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Pericarp anatomy of wild roses (Rosa L., Rosaceae)
ARTICLE IN PRESS Flora 205 (2010) 363–369
Contents lists available at ScienceDirect
Flora journal homepage: www.elsevier.de/flora
Pericarp anatomy of wild roses (Rosa L., Rosaceae) Jerzy Zielin´ski a,n, Marzenna Guzicka a, Dominik Tomaszewski a, Irmina Maciejewska-Rutkowska b a b
´rnik, Poland Polish Academy of Sciences, Institute of Dendrology, Parkowa 5, PL-62-035 Ko ´ , Poland University of Life Sciences, Department of Forest Natural Foundations, Wojska Polskiego 71 D, PL-60-625 Poznan
a r t i c l e in fo
abstract
Article history: Received 14 January 2009 Accepted 6 June 2009
The pericarp anatomy of representatives of all subgenera and sections of the genus Rosa was studied. All species have the same basic pericarp structure: it is composed of inner and outer endocarps, mesocarp and exocarp formed by the epidermis and hypodermis. The differences concern mainly the thickness of particular layers, and the shape and size of their cells. Cells of the endocarp and mesocarp are thickwalled. The only exception is Rosa rugosa mesocarp, which is composed of rather thin-walled cells with a large lumen. The endocarp structure of Rosa achenes resembles the drupe of the genus Prunus s.l. and drupelets of Rubus species. & 2009 Elsevier GmbH. All rights reserved.
Keywords: Rosa Achenes Pericarp Anatomy
1. Introduction The family Rosaceae is one of the most polymorphic groups of European higher plants. Botanists still do not agree on the number of genera within Rosaceae, because the range of many of them is interpreted in different ways. The traditional basis for classification of the family is the morphology and anatomy of the fruit. Most manuals describe four subfamilies: Rosoideae, Spiraeoideae, Maloideae and Prunoideae. This is a simple and practical classification, but does not reflect the real diversity in the family (Potter et al., 2007). In more recent studies tribes have been separated. Some of them are monotypic, such as the tribe Rosae Focke, containing the genus Rosa L. (Hutchinson, 1964; Kalkman, 2004). The genus Rosa belongs to the most characteristic group within the family solely on account of its fruits. Free unicarpellate pistils are enclosed within a deep urceolate hypanthium that becomes fleshy when mature. The true fruits are achenes (Lawrence, 1958; Kla´sˇ tersky´, 1968; Stace, 1997; Kalkman, 2004). We use this more practical term, instead of ‘‘nutlet’’ as proposed by some authors (Artiushenko and Teodorov, 1986; Henker, 2000), because the distinction between achene and nutlet is not always possible. Within the family Rosaceae the genus Rosa is usually placed next to the genus Rubus, but in the latter taxon drupelets are situated on a convex or flat receptacle. What is important, however, is that in both genera the fruit is collective. Existing data on the anatomical and morphological structure of Rosa achenes are very vague. Generally it is thought that the pericarp of roses consists of three main layers: exocarp, mesocarp and endocarp. The most exhaustive account devoted to the
n
Corresponding author. E-mail address: [email protected] (J. Zielin´ski).
0367-2530/$ - see front matter & 2009 Elsevier GmbH. All rights reserved. doi:10.1016/j.flora.2009.12.002
anatomy of the pericarp can be found in the papers by Starikova (1973, 1975, 1977, 1983). She described the anatomical structure of the achenes of 19 species – all belonging to the subgenus Rosa, and confirmed the presence of the three layers in the pericarp. She also examined differences in the pericarp anatomy between species and suggested that these differences may be of taxonomic value at the species level. The structure of Rosa achenes was also studied by Khrzhanovskii et al. (1985), who analysed 24 species, all belonging to the subgenus Rosa. Some very general data concerning achene anatomy were also recorded by Tantawy and Naser (2003).
2. Aim of study, material and methods There has been much variation and inaccuracy in the resulting interpretations in the literature about pericarp anatomy in roses, especially regarding the number of layers, their layout and classification. The aim of this study was to verify information obtained to date and to determine to what degree the pericarp anatomy is of significance in the taxonomy of the group. The subject of the study was the fully ripe achenes of roses representing all subgenera and sections of the genus Rosa. Herbarium specimens were checked to validate their identity. Achenes of 20 species were analysed. 2.1. List of analysed Rosa species Subgen. Hulthemia: Rosa persica Michx. Subgen. Rosa: sect. Pimpinellifoliae – R. spinosissima L. sect. Rosa – R. majalis Herrm.; R. pendulina L.; R. rugosa Thunb.
