Acta Bot. Neerl.39(3), September 1990, p. 305-320 Meetings of the Royal Botanical Society of The Netherlands MEETING OF THE SECTION FOR PLANT MORPHOLOGY, ANATOMY AND CYTOLOGY ON 1 DECEMBER 1989 Organization of Cellulose Microfibrils and cells have a random texture. Since the authors men- tioned above also found a random orientation of Cortical Microtubules in the Shoot Apex microtubules in the conclusion is corpus cells, our M.M.A. Sassen and A.M.C. Wolters-Arts. that no co-alignmentoccurs between microfibrils and Department of Experimental Botany, University of microtubules in these cells. corpus Nijmegen, Toernooiveld,6525 ED Nijmegen,The Netherlands Freeze SubstitutionofMature Papaver The arrangement of cellulose microfibrils (CMFs) is rhoeas Pollen different in various of the shoot anti- regions apex: A.C. Van Aelst and M. Cresti 1 . Department of Plant clinal in tunica cells, random in corpus cells and trans- Cytology and Morphology, Wageningen verse in cells of the rib meristem (Sakaguchi el al. AgriculturalUniversity, Arboretumlaan 4, 6703 BD Planla 1988, 175: 403-411). These data are based on Wageningen, The Netherlands, and 'Dipartimento di examinations of cryosections of Vinca major apices BiologiaAmbientale,Universita di Siena, Via P.A. with the polarizing microscope. Careful examination Mattioli 4, 53100 Siena, Italy with EM on Petunia and Vinca apices confirmed the above for tunica and rib meristem but Fast in used findings cells, a freezing liquid propane was to create an different type ofCMF arrangement was found for the absolute moment fixation of all cell constituents. cells. Water inside and outside the cells into the corpus changed Apices of Petunia hybrida and Vinca major were vitrified solid state. Freeze substitution in acetone or fixed with a mixture of p-formaldehyde and glutar- methanol, in which 2% osmium tetroxide and 1% aldehyde, and embedded in polyethylene glycol. uranylacetate is dissolved,was carried out in a special sections 5 in thickness freeze substitution device Longitudinal pm were selected, (CS auto, Reichert) at transferred to nickel oyster grids and extracted with — 80°C. hydrogen peroxide and glacial acetic acid for 30 min at Three fixation procedures were compared. A con- 90°C. After rinsing with water the grids were covered ventional chemical fixation in water and two freeze with a forravar film, air-dried, shadowcasted with substitution procedures (acetone and methanol), platinum, and studied with TEM. resulted in striking differences in electron microscopi- In corpus cells microfibrils aredepositedin lamella- cal images. In freeze-substituted material, structures like sheets, each of which consists of parallel-oriented containing carbohydrates were highly contrasted, CMFs. Microfibrils of adjacent lamellae are some- while (phospho)lipid-containingstructures were elec- times interwoven, which means that these lamellae are tron transparent. The conventional chemical-fixed depositedmore or less at the sametime but in different material showed the opposite: a high contrast of struc- directions. Dependingon the number of divisions and tures with a (phospho)lipidorigin and electron trans- on the direction of division, corpus cell walls consist parency of the carbohydrate-containing structures. of varying numbers of lamellae. Near the pit fields, Substitution fluids are organic solvents which microfibrils in onelamella deviate, which supports the have to dehydrate the cell cytoplasm and cell wall by idea of a random orientation of CMFs. The orien- dissolving the ice followed by the diffusion of water tation ofCMFs in tunica cells is parallel to the newly molecules. In order to fix and create contrasted struc- formed cell wall, i.e. anticlinal. Cell walls of the rib tures inside the cell, a reaction of (glyco)proteins, meristem show parallel-oriented microfibrils perpen- (phospho)lipids and carbohydrates with osmium dicular to the direction of extension of these cells. tetroxide and uranyl acetate has to take place. Un- As the direction of microfibrils is different for each fortunately, these chemical fixatives start reacting at lamella,it is understandable that the average arrange- about — 60°C. This meansthat duringthe substitution is — selective of ment, as seen with the polarizing microscope, procedure at 80°C a extraction cell random. TEM studies, however, show that the newly constituents occurs. synthesized CMFs in Petunia and Vinca corpus cells It is concluded that chemical fixation and freeze in less This are deposited more or parallel arrays. con- fixation followed by dehydrationprocedures result in tradicts the generally accepted view that meristematic different electron microscopical images which are 305 306 MEETINGS additional to each other in the visualization of