Transformation of the Golgi apparatus in the cell cycle,especially at the resting and earliest developmental stages of a green alga,Micrasterias americana

Summary Transformation of the Golgi apparatus inMicrasterias americana at various stages after full growth and at the earliest stage of cell growth was investigated using an electron microscope. Silver-hexamine staining and the acid phosphatase (ACPase) test were also carried out. In cells cultured for two days after full growth, dictyosomes began to produce hypertrophied vesicles (HVs) along their five peripheral reagions. The HVs contained fibrous material, which was stained by silver-hexamine, and small granules which reacted with ACPase. The HVs were pinched off the dictyosomes and fused with each other and with the vacuoles. In the earliest stage of cell growth, the cisternae of the dictyosomes were stretched in one direction, which modified the shape from circular to elliptical and the dictyosomes curved along the long axis of the ellipse. These curved dictyosomes which produced middle sized vesicles (MVs) from the distal networks, divided into two identical parts along the short axis of the ellipse.     

Engineering of betaine biosynthesis and transport for abiotic stress tolerance in plants

Drought and salinity are the major factors that decrease crop yield. Organisms thriving in osmotic stress environments need adaptive mechanisms for adjusting their intracellular environment to external osmotic stress conditions. One such mechanism, to prevent water loss from the cells is to accumulate large amounts of low molecular weight organic compatible solutes such as proline, betaine and polyols to balance internal osmolarity of the cells. Accumulation of compatible solutes can be achieved by enhanced synthesis and/or reduced catabolism. Certain plants synthesize betaine in chloroplasts via a two-step oxidation of choline and betaine accumulation is associated with enhanced stress tolerance. Many important crop plants have low levels of betaine or none at all. Hence, betaine biosynthetic pathway is a target for metabolic engineering to enhance stress tolerance in crops. Introduction of betaine synthesis pathway into betaine non-accumulating plants has often improved stress tolerance. However, betaine levels of the engineered plants were generally low. To further enhance the betaine accumulation levels, we need to diagnose factors limitng betaine accumulation in engineered plants. Here we discuss recent progress on metabolic engineering of choline precursors for abiotic stress tolerance in plants.     

Temporal and spatial immunolocalization of glucomannans in differentiating earlywood tracheid cell walls of Cryptomeria japonica

We investigated the deposition of glucomannans (GMs) in differentiating earlywood tracheids of Cryptomeria japonica using immunocytochemical methods. GMs began to deposit at the corner of the cell wall at the early stages of S₁ formation and showed uneven distribution in the cell wall during S₁ formation. At the early stages of S₂ formation, limited GM labeling was observed in the S₂ layer, and then the labeling increased gradually. In mature tracheids, the boundary between the S₁ and S₂ layers and the innermost part of the cell wall showed stronger labeling than other parts of the cell wall. Deacetylation of GMs with mild alkali treatment led to a significant increase in GM labeling and a more uniform distribution of GMs in the cell wall than that observed before deacetylation, indicating that some GM epitopes may be masked by acetylation. However, the changes in GM labeling after deacetylation were not very pronounced until early stages of S₂ formation, indicating that GMs deposited in the cell wall at early stages of cell-wall formation may contain fewer acetyl groups than those deposited at later stages. Additionally, the density of GM labeling increased in the cell wall in both specimens before and after GM deacetylation, even after cell-wall formation was complete. This finding suggests that some acetyl groups may be removed from GMs after cell-wall formation is complete as part one of the tracheid cell aging processes.     

Anatomy and lignin distribution in reaction phloem fibres of several Japanese hardwoods

Background and Aims Although tension wood formation and the structure of gelatinous fibres (G-fibres) have been widely investigated, studies of the influence of the reaction phenomenon on phloem fibres have been few and incomplete in comparison with those of xylem wood fibres. This study was undertaken to clarify the influence of stem inclination on phloem fibres using several Japanese hardwood species that produce different G-fibre types in tension wood. Methods Eight hardwood species were inclined at 30-45° at the beginning of April. Specimens were collected in July and December. The cell-wall structure and lignin distribution of phloem fibres on both the tension and opposite sides were compared by light microscopy, ultraviolet microscopy, confocal laser scanning microscopy after staining with acriflavine, and transmission electron microscopy after staining with potassium permanganate. Key Results Three types of changes were found in tension-side phloem fibres: (1) increases in the proportion of the syringyl unit in lignin in the S(1) and S(2) layers and compound middle lamella (Cercidiphyllum japonicum), (2) formation of unlignified gelatinous layers (Melia azedarach and Acer rufinerve) and (3) increases in the number of layers (n) in the multi-layered structure of S(1) + S(2) + n (G + L) (Mallotus japonicus). Other species showed no obvious change in cell-wall structure or lignin distribution. Conclusions Phloem fibres of the tree species examined in our study showed three types of changes in lignin distribution and cell-wall structure. The reaction phenomenon may vary with tree species and may not be closely related to G-fibre type in tension wood.     