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sect. Caninae – R. agrestis Savi; R. canina L.; R. dumalis Bechst.; R. inodora Fries; R. jundzillii Besser; R. rubiginosa L.; R. sherardii Davies; R. tomentosa Sm.; R. villosa L.; R. zalana Wiesb. sect. Gallicanae – R. gallica L. sect. Carolinae – R. virginiana Mill. sect. Synstylae – R. arvensis Huds. Subgen. Platyrhodon: R. roxburghii Tratt. Subgen. Hesperhodos: R. stellata Wooton
Scanning electron microscopy (SEM) was used for histological analysis. Achenes are very hard and especially difficult to cut precisely. Thus they first had to be macerated. Fruits obtained from herbarium specimens were kept for several weeks in a mixture of glycerol and 70% ethyl alcohol (1:1 vol.). Achenes taken directly from fresh, living hypanthia were first preserved in FAA (formalin 5%, acetic acid 5%, ethyl alcohol 90%), and then macerated in glycerol and 70% ethyl alcohol mixture (1:1 vol.). Sections through the achenes were obtained using a
Fig. 1. Anatomical section of Rosa pericarp – schema of anatomical structure is similar for all observed species. A – cross-section through the pericarp of Rosa sherardii. Visible testa and cotyledons of the embryo, scale bar = 500 mm; B – longitudinal section through the pericarp of R. sherardii, scale bar =200 mm; C – cross-section through the pericarp of R. majalis, scale bar =200 mm; D – cross-section through the pericarp of R. zalana, scale bar = 250 mm; E – cross-section through the pericarp of R. pendulina, scale bar =500 mm; F – longitudinal section through the pericarp of R. pendulina, scale bar= 250 mm.
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cryomicrotome after rinsing the samples in distilled water. Slices were dehydrated in a series of acetone, placed on a holder, coated with gold and analysed by SEM (Hitachi S3000 N SEM belonging to the Institute of Plant Protection in Poznan´, and Leo belonging to the Department of Biology UAM in Poznan´).
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3. Results and discussion There are visible differences in the anatomy of particular fruits in the cross-sections of numerous analysed achenes, however the anatomical structure of the pericarp is similar for all species of
Fig. 2. A – cross-section through the pericarp of R. inodora, scale bar= 500 mm; B – longitudinal section through the pericarp of R. inodora, scale bar= 250 mm; C – crosssection through the pericarp of R. gallica, scale bar = 500 mm; D – cross-section through the pericarp of R. tomentosa, scale bar = 200 mm; E – longitudinal section through the pericarp of R. agrestis, scale bar = 500 mm; F – cross-section through the pericarp of R. dumalis, scale bar = 250 mm.
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Rosa (Figs. 1–5, 7). The pericarp is composed of three layers: exocarp, mesocarp and endocarp. The figures indicate that the endocarp of roses consists not of one, but two layers, visible both
on transverse and longitudinal pericarp sections. Different authors have presented different opinions about the issue. In her first paper (1973), Starikova stated that mesocarp cells were
Fig. 3. A – cross-section through the pericarp of R. canina. Visible unequal thickness of outer endocarp, black–marked borderline between b and c1; B – Longitudinal section through the pericarp of R. canina (a – exocarp, b – mesocarp, c1 – outer endocarp, c2 – inner endocarp), scale bars= 500 mm.
Fig. 4. A – cross-section through the pericarp of R. rubiginosa. Layers of inner and outer endocarps oriented obliquely towards each other; B – longitudinal section through the pericarp of R. rubiginosa. Visible vascular bundles in mesocarp (a – exocarp, b – mesocarp, c1 – outer endocarp, c2 – inner endocarp), scale bars=500 mm.
Fig. 5. A – deeply furrowed pericarp of R. arvensis with large cells of epidermis – arrow (cross-section). In some cells remnants of protoplast are visible, scale bar = 500 mm; B – Longitudinal section through the pericarp of R. arvensis (c1 – outer endocarp, c2 – inner endocarp), scale bar= 250 mm.
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Fig. 6. A – endocarp of Rubus chamaemorus, scale bar= 200 mm; B – endocarp of Rubus stellatus (c1 – outer endocarp, c2 – inner endocarp), scale bar =100 mm.
