AOBPreview originally published online on April 23, 2008
Annals of Botany 2008 102(1):31-37; doi:10.1093/aob/mcn058
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Characteristic Thickened Cell Walls of the Bracts of the ‘Eternal Flower’ Helichrysum bracteatum
1 Vegetable and Ornamental Horticulture, Division of Agriculture, Kyoto University, Oiwake-cho, Kitashirakawa, Kyoto 606-8502, Japan
2 AJINOMOTO Integrative Research for Advanced Dieting, Graduate School of Agriculture, Kyoto University, Oiwake-cho, Kitashirakawa, Kyoto 606-8502, Japan
3 Tree Cell Biology, Division of Forest and Biomaterials Science, Kyoto University, Oiwake-cho, Kitashirakawa, Kyoto 606-8502, Japan
* For correspondence. E-mail hiroaki{at}kais.kyoto-u.ac.jp
Received: 31 January 2008 Returned for revision: 20 February 2008 Accepted: 20 March 2008 Published electronically: 23 April 2008
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Background and Aims: Helichrysum bracteatum is called an ‘eternal flower’ and has large, coloured, scarious bracts. These maintain their aesthetic value without wilting or discoloration for many years. There have been no research studies of cell death or cell morphology of the scarious bract, and hence the aim of this work was to elucidate these characteristics for the bract of H. bracteatum.
Methods: DAPI (4'6-diamidino-2-phenylindol dihydrochloride) staining and fluorescence microscopy were used for observation of cell nuclei. Light microscopy (LM), transmission electron microscopy (TEM) and polarized light microscopy were used for observation of cells, including cell wall morphology.
Key Results: Cell death occurred at the bract tip during the early stage of flower development. The cell wall was the most prominent characteristic of H. bracteatum bract cells. Characteristic thickened secondary cell walls on the inside of the primary cell walls were observed in both epidermal and inner cells. In addition, the walls of all cells exhibited birefringence. Characteristic thickened secondary cell walls have orientated cellulose microfibrils as well as general secondary cell walls of the tracheary elements. For comparison, these characters were not observed in the petal and bract tissues of Chrysanthemum morifolium.
Conclusions: Bracts at anthesis are composed of dead cells. Helichrysum bracteatum bracts have characteristic thickened secondary cell walls that have not been observed in the parenchyma of any other flowers or leaves. The cells of the H. bracteatum bract differ from other tissues with secondary cell walls, suggesting that they may be a new cell type.
Key words: Helichrysum bracteatum, scarious bract, secondary cell wall, primary cell wall, cell morphology, birefringence, orientated cellulose microfibrils, cell death, DAPI, transmission electron microscopy, polarized light microscopy
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Helichrysum bracteatum has compound flowers comprised of many tubular flowers and scarious bracts (Everett, 1980). The scarious bracts are large and coloured like a corolla. They maintain their aesthetic value without wilting or discoloration for many years, even after cutting. Helichrysum bracteatum is, therefore, suitable as a dried flower. Many species in the Compositae family Inurae tribe have such characteristic flowers, including Ammobium alatum, Anaphalis margaritacea, Antennaria dioica, Acroclinium roseum, H. bracteatum and Rhodanthe manglesi. In the Cardueae tribe, Carlina acaulis and Xeranthemum annuum have similarly characteristic flowers. The same can be said of Gomphrena globosa and Gomphrena haageana in the Amaranthaceae family and of Limonium sinuatum in the Plumbaginaceae family. In all these plants, the scarious bracts or sepals of their flowers are large and coloured like a corolla, similarly to those in H. bracteatum.
While the water content of the petals of Chrysanthemum morifolium ‘seikounoaki’ was found to be 88·5 %, that of the scarious bracts of H. bracteatum ‘Jumbo Yellow’ was 38·6 %, and that of the scarious sepals of L. sunuatum ‘Sundaeviolet’ was 21·2 %. Water contents of the leaves of these species were 88·9 %, 91·0 % and 75·9 %, respectively. Thus, scarious tissues have a low water content, while growing plant tissues typically contain 80 to 90 % water. Wood is composed mostly of dead cells, and has a low water content. For instance, the sapwood that functions in transport in via the xylem contains 35–75 % water (Taiz and Zeiger, 2002). The scarious bract of C. acaulis is composed of dead cells (Troll, 1957). These observations suggest that H. bracteatum scarious bracts and L. sunuatum scarious sepals are composed of dead cells. However, to the best of our knowledge, no research studies show this, nor are there reports of the cell morphology of scarious bracts and sepals.
