Circumnutational movement in rice coleoptiles involves the gravitropic response: analysis of an agravitropic mutant and space‐grown seedlings

Plants exhibit helical growth movements known as circumnutation in growing organs. Some studies indicate that circumnutation involves the gravitropic response, but this notion is a matter of debate. Here, using the agravitropic rice mutant lazy1 and space‐grown rice seedlings, we found that circumnutation was reduced or lost during agravitropic growth in coleoptiles. Coleoptiles of wild‐type rice exhibited circumnutation in the dark, with vigorous oscillatory movements during their growth. The gravitropic responses in lazy1 coleoptiles differed depending on the growth stage, with gravitropic responses detected during early growth and agravitropism during later growth. The nutation‐like movements observed in lazy1 coleoptiles at the early stage of growth were no longer detected with the disappearance of the gravitropic response. To verify the relationship between circumnutation and gravitropic responses in rice coleoptiles, we conducted spaceflight experiments in plants under microgravity conditions on the International Space Station. Wild‐type rice seeds were germinated, and the resulting seedlings were grown under microgravity or a centrifuge‐generated 1 g environment in space. We began filming the seedlings 2 days after seed imbibition and obtained images of seedling growth every 15 min. The seed germination rate in space was 92–100% under both microgravity and 1 g conditions. LED‐synchronized flashlight photography induced an attenuation of coleoptile growth and circumnutational movement due to cumulative light exposure. Nevertheless, wild‐type rice coleoptiles still showed circumnutational oscillations under 1 g but not microgravity conditions. These results support the idea that the gravitropic response is involved in plant circumnutation.     

Disruption of phospholipase B gene, PLB1, increases the survival of baker's yeast Torulaspora delbrueckii

Abstract An uracil auxotrophic mutant of baker's yeast Torulaspora delbrueckii , which is resitant to 5-fluoro-orotic acid, was complemented by transformation with YEp24 which harbors 2 μm origin and URA3 derived from Saccharomyces cerevisiae . The phospholipase B in T. delbrueckii cells is active in both acidic and alkaline conditions. However, activity of phospholipase B gene ( PLB1 ) in cells of disruption mutant ( plbI : : URA3 ) was lost in both conditions, which indicates that all phospholipase B activity is encoded by a single gene (or a single polypeptide) in these yeast cells. Over-expression of PLB1 with YEp plasmid vector in T. delbrueckii cells showed ∼ 2.5-fold increase in phospholipase B activity, comparing with that in wild-type cells. Cells of plb1 Δ mutant showed increased survival when cells of plb1 Δ mutant and wild-type strain were incubated in water at 30 °C. Cells of PLB1 -over-expressed strain died rapidly even during the cultivation period, indicating that phospholipase B activity may be a determinant for the survival of this yeast.     

Accumulation of anthranilic acid and N-glucosylanthranilic acid by a Corynebacterium glutamicum mutant resistant to DL-serine hydroxamate

During a study on the effect of DL-serine hydroxamate on Corynebacterium glutamicum (JCM1318, a wild strain), a mutant resistant to the drug, strain TO3002, was isolated. This mutant accumulated five Ehrlich's reagent positive fluorescent substances in the culture medium. Two major and one minor fluorescent products were isolated by preparative high-performance liquid chromatography following charcoal column chromatography from the culture supernatant. One major product was identified as anthranilic acid whose molecular ion was confirmed to be 137 by a measurement of liquid chromatography-mass spectrometry (LC-MS), and NMR spectrum coincided with that of anthranilic acid. LC-MS spectra of another major and the minor product showed that they had the same molecular weight of 299. This major product was supported to be N-glucosylanthranilic acid (N-o-carboxyphenyl-1-beta-glucosylamine) by two-dimensional (1)H and (13)C NMR analyses. The minor product was speculated to be an Amadori compound derived from N-glucosylanthranilic acid. N-Glucosylanthranilic acid accumulated in the early phase, then decreased in the late phase of the culture. In contrast, the accumulation of anthranilic acid increased remarkably in the late phase of the fermentation. Based on this phenomenon, it was assumed that N-glucosylanthranilic acid once accumulated was decomposed to form anthranilic acid, at least in large part, with the progress of fermentation. The strain TO3002 showed a leaky requirement for L-tryptophan or indole (but did not for anthranilic acid) and resistance to DL-serine hydroxamate.     