Fig. 7. Cross-section (A) and longitudinal (B) section through pericarp of R. rugosa, scale bars= 200 mm.
of various sizes, and the deeper they occurred, the smaller they were. She also distinguished two sub-layers, and several rows of elongated sclereids that form a very prominent endocarp. In subsequent papers (Starikova, 1975, 1977, 1983) she still distinguished the same pericarp layers, but ascribed cells from the inner part of the mesocarp to the endocarp, therefore implying that the endocarp is formed by two sub-layers. However, Khrzhanovskii et al. (1985) did not keep the division of the endocarp into two sub-layers. What Starikova described as the outer part of the endocarp, they ascribed to the mesocarp. Twenty species belonging to different subgenera were analysed in the present study. In every case the achene structure was the same. The pericarp consists of three layers: exocarp, mesocarp and endocarp. Central transverse and longitudinal crosses were done, and the results indicated that the endocarp is composed of two distinct sub-layers. Starikova (1983) indicated that (1) in some species the endocarp and mesocarp are clearly distinguished, (2) in some species the mesocarp is gradually becoming stone cells of the outer part of the endocarp (thus it is impossible to precisely distinguish this sub-layer). However, analysis of longitudinal cross-sections revealed that in each case the outer endocarp is clearly distinguishable, and is formed by sclereids that differ from those found in the mesocarp. The cells from the outer and inner endocarp sub-layers are oriented perpendicularly towards each other. The multiseriate layers, which according to Reeve (1953) can be described as the inner and outer endocarp, are composed of
long narrow thick-walled fibres oriented differently in different layers. These are not always in opposite planes with their long axes, but are often positioned diagonally. The inner endocarp has tangentially elongated fibres, is rather uniform and of 7equal thickness (usually 4–5 layers of cells) (Figs. 1–5, 8A, 8B). The regular arrangement of its cells is often visible on the inner surface of the pericarp. In contrast to the inner endocarp, the structure of the outer endocarp is more irregular. It is usually of varying thickness in its different parts, with prominences and depressions, and sometimes it penetrates deeply into the mesocarp layer. The prominences and depressions and other irregularities are visible both in horizontal and longitudinal section, such that the surface of the outer endocarp is hollowed like the endocarp in the majority of Rubus species (Fig. 6). The mesocarp, being the thickest part of the pericarp, is composed of sclereids of very different shape and size, from isodiametric to 7elongated, often with thinner walls and a larger lumen. Their arrangement is more irregular than in the outer endocarp, but in most cases, long7radially set sclereids dominate. Between them there are usually shorter, often curved, sclereids filling the free space. In mature fruits, the walls of the mesocarp cells are usually thick (Figs. 1–5). The mesocarp of Rosa rugosa is an exception; it is composed of uniform, isodiametric, thin-walled cells resembling those of parenchyma. In contrast to the mesocarp, both endocarp layers of this species appear ‘‘normal’’, in that they are composed of long fibres. The external surface of the outer endocarp however is more uniform than in other species; the external surface is flat, not hollowed (Fig. 7).
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Fig. 8. A – fragment of the cross-section through the pericarp of R. inodora. Layers of inner and outer endocarps oriented obliquely towards each other, scale bar =100 mm; B – outer and inner endocarp of R. spinosissima, scale bar =100 mm; C – pericarp of R. sherardii (cross-section), fibres of inner endocarp are visible; scale bar = 200 mm; D – R. spinosissima (cross-section) pericarp suture is visible, scale bar = 250 mm; E – exocarp of R. tomentosa (cross-section), scale bar = 200 mm; F – exocarp of R. majalis composed of two cell layers, thick cuticle is visible (cross-section); scale bar= 100 mm; Cross-section (G, scale bar= 100 mm) and longitudinal section (H, scale bar = 250 mm) through the pericarp of Rosa roxburghii. Mesocarp with irregularly oriented sclereids.
