Measuring maximum root growth instead of longest root elongation in metal tolerance tests for grasses (Agrostis capillaris,Agrostis delicatula and Agrostis castellana)

Longest root elongation diminished significantly in the three species tested from 6 mm d^-1 to 3 mm d^-1 in 3 weeks. During this period S.D. increased considerably (from 49% to 112%, A. castellana), and accounted on the average for 68% (A. capillaris) till 94% (A. castellana) of the mean. Maximum root growth stabilized at 6 mm d^-1 and showed less variation in the measurements (S.D. 52% of the mean). Growth of the originally longest root approaches zero in all three species, in accordance with the natural cease of growth of roots in grasses fascicular root system. Measuring maximum root growth instead of longest root elongation is proposed for testing metal tolerance of grasses in sequential experiments.     

Heavy metal tolerance in Festuca ovina L. from contaminated sites in the Eifel Mountains,Germany

Extremely high degrees of lead tolerance, measured by comparing rates of root extension in culture solutions, are reported from populations of Festuca ovina growing at two lead-mining sites (Westschacht and Keldenich-II) near Mechernich in the Eifel Mountains, Germany. Other populations from nearby heavy metal-contaminated areas show a considerably smaller degree of lead tolerance. Samples of Festuca ovina collected in the field at Westschacht and Keldenich-II contain higher levels of lead in their aerial organs than do those from other lead-contaminated sites. The main soil factor determining the high degree of lead tolerance is the high Pb/Ca ratio. Populations from soils with a low Pb/Ca ratio display a very low degree of tolerance. It is therefore concluded that in Westschacht and Keldenich-II plants, a genuine intracellular tolerance mechanism is present, allowing the accumulation of lead in aerial organs.Leaf samples of zinc-tolerant Festuca contain higher levels of zinc than do samples of non-tolerant plants. Lead and zinc amounts in leaves are correlated with the soil ratios of Pb/Ca and Zn/Ca, respectively, rather than with the absolute soil-metal levels.In a slightly lead-tolerant, but highly zinc-tolerant clone of Festuca ovina from a site contaminated with large amounts of lead and zinc (Plombières), lead was found to be the major factor affecting the inhibition of root extension with combined treatments of lead and zinc in culture solutions. In the highly lead-tolerant, zinc-sensitive population from Westschacht, zinc governs the response of root growth to combinations of the two metals. The results are discussed in terms of discriminating distinct types of heavy-metal tolerance.     

Indole-3-acetic acid levels after phytochrome-mediated changes in the stem elongation rate of dark- and light-grownPisum seedlings

The effect of red (R) and far-red (FR) light on stem elongation and indole-3-acetic acid (IAA) levels was examined in dwarf and tall Pisum sativum L. seedlings. Red light reduced the extension-growth rate of etiolated seedlings by 70–90% after 3 h, and this inhibition was reversible by FR. Inhibition occurred throughout the growing zone. After 3 h of R, the level of extractable IAA in whole stem sections from the growing zone of etiolated plants either increased or showed no change. By contrast, extractable IAA from epidermal peels consistently decreased 3 h after R treatments. Decreases of 40% were observed for epidermal peels from the top 1 cm of tall plants receiving 3 h R. Brief R treatments resulted in smaller decreases in epidermal IAA levels and these decreases were not as great when FR followed R. In lightgrown plants, end-of-day FR stimulated growth during the following dark period in a photoreversible manner. The uppermost 1 cm of expanding third internodes was most responsive to the FR. Extractable IAA from epidermal peels from the upper 1 cm of third internodes increased by 30% or more 5 h after FR. When R followed the FR the increases were smaller. Levels of IAA in whole stem sections did not change and were twofold greater than in dark-grown plants. In both dark- and light-grown tall plants, IAA levels were lower in epidermal peels than in whole stem segments. These results provide evidence that IAA is compartmentalized at the tissue level within the growing stem and that phytochrome regulation of stem elongation rates may be partly based on modulating the level of IAA within the epidermis.Abbreviations IAA indole-3-acetic acid - R red light - FR farred light We thank Yu-Xian Zhu for helping to develop methods for IAA analysis, James Reid for supplying the genetic lines of Pisum and Richard Cyr for the use of microscopy equipment. This work was supported by NSF grant DCB-8801880 and by Hatch funds from the College of Agriculture and Life Sciences at Cornell University. The gas chromatograph-mass spectrometer was funded by NSF grant DMB-8505974 and funds from the College of Agriculture and Life Sciences at Cornell University. A preliminary report of some of these experiments has appeared in Plant Growth Substances, 1991 (Behringer et al. 1992 b).     

The activation process of Arabidopsis thaliana A1 gene encoding the translation elongation factor EF-1α is conserved among angiosperms

In Arabidopsis thaliana, the activation process of the A1 EF-1 gene depends on several elements. Using the GUS reporter gene, transient expression experiments have shown that mutations of upstream cis-acting elements of the A1 promoter, or the deletion of an intron located within the 5 non-coding region, similarly affect expression in dicot or monocot protoplasts. The results reported here strongly suggest that this 5 intron is properly spliced in Zea mays. We show that two trans-acting factors, specifically interacting with an upstream activating sequence (the TEF 1 box), are present in nuclear extracts prepared from A. thaliana, Brassica rapa, Nicotiana tabacum and Z. mays. In addition, a DNA sequence homologous to the TEF 1 box, found at approximately the same location within a Lycopersicon esculentum EF-1 promoter, interacts with the same trans-acting factors. Homologies found between the A. thaliana and L. esculentum TEF 1 box sequences have allowed us to define mutations of this upstream element which affect the interaction with the corresponding trans-acting factors. These results support the notion that the activation processes of A. thaliana EF-1 genes have been conserved among angiosperms and provide interesting data on the functional structure of the TEF 1 box.     

