Changes in plant growth processes under microgravity conditions simulated by a three-dimensional clinostat

We developed a three-dimensional (3-D) clinostat to simulate a microgravity environment and studied the changes in plant growth processes under this condition. The rate of germination of cress (Lepidium sativum), maize (Zea mays), rice (Oryza sativa), pea (Pisum sativum), or azuki bean (Vigna angularis) was not affected on the clinostat. The clinostat rotation did not influence the growth rate of their roots or shoots, except for a slight promotion of growth in azuki roots and epicotyls. On the contrary, the direction of growth of plant organs clearly changed on the 3-D clinostat. On the surface of the earth, roots grow downward while shoots upward in parallel to the gravity vector. On the 3-D clinostat, roots of cress elongated along the direction of the tip of root primordia after having changed the direction continuously. Rice roots also grew parallel to the direction of the tip of root primordia. On the other hand, roots of maize, pea, and azuki bean grew in a random fashion. The direction of growth of shoots was more controlled even on the 3-D clinostat. In a front view of embryos, shoots grew mostly along the direction of the tip of primordia. In a side view, rice coleoptiles showed an adaxial (toward the caryopsis) while coleoptiles of maize and epicotyls of pea and azuki bean an abaxial curvature. The curvature of shoots became larger with their growth. Such an autotropism may have an important role in regulation of life cycle of higher plants under a microgravity environment.     

Correlation between cell wall extensibility and the content of diferulic and ferulic acids in cell walls of Oryza sativa coleoptiles grown under water and in air

Rice ( Oryza sativa L. cv. Sasanishiki) coleoptiles grown under water achieved greater length than those grown either in air or under water with constant air bubbling. The extensibility of cell walls in coleoptiles grown under water was larger than that in the other treatments. Per unit length of the coleoptile, the content of ferulic and diferulic acids ester-linked to hemicelluloses was higher in air and bubbling type coleoptiles than in water type ones. The extensibility of the coleoptile cell walls correlated with the content of diferulic acids per unit length and per hemicellulose, suggesting that the enhancement of the formation of diferulic acid bridges in hemicelluloses in air or under water with air bubbling makes the cell walls mechanically rigid; thereby inhibiting cell elongation in rice coleoptiles. In addition, the ratio of diferulic acid to ferulic acid was almost constant irrespective of coleoptile age, zone and growth conditions, suggesting that the feruloylation of hemicelluloses is rate-limiting in the formation of diferulic acid bridges in the cell walls of rice coleoptiles.     

Inhibition of auxin-induced elongation and xyloglucan breakdown in azuki bean epicotyl segments by fucose-binding lectins

Auxin-induced elongation of epicotyl segments of azuki bean ( Vigna angularis Ohwi and Ohashi cv. Takara) was suppressed by fucose-binding lectins from Tetragonolobus purpureus Moench and Ulex europaeus L. These lectins also inhibited auxin-induced cell wall loosening (decrease in the minimum stress-relaxation time of the cell walls) of segments. Auxin caused a decrease in molecular mass of xyloglucans extracted with 24% KOH from the cell walls. The lectins inhibited auxin-induced changes in molecular mass of the xyloglucans. The autolytic release of xylose-containing products from the pectinase-treated cell walls was also suppressed by the lectins. Fucose-binding lectins pretreated with fucose exhibited little or no inhibitory effect on auxin-induced elongation, cell wall loosning, or breakdown of xyloglucans. These results support the view that the breakdown of xyloglucans is involved in the cell wall loosening responsible for auxin-induced elongation in dicotyledons.     

Effect of Xyloglucan Nonasaccharide on Cell Elongation Induced by 2,4-Dichlorophenoxyacetic Acid and Indole-3-acetic Acid

Xyloglucan nonasaccharide (XG9) is recognized as an inhibitorof 2,4-D-induced long-term growth of segments of pea stems.In the presence of 10^–5 M 2,4-D, inhibition by 10^–9M XG9 of elongation of third internode segments of pea seedlingswas detected within 2 h after the start of incubation, in someexperiments. Analysis by double-reciprocal (Lineweaver-Burk)plots of elongation in the presence of various concentrationsof 2,4-D, with or without XG9, gave parallel lines, indicatingthat XG9 inhibited 2,4-D-induced elongation in an uncompetitivemanner. XG9 did not influence the 2,4-D-induced cell wall loosening.Thus, XG9 does not fulfill the proposed definition of an "antiauxin". XG9 at 10^–11 to 10^–6 M did not influence IAA-inducedelongation of segments from pea third internodes, azuki beanepicotyls, cucumber hypocotyls, or oat coleoptiles. Inhibitionof IAA-induced elongation by XG9 was not observed even whenthe segments from pea or azuki bean were abraded. Furthermore,fucosyl-lactose at 10^–11 to 10^–4 M did not affectthe IAA-induced elongation of segments of pea internodes orof azuki bean epicotyls. XG9 may be incapable of inhibitingthe IAA-induced cell elongation (especially in oat) or, alternatively,the endogenous levels of XG9 may be so high that exogenouslyapplied XG9 has no inhibitory effect on IAA-induced elongation. (Received February 28, 1991; Accepted May 25, 1991)     