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The uniqueness of R. rugosa in this respect has been confirmed by samples of different origin. The exocarp (Figs. 1–5, 8F–H) is usually composed of epidermis and hypodermis. R. arvensis has exceptionally large epidermal cells (Fig. 5A). In some of them the remnants of protoplast can be observed, so it may be supposed that cells of this part of the pericarp die shortly before full ripening of the fruit. Under the exocarp there is a single to several-layered hypodermis with rather thin walls. Its thickness may be different in different parts of the pericarp; sometimes it penetrates deeply into the mesocarp. Its cells are isodiametric or more often elongated tangentially (Fig. 8F–H). On the outer surface of the exocarp there is a distinct cuticle layer of a different pattern. Usually it is so thick that the outlines of epidermal cells are not visible. The exceptions are R. roxburghii, R. bracteata and R. virginiana, having both a thin cuticle and visible epidermal cells. The fruit is closed with a pericarp suture, originating from the fusion of carpel margins. It differs from the structure of other parts of the pericarp. This area is filled with long, narrow fibres belonging to the inner and outer endocarp. Here they change their normal orientation and bend toward the pericarp surface (Fig. 8D). The results obtained during the present study have shown that descriptions of the rose pericarp need to be corrected and supplemented. All tissue layers are visible on the pericarp drawings presented by Starikova (1973). She found that the endocarp was formed from stone cells. Inaccuracies certainly arose because only transverse pericarp sections were analysed by the author. On such sections sclereids of the outer endocarp appear to be isodiametric and resemble stone cells, which is why she thought that they belonged to the mesocarp. For similar reasons she did not mention the hypodermis either. Both the transverse and longitudinal crosses of the inner endocarp indicate that this sub-layer is composed of fibres represented by a relatively constant number of cell rows, whereas the outer endocarp is formed by very long fibres or sclereids, and never by isodiametric cells. The exocarp is made almost exclusively of only one layer of epidermal cells covered by cuticle, and one to three rows of hypodermal cells. The two-layered epidermis is probably an unusual and incidental phenomenon. Starikova (1973) only found it in R. tomentosa. Khrzhanovskii et al. (1985) only observed it in Rosa pulverulenta (as R. glutinosa), whereas the epidermis of R. tomentosa that they analysed was single-layered. When comparing the anatomy of rose achenes with the fruit structure of the other genera within the family Rosaceae, it is clear that the achene has a lot in common with the drupe, strictly speaking with the drupe of the genus Prunus s.l. and drupelet of Rubus species. The same layers occur in both cases although in Prunus the mesocarp is fleshy (Sterling, 1953; Tukey and Young, 1939). Reeve (1954) showed that the endocarp of brambles is composed of two perpendicularly oriented layers of fibres and –
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as with roses – their outer endocarp is usually pitted (Fig. 6). This is proof of a close relationship between the two genera. The results also show that the pericarp anatomy of roses is of rather small significance for systematics of the genus Rosa. Anatomical differences, if any, are usually not correlated with taxonomic units. As mentioned above, the exception is Rosa rugosa, which has a spongy mesocarp. It is not impossible that this rare feature is connected with the biology and ecology of the species. It grows naturally in the Far East in a narrow belt along seashores, possibly because the spongy mesocarp, which is filled with air, allows the achenes of this species to be transported and spread by water.
Acknowledgements This study was supported by the Ministry of Science and Higher Education (Project no. 2P04C 036 027) and Institute of Dendrology PAS in Ko´rnik. We are very grateful to Magdalena Gawlak for her excellent technical assistance and to two anonymous referees for their comments and suggestions.