Sulfated sialic acid-polymers inhibit the cytotoxic action of bee and snake venom

Colominic acid is an 2,8-linked sialic acid polymer produced by Escherichia coli. We found that synthetic sulfated-colominic acids (SC) remarkably inhibited the cytotoxicity of bee and snake venom toward mouse fibroblast cells, but colominic acids showed no inhibition themselves, indicating the important role of sulfate groups in the inhibitory activity of SC. Other sulfated carbohydrates such as chondroitin sulfates, heparin and heparan sulfate showed no inhibition. SC also exhibited potent inhibition of melittin, a highly basic peptide, which is a major cytotoxic component of bee venom. SC did not inhibit phospholipase A₂ activity in bee venom. This suggests that the inhibition of bee and snake venom by SC is due to inhibition of melittin and cardiotoxin, which is a cytolytic peptide in snake venom, respectively. SC with a higher sulfur content and a larger molecular mass showed more potent activity. The interaction between SC and melittin basically seems an ionic one, however, the conformation of SC is also likely important. For the binding of SC to melittin leading loss of its cytotoxic activity, the sulfate groups of SC must be properly arranged to interact with lysine and arginine residues of melittin molecules, which play an important role in the cytolytic activity. A higher molecular mass of SC substituted with more sulfate groups is required for more obvious inhibition of the cytotoxic activity.     

Galectin-3 and metastasis

Galectin-3, a 31 kDa member of the beta-galactoside-binding proteins, is an intracellular and extracellular lectin which interacts with intracellular glycoproteins, cell surface molecules and extracellular matrix proteins. Galectin-3 is expressed widely in epithelial and immune cells and its expression is correlated with cancer aggressiveness and metastasis. Galectin-3 is involved in various biological phenomena including cell growth, adhesion, differentiation, angiogenesis and apoptosis. Recent research revealed that galectin-3 is associated with several steps of invasion and metastasis, like angiogenesis, cell-matrix interaction, dissemination through blood flow and extravasation. Recently, we and others have shown that galectin-3 can be a reliable diagnostic marker in certain cancers and one of the target proteins of cancer treatment. In this review, we describe the involvement of galectin-3 in each steps of metastasis and clinical significance of galectin-3.     

Interaction between a negative regulator (Msa2/Nrd1) and a positive regulator (Cpc2) of sexual differentiation in Schizosaccharomyces pombe

The sexual differentiation of Schizosaccharomyces pombe is controlled by many cellular components which have not been fully characterized. We isolated a gene called msa2 as a multi-copy suppressor of a sporulation abnormal mutant (sam1). Msa2p is identical with Nrd1p which has been characterized as a factor that blocks the onset of sexual differentiation. The yeast two-hybrid system was used to identify Cpc2p, a fission yeast homolog of the RACK1 protein, that interacted with Msa2p/Nrd1p. We confirmed that Msa2p/Nrd1p interacted with Cpc2p in S. pombe cells. An epistatic analysis of msa2/nrd1 and cpc2 suggests that Msa2p/Nrd1p was an upstream regulator for Cpc2p. A localization analysis of Cpc2p and Msa2p/Nrd1p indicates that both proteins were predominantly localized in the cytoplasm. The interaction of negative regulator Msa2p/Nrd1p with positive regulator Cpc2p suggests a new regulatory circuit in the sexual differentiation of S. pombe.     

Specification of amino acid residues essential for the catalytic reaction of cold-active protein-tyrosine phosphatase of a psychrophile, Shewanella sp

Protein-tyrosine phosphatase [EC 3.1.3.48] from a psychrophile, Shewanella sp. shows high activity at low temperatures and has the conserved amino acid sequence of protein-Ser/Thr-phosphatases. Site-directed mutagenesis with the conserved amino acid residues indicated that His148 could be important as a general acid catalyst and Asp115 assists the protonation with His148 of the leaving group of a substrate, and that Asp76 and Asp112 were involved in binding to magnesium ions.