Anatomical aspects of hormonal regulation of abscission in citrus – The shoot-peduncle abscission zone in the non-abscising stage

Although mature citrus fruits [ Citrus sinensis (L.) Osbeck cv. Shamouti] did not abscise at the peduncle-shoot abscission zone (AZ–A) when incubated in ethylene environment, abscission processes did occur in a limited number of cell layers situated in the inner bark, the starch sheath region, and in the pith of AZ–A. These processes were regulated by 2,4-D and ethylene treatments. Cells responding to the "separation processes", particularly in the ethylene treatment, underwent either (a) cell wall swelling, dissolving and breakdown, or (b) growth and expansion in a radial plane. Further away from the dissolving area, the response of some cells of the mid and outer bark took the form of divisions or growth in a circumferential plane, while other cells remained unchanged. Non-responding tissues of the outer bark formed a "sleeve" of undissolved cells, and the vascular cylinder produced no abscission in AZ–A. It is concluded that the partial cell wall dissolution in AZ–A explains the increased activity of cellulase and polygalacturonase in the non-abscising AZ–A of the mature fruit (Greenberg et al. 1975. Physiol. Plant. 37: 1–7).     

Studies on dissimilatory sulfate-reducing bacteria that decompose fatty acids

Gliding motility, ultrastructure and nutrition of two newly isolated filamentous sulfate-reducing bacteria, strains 5ac10 and 4be13, were investigated. The filaments were always attached to surfaces. Growth was supported by addition of insoluble aluminium phosphate or agar as substrata for gliding movement. Electron microscopy of ultrathin sections revealed cell walls characteristic of Gramnegative bacteria; the undulated structure of the outer membrane may pertain to the translocation mechanism. Intracytoplasmic membranes were present. Acetate, higher fatty acids, succinate or fumarate served as electron donors and carbon sources. Strain 5ac10 grew also with lactate, but not with benzoate that was used only by strain 4be13. Strain 5ac10 was able to grow slowly on H₂ plus CO₂ or formate in the presence of sulfate without additional organic carbon source. The capacity of complete oxidation was shown by stoichiometric measurements with acetate plus sulfate. Both strains contained b- and c-type cytochromes. Desulfoviridin was detected only in strain 5ac10. The two filamentous gliding sulfate reducers are described as new species of a new genus, Desulfonema limicola and Desulfonema magnum.     

Taxol maintains organized microtubule patterns in protoplasts which lead to the resynthesis of organized cell wall microfibrils

Summary We have investigated the effects of microtubule stabilizing conditions upon microtubule patterns in protoplasts and developed a new method for producing protoplasts which have non-random cortical microtubule arrays. Segments of elongating pea epicotyl tissue were treated with the microtubule stabilizing drug taxol for 1 h before enzymatic digestion of the cell walls in the presence of the drug. Anti-tubulin immunofluorescence showed that 40 M taxol preserved regions of ordered microtubules. The microtubules in these regions were arranged in parallel arrays, although the arrays did not always show the transverse orientation seen in the intact tissue. Protoplasts prepared without taxol had microtubules which were random in distribution. Addition of taxol to protoplasts with random microtubule arrangements did not result in organized microtubule arrays. Taxol-treated protoplasts were used to determine whether or not organized microtubule arrays would affect the organization of cell wall microfibrils as new walls were regenerated. We found that protoplasts from taxol-treated tissue which were allowed to regenerate cell walls produced organized arrays of microfibrils whose patterns matched those of the underlying microtubules. Protoplasts from untreated tissue synthesized microfibrils which were disordered. The synthesis of organized microfibrils by protoplasts with ordered microtubules arrays shows that microtubule arrangements in protoplasts influence the arrangement of newly synthesized microfibrils.Abbreviations DIC differential interference contrast - DMSO dimethyl sulfoxide - FITC fluorescein isothiocyanate - IgG immunoglobulin G - PIPES piperazine-N,N-bis[2-ethane-sulfonic acid] - PBS phosphate buffered saline     

