J. Jpn. Bot. 86: 294–302 (2011) Morphology and Anatomy of Winter Bud of Pteridophyllum racemosum (Pteridophyllaceae) Yasuhiko endoa, *, Jun saitoa and Keiichi oonob a College of Science, Ibaraki University, Mito, 310-8512 JAPAN b Natural Science Museum and Institute, Chiba, 955-2, Aoba-cho, Chuo-ku, Chiba, 260-8682 JAPAN *Corresponding author: [email protected] (Accepted on May 10, 2011) Pteridophyllum racemosum (Pteridophyllaceae), an evergreen herb endemic to Japan, produces winter buds on the ground surface. Buds consist of three to four bud scales, young leaves, axillary buds, and a young inflorescence. Young leaves and the young inflorescence curve downward in the bud. Young leaves show circinate vernation. Bud scale tissues are composed of an epidermis, cortex, and a vascular bundle. The cortex is characterized by relatively wide intercellular spaces and deposition of starch grains in the cells. Key words: Circinate vernation, intercellular space, phyllotaxis, prophyll, Pteridophyllum racemosum, winter bud. Pteridophyllum racemosum Siebold & morphology and anatomy of P. racemosum Zucc. (Pteridophyllaceae) is an evergreen herb winter buds. We could also get some information endemic to Japan where it is distributed in the about vernation and phyllotaxis of the species mountainous and subalpine areas of the central by the present analysis of the winter bud internal and northern parts of Honshu (Mizuno et al. structures. 1975, Oono 1999, Akiyama 2006). Leaves Materials and Methods are pectinate, radical, and form a rosette; the inflorescence is a raceme and stands at the center Winter buds were fixed in FAA (50% of the rosette; flowers have 2 sepals, 4 petals, aqueous ethanol : formaldehyde : acetic acid = 4 stamens, and 1 pistil and open from June to 9 : 0.5 : 0.5). The outer morphological features August (Ohwi 1965, 1982, Akiyama 2006). After were observed using a dissecting microscope flowering, winter buds grow approximately at and were sketched or photographed. Internal the center of the rosette, on the ground surface structures were examined by cutting the buds (Kimura 1970a, 1970b, Mizuno et al. 1975). To transversely into 4 to 7 µm thick sections using understand the resistance mechanism by which a manual rotary microtome. Sections were aboveground winter buds resist environmental stained using a combination of Heidenhain’s stresses, especially freezing, we studied the haematoxylin, safranin, and Fast Green FCF, morphological features and internal structures before observation under a light microscope. of winter buds. This is be the first report on the —294— October 2011 Journal of Japanese Botany Vol. 86 No. 5 295 Fig. 1. Outer morphology of winter bud of Pteridophyllum racemosum, collected at Mt. Kinunuma-yama, Tochigi Pref. on 22 Oct. 2009. a. Entire bud. b–e. Bud scales. The position of each bud scale is shown in Fig. 1a. e. An innermost bud scale covered by other three bud scales (b–d). b–d. Abaxial side. e. Adaxial side. p. Petiole. Scale bar = 1mm. Results and Discussion appeared in the same order. On the other hand, Morphological features sometimes the apical young leaves (y’7–y’10) The outermost edge of buds was composed appeared in a clockwise order. Such change of of three to four bud scales (Fig. 1). Some bud leaf arrangement has been reported to appear scales had a small leaf blade at their apex. between the main axis and the lateral branch Therefore, bud scales appeared to originate from (Tucker 1963, Kumazawa 1960, 1963a, 1963b, a petiole. Bud scales were semi-circular, fringed 1967, 1979, Kumazawa and Kumazawa 1970, by short hairs, and distinguishable from the Gómez-Campo 1970, Iwamoto et al. 2005). petioles of foliage leaves (Fig. 1). Therefore, we presume that the apical leaves Only the outermost one or two bud scales (y’7–y’10) would be originated from the axillary subtended an axillary bud (Fig. 2). Inside the bud (of which the subtending leaf would be scales, there were four to seven young leaves y6) (Fig. 2). This means that the inflorescence and a young inflorescence (Figs. 2, 6, 7). When originated from an apical bud, and that the the helically arranged bud scales (s0–s3 in branching of the stem in the bud would be Fig. 2) appeared in a counterclockwise order, sympodial. the basal young leaves (y4–y6) in the bud There were two or three axillary buds in a 296 植物研究雑誌　第86巻　第5号 2011年10月 Fig. 2. Transverse section of the basal part of winter bud, including reproductive shoot, of Pteridophyllum racemosum, collected at Misato-machi, Daisen-shi, Akita Pref. on 18 Oct. 2010 (Endo 3652, TUS), showing an arrangement of bud scales, young leaves, inflorescence, and axillary buds. a. Entire section. b. A schematic diagram of entire section. c. A schematic diagram of axillary bud “ab1”. d. A schematic diagram of axillary bud “ab2”. aa. Apex of axillary bud. aab. Axis of axillary bud. ab. Axillary bud. al. Apical part of leaf. i. Inflorescence. ll. Leaf lobe. lv. Lateral vein. m. Main axis of winter bud. mv. Midvein. s, s’, s’’. Bud scale. vb. Vascular bundle. y, y’, y’’. Young leaf. Closed triangle indicates position of the midvein of bud scale or young leaf. The numbers alongside the abbreviations indicate their relative position in the winter bud, i.e., higher numbers indicate