewed and summarized and relationships between both root biomass density (Mg ha⁻¹) and root:shoot ratios (R/S) as dependent variables and various edaphic and climatic independent variables, singly and in combination, were statistically tested. None of the tested independent variables of aboveground biomass density, latitude, temperature, precipitation, temperature:precipitation ratios, tree type, soil texture, and age had important explanatory value for R/S. However, linear regression analysis showed that aboveground biomass density, age, and latitudinal category were the most important predictors of root biomass density, and together explained 84% of the variation. A comparison of root biomass density estimates based on our equations with those based on use of generalized R/S ratios for forests in the United States indicated that our method tended to produce estimates that were about 20% higher. Received: 3 July 1996 / Accepted: 23 January 1997     

Anti-herbivore structures of Paulownia tomentosa: morphology, distribution, chemical constituents and changes during shoot and leaf development

Background and Aims: Recent studies have shown that small structures on plant surfacesserve ecological functions such as resistance against herbivores.The morphology, distribution, chemical composition and changesduring shoot and leaf development of such small structures wereexamined on Paulownia tomentosa. Methods: The morphology and distribution of the structures were studiedunder light microscopy, and their chemical composition was analysedusing thin-layer chromatography and high-performance liquidchromatography. To further investigate the function of thesestructures, several simple field experiments and observationswere also conducted. Key Results: Three types of small structures on P. tomentosa were investigated:bowl-shaped organs, glandular hairs and dendritic trichomes.The bowl-shaped organs were densely aggregated on the leavesnear flower buds and were determined to be extrafloral nectarines(EFNs) that secrete sugar and attract ants. Nectar productionof these organs was increased by artificial damage to the leaves,suggesting an anti-herbivore function through symbiosis withants. Glandular hairs were found on the surfaces of young and/orreproductive organs. Glandular hairs on leaves, stems and flowerssecreted mucilage containing glycerides and trapped small insects.Secretions from glandular hairs on flowers and immature fruitscontained flavonoids, which may provide protection against someherbivores. Yellow dendritic trichomes on the adaxial side ofleaves also contained flavonoids identical to those secretedby the glandular hairs on fruits and flowers. Three specialtypes of leaves, which differed from the standard leaves inshape, size and identity of small structures, developed nearyoung shoot tips or young flower buds. The density of smallstructures on these leaf types was higher than on standard leaves,suggesting that these leaf types may be specialized to protectyoung leaves or reproductive organs. Changes in the small structuresduring leaf development suggested that leaves of P. tomentosaare primarily protected by glandular hairs and dendritic trichomesat young stages and by the EFNs at mature stages. Conclusions: The results indicate that P. tomentosa protects young and/orreproductive organs from herbivores through the distributionand allocation of small structures, the nature of which dependson the developmental stage of leaves and shoots.     

Improved shoot regeneration protocol for hairy roots of the legume Astragalus sinicus

An improved protocol for shoot regeneration from hairy roots transformed by Agrobacterium rhizogenes of the legume species Astragalus sinicus (Chinese milk vetch) has been developed. The A. rhizogenes strain DC-AR2 harboring the binary vector pBI121 which carries the uidAgene encoding -glucuronidase activity and the kanamycin resistance gene nptII, was used to transform cut ends of plantlet hypocotyls. Transformed hairy roots were selected on medium containing 75 g ml^–1 kanamycin, and transformation was monitored by detection of the opine mikimopine, histochemical -glucuronidase activity, the polymerase chain reaction, and Southern blot analysis. The cytokinins benzylaminopurine, kinetin, and thidiazuron suppressed the growth of 8-month and 3-year-old hairy roots, but were necessary for adventitious shoot formation that could occur with some lines. Putative somatic embryos developed from transformed roots on medium with 7.5-10.0 mg l^–1 2,4-dichlorophenoxyacetic acid. Light did not affect shoot regeneration from transformed hairy roots. This transformation and shoot regeneration system should be useful for testing gene expression quickly and be amenable to studies of shoot morphogenesis and interactions with rol gene expression.     

Meristem-specific gene expression directed by the promoter of the S-phase-specific gene,cyc07, in transgenic Arabidopsis

A genomic clone for the cyc07 gene, which is expressed specifically at the S phase during the cell cycle in synchronous cultures of periwinkle (Catharanthus roseus) cells, was isolated. Determination of the nucleotide sequence of the clone revealed that the cyc07 gene consists of seven exons separated by six introns. Genomic Southern analysis indicated that the cyc07 gene is present as a single copy per haploid genome in periwinkle. Expression of related genes was detected in a wide range of other plants. Transgenic Arabidopsis plants were generated that expressed the gene for -glucuronidase (GUS) under the control of the promoter of the cyc07 gene. The tissue-specific pattern of expression directed by the promoter was investigated by analysis of GUS activity. Histochemical tests demonstrated that 589 bp of the 5-upstream sequence of the cyc07 gene could direct specifical expression of the GUS reporter gene in meristematic tissues in transgenic plants. The spatial pattern of expression directed by the promoter was closely correlated with meristematic activity and cell proliferation, suggesting an association between the function of the cyc07 gene and cell proliferation.