We investigated whether the cells of the scarious bracts of H. bracteatum ‘Monstrosa’ are dead or alive by observing nuclei of such cells stained by DAPI (4'6-diamidino-2-phenylindol dihydrochloride) under a fluorescence microscope, and examined the morphology of scarious bract cells under a light microscope, a transmission electron microscope and a polarized light microscope.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Plants of Helichrysum bracteatum ‘Monstrosa’ were cultivated in a plastic greenhouse at Kyoto University in Japan. They were grown in pots containing the growing medium Metro-Mix 360 (Sun Gro Horticulture Canada Ltd, Seba Beach, Canada) under natural sunlight. The composition of this medium is peat moss, vermiculite, bark ash, bark, dolomitic limestone and a wetting agent. The solid fertilizer IBS1 (N : P : K = 1 : 1 : 1; JA Group, Tokyo, Japan) was applied. Flowers of these plant were used in the following experiments.
DAPI staining and fluorescence microscopy
Seven stages of H. bracteatum flower development were considered (Fig. 1A): stage 1, bud <8·0 mm wide; stage 2, bud 8·0 
10 mm wide; stage 3, bud 10 12 mm wide; stage 4, bud 12 14 mm wide, with its second layers of bracts starting to open; stage 5: 4th 5th bracts of the bud starting to open; stage 6, innermost bracts of the bud starting to open; and stage 7, all bracts completely opened (anthesis). The innermost bracts at each stage of flower development, or bracts adjacent to tubular flowers, were used in the following experiments, which were performed according to Gladish et al. (2006). Bracts at each stage were stained with 1 mg L–1 DAPI (4'6-diamidino-2-phenylindol dihydrochloride) in 10 mmol L–1 Tris/HCl buffer (pH 7·4). The bracts were soaked in DAPI solution in a vacuum pump in the dark overnight to completely stain the nuclei of all cells of the bracts. Nuclei of the bract cells were observed after excitation at 340–380 nm under a fluorescence microscope (Olympus BX60). Each bract was divided into four equal lengths, and tip–1/4 and 1/4–2/4 were used in this experiment (Fig. 1B). Nuclei and epidermal cells were counted and the proportion of nuclei to epidermal cells of each part was determined. Three bracts were used at each stage.
|
Light microscopy (LM) and transmission electron microscopy (TEM)
A bract of H. bracteatum ‘Monstrosa’ at stage 7 (anthesis) was used. A petal and a bract of Chrysanthemum morifolium ‘Piato’ were also used for comparison. A razor blade was used to hand-section 3-mm wide segments of each tissue, which were fixed in 3 % glutaraldehyde in 0·05 mol L–1 phosphate buffer (pH 7·2) overnight at 4 °C. The segments were rinsed six times in 0·05 mol L–1 phosphate buffer for 10 min each. They were post-fixed in 2 % osmium tetroxide in 0·05 mol L–1 phosphate buffer for 2 h at room temperature, and were rinsed three times in the same buffer for 10 min each. The segments were dehydrated through a graded ethanol series: 30 %, 50 %, 70 %, 80 %, 90 %, 95 %, 95 %, 95 %, 99·5 %, 99·5 % and 99·5 % for 10 min each. The segments were then substituted four times with propylene oxide for 10 min each and were embedded in epon resin. Semi-thin sections were cut using an ultramicrotome (Reichert-Jung) and were stained with safranine and observed under a light microscope (Olympus BX60). Ultra-thin sections were cut using an ultramicrotome (Reichert-Jung). These were stained with 2 % aqueous uranyl acetate and Reynold's lead citrate and observed under a transmission electron microscope (JOEL JEM-1220).