Overexpression of RCI2A decreases Na+ uptake and mitigates salinity-induced damages in Arabidopsis thaliana plants

We have investigated whether the overexpression of RCI2A gene causes an enhanced salt-tolerant phenotype in Arabidopsis thaliana . Although the growth of RCI2A -overexpressing transgenic plants was comparable with that of wild type under normal conditions, high salinity treatment caused decreased accumulation of Na⁺ and ameliorated suppression of the shoot growth of transgenic plants than that of wild type. Under high salinity treatment, the chlorophyll content of the shoots of wild-type plants significantly decreased compared with transgenic plants. The increases of malondialdehyde (MDA) and of H₂O₂ production caused by high salinity were greater in the shoots of wild type than in that of transgenic plants. These results suggest that overexpression of RCI2A can alleviate salinity-induced growth suppression and photooxidative damages via reducing Na⁺ uptake into the shoots.     

Immunolocalization of 8-5′ and 8-8′ linked structures of lignin in cell walls of Chamaecyparis obtusa using monoclonal antibodies

Mouse monoclonal antibodies were generated against dehydrodiconiferyl alcohol- or pinoresinol-p-aminohippuric acid (pAHA)-bovine serum albumin (BSA) conjugate as probes that specifically react with 8-5′ or 8-8′ linked structure of lignin in plant cell walls. Hybridoma clones were selected that produced antibodies that positively reacted with dehydrodiconiferyl alcohol- or pinoresinol-pAHA–BSA and negatively reacted with pAHA–BSA and guaiacylglycerol-beta-guaiacyl ether-pAHA–BSA conjugates containing 8-O-4′ linkage. Eight clones were established for each antigen and one of each clone that positively reacted with wood sections was selected. The specificity of these antibodies was examined by competitive ELISA tests using various lignin dimers with different linkages. The anti-dehydrodiconiferyl alcohol antibody reacted specifically with dehydrodiconiferyl alcohol and did not react with other model compounds containing 8-O-4′, 8-8′, or 5-5′ linkages. The anti-pinoresinol antibody reacted specifically with pinoresinol and syringaresinol and did not react with the other model compounds containing 8-O-4′, 8-5′, or 5-5′ linkages. The antibodies also did not react with dehydrodiconiferyl alcohol acetate or pinoresinol acetate, indicating that the presence of free phenolic or aliphatic hydroxyl group was an important factor in their reactivity. In sections of Japanese cypress (Chamaecyparis obtusa), labeling by the anti-dehydrodiconiferyl alcohol antibody was found in the secondary walls of phloem fibers and in the compound middle lamellae, and secondary walls of tracheids. Weak labeling by the anti-pinoresinol antibody was found in secondary walls of phloem fibers and secondary walls and compound middle lamellae of developed tracheids. These labelings show the localization of 8-5′ and 8-8′ linked structure of lignin in the cell walls.     

Interleukin-1β-induced Reduction of CD44 Ser-325 Phosphorylation in Human Epidermal Keratinocytes Promotes CD44 Homomeric Complexes,Binding to Ezrin,and Extended,Monocyte-adhesive Hyaluronan Coats

The proinflammatory cytokine interleukin-1β (IL-1β) attracts leukocytes to sites of inflammation. One of the recruitment mechanisms involves the formation of extended, hyaluronan-rich pericellular coats on local fibroblasts, endothelial cells, and epithelial cells. In the present work, we studied how IL-1β turns on the monocyte adhesion of the hyaluronan coat on human keratinocytes. IL-1β did not influence hyaluronan synthesis or increase the amount of pericellular hyaluronan in these cells. Instead, we found that the increase in the hyaluronan-dependent monocyte binding was associated with the CD44 of the keratinocytes. Although IL-1β caused a small increase in the total amount of CD44, a more marked impact was the decrease of CD44 phosphorylation at serine 325. At the same time, IL-1β increased the association of CD44 with ezrin and complex formation of CD44 with itself. Treatment of keratinocyte cultures with KN93, an inhibitor of calmodulin kinase 2, known to phosphorylate Ser-325 in CD44, caused similar effects as IL-1β (i.e. homomerization of CD44 and its association with ezrin) and resulted in increased monocyte binding to keratinocytes in a hyaluronan-dependent way. Overexpression of wild type CD44 standard form, but not a corresponding CD44 mutant mimicking the Ser-325-phosphorylated form, was able to induce monocyte binding to keratinocytes. In conclusion, treatment of human keratinocytes with IL-1β changes the structure of their hyaluronan coat by influencing the amount, post-translational modification, and cytoskeletal association of CD44, thus enhancing monocyte retention on keratinocytes.