References Artiushenko, Z., Teodorov, A., 1986. Organographia illustrata plantarum vascularium. Fructus, Leninopoli. Nauka in Russian. Henker, H., 2000. Rosa L. In: Conert, H.J., Jager, E.J., Kadereit, J.W., Schulze-Motel, W., Wagenitz, G., Weber, H.E. (Eds.), Hegi, Illustrierte Flora von Mitteleuropa, vol. 4 (2C). Blackwell, Berlin. Hutchinson, J., 1964. In: The genera of flowering plants. 1. Clarendon Press, Oxford. Kalkman, C., 2004. Rosaceae. In: Kubitzki, K. (Ed.), The families and genera of vascular plants, vol. 6. Springer, Berlin, Heidelberg, pp. 386–443. Khrzhanovskii, V.G., Ponomarenko, S.F., Kolobov, E.S., 1985. Mikromorfologicheskaya kharakteristika plodov shipovnika v svyazi s sistematikoi roda Rosa L. Byull. Glav. Bot. Sada 137, 47–53 in Russian. Kla´sˇ tersky´, I., 1968. Rosa L. In: Tutin, T.G., Heywood, V.H., Burges, N.A., Moore, D.M., Valentine, D.H., Walters, S.M., Webb, D.A. (Eds.), Flora Europaea., vol. 2. Cambridge University Press, Cambridge, pp. 25–32. Lawrence, G., 1958. In: Taxonomy of vascular plants. Macmillan, New York. Potter, D., Eriksson, T., Evans, R., Oh, S., Smedmark, J., Morgan, D., Kerr, M., Robertson, K., Arsenault, M., Dickinson, T., Campbell, C., 2007. Phylogeny and classification of Rosaceae. Plant Syst. Evol. 266, 5–43. Reeve, R.M., 1954. Fruit histogenesis in Rubus strigosus. Am. J. Bot. 41 (152–160), 173–181. Stace, C., 1997. New flora of the British Isles, 2nd ed. Cambridge University Press, Cambridge. Starikova, V.V., 1973. Morphological-anatomical characteristics of the nutlets in some Rosa species. Bot. Zhurn. 58, 893–898 in Russian. Starikova, V.V., 1975. Anatomo-morphological characteristics of nuts of Rosa rugosa Thunb. in the process of their development. Bot. Zhurn. 60, 558–563 in Russian. Starikova, V.V., 1977. Morphologo-anatomical characterization of nutlets of some Rosa species (Rosaceae). Bot. Zhurn. 62, 1500–1504 in Russian. Starikova, V.V., 1983. Morphological-anatomical characteristics of nutlets in some species of Rosa (Rosaceae). Bot. Zhurn. 68, 522–524 in Russian. Sterling, C., 1953. Developmental anatomy of the fruit of Prunus domestica L. Bull. Torrey Bot. Club 80, 457–477. Tantawy, M.E., Naser, M.M., 2003. A contribution to the achene knowledge of Rosoideae (Rosaceae) LM and SM. Int. J. Agricult. & Biol. 5, 105–112. Tukey, H.B., Young, J.O., 1939. Histological study of the developing fruit of the sour cherry. Bot. Gaz. 100, 723–749.
Contents lists available at ScienceDirect
Flora journal homepage: www.elsevier.de/flora
Pericarp anatomy of wild roses (Rosa L., Rosaceae) Jerzy Zielin´ski a,n, Marzenna Guzicka a, Dominik Tomaszewski a, Irmina Maciejewska-Rutkowska b a b
´rnik, Poland Polish Academy of Sciences, Institute of Dendrology, Parkowa 5, PL-62-035 Ko ´ , Poland University of Life Sciences, Department of Forest Natural Foundations, Wojska Polskiego 71 D, PL-60-625 Poznan
a r t i c l e in fo
abstract
Article history: Received 14 January 2009 Accepted 6 June 2009
The pericarp anatomy of representatives of all subgenera and sections of the genus Rosa was studied. All species have the same basic pericarp structure: it is composed of inner and outer endocarps, mesocarp and exocarp formed by the epidermis and hypodermis. The differences concern mainly the thickness of particular layers, and the shape and size of their cells. Cells of the endocarp and mesocarp are thickwalled. The only exception is Rosa rugosa mesocarp, which is composed of rather thin-walled cells with a large lumen. The endocarp structure of Rosa achenes resembles the drupe of the genus Prunus s.l. and drupelets of Rubus species. & 2009 Elsevier GmbH. All rights reserved.
Keywords: Rosa Achenes Pericarp Anatomy
1. Introduction The family Rosaceae is one of the most polymorphic groups of European higher plants. Botanists still do not agree on the number of genera within Rosaceae, because the range of many of them is interpreted in different ways. The traditional basis for classification of the family is the morphology and anatomy of the fruit. Most manuals describe four subfamilies: Rosoideae, Spiraeoideae, Maloideae and Prunoideae. This is a simple and practical classification, but does not reflect the real diversity in the family (Potter et al., 2007). In more recent studies tribes have been separated. Some of them are monotypic, such as the tribe Rosae Focke, containing the genus Rosa L. (Hutchinson, 1964; Kalkman, 2004). The genus Rosa belongs to the most characteristic group within the family solely on account of its fruits. Free unicarpellate pistils are enclosed within a deep urceolate hypanthium that becomes fleshy when mature. The true fruits are achenes (Lawrence, 1958; Kla´sˇ tersky´, 1968; Stace, 1997; Kalkman, 2004). We use this more practical term, instead of ‘‘nutlet’’ as proposed by some authors (Artiushenko and Teodorov, 1986; Henker, 2000), because the distinction between achene and nutlet is not always possible. Within the family Rosaceae the genus Rosa is usually placed next to the genus Rubus, but in the latter taxon drupelets are situated on a convex or flat receptacle. What is important, however, is that in both genera the fruit is collective. Existing data on the anatomical and morphological structure of Rosa achenes are very vague. Generally it is thought that the pericarp of roses consists of three main layers: exocarp, mesocarp and endocarp. The most exhaustive account devoted to the
n
Corresponding author. E-mail address: [email protected] (J. Zielin´ski).