Polarized light microscopy
A bract of H. bracteatum ‘Monstrosa’ at stage 7 (anthesis) was used. A petal and a bract of C. morifolium ‘Piato’ were also used for comparison. A razor blade was used to hand-section 3-mm wide segments of each tissue, which were fixed in FAA [100 % ethanol : DW : formalin : acetic acid = 12 : 6 : 1 : 1 (v/v)] overnight at room temperature, and dehydrated through a graded ethanol series: 30 %, 50 %, 70 %, 80 %, 90 %, 90 %, 90 %, 99·5 % and 99·5 % for 60 min each. They were embedded in Technovit 7100 resin (Heraeus Kuzer). Semi-thin sections were cut using a rotary microtome (Leica RM2155), and were observed under a light microscope (Olympus BX60), a polarized light microscope (Olympus BHA-751P), and the same polarlized light microscope with compensator. Sections stained with safranine were observed under a light microscope.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Nuclei in cells of bracts at each stage
Fluorescence of many nuclei in individual cells was observed at the bract tip at stage 1 (Fig. 2A); fewer nuclei were observed at stages 2 and 3 (Fig. 2B, C) and most had disappeared at stage 4 (Fig. 2D). In contrast, fluorescence of many nuclei was observed in bract bases at all stages (data not shown). The ratio of nuclei to epidermal cells in the parts tip–1/4 and 1/4–2/4 decreased with stage advancement (Fig. 3). The ratio in the 1/4–2/4 part at stages 1 and 2 were over 1·0; the reason for this is that the number of nuclei was determined in both the underlying layers of the epidermis as well as in the epidermis itself, whereas the cell number was only counted in the latter. No nuclei were observed in the tip–1/4 part at stage 5; thus, cell death occurred at the bract tip at the early stage of flower development. Most nuclei disappeared in the upper half of the bract by stage 5 (before anthesis).
|
|
Cell morphology and characteristic secondary cell wall
Spongy parenchyma was observed in petal and bract tissues of C. morifolium (Fig. 4B, C), but not in H. bracteatum bract tissue (Fig. 4A). Cells of H. bracteatum were closely arranged and smaller than those of C. morifolium.
|
, characteristic thickened secondary cell wall. Scale bars: (D–H) = 4 µm; I = 8 µm.A large vacuole was observed at the centre of cells of the petal and bract tissues of C. morifolium (Fig. 4F–I), with cytoplasm surrounding the vacuole. Some organelles, such as the nucleus and chloroplasts, were observed in the cytoplasm. On the other hand, no organelles were observed in the cells of H. bracteatum bract tissue (Fig. 4D, E). The cell walls were the most prominent characteristic of cells of the H. bracteatum bract. The primary cell walls form the outermost layer of cells in all tissues of the two species. Only primary cell walls were observed in the cells of the petal and bract of C. morifolium (Fig. 4F–I), whereas characteristic thickened secondary cell walls on the inside of the primary walls were observed in both epidermal and inner cells of the H. bracteatum bract (Fig. 4D, E). The outer periclinal walls of all epidermal cells were thickened primary cell walls in petal and bract tissue of C. morifolium (Fig. 4F, H). On the other hand, there were two layers, comprised of a thin primary cell wall and a thickened secondary cell wall, in all epidermal cells in the bract tissue of H. bracteatum (Fig. 4D). A cuticle layer was observed on the outside of the primary cell walls in all the tissues of the two species that were examined. Only flat primary cell walls of all inner cells, except for tracheary elements, were observed in the petals and bracts of C. morifolium (Fig. 4G, I), whereas in bract tissue of H. bracteatum, secondary cell walls on the inside of flat primary cell walls of all the inner cells had irregular thickening as lobes (Fig. 4E).
Birefringent properties of cell walls
The general secondary cell wall in tracheary elements (tracheid and vessel) or fibres has a highly birefringent property that can be observed under a polarized light microscope (Leney, 1981; Lev-Yadun, 1997; Jang, 1998; Bergander et al., 2002; Donaldson and Xu, 2005; Thygesen and Hoffmeyer, 2005; Lev-Yadun et al., 2005). This is because cellulose, which is the main component of the secondary cell wall, has crystalline properties resulting from the orderly arrangement of cellulose molecules in microfibrils (Smith et al., 1998). The orientation of cellulose microfibrils is neatly aligned parallel to each other in secondary cell walls (Taiz and Zeiger, 2002), so that birefringence is generated when viewed under polarized light (Evert, 2006). The primary cell wall cannot be observed under a polarized light microscope because it has a rather random arrangement of microfibrils.