Mischarging mutants of Su+2 glutamine tRNA in E. coli. II. Amino acid specificities of the mutant tRNAs

Among the mischarging mutants isolated from strains with Su+2 glutamine tRNA, two double-mutants, A37A29 and A37C38, have been suggested to insert tryptophan at the UAG amber mutation site as determined by the suppression patterns of a set of tester mutants of bacteria and phages (Yamao et al., 1988). In this paper, we screened temperature sensitive mutants of E. coli in which the mischarging suppression was abolished even at the permissive temperature. Four such mutants were obtained and they were identified as the mutants of a structural gene for tryptophanyl-tRNA synthetase (trpS). Authentic trpS mutations, such as trpS5 or trpS18, also restricted the mischarging suppression. These results strongly support the previous prediction that the mutant tRNAs of Su+2, A37A29 and A37C38, are capable of interacting with tryptophanyl-tRNA synthetase and being misaminoacylated with tryptophan in vivo. However, in an assay to determine the specificity of the mutant glutamin tRNAs, we detected predominantly glutamine, but not any other amino acid, being inserted at an amber codon in vivo to any significant degree. We conclude that the mutant tRNAs still accept mostly glutamine, but can accept tryptophan in an extent for mischarging suppression. Since the amber suppressors of Su+7 tryptophan tRNA and the mischarging mutants of Su+3 tyrosine tRNA are charged with glutamine, structural similarity among the tRNAs for glutamine, tryptophan and tyrosine is discussed.     

The complete nucleotide sequence of the group II RNA coliphage GA

The complete nucleotide sequence of the RNA coliphage GA, a group II phage, is presented. The entire genome comprises 3466 bases. Three large open reading frames were identified, which correspond to the maturation protein gene (390 amino acids), the coat protein gene (129 amino acids) and the replicase beta-subunit protein gene (531 amino acids). In addition, untranslated regions occur at the 5' (135 bases) and 3' (122 bases) ends of the molecule. Two intercistronic untranslated regions occur between the cistrons for the maturation and coat proteins, and between the coat and beta-subunit proteins. We have compared the nucleotide sequence of GA RNA with the published sequence of MS2 RNA, and show that they are related. The comparative structures of two important regulatory regions are presented; the coat protein binding site which is involved in translational repression of the replicase beta-subunit protein gene, and a hairpin in a region proximal to the lysis protein gene.     

Analysis of the active center of hydrogenase from Desulfovibrio vulgaris Miyazaki by magnetic measurements

Hydrogenase [hydrogen: ferricytochrome c3 oxidoreductase, EC 1.12.2.1] solubilized and purified from the particulate fraction of Desulfovibrio vulgaris Miyazaki F (IAM 12604) contains 8 iron and 8 labile sulfide ions in one molecule which is composed of two unequal subunits (Mr: 60,000 + 29,000). It does not contain nickel atoms. The EPR (electron paramagnetic resonance) spectrum has an isotropic signal at g = 2.017 which is independent of the temperature. The peak-to-peak width of the signal is about 20 G. The signal intensity is nearly equivalent to 1 unpaired electron per molecule. No other signals can be detected in the field range between 2,240 and 4,240 G (which corresponds to g-values between 2.91 and 1.54). Ferricyanide has only a little effect on the shape and intensity of the EPR signal. The hydrogenase reduced under H2 is EPR silent. The M?ssbauer spectrum has no hyperfine splitting at 4K. The isomer shift and quadrupole splitting at 77K are 0.38 and 0.87 mm/s, respectively. Based on these magnetic measurements, the structure of the active center of hydrogenase was suggested to be [4Fe-4S]3+ + [4Fe-4S]2+.     

Control of K+ conductance by cholecystokinin and Ca2+ in single pancreatic acinar cells studied by the patch-clamp technique

Summary The effect of cholecystokinin (CCK) and internal Ca²⁺ on outward K⁺ current in isolated pig pancreatic acinar cells has been investigated using the patch-clamp method for whole-cell current recording under voltage-clamp conditions. CCK (2 × 10^–10 M) applied to the bath evoked a marked increase in the outward K⁺ current associated with depolarizing voltage steps, and this effect was fully reversible and acutely dependent on the presence of external Ca²⁺. When strongly buffered Ca²⁺-EGTA solutions were used inside the cells CCK failed to evoke an effect. Increasing the internal Ca²⁺ concentration ([Ca²⁺] _i ) from 5 × 10^–10 M to 10^–7 and 5 × 10^–7 M mimicked the effect of CCK. It would appear therefore that CCK controls K⁺ conductance in the acinar cells via changes in the internal free ionized Ca²⁺ concentration.