0367-2530/$ - see front matter & 2009 Elsevier GmbH. All rights reserved. doi:10.1016/j.flora.2009.12.002
anatomy of the pericarp can be found in the papers by Starikova (1973, 1975, 1977, 1983). She described the anatomical structure of the achenes of 19 species – all belonging to the subgenus Rosa, and confirmed the presence of the three layers in the pericarp. She also examined differences in the pericarp anatomy between species and suggested that these differences may be of taxonomic value at the species level. The structure of Rosa achenes was also studied by Khrzhanovskii et al. (1985), who analysed 24 species, all belonging to the subgenus Rosa. Some very general data concerning achene anatomy were also recorded by Tantawy and Naser (2003).
2. Aim of study, material and methods There has been much variation and inaccuracy in the resulting interpretations in the literature about pericarp anatomy in roses, especially regarding the number of layers, their layout and classification. The aim of this study was to verify information obtained to date and to determine to what degree the pericarp anatomy is of significance in the taxonomy of the group. The subject of the study was the fully ripe achenes of roses representing all subgenera and sections of the genus Rosa. Herbarium specimens were checked to validate their identity. Achenes of 20 species were analysed. 2.1. List of analysed Rosa species Subgen. Hulthemia: Rosa persica Michx. Subgen. Rosa: sect. Pimpinellifoliae – R. spinosissima L. sect. Rosa – R. majalis Herrm.; R. pendulina L.; R. rugosa Thunb.
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sect. Caninae – R. agrestis Savi; R. canina L.; R. dumalis Bechst.; R. inodora Fries; R. jundzillii Besser; R. rubiginosa L.; R. sherardii Davies; R. tomentosa Sm.; R. villosa L.; R. zalana Wiesb. sect. Gallicanae – R. gallica L. sect. Carolinae – R. virginiana Mill. sect. Synstylae – R. arvensis Huds. Subgen. Platyrhodon: R. roxburghii Tratt. Subgen. Hesperhodos: R. stellata Wooton
Scanning electron microscopy (SEM) was used for histological analysis. Achenes are very hard and especially difficult to cut precisely. Thus they first had to be macerated. Fruits obtained from herbarium specimens were kept for several weeks in a mixture of glycerol and 70% ethyl alcohol (1:1 vol.). Achenes taken directly from fresh, living hypanthia were first preserved in FAA (formalin 5%, acetic acid 5%, ethyl alcohol 90%), and then macerated in glycerol and 70% ethyl alcohol mixture (1:1 vol.). Sections through the achenes were obtained using a
Fig. 1. Anatomical section of Rosa pericarp – schema of anatomical structure is similar for all observed species. A – cross-section through the pericarp of Rosa sherardii. Visible testa and cotyledons of the embryo, scale bar = 500 mm; B – longitudinal section through the pericarp of R. sherardii, scale bar =200 mm; C – cross-section through the pericarp of R. majalis, scale bar =200 mm; D – cross-section through the pericarp of R. zalana, scale bar = 250 mm; E – cross-section through the pericarp of R. pendulina, scale bar =500 mm; F – longitudinal section through the pericarp of R. pendulina, scale bar= 250 mm.
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cryomicrotome after rinsing the samples in distilled water. Slices were dehydrated in a series of acetone, placed on a holder, coated with gold and analysed by SEM (Hitachi S3000 N SEM belonging to the Institute of Plant Protection in Poznan´, and Leo belonging to the Department of Biology UAM in Poznan´).
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3. Results and discussion There are visible differences in the anatomy of particular fruits in the cross-sections of numerous analysed achenes, however the anatomical structure of the pericarp is similar for all species of
Fig. 2. A – cross-section through the pericarp of R. inodora, scale bar= 500 mm; B – longitudinal section through the pericarp of R. inodora, scale bar= 250 mm; C – crosssection through the pericarp of R. gallica, scale bar = 500 mm; D – cross-section through the pericarp of R. tomentosa, scale bar = 200 mm; E – longitudinal section through the pericarp of R. agrestis, scale bar = 500 mm; F – cross-section through the pericarp of R. dumalis, scale bar = 250 mm.