the by the plasmalemma. It is attached to the cell wall by a ultrastructure of plant cells. cupule, a bell-like protrusion of the inner wall layer. The plastids contain small plastoglobuli, presumably oil. Larger oil droplets appear loosely scattered in the Experimental Manipulation ofthe Plane of cytoplasm and often situated near the oil cavity, where Cell Division by Wounding they apparently pass through the plasmalemma sur- C.J. Venverloo. DepartmentofPlant Molecular rounding the oil cavity. Two specific cell organelles, Biology, University of Leiden, Nonnensteeg 3, 2311 not reportedpreviously for oil cells, occur in this stage: VJ Leiden, The Netherlands smooth tubular endoplasmic reticulum,appearing as bundles of linearly arranged tubules, and groups of In vacuolated cells a phragmosome (PS) is formed crystalline bodies, which are probably of protein- before mitosis. The PS is a thin cytoplasmic sheath aceous In the course of 3 the thickness of that is positioned at the site of the future cell wall. One origin. stage the inner wall layer, the relative volume of the oil of the functions of the PS is to guide the cell plate cavity, and cell size increase. duringcytokinesis. The question is whether the plane of cell division becomes fixed before or during the formation of a PS. The epidermis cells of small DistributionofNon-Articulated Branched explants of Nautilocalyx leaves divided periclinally, Laticifers ofMorus nigra L. (Moraceae) transversely or longitudinally. When the explants R.W. den Outer and W.L.H. van Veenendaal. into cut, were separated two parts by a longitudinal Department of Plant Cytology and Morphology, most cells near the wound divided longitudinally. WageningenAgricultural University, before Cells which had a non-longitudinalPS already Arboretumlaan 4,6703 BD Wageningen,The different the wound was made showed reactions: all Netherlands cells at some distance (100-150 pm) from the wound The origin, development and arrangement of the and half of the cells close to the wound (0-100 pm) branched, non-articulated laticiferous system of divided in accordance with the PS. In some ofthe cells Morus nigra L. (Moraceae) were studied. Embryos, close to the wound the original PS was replaced by a seedlings, leaves, stems and roots ofyoung and mature longitudinal PS and a longitudinal cell wall was plants were investigated using light and scanning formed. In some other cells the original PS was more electron There laticiferous microscopy. are two sys- or less disturbed and an obliquecell wall was formed. tems present in the older plant, a primary and a These results show that the planeof cell division can secondary one.The primary laticifers arise from eight easily be changed in cells without a PS, but that a ini tials in the outer ofthe future it periphery procambium strong signal is needed to change in cells with a PS. near the cotyledonary node ofthe young heart-shaped In the last case a new PS is formed. This suggests that the first-formed embryo. They produce transport sys- the plane of cell division is being fixed during PS for- tem of the plant. No additional primary laticifers are mation, not earlier (a full account of this study has formed in other primary tissues. Secondary laticifers been submitted to Protoplasma). of the same type as the primary onesare produced by initials of the vascular cambium in stem and root. An Ultrastructural of the Study Their number is larger and variable. No fusions of Development of Oil Cells in Annona laticiferous cells with one another or adjoining paren- muricata chyma cells were observed. The extremely elongated, branched laticiferous cells devoid of M E. Bakker. Rijksherbarium, PO Box 9514, 2300 thin-walled, are exhibit combination ofintrusive and RA Leiden, The Netherlands pits. They a sym- plastic growth; penetrations of other cells were not The ultrastructure of developing and mature oil idio- Laticifers observed. are present in all vegetative tissues blasts in the shoot and leaves of Annona apex with the exception of epidermis, and primary and has been studied with muricata (Annonaceae) light, secondary xylem. The close developmentaland distri- fluorescence and transmission electron microscopy. butional relationship between laticifers and phloem Three developmental stages can be recognized. suggest a possible functional relationship. Stage I. The small cells do not differ from the sur- rounding cells by their size, but can be recognized by Wood Anatomical Research—its Current their less electron-dense cytoplasm, plastids lacking Status thylakoids, and vacuoles devoid of deposits. Stage 2 P. Baas. Rijksherbarium/Hortus Botanicus, PO Box resembles stage 1, but in the cells a suberized layer has 9514, 2300 RA Leiden, The Netherlands. been deposited against