Extraordinarily low bone mineral density in an old female chimpanzee (<Emphasis Type="Italic">Pan troglodytes schweinfurthii</Emphasis>) from the Mahale Mountains National Park

We examined bone mineral density (BMD) of the femoral neck and lumbar vertebrae of four chimpanzee skeletons from Mahale Mountains National Park, Tanzania, and four captive ones, with a dual energy X-ray absorptiometer. The BMD of Wansombo, an old female chimpanzee from Mahale , was remarkably lower than the mean of the other six younger adult female chimpanzees and categorized as osteoporosis. Posture, locomotion, and trunk-sacral anatomy of chimpanzees may have prevented fractures in Wansombo, whose BMD was below human osteoporosis criteria. Electronic Publication     

<Emphasis Type="Italic">Arabidopsis</Emphasis> glucosyltransferases with activities toward both endogenous and xenobiotic substrates

Arabidopsis thaliana Heynh. harbors UDP-glucose-dependent glucosyltransferase (UGT; EC 2.4.1.-) activities that are able to glucosylate xenobiotic substrates as a crucial step in their detoxification, similar to other plants. However, it has remained elusive whether side-activities of UGTs acting on endogenous substrates could account for that property. Therefore, seven recombinantly expressed A. thaliana enzymes were tested using the phytotoxic xenobiotic model compound 2,4,5-trichlorophenol (TCP) as a substrate. The enzymes were selected from the large Arabidopsis UGT gene family because their previously identified putative endogenous substrates comprised both carboxylic acid, and phenolic and aliphatic hydroxyl moieties as biochemical targets. In addition, UGT75D1, which was shown to accept the endogenous flavonoid kaempferol as a substrate, was included. All enzymes tested, except the sterol-conjugating UGT80A2, glucosylated TCP as a parallel activity. The K(m) values for TCP ranged from 0.059 to 1.25 mM. When tested at saturating concentrations of the native substrates the glucosylation of TCP by the glucose-ester-forming UGT84A1 and UGT84A2 was suppressed by p-coumaric acid and sinapic acid, respectively. In contrast, the activities of UGT72E2 and UGT75D1 toward their phenolic native substrates and the xenobiotic TCP were mutually inhibited. TCP was a competitive inhibitor of sinapyl alcohol glucosylation by UGT72E2. These overlapping in vitro activities suggest cross-talk between the detoxification of xenobiotics and endogenous metabolism at the biochemical level, depending on the presence of competing substrates and enzymes.     

Cytosolic potassium homeostasis revisited: <Superscript>42</Superscript>K-tracer analysis in<Emphasis Type="Italic"> Hordeum vulgare</Emphasis> L. reveals set-point variations in [K<Superscript>+</Superscript>]

Current models of potassium acquisition and cytochemical processes in plants assume that potassium concentrations in the cytosol ([K+]cyt) are maintained homeostatically at approximately 100 mM. Here, we use 42K radiotracer data in the model plant species Hordeum vulgare L. (barley) to show that this assumption is incorrect. Our study reveals that [K+]cyt in root cells of intact barley seedlings is held at a minimum of two physiological set points, coinciding with two fundamentally distinct modes of K+ transport, each of which is characterized by a unique network of fluxes to and from the cytosol, and reflects variations in mechanisms and energetics of K+ transport, cytosolic K+ turnover, flux partitioning, and sensitivity to NH4+. Increased external potassium or ammonium concentrations caused a substantial drop in [K+]cyt, as well as a switch from a transport mode dominated by high-affinity, energy-dependent, influx to a mode dominated by channel-mediated fluxes in both directions across the plasma membrane. Our study provides the first subcellular demonstration of the flexibility, rather than strict homeostasis, of cellular K+ maintenance, and of the dynamic interaction between plant membrane fluxes of the two major nutrient cations K+ and NH4+.     

Atomic force microscopy of microfibrils in primary cell walls

Examination of angiosperm primary cell walls by transmission electron microscopy shows that they contain microfibrils that probably consist of cellulose microfibrils surrounded by associated non-cellulosic polysaccharides. Previous studies using solid-state (13)C NMR spectroscopy have shown that the cellulose is all crystalline with crystallites of cross-sectional dimensions of 2-3 nm. However, it is not known if each microfibril contains only one, or more than one crystallite because there is no agreement about the dimensions of the microfibrils. Partially hydrated primary cell walls isolated from onion ( Allium cepa L.) and Arabidopsis thaliana (L.) Heynh. were examined by atomic force microscopy and the microfibril diameters determined. The cell walls of both species contained tightly interwoven microfibrils of uniform diameter: 4.4+/-0.13 nm in the onion and 5.8+/-0.17 nm in A. thaliana. The effect was also examined of extracting the A. thaliana cell walls to remove pectic polysaccharides. The microfibrils in the extracted cell walls of A. thaliana were significantly narrower (3.2+/-0.13 nm) than those in untreated walls. The results are consistent with the microfibrils containing only one cellulose crystallite.     

Ionic and osmotic disruptions of the lily pollen tube oscillator: testing proposed models

Two mechanisms have been proposed as the primary control of oscillating tip growth in Lilium longiflorum Thunb. pollen tubes: changes in cell wall strength (Holdaway-Clarke et al. 1997) or alternatively, changes in turgor pressure (Messerli et al. 2000). Here we have modified the ionic and osmotic concentrations of the growth medium to test predictions derived from both models. Raising the [Ca2+]o tenfold above normal reduced the amplitude of the [Ca2+]i oscillations and growth oscillations while it raised the basal [Ca2+]i and growth rate such that the average growth rate did not change. Raising the [H+] of the growth medium tenfold reversibly decreased and sometimes eliminated the [Ca2+]i and growth oscillations without changing the average growth rate. Lowering the [H+] tenfold led to irregular frequency and amplitude [Ca2+]i oscillations, reduced the average growth rate of tubes and led to cell bursting in 33% of tubes. Addition of 50 mM H+ buffer, MES, to prevent pH changes in the cell wall increased the period, amplitude and duration of both [Ca2+]i and growth oscillations. Changing the [K+]o did not markedly effect [Ca2+]i oscillations. Reducing the osmolarity of the medium led to transient large-amplitude [Ca2+]i and growth oscillations while reducing large-amplitude oscillations over long periods. In many different conditions under which growth still occurs, lily pollen tubes maintain growth oscillations, albeit with modified frequency, amplitude and duration. We conclude that modifications to both proposed models are necessary to explain oscillating growth in this system.     