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Rosa (Figs. 1–5, 7). The pericarp is composed of three layers: exocarp, mesocarp and endocarp. The figures indicate that the endocarp of roses consists not of one, but two layers, visible both
on transverse and longitudinal pericarp sections. Different authors have presented different opinions about the issue. In her first paper (1973), Starikova stated that mesocarp cells were
Fig. 3. A – cross-section through the pericarp of R. canina. Visible unequal thickness of outer endocarp, black–marked borderline between b and c1; B – Longitudinal section through the pericarp of R. canina (a – exocarp, b – mesocarp, c1 – outer endocarp, c2 – inner endocarp), scale bars= 500 mm.
Fig. 4. A – cross-section through the pericarp of R. rubiginosa. Layers of inner and outer endocarps oriented obliquely towards each other; B – longitudinal section through the pericarp of R. rubiginosa. Visible vascular bundles in mesocarp (a – exocarp, b – mesocarp, c1 – outer endocarp, c2 – inner endocarp), scale bars=500 mm.
Fig. 5. A – deeply furrowed pericarp of R. arvensis with large cells of epidermis – arrow (cross-section). In some cells remnants of protoplast are visible, scale bar = 500 mm; B – Longitudinal section through the pericarp of R. arvensis (c1 – outer endocarp, c2 – inner endocarp), scale bar= 250 mm.
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Fig. 6. A – endocarp of Rubus chamaemorus, scale bar= 200 mm; B – endocarp of Rubus stellatus (c1 – outer endocarp, c2 – inner endocarp), scale bar =100 mm.
Fig. 7. Cross-section (A) and longitudinal (B) section through pericarp of R. rugosa, scale bars= 200 mm.
of various sizes, and the deeper they occurred, the smaller they were. She also distinguished two sub-layers, and several rows of elongated sclereids that form a very prominent endocarp. In subsequent papers (Starikova, 1975, 1977, 1983) she still distinguished the same pericarp layers, but ascribed cells from the inner part of the mesocarp to the endocarp, therefore implying that the endocarp is formed by two sub-layers. However, Khrzhanovskii et al. (1985) did not keep the division of the endocarp into two sub-layers. What Starikova described as the outer part of the endocarp, they ascribed to the mesocarp. Twenty species belonging to different subgenera were analysed in the present study. In every case the achene structure was the same. The pericarp consists of three layers: exocarp, mesocarp and endocarp. Central transverse and longitudinal crosses were done, and the results indicated that the endocarp is composed of two distinct sub-layers. Starikova (1983) indicated that (1) in some species the endocarp and mesocarp are clearly distinguished, (2) in some species the mesocarp is gradually becoming stone cells of the outer part of the endocarp (thus it is impossible to precisely distinguish this sub-layer). However, analysis of longitudinal cross-sections revealed that in each case the outer endocarp is clearly distinguishable, and is formed by sclereids that differ from those found in the mesocarp. The cells from the outer and inner endocarp sub-layers are oriented perpendicularly towards each other. The multiseriate layers, which according to Reeve (1953) can be described as the inner and outer endocarp, are composed of
long narrow thick-walled fibres oriented differently in different layers. These are not always in opposite planes with their long axes, but are often positioned diagonally. The inner endocarp has tangentially elongated fibres, is rather uniform and of 7equal thickness (usually 4–5 layers of cells) (Figs. 1–5, 8A, 8B). The regular arrangement of its cells is often visible on the inner surface of the pericarp. In contrast to the inner endocarp, the structure of the outer endocarp is more irregular. It is usually of varying thickness in its different parts, with prominences and depressions, and sometimes it penetrates deeply into the mesocarp layer. The prominences and depressions and other irregularities are visible both in horizontal and longitudinal section, such that the surface of the outer endocarp is hollowed like the endocarp in the majority of Rubus species (Fig. 6). The mesocarp, being the thickest part of the pericarp, is composed of sclereids of very different shape and size, from isodiametric to 7elongated, often with thinner walls and a larger lumen. Their arrangement is more irregular than in the outer endocarp, but in most cases, long7radially set sclereids dominate. Between them there are usually shorter, often curved, sclereids filling the free space. In mature fruits, the walls of the mesocarp cells are usually thick (Figs. 1–5). The mesocarp of Rosa rugosa is an exception; it is composed of uniform, isodiametric, thin-walled cells resembling those of parenchyma. In contrast to the mesocarp, both endocarp layers of this species appear ‘‘normal’’, in that they are composed of long fibres. The external surface of the outer endocarp however is more uniform than in other species; the external surface is flat, not hollowed (Fig. 7).