Mechanisms of somatic embryogenesis in cell cultures: Physiology,biochemistry, and molecular biology

Summary One of the most characteristic cell functions in plants is totipotency. Somatic embryogenesis can be regarded as a model system for the investigation of mechanisms of totipotency, because a high frequency and synchronous embryogenic system from single somatic cells has been established in carrot suspension cultures. Four phases are recognized in this process, and several molecular markers, viz. polypeptides, mRNAs, antigens against monoclonal antibodies, can be detected during the expression of totipotency, but they disappear during its loss. Four organ-specific genes have been isolated from hypocotyls and roots by differential screening. They were expressed preferentially after the globular-heart stages of embryogenesis, and were strongly suppressed by auxin. A CEM 1 gene was isolated by differential screening of embryogenic cell clusters. This gene was expressed strongly and transiently during the proglobular and globular stages. The sequence of CEM 1 was found to encode a polypeptide showing high homology to the elongation factor isolated from eucaryotic cells. Thus good progress is being made in understanding the basic mechanisms of somatic embryogenesis. Presented in the Session-in-Depth Developmental Biology of Embryogenesis at the 1991 World Congress on Cell and Tissue Culture, Anaheim, California, June 16–20, 1991.     

Archaebacterial elongation factor Tu insensitive to pulvomycin and kirromycin

A spermine-dependent, polyphenylalanine-synthesizing cell-free system having an optimum activity at 75-85 degrees C, has been developed from the extremely thermoacidophilic archaebacterium Caldariella acidophila. The C. acidophila system is totally insensitive to the EF-Tu targeted antibiotics pulvomycin (at 40 degrees C) and kirromycin (at 47-72 degrees C) contrary to control systems derived from both mesophilic (Escherichia coli) and thermoacidophilic (Bacillus acidocaldarius) eubacteria. The archaebacterial EF-Tu-equivalent factor is also immunologically unrelated to eubacterial EF-Tu and does not cross react with antibodies against Escherichia coli EF-Tu. The pulvomycin and kirromycin reactions thus provide new phyletic markers for archaebacterial ancestry.     

Effects of gibberellin and colchicine on microfibril arrangement in epidermal cell walls of Vigna angularis Ohwi et Ohashi epicotyls

Gibberellic-acid (GA₃) treatment of azukibean epicotyls resulted in alterations of the direction of newly deposited microfibrils, on the cell walls. Cells having transverse microfibrils on the inner surface of the wall were observed more frequently in GA₃-treated epicotyls than in untreated or water-treated ones. This effect of GA₃ was negated by simultaneously supplied colchicine. A crossed polylamellate structure was observed in the inner portion of the walls of GA₃-treated cells, but not in the inner portion of the walls of colchicine-treated cells. The wall formed under the influence of colchicine consisted of microfibrils running in the same direction.Abbreviations GA gibberellin - GA₃ gibberellic acid (gibberellin A₃)     

Attachment and Short-Term Maintenance of Motility and Viability of Entamoeba Histolytica In A Defined Medium*

Organic requirements for attachment to glass, elongation, and motility of Entamoeba histolytica, have been determined. the trophozoite, which has been grown axenically only in highly complex media with reduced oxygen tensions, remains rounded and detached when placed in a Tris-HCl buffered solution containing NaCI, KCI, MgCI₂, and CaCI₂. A maintenance medium in which the amebae could attach to glass, elongate, and remain motile and viable for 12 to 24 h was devised with the addition of cysteine, ascorbic acid, bovine serum albumin, and the vitamin solution of medium NCTC #107. Tris-HCI was the most effective buffer tested and the optimal pH was 6.9 to 7.0. Survival, but not attachment, of the amebae was decreased at osmolalities ranging between 110 and 180 milliosmoles/kg, whereas both functions were decreased above ～260 milliosmoles/kg. Bovine serum albumin, the most effective of the proteins tested, and the vitamin solution helped maintain attachment of some ameba strains, but were not required by other strains. the requirements for cysteine and ascorbic acid were absolute and highly specific. During incubation in the maintenance medium, cell volumes decreased. Sensitivity of the organisms to agglutination by concanavalin A, wheat germ agglutinin, soybean agglutinin and fucose binding protein remained unchanged.     

Discrimination between aminoacyl groups on su+ 7 tRNA by elongation factor Tu

The su⁺7 nonsense suppressor of Escherichia coli is a mutant tRNA^Trp that can be aminoacylated with either tryptophan or glutamine. We have compared the ternary complexes of glutaminyl and tryptophanyl-su⁺7 tRNA with elongation factor Tu and GTP. Glutaminyl-su⁺7 tRNA binds more strongly than tryptophanyl-su⁺7 tRNA to EF Tu · GTP. The greatest distinction between the two species of the tRNA is seen in their dissociation rates from the complex, which differ by as much as fivefold. The distinction is affected by pH values around neutrality. These results show that EF Tu can distinguish between two aminoacyl-tRNAs which differ only in the aminoacyl group. The implications for the unusual amino acid specificity of su⁺7 tRNA are discussed.