Stabilization of cortical microtubules by the cell wall in cultured tobacco cells

Cortical microtubules (MTs) in protoplasts prepared from tobacco (Nicotiana tabacum L.) BY-2 cells were found to be sensitive to cold. However, as the protoplasts regenerated cell walls they became resistant to cold, indicating that the cell wall stabilizes cortical MTs against the effects of cold. Since poly-l-lysine was found to stabilize MTs in protoplasts, we examined extensin, an important polycationic component of the cell wall, and found it also to be effective in stabilizing the MTs of protoplasts. Both extensin isolated from culture filtrates of tobacco BY-2 cells and extensin isolated in a similar way from cultures of tobacco XD-6S cells rendered the cortical MTs in protoplasts resistant to cold. Extensin at 0.1 mg·ml⁻¹ was as effective as the cell wall in this respect. It is probable that extensin in the cell wall plays an important role in stabilizing cortical MTs in tobacco BY-2 cells.     

Cellulose and xylans in the interface capsule in symbiotic cells of actinorhizae

Summary Enzyme-gold affinity labeling was used to show that in mature infected cells of actinorhizal symbioses the capsule on the plant host side of the symbiotic interface contained cellulose and xylans. Host species examined for cellulose wereAlnus rubra, Casuarina equisetifolia, C. glauca, Ceanothus cuneata, C. velutinus, Elaeagnus pungens, andMyrica cerifera.. Cellulose was in the capsule throughout the infected cell, implying that during development cellulose synthase was present in the host cell membrane component of the symbiotic interface. Any possible degradation of capsule cellulose by the microsymbiont was either incomplete or transient, because the polymer was present in mature infected cells. Cellulose labeling inCeanothus andElaeagnus was less consistent than in the other species. Dual labeled capsules inCasuarina glauca andAlnus rubra showed a similar distribution of xylans and cellulose. Cytochemical studies indicate that the capsule contains three major classes of cell wall polysaccharides: cellulose, hemicellulose (xylans), and pectins (shown previously). This suggests that the capsule is essentially a thin, internal, tubular plant cell wall.Abbreviations Au₅ Au₁₅ colloidal gold particles with mean diameter of 5 and 15 nm, respectively - CBHI cellobiohydrolase I - CBHII cellobiohydrolase II - PBS phosphate-buffered saline     

Wall extensibility and gravitropic curvature of sunflower hypocotyls: correlation between timing of curvature and changes in extensibility

Abstract. Gravitropic curvature results from unequal growth rates on the upper and lower sides of horizontal stems. These unequal growth rates cold be due to differences in wall extensibility between the two sides. To test this, the time course of curvature of horizontal sunflower ( Helianthus anmus L.) hypocotyls was determined and compared with the time courses of changes in Instron-measured wall extensibility (PEx) of the upper and lower epidermal layers. As gravicurvature developed, so did the difference in PEx between the upper and lower epidermis. The enhanced growth rate on the lower side during the period of maximum increase in curvature was matched by PEx values greater than those of the vertical control, while the inhibited growth rate on the upper side was accompanied by PEx values below that of the control. The close correlation between changes in growth rates and alterations in PEx demonstrates that changes in wall extensibility play a major role in controlling gravicurvature.     

El Tor型霍乱弧菌及其细胞壁缺陷型分子遗传学背景的研究

El Tor 型霍乱弧菌(以下简称 El Tor 弧菌)可以在人工培养条件下长期存活。当微环境改变时可形成细胞壁有不同程度缺陷的菌株如抗噬菌体突变株或 L 型菌株。我们以 DNA 酶切图谱和 El Tor 弧菌溶血素、神经氨酸酶基因探针杂交图谱为参数对 El Tor 弧菌的野生型及其细胞壁缺陷型变异株在遗传背景上进行了比较分析研究。结果提示细胞壁缺陷型菌株与其野生型在DNA 水平上高度同源。此外,文中还介绍了一种从 L 型菌株中制备 DNA 的方法。     

