Roles of cell walls and intracellular contents in supercooling capability of xylem parenchyma cells of boreal trees.

The supercooling capability of xylem parenchyma cells (XPCs) in boreal hardwood species differs depending not only on species, but also season. In this study, the roles of cell walls and intracellular contents in supercooling capability of XPCs were examined in three boreal hardwood species, Japanese beech, katsura tree and mulberry, whose supercooling capability differs largely depending on species and season. XPCs in these species harvested in winter and summer were treated by rapid freezing and thawing (RFT samples) or by RFT with further washing (RFTW samples) to remove intracellular contents from XPCs in order to examine the roles of cell walls in supercooling. RFT samples were also treated with glucose solution (RFTG samples) to examine roles of intracellular contents in supercooling. The supercooling capabilities of these samples were examined by differential thermal analysis after ultrastructural observation of XPCs by a cryo-scanning electron microscope to confirm effects of the above treatments. XPCs in RFTW samples showed a large reduction in supercooling capability to similar temperatures regardless of species or season. On the other hand, XPCs in RFTG samples showed a large increase in supercooling capability to similar temperatures regardless of species or season. These results indicate that although cell walls have an important role in maintenance of supercooling, change in supercooling capability of XPCs is induced by change in intracellular contents, but not by change in cell wall properties.

Localization of mucilaginous polysaccharides in mulberry leaves.

Mulberry tree leaves were shown to have mucilaginous polysaccharides. The extracted water-soluble mucilage was separated into three fractions via a cetylpyridinum chloride complex and purified by anion-exchange chromatography. Five acidic polysaccharides were separated from these fractions, one of which was a major polysaccharide (Mp-3) that was structurally analyzed and used for antibody preparation. The Mp-3 polysaccharide contained rhamnose, galactose, glucose, galacturonic acid, and glucuronic acid in a molar ratio of 1 : 0.2 : 0.5 : 2.3 : 1.5 as constituent monosaccharides. Methylation and gas chromatography-mass spectrometry analysis indicated that the polysaccharide was a rhamnogalacturonan mainly consisting of 1,2,3-linked rhamnose residues, 1,3,4- and 1,4-linked uronic acid residues, and terminal uronic acid residues. Its molecular weight was estimated to be 5.5 x 10(5). Immunohistological observation revealed that the Mp-3 polysaccharide is specifically localized in inner epidermal cells situated in adaxial leaves, and electron microscopy showed that its subcellular location is between the plasma membrane and the cell wall. In young leaves, numerous secretory vesicles were present in a shrunken cytoplasm that was surrounded by fibers. In mature leaves, more than 20% of total epidermal cells were these inner cells in which polysaccharide deposition was significantly increased. The deposits appeared as a rounded electron-dense mass throughout the inner cells by electron microscopy.

Ultrastructural and immunochemical features of the cell wall sac formed in mulberry (Morus alba) idioblasts.

A peculiar inward growth, named a "cell wall sac", formed in mulberry (Morus alba) idioblasts, is a subcellular site for production of calcium carbonate crystals. On the basis of ultrastructural observations, a fully expanded cell wall sac could be divided into two parts-an amorphous complex consisting of multi-layered compartments with multiple fibers originating from the innermost cell wall layer, and a peripheral plain matrix with fiber aggregates. Immunofluorescent localization showed that low and highly esterified pectin epitopes were detected at the early stages of development of the cell wall sac, followed by complete disappearance from the both parts of fully enlarged mature sac. In contrast, the xyloglucan epitope remained in the compartment complex; this was supported by the observation that the xyloglucan epitope labeled with immuno-gold particles is found on fibers in the complex part.

Cell wall sheath surrounding calcium oxalate crystals in mulberry idioblasts.

The distribution and ultrastructural features of idioblasts containing calcium oxalate crystals were studied in leaf tissues of mulberry, Morus alba L. In addition to the calcium carbonate crystals formed in epidermal idioblasts, large calcium oxalate crystals were deposited in cells adjacent to the veins and surrounded by a cell wall sheath which had immunoreactivity with an antibody recognizing a xyloglucan epitope. The wall sheath formation indicates exclusion of the mature crystal from the protoplast.

Calcium carbonate deposition in a cell wall sac formed in mulberry idioblasts.