Tracheary elements exhibited birefringence in petal and bract tissues of C. morifolium (Fig. 5E, H), because they have a secondary cell wall. The outer periclinal wall of epidermal cells also exhibited birefringence in C. morifolium bract tissue (Fig. 5H); although it is a primary cell wall, it consists of many layers (Fig. 4H) and so it exhibited birefringence. Observation under a polarized light microscope with a compensator showed the orientation of cellulose (Fig. 5C, F, I). In the figure, blue and yellow interference colours are vertical; blue interference colour shows that the orientation of cellulose is parallel to the x-axis, whilst yellow interference colour shows that the orientation of cellulose is parallel to the z-axis. Tracheary elements in petal and bract tissues of C. morifolium had two vertical orientations of cellulose (Fig. 5F, I). However, the cell walls of parenchyma cells, except for those of tracheary elements and the outer periclinal walls, exhibited no birefringence in C. morifolium petal and bract tissues. On the other hand, cell walls of all the cells exhibited birefringence in H. bracteatum bract tissue (Fig. 5B). They had the same orientation of cellulose as tracheary elements in C. morifolium petal and bract tissues (Fig. 5C). Moreover, the orientation of cellulose of the outer periclinal walls was parallel to the x-axis, not parallel to the z-axis in the H. bracteatum bract (Fig. 5C).
|
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Most nuclei disappeared in the upper half of the bract of H. bracteatum before anthesis, as observed by DAPI staining and fluorescence microscopy (Figs 2, 3); moreover, no organelles were observed in the cells of the H. bracteatum bract (Fig. 4D, E). For these reasons, it is shown that the bracts at anthesis are composed of dead cells. Characteristic thickened secondary cell walls on the inside of the primary cell wall were observed in all cells of the bract tissue of H. bracteatum by TEM (Fig. 4D, E). The walls of all the cells of H. bracteatum bract tissue exhibited birefringence, as determined by polarized light microscopy (Fig. 5B, C); the birefringence arises from the characteristic thickened secondary cell wall. It is therefore suggested that these walls of H. bracteatum bract cells have orientated cellulose microfibrils, as do the secondary cell walls of the tracheary elements of petal and bract tissues of C. morifolium. The birefringence at the outer periclinal walls of the epidermal cells of C. morifolium bract tissue (Fig. 4H, I) may be from many layers of primary cell walls. In summary, the bract of H. bracteatum is composed of dead cells, which have characteristic thickened secondary cell walls. These secondary cell walls have orientated cellulose microfibrils.
Cell walls of plants are classified into two types, primary and secondary. Growing cells, which have a viscoelastic property and can expand, form primary cell walls. Secondary cell walls are formed on the inside of primary cell walls after cell growth has ceased. They function in mechanical support in plants. They contain a higher proportion of cellulose than primary cell walls, and the orientation of cellulose microfibrils may be more neatly aligned parallel to each other than in primary cell walls (Taiz and Zeiger, 2002). Due to this property, only secondary cell walls exhibit birefringence. Moreover, cells with secondary cell walls are often dead. Are the characteristic secondary cell walls of the H. bracteatum bract the same as general secondary cell walls? We compared cells of the bract of H. bracteatum with taxonomical cells with general secondary cell walls.
Plant cells are classified into many cell types. According to the classification of Raven et al. (2005), cells with secondary cell walls are classified into three types: specialized parenchyma cells, sclerenchyma cells, and cells of tracheary elements. Sclerenchyma consists of fibres and sclereids, whilst tracheary elements consist of vessels and tracheids.
Leaves and petals contain a high amount water, and are composed mostly of parenchyma cells with primary cell walls and living cytoplasms. The cells of petal and bract tissues of C. morifolium had only a primary cell wall (Fig. 4F–I) and no birefringent properties (Fig. 5E, F, H, I). ‘Transfer cells’ are specialized parenchyma cells with secondary cell walls. Morphologically two categories of cell wall ingrowths can be recognized for most transfer cells; reticulate and flange (Pate and Gunning, 1972; Talbot et al., 2002). The shape of the secondary cell walls of the H. bracteatum bract is similar to that of transfer cells; however, cells of the H. bracteatum bract differ from transfer cells in their function, their non-living state and their location. Lobes of the secondary cell walls of transfer cells are for the transfer of solutes over short distances (Gunning and Pate, 1969; Gunning, 1977; McDonald et al., 1996; Harrington et al., 1997), and hence these cells are not dead. The locations of transfer cells are potential sites of intensive short-distance solute transfer, for example xylem, phloem and tissues of reproductive and glandular structures (Gunning et al., 1970; Rost and Lersten, 1970; Diane et al., 2002; Pate and Gunning, 1972).
