Chromosome length values in digenomic buttercups [Ranunculaceae] and the relation to DNA content

Root-tip chromosome complement length ratios were determined in F1 hybrids combinining two haploid (n = 8) genomes each from different species, to form a series AB, AC, AD, ... AI. The observed values, for the length ratios B/A, C/A, etc., ranged from 0.53 to 1.0. It is noted that the values form a quasilinear distribution, with a slope of 1.0, when plotted against the known 4C DNA values of the species having a range from appr. 1.1 to 2.2 × 10^?11 g. Also observed, but not numerically evaluated was some apparently related variation in chromosome “width”. DNA-related variation in root-tip chromosome size in these buttercups may be three-dimensional; however, the magnitude of the observed length differentials and the 1∶1 correlation with DNA content suggest that it occupies predominantly the first dimension.     

Isolation of root hairs from seedlings of Pisum sativum. Identification of root hair specific proteins by in situ labeling

A procedure was developed which allows the large-scale isolation of root hairs from seedlings of Pisum sativum . L. cvs. Kleine Rheinländerin and Rosa Krone. The method may yield up to 50 g fresh weight of root hairs per 3.10⁴ seedlings. In a modified form considerable amounts of root hair material may be harvested, even after incubation of the roots in aqueous solutions. Thus, detailed biochemical studies on the root hair system have become feasible.
The occurrence of specific proteins in membrane fractions of P. sativum root hairs was demonstrated as follows: Incubation of root hairs in situ with 3-azidonaphthalene-2,7-disulfonate – a strongly anionic, photoactivated fluorescent marker – followed by gel electrophoresis of membrane fractions showed the presence of root-hair specific proteins which, since the system was intact, suggests that they are on the outer surface of the cells.     

In vitro synthesis of bean (Phaseolus vulgaris) chloroplastic and cytoplasmic leucyl-tRNA synthetases. Characterization and processing of a precursor polypeptide for the chloroplast enzyme

Bean (Phaseolus vulgaris) chloroplastic and cytoplasmic leucyl-tRNA synthetases differ in their structural and catalytic properties and do not share common antigenic determinants. Polyadenylated mRNAs, prepared from young bean leaves, have been translated in vitro in a rabbit reticulocyte lysate cell-free system. The newly synthesized polypeptides have been submitted to immunoadsorption on protein A-Sepharose in the presence of the antibodies raised against the chloroplastic or the cytoplasmic leucyl-tRNA synthetase. The specificity of the immunoadsorption has been checked by competition experiments involving the pure enzymes. Bean chloroplastic leucyl-tRNA synthetase is synthesized in vitro from a polyadenylated mRNA as a precursor polypeptide of 130 kDa, which is somewhat larger than the mature enzyme of 120 kDa. Bean cytoplasmic leucyl-tRNA synthetase is synthesized in vitro as a polypeptide which has the size of the mature monomer (130 kDa). Processing of the precursor polypeptide of the chloroplastic leucyl-tRNA synthetase, yielding the mature enzyme, has been obtained by performing the in vitro translation in the presence of canine pancreatic microsomal membranes. These results suggest that in vivo bean chloroplastic leucyl-tRNA synthetase could be synthesized in the cytoplasm as a precursor which would be transported into the chloroplasts.     

Sequential appearance of epidermal growth factor in plasma membrane-associated and intracellular vesicles during endocytosis

Receptor-mediated internalization of epidermal growth factor (EGF) occurs by a process involving initially clathrin-coated pits on the cell surface and the subsequent formation of ligand-containing endosomes. Using a modified acid wash technique, cell surface-bound EGF was removed. Utilizing sucrose density centrifugation, the residual cell-associated EGF was separated into plasma membrane-associated and intracellular vesicle-associated forms. Using these procedures we have identified a transient form of cell-associated EGF that is still attached to the plasma membrane but not accessible to the extracellular fluid. This form of EGF appears to be the precursor for endosomic EGF. We suggest that this intermediate form represents the receptor-ligand complex shown by electronmicroscopy to be located in narrow-necked plasma membrane invaginations (Willingham, M. C., and Pastan, I. (1980) Cell 21, 67-77).     