A SPOROPHYTE CELL WALL PROTEIN OF THE RED ALGA PORPHYRA PURPUREA (RHODOPHYTA) IS A NOVEL MEMBER OF THE CHYMOTRYPSIN FAMILY OF SERINE PROTEASES1

A complementary DNA (cDNA) clone from a Porphyra purpurea (Roth) C. Agardh sporophyte-specific subtracted cDNA library was found to encode a protein similar to serine proteases of the chymotrypsin class. The encoded protein contains a typical signal peptide and is particularly similar to chymotrypsins in the regions surrounding the active site residues and the activation site where cleavage of the propeptide occurs. In addition, the six cysteine residues characteristic of chymotrypsins are conserved. However, two of the three residues of the active site His/Asp/Ser charge relay triad have been replaced, indicating that the protein is unlikely to have peptidase activity. Northern hybridization confirmed that this cDNA is derived from an abundant, sporophyte-specific messenger RNA (mRNA). The presence of signal peptide on the encoded protein and the abundance of its mRNA suggested that this protein might be localized in the cell wall. Consequently, sporophyte cell walls were isolated and a major protein having a molecular weight similar to that estimated for the encoded protein was purified. N-terminal sequence analysis indicated that this cell wall protein is identical to that encoded by the cDNA with the amino terminus of the mature protein beginning at the activation site. This cell wall structural protein appears to have evolved from a chymotrypsin-like progenitor but has been adapted to bind cell wall proteins and/or polysaccharides rather than to cleave proteins.     

chs-4, a class IV chitin synthase gene fromNeurospora crassa

InSaccharomyces cerevisiae, most of the cellular chitin is produced by chitin synthase III, which requires the product encoded by theCSD2/CAL1/DIT101/KT12 gene. We have identified, isolated and structurally characterized aCSD2/CAL1/DIT101/KT12 homologue in the filamentous ascomyceteNeurospora crassa and have used a reverse genetics approach to determine its role in vivo. The yeast gene was used as a heterologous probe for the isolation of aN. crassa gene (designatedchs-4) encoding a polypeptide belonging to a class of chitin synthases which we have designated class IV. The predicted polypeptide encoded by this gene is highly similar to those ofS. cerevisiae andCandida albicans. N. crassa strains in whichchs-4 had been inactivated by the Repeat-Induced Point mutation (RIP) process grew and developed in a normal manner under standard growth conditions. However, when grown in the presence of sorbose (a carbon source which induces morphological changes accompanied by elevated chitin content), chitin levels in thechs-4 ^RIP strain were significantly lower than those observed in the wild type. We suggest that CHS4 may serve as an auxiliary enzyme inN. crassa and that, in contrast to yeasts, it is possible that filamentous fungi may have more than one class IV chitin synthase.A. Beth Din and C. A. Specht contributed equally to this work     

Potential for host range expansion in Ceratitis capitata flies: impact of proximity of adult food to egg-laying sites

Abstract.

• 1 In field cage and field tests, female Mediterranean fruit flies, Ceratitis capitata (Wiedemann), in trees alighted in significantly greater numbers upon sticky-coated (non-odour-emitting) kumquats, Fortunella japonica, that were in the vicinity of odorous natural proteinaceous food (bird faeces) or synthetic food odour than on similar kumquats distant from bird faeces or synthetic food odour.
• 2 In field cage tests, oviposition in non-sticky kumquats nearby bird faeces was significantly greater than in non-sticky kumquats distant from bird faeces.
• 3 In field tests, medflies laid significantly more eggs in host kumquat and non-host hawthorn, Crataegus mollis, fruit adjacent to bird faeces and synthetic food odour than in fruit of these types distant from food-type stimuli.
• 4 These findings suggest that odour of natural food of medflies could lure flies to plants whose fruit emit little or no attractive odour and are not permanent hosts but which are nonetheless susceptible to egg-laying and larval development, resulting in temporary expansion of host range.