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Fig. 8. A – fragment of the cross-section through the pericarp of R. inodora. Layers of inner and outer endocarps oriented obliquely towards each other, scale bar =100 mm; B – outer and inner endocarp of R. spinosissima, scale bar =100 mm; C – pericarp of R. sherardii (cross-section), fibres of inner endocarp are visible; scale bar = 200 mm; D – R. spinosissima (cross-section) pericarp suture is visible, scale bar = 250 mm; E – exocarp of R. tomentosa (cross-section), scale bar = 200 mm; F – exocarp of R. majalis composed of two cell layers, thick cuticle is visible (cross-section); scale bar= 100 mm; Cross-section (G, scale bar= 100 mm) and longitudinal section (H, scale bar = 250 mm) through the pericarp of Rosa roxburghii. Mesocarp with irregularly oriented sclereids.
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The uniqueness of R. rugosa in this respect has been confirmed by samples of different origin. The exocarp (Figs. 1–5, 8F–H) is usually composed of epidermis and hypodermis. R. arvensis has exceptionally large epidermal cells (Fig. 5A). In some of them the remnants of protoplast can be observed, so it may be supposed that cells of this part of the pericarp die shortly before full ripening of the fruit. Under the exocarp there is a single to several-layered hypodermis with rather thin walls. Its thickness may be different in different parts of the pericarp; sometimes it penetrates deeply into the mesocarp. Its cells are isodiametric or more often elongated tangentially (Fig. 8F–H). On the outer surface of the exocarp there is a distinct cuticle layer of a different pattern. Usually it is so thick that the outlines of epidermal cells are not visible. The exceptions are R. roxburghii, R. bracteata and R. virginiana, having both a thin cuticle and visible epidermal cells. The fruit is closed with a pericarp suture, originating from the fusion of carpel margins. It differs from the structure of other parts of the pericarp. This area is filled with long, narrow fibres belonging to the inner and outer endocarp. Here they change their normal orientation and bend toward the pericarp surface (Fig. 8D). The results obtained during the present study have shown that descriptions of the rose pericarp need to be corrected and supplemented. All tissue layers are visible on the pericarp drawings presented by Starikova (1973). She found that the endocarp was formed from stone cells. Inaccuracies certainly arose because only transverse pericarp sections were analysed by the author. On such sections sclereids of the outer endocarp appear to be isodiametric and resemble stone cells, which is why she thought that they belonged to the mesocarp. For similar reasons she did not mention the hypodermis either. Both the transverse and longitudinal crosses of the inner endocarp indicate that this sub-layer is composed of fibres represented by a relatively constant number of cell rows, whereas the outer endocarp is formed by very long fibres or sclereids, and never by isodiametric cells. The exocarp is made almost exclusively of only one layer of epidermal cells covered by cuticle, and one to three rows of hypodermal cells. The two-layered epidermis is probably an unusual and incidental phenomenon. Starikova (1973) only found it in R. tomentosa. Khrzhanovskii et al. (1985) only observed it in Rosa pulverulenta (as R. glutinosa), whereas the epidermis of R. tomentosa that they analysed was single-layered. When comparing the anatomy of rose achenes with the fruit structure of the other genera within the family Rosaceae, it is clear that the achene has a lot in common with the drupe, strictly speaking with the drupe of the genus Prunus s.l. and drupelet of Rubus species. The same layers occur in both cases although in Prunus the mesocarp is fleshy (Sterling, 1953; Tukey and Young, 1939). Reeve (1954) showed that the endocarp of brambles is composed of two perpendicularly oriented layers of fibres and –
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as with roses – their outer endocarp is usually pitted (Fig. 6). This is proof of a close relationship between the two genera. The results also show that the pericarp anatomy of roses is of rather small significance for systematics of the genus Rosa. Anatomical differences, if any, are usually not correlated with taxonomic units. As mentioned above, the exception is Rosa rugosa, which has a spongy mesocarp. It is not impossible that this rare feature is connected with the biology and ecology of the species. It grows naturally in the Far East in a narrow belt along seashores, possibly because the spongy mesocarp, which is filled with air, allows the achenes of this species to be transported and spread by water.
Acknowledgements This study was supported by the Ministry of Science and Higher Education (Project no. 2P04C 036 027) and Institute of Dendrology PAS in Ko´rnik. We are very grateful to Magdalena Gawlak for her excellent technical assistance and to two anonymous referees for their comments and suggestions.
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