Complementarity of particles and pits in freeze-fractured hepatic and cardiac gap junctions

Summary Particles and pits of freeze-fractured gap junctions are considered as complementary structures despite the frequent observations of more regular and closer spacings of pits, ascribed to plastic deformation of particle arrays. Recently, however, the noncomplementarity of pits and particles in Purkinje fibers has been reported. To ascertain the relationship between both structures, gap junctions from fixed, cryoprotected liver and myocardium were investigated using spacing and density measurements and complementary replicas.In hepatocyte gap junctions, the center-to-center distances (mean±sd) among pits, 9.57±1.49 nm, and particles, 9.70±1.77 nm, are not significantly different. Density determinations yielded a slightly higher value for the pits, (11,510±830)/m², than for the particles, (11,230±950)/m². In the myocardium, the spacing of the regularly arrayed pits, 9.55±1.33 nm barely exceeds the value of 9.44±1.62 nm for the particles, which show some clustering. However, the packing density for the pits, (10,090±740)/m², appears a little higher than that of the particles (9,890±920)/m². As density and spacing measurements provided no decisive answers, the positions of individual pits and particles of complementary junctional faces were recorded on transparent sheets and compared. In this fashion, a one-to-one correspondence between particles and pits could be established, while small discrepancies may be attributed to plastic deformation. Moreover, the collinearity of pits and particles may be suggested by the observation of a platinum grain in the center of many pits.     

A relationship between the inhibition of heparan sulfate and chondroitin sulfate synthesis and the inhibition of molting by selenate in the hemipteran Rhodnius prolixus

The insect Rhodnius prolixus synthesizes heparan sulfate and chondroitin sulfate after a blood meal containing [35S]-inorganic sulfate. A 40 to 80% inhibition of heparan sulfate synthesis was obtained when the meal was supplemented with 10(-5) and 10(-4) M sodium selenate respectively. Likewise an inhibition of the molting in the order of 30 to 60% was observed when the insects were fed with blood containing 10(-5) and 10(-4) M selenate respectively. The insects after a subsequent meal without selenate molted normally. Except for the inhibition of the ecdysis no gross physiological or morphological changes could be observed in the insects. Based on these and other findings the possible role of sulfated glycosaminoglycans in the control of cell growth is discussed.     

Amyloplasts are necessary for full gravitropic sensitivity in roots of Arabidopsis thaliana

The observation that a starchless mutant (TC7) of Arabidopsis thaliana (L.) Heynh. is gravitropic (T. Caspar and B.G. Pickard, 1989, Planta 177, 185–197) raises questions about the hypothesis that starch and amyloplasts play a role in gravity perception. We compared the kinetics of gravitropism in this starchless mutant and the wild-type (WT). Wild-type roots are more responsive to gravity than TC7 roots as judged by several parameters: (1) Vertically grown TC7 roots were not as oriented with respect to the gravity vector as WT roots. (2) In the time course of curvature after gravistimulation, curvature in TC7 roots was delayed and reduced compared to WT roots. (3) TC7 roots curved less than WT roots following a single, short (induction) period of gravistimulation, and WT, but not TC7, roots curved in response to a 1-min period of horizontal exposure. (4) Wild-type roots curved much more than TC7 roots in response to intermittent stimulation (repeated short periods of horizontal exposure); WT roots curved in response to 10 s of stimulation or less, but TC7 roots required 2 min of stimulation to produce a curvature. The growth rates were equal for both genotypes. We conclude that WT roots are more sensitive to gravity than TC7 roots. Starch is not required for gravity perception in TC7 roots, but is necessary for full sensitivity; thus it is likely that amyloplasts function as statoliths in WT Arabidopsis roots. Furthermore, since centrifugation studies using low gravitational forces indicated that starchless plastids are relatively dense and are the most movable component in TC7 columella cells, the starchless plastids may also function as statoliths.Abbreviations S2 story two - S3 story three - WT wild-type