Apical meristem organization and lack of establishment of the quiescent center in Cactaceae roots with determinate growth

Some species of Cactaceae from the Sonoran Desert are characterized by a determinate growth pattern of the primary root, which is important for rapid lateral-root formation and seedling establishment. An analysis of the determinate root growth can be helpful for understanding the mechanism of meristem maintenance in plants in general. Stenocereus gummosus (Engelm.) Gibson & Horak and Pachycereus pringlei (S. Watson) Britton & Rose are characterized by an open type of root apical meristem. Immunohistochemical analysis of 5-bromo-2-deoxyuridine incorporation into S. gummosus showed that the percentage of cells passing through the S-phase in a 24-h period is the same within the zone where a population of relatively slowly proliferating cells could be established and above this zone in the meristem. This indicated the absence of the quiescent center (QC) in S. gummosus. During the second and the third days of growth, in the distal meristem portion of P. pringlei roots, a compact group of cells that had a cell cycle longer than in the proximal meristem was found, indicating the presence of the QC. However, later in development, the QC could not be detected in this species. These data suggest that during post-germination the absence of the establishment of the QC within the apical meristem and limited proliferative activity of initial cells are the main components of a determinate developmental program and that establishment of the QC is required for maintenance of the meristem and indeterminate root growth in plants.Abbreviations QC quiescent center - RCP root cap-protoderm - BrdU 5-bromo-2-deoxyuridine - FITC fluorescein isothiocyanate - DAPI 4,6-diamidino-2-phenylindole     

Ethylene regulates the timing of anther dehiscence in tobacco

We investigated the involvement of ethylene signaling in the development of the reproductive structures in tobacco ( Nicotiana tabacum L.) by studying flowers that were insensitive to ethylene. Ethylene-insensitivity was generated either by expression of the mutant etr1-1 ethylene-receptor allele from Arabidopsis thaliana or by treatment with the ethylene-perception inhibitor 1-methylcyclopropene (MCP). Development of ovaries and ovules was unaffected by ethylene-insensitivity. Anther development was also unaffected, but the final event of dehiscence was delayed and was no longer synchronous with flower opening. We showed that in these anthers degeneration of the stomium cells and dehydration were delayed. In addition, we found that MCP-treatment of detached flowers and isolated, almost mature anthers delayed dehiscence whereas ethylene-treatment accelerated dehiscence. This indicated that ethylene has a direct effect on a process that takes place in the anthers just before dehiscence. Because a similar function has been described for jasmonic acid in Arabidopsis, we suggest that ethylene acts similarly to or perhaps even in concurrence with jasmonic acid as a signaling molecule controlling the processes that lead to anther dehiscence in tobacco.     

<Emphasis Type="Italic">tla1</Emphasis>, a DNA insertional transformant of the green alga<Emphasis Type="Italic"> Chlamydomonas reinhardtii</Emphasis> with a truncated light-harvesting chlorophyll antenna size

DNA insertional mutagenesis and screening of the green alga Chlamydomonas reinhardtii was employed to isolate tla1, a stable transformant having a truncated light-harvesting chlorophyll antenna size. Molecular analysis showed a single plasmid insertion into an open reading frame of the nuclear genome corresponding to a novel gene ( Tla1) that encodes a protein of 213 amino acids. Genetic analysis showed co-segregation of plasmid and tla1 phenotype. Biochemical analyses showed the tla1 mutant to be chlorophyll deficient, with a functional chlorophyll antenna size of photosystem I and photosystem II being about 50% and 65% of that of the wild type, respectively. It contained a correspondingly lower amount of light-harvesting proteins than the wild type and had lower steady-state levels of Lhcb mRNA. The tla1 strain required a higher light intensity for the saturation of photosynthesis and showed greater solar conversion efficiencies and a higher photosynthetic productivity than the wild type under mass culture conditions. Results are discussed in terms of the tla1 mutation, its phenotype, and the role played by the Tla1 gene in the regulation of the photosynthetic chlorophyll antenna size in C. reinhardtii.     

Localization of dibenzodioxocin substructures in lignifying Norway spruce xylem by transmission electron microscopy–immunogold labeling

The lignification process in mature Norway spruce [Picea abies (L.) H. Karsten] xylem cell walls was studied using transmission electron microscopy (TEM)–immunogold detection with a polyclonal antibody raised against a specific lignin substructure, dibenzodioxocin. The study reveals for the first time the exact location of this abundant eight-ring structure in the cell wall layers of wood. Spruce wood samples were collected in Southern Finland at the time of active growth and lignification of the xylem cell walls. In very young tracheids where secondary cell wall layers were not yet formed, the presence of the dibenzodioxocin structure could not be shown at all. During secondary cell wall thickening, the dibenzodioxocin structure was more abundant in the secondary cell wall layers than in the middle lamella. The highest number of gold particles revealing dibenzodioxocin was in the S2+S3 layer. Statistically significant differences were found in the frequency of gold particles present in various cell wall layers. For comparison, wood sections were also cut with a cryomicrotome for light and fluorescence microscopy.