Although calcium carbonate is known to be a common biomineral in plants, very little attention has been given to the biological control of calcium carbonate deposition. In mulberry leaves, a subcellular structure is involved in mineral deposition and is described here by a variety of cytological techniques. Calcium carbonate was deposited in large, rounded idioblast cells located in the upper epidermal layer of mulberry leaves. Next to the outmost region ("cap") of young idioblasts, we found that the inner cell wall layer expanded to form a peculiar outgrowth, named cell wall sac in this report. This sac grew and eventually occupied the entire apoplastic space of the idioblast. Inside the mature cell wall sac, various cellulosic membranes developed and became the major site of Ca carbonate deposition. Concentrated Ca2+ was pooled in the peripheral zone, where small Ca carbonate globules were present in large numbers. Large globules were tightly packed among multiple membranes in the central zone, especially in compartments formed by cellulosic membranes and in their neighboring membranes. The maximum Ca sink capacity of a single cell wall sac was quantified using enzymatically isolated idioblasts as approximately 48 ng. The newly formed outgrowth in idioblasts is not a pure calcareous body but a complex cell wall structure filled with substantial amounts of Ca carbonate crystals.

[Research on microstructure of caulis herb].

OBJECTIVE: To provide reference for the microscopic identification of caulis herb. METHOD: Systematic arrangement and comparative studies were carried out on the microstructure of medicinal herb of different groups and shapes. RESULT: The rule and characteristics of the microstructure of caulis herb were discussed, and the sorting search list of the microstructure of common caulis herb was established. CONCLUSION: The microstructure characteristics of caulis herb, as the reference of the microscopic identification, are of research value.

Tropic failure of Phyllactinia corylea contributes to the mildew resistance of mulberry genotypes.

Different mulberry genotypes show great variation in their resistance to the powdery mildew Phyllactinia corylea. Conidial germination and hyphal growth of P. corylea on the leaf surface of two susceptible mulberry genotypes, viz., Kanva 2 (K2) and Victory 1 (V1) varieties of Morus indica, and on two resistant species, viz,, M. laevigata and M. serrata were studied by scanning electron microscopy. Conidial germination and growth of germ tubes were normal on all the leaves. The hyphae of P. corylea identify stomata on host leaves by their topographical features to produce the stomatopodia precisely over them. The holes and/or the grooves of stomata appear to provide the signals for the initiation of stomatopodia and similar structures are erratically developed over many local depressions or grooves on leaf surface. The abaxial surface of K2 leaf is smooth without prominent undulations of epidermal cell surface, and the stomata are flush with the leaf surface. Although successful penetration is also achieved on V1 leaf, its slightly undulated surface occasionally provides inaccurate tropic signals to the hyphae, inducing the development of stomatopodia away from the stomata. The leaf surfaces of M. laevigata and M. serrata are very rough with highly sculptured cuticle and abundant epidermal outgrowths. Stomata mostly remain sunken or hidden amidst the cuticular ornamentations and the hyphae fail to recognise the precise signals from them. As the surface architecture of the leaves provides many immense sources of tropic signals, stomatopodia are often produced over local depressions or grooves. In these cases the fungus fails to penetrate the leaf, does not develop beyond 24 h and penetration is rarely achieved on the leaves of the resistant plants. The study indicates that the stimulatory effect of the leaf surface topography of resistant varieties misleads the pathogen from successful penetration, thus contributing to the plant's resistance.

[Ultrastructures of a mycoplasma-like organism causing mulberry dwarf disease].

The pathogen causing the dwarf disease of mulberry in Tongxiang, Zhejiang Province was investigated based on transmission electronic microscopy of the leaf vein of diseased plants collected in the field. A mycoplasma-like organism was identified in the sieve tube, companion, and parenchyma cells of the phloem tissues infected. The organism was spheric or oval in shape, ranging from 50 nm to 160 nm in diameter, and with bilamina unit membrane of 8-10 nm in thickness, and was filled with nuclear strands or fibrous material. Some nuclei of mesophyll cells in the diseased leaves were found disrupted as their nuclear membrane was broken, followed by of nucleo-cytoplasmic matrix and dispersive disappearance of nucleoli. Furthermore, other ultrastructural aberration including depletion of chloroplast stroma, disruption of chloroplast grana, increase of mitochondria and rough endoplasmic reticulum, and discomposition of some mitochondrial cristae were also observed associated with the pathological changes caused by the mycoplasma-like organism. In contrast, this type of organism was not found in healthy plants examined. Thus, the mycoplasma-like organism is likely to be a pathogen attributable to the mulberry dwarf disease.