Cells of the H. bracteatum bract are similar to sclerenchyma cells in function. The principal function of sclerenchyma cells is mechanical support, and these cells have secondary cell walls. However, cells of the H. bracteatum bract differ from fibres, which are a kind of sclerenchyma cell, in the location and the shape of secondary cell walls. The locations of fibres are the xylem, phloem, hypodermis, cortex and central cylinder (Evert, 2006), and secondary cell walls of fibre cells form a flat, thickened layer (Evert, 2006). Another type of sclerenchyma cell, sclereids, also have various types; leaves are a rich source of sclereids (Foster, 1955, 1956; Esau, 1977; Karabourniotis et al., 1994; Karabourniotis, 1998). Cells of the H. bracteatum bract also differ from sclereids in their overall shape, the shape of the secondary cell walls, their non-living state and their location. The sclereids of leaves have numerous simple pits, are often alive at maturity, and are located in particular parts of leaves, for example the ends of small veins, patches, epidermis and intercellular spaces.
Cells of the H. bracteatum bract are similar to those of tracheary elements in their non-living state and the shape of the secondary cell walls. Cells of tracheary elements are dead at maturity and their secondary cell walls have irregular thickeness and form some lobes (Esau and Charvat, 1978; Burgess and Linstead, 1984; Groover et al., 1997; Karlsson et al., 2005). However, cells of the H. bracteatum bract differ from tracheary elements in their function; the principal function of tracheary elements is in water conduction.
In conclusion, cells of the H. bracteatum bract differ from those of other tissues whose characterized cells have secondary cell walls, and they may be a new cell type. All cells of the H. bracteatum bract have characteristic thickened secondary cell walls that have not been reported in the parenchyma of any other flowers or leaves. Cells of the H. bracteatum bract are therefore an interesting subject for further research on differentiation and development.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
-
Bergander A, Brändstörm J, Daniel G, Salmén L. Fibril angle variability in earlywood of Norway spruce using soft rot cavities and polarisation confocal microscopy. Journal of Wood Science (2002) 48:255–263.[CrossRef][Web of Science]
Burgess J, Linstead P. In vitro tracheary element formation: structural studies and the effect of tri-iodobenzoic acid. Planta (1984) 160:481–489.[CrossRef][Web of Science]
Diane N, Hilger HH, Gottschling M. Transfer cell in the seeds of Boraginales. Botanical Journal of the Linnean Society (2002) 140:155–164.[CrossRef][Web of Science]
Donaldson L, Xu P. Microfibril orientation across the secondary cell wall of Radiata pine tracheids. Trees (2005) 19:644–653.[CrossRef]
Esau K. Anatomy of seed plants (1977) 2nd edn. New York: Wiley.
Esau K, Charvat I. On vessel member differentiation in the bean (Phaseolus vulgaris L.). Annals of Botany (1978) 42:665–677.
Everett TH. The New York Botanical Garden illustrated encyclopedia of horticulture (1980) New York, London: Garland Publishing, Inc.
Evert RF. Esau's plant anatomy. Meristems, cells, and tissues of the plant body: their structure, function, and development (2006) 3rd edn. Hoboken, NJ: John Wiley & Sons, Inc.
Foster AS. Structure and ontogeny of terminal sclereids in Boronia serrulata. American Journal of Botany (1955) 42:551–560.[CrossRef][Web of Science]
Foster AS. Plant idioblasts: remarkable examples of cell specialization. Protoplasma (1956) 46:184–193.[CrossRef][Web of Science]
Gladish DK, Xu J, Niki T. Apoptosis-like programmed cell death occurs in procambium and ground meristem of Pea (Pisum sativum) root tips exposed to sudden flooding. Annals of Botany (2006) 97:895–902.
Groover A, DeWitt N, Heidei A, Jones A. Programmed cell death of plant tracheary elements differentiating in vitro. Protoplasma (1997) 196:197–211.[CrossRef][Web of Science]
Gunning BES. Transfer cells and their role in transport of solutes in plants. Science Progress, Oxford (1977) 64:539–568.
Gunning BES, Pate JS. ‘Transfer cells.’ Plant cells with wall ingrowths, specialized in relation to short distance transport of solutes. Their occurrence, structure, and development. Protoplasma (1969) 68:107–133.[CrossRef][Web of Science]
Gunning BES, Pate LS, Green LW. Transfer cells in the vascular system of stems: taxonomy, association with nodes, and structure. Protoplasma (1970) 71:147–171.[CrossRef][Web of Science]
Harrington GN, Franceschi VR, Offler CE, Patrick JW, Tegeder M, Frommer WB, Harper JF, Hitz WD. Cell specific expression of three genes involved in plasma membrane sucrose transport in developing Vicia faba seed. Protoplasma (1997) 197:160–173.[CrossRef][Web of Science]
Jang HF. Measurement of fibril angle in wood fibres with polarization confocal microscopy. Journal of Pulp and Paper Science (1998) 24:224–230.[Web of Science]
Karabourniotis G. Light-guiding function of foliar sclereids in the evergreen sclerophyll Phillyrea latiforia: a quantitative approach. Journal of Experimental Botany (1998) 49:739–746.
Karabourniotis G, Papastergiou E, Kabanopoulou E, Fasseas C. Foliar sclereids of Olea europaea may function as optical fibres. Canadian Journal of Botany (1994) 72:330–336.
Karlsson M, Melzer M, Prokhorenko I, Johansson T, Wingsle G. Hydrogen peroxide and expression of hipl-superoxide dismutase are associated with development of secondary cell walls in Zinnia elegans. Journal of Experimental Botany (2005) 56:2085–2093.
Leney L. A technique for measuring fibril angle using polarized light. Wood Fiber (1981) 13:13–16.
Lev-Yadun S. Fibres and fibre-sclereids in wild-type Arabidopsis thaliana. Annals of Botany (1997) 80:125–129.
Lev-Yadun S, Wyatt SE, Flaishman MA. The inflorescence stem fibers of Arabidopsis thaliana Revoluta (ifl1) mutant. Journal of Plant Growth Regulation (2005) 23:301–306.
McDonald R, Fieuw S, Patrick JW. Sugar uptake by the dermal transfer cells of developing cotyledons of Vicia faba L. Mechanism of energy coupling. Planta (1996) 198:502–509.[Web of Science]
Pate JS, Gunning BES. Transfer cells. Annual Review of Plant Physiology (1972) 23:173–196.
Raven PR, Evert RF, Eichhorn SE. Biology of plants (2005) 7th edn. New York: Freeman.
Rost TL, Lersten NR. Transfer aleurone cells in Setaria lutescens (Gramineae). Protoplasma (1970) 71:403–408.[CrossRef][Web of Science]
Smith BG, Harris PJ, Melton LD, Newman RH. Crystalline cellulose in hydrated primary cell walls of three monocotyledons and one dicotyledon. Plant and Cell Physiology (1998) 39:711–720.
Taiz L, Zeiger E. Plant physiology (2002) 3rd edn. Sunderland, MA: Sinauer Associates, Inc.
Talbot MJ, Offler CE, McCurdy DW. Transfer cell wall architecture: a contribution towards understanding localized wall diposition. Protoplasma (2002) 219:197–209.[CrossRef][Web of Science][Medline]
Thygesen LG, Hoffmeyer P. Image analysis for the quantification of dislocations in hemp fibres. Industrial Crops and Products (2005) 21:173–184.[CrossRef][Web of Science]
Troll W. Praktische Einführung in die Pflanzenmorphologie. Die blühende Pflanze (1957) Stuttgart: G. Fischer.
CiteULike 
Connotea 
Del.icio.us What's this?
Related articles in Ann Bot:
- ContentSnapshots
Ann Bot 2008 102: iii.[Extract] [Full Text] - John Bryant takes a closer look at some of this month's Original Articles
- J. A. Bryant
Ann Bot 2008 102: v.[Extract] [Full Text]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||