positions toward the center of the bud for the same organ type. Scale bar = 1 mm. October 2011 Journal of Japanese Botany Vol. 86 No. 5 297 Fig. 3. Schematic diagrams of axillary buds of a winter bud of Pteridophyllum racemosum in Fig. 2, indicating the direction of the phyllotactic helix. a. Axillary bud “ab1” in Fig. 2. b. Axirally bud “ab2” in Fig. 2. c. Axillary bud “ab3” in Fig. 2. aa. Apex of axillary bud. aab. Axis of axillary bud. i. Inflorescence. m. Main axis of winter bud. s’, s’’. Bud scale. y’, y’’. Young leaf. Closed triangle indicates position of the midvein of bud scale or young leaf. The numbers alongside the abbreviations indicate their relative position in the winter bud, i.e., higher numbers indicate positions toward the center of the bud for the same organ type. The arrows indicate the direction of phyllotactic helix, i.e., long arrow for foliar organs of main axis and short one for those of axillary bud. winter bud of P. racemosum (ab1, ab2, and ab3 In monocotyledonous plants, the prophyll is in Figs. 2a–d). These axillary buds consisted usually only one and positioned at the opposite of young leaves and/or bud scales (Figs. 2a– side of the subtending leaf (Kumazawa 1979). d). The two most basal foliar organs of the However, the arrangement of prophylls in P. axillary buds have been called prophylls (Blaser racemosum may be specialized among seed 1944, Kumazawa 1979). Therefore, the pairs plants. To understand the systematic implications of young leaves, s’1 and s’2 of the axillary bud of the specialized arrangement of the prophylls, ‘ab1’, s’’1 and s’’2 of bud ‘ab2’, and y’7 and comparative morphology on the related species y’8 of bud ‘ab3’, would be prophylls (Fig. 2). of P. racemosum would be needed. The divergent angle between the two prophylls, In a winter bud of P. racemosum, foliar y’7 and y’8, was ca. 135° (Figs. 2a, b). In the organs of some axillary buds appeared in two prophylls, the more basal one (y’7 in Figs. a clockwise order (Figs. 3a, c), but those 2a, b) and the subtending leaf of the axillary of the other axillary buds appeared in a bud (y6 in Figs. 2a, b) show a divergent angle counterclockwise order (Fig. 3b). This difference ‘ca. 135°’ between them (Figs. 2a, b). On the of the direction of the phyllotactic helix would other hand, dicotyledonous plants have been be shown as the difference of the relative reported to show the divergent angle ‘ca. 180°’ position between the most basal prophyll and between the prophylls as typical (Kumazawa the subtending leaf of the axillary bud, i.e., when 1979). These prophylls usually position in the most basal prophyll appeared in clockwise a direction perpendicular to the subtending order (s’1 in Fig. 3a, and y’7 in Fig. 3c) against leaf of the axillary shoot (Kumazawa 1979). the subtending leaf of the axillary bud (s0 in Fig. 298 植物研究雑誌　第86巻　第5号 2011年10月 Fig. 4. Transverse section of a part of Pteridophyllum racemosum winter bud scale near the vascular bundle, collected at Mt. Taihei-zan, Akita Pref. on 11 Aug. 2007 (Endo 3569, TUS), showing intracellular starch grains and relatively wide intercellular spaces. is. Intercellular space. sg. Starch grain. vb. Vascular bundle. Scale bar = 0.1 mm. Fig. 5. Transverse section of petiole of Pteridophyllum racemosum, collected at Mt. Ontake-san, Gifu Pref. on 29 Oct. 2009 (Endo 3640, TUS), showing three vascular bundles and relatively wide inter cellular spaces. a. A whole part. b. Enlargement of the cortex and vascular bundle of the petiole. cv. Cavity. is. Intercellular space. lv. Lateral vein. mv. Midvein. Scale bar = 0.1 mm. October 2011 Journal of Japanese Botany Vol. 86 No. 5 299 Fig. 6. Transverse section of the apical part of a winter bud of Pteridophyllum racemosum, collected at Mt. Ontake- san, Gifu Pref. on 29 Oct. 2009 (Endo 3640, TUS), showing the positions of young leaves and inflorescence, and the internal structure of flower buds. f. Flower bud. p. Pollen mother cell. pe. Petal. pi. Pistil. s. Bud scale. se. Sepal. t. Theca. y. Young leaf. Scale bar = 0.1 mm. 3a, and y6 in Fig. 3c), other foliar organs of the 1963a, 1963b, 1967, 1979, Kumazawa and bud appeared in the same order successively Kumazawa 1970). Therefore, a variation of the (s’2 in Fig. 3a, and y’8, y’9, and y’10 in Fig. direction of the phyllotactic helix of axillary 3c); when the most basal prophyll appeared in buds, observed in a winter bud of P. racemosum, counterclockwise order (s’’2 in Fig. 3b) against would not be unusual in Dicotyledons. How the the subtending leaf of the axillary bud (s1 in position of the most basal prophyll relative to the Fig. 3b), other foliar organs of the bud appeared subtending leaf is determined is still in question. in counterclockwise order successively (s’’3, The flower buds showed two sepals, four y’’4, and y’’5 in Fig. 3b). Such variation of the petals, a pistil and four stamens with thecae (Fig. position of the most basal prophyll relative to 6). the subtending leaf among the axillary shoots The phyllotaxis was determined to be spiral in one individual has been reported in many from the bud structure (Figs. 2a, 2b). The dicotyledonous species (Kumazawa 1960, divergence may be 3/8 (Figs. 2a, b). The young 300 植物研究雑誌　第86巻　第5号 2011年10月 Fig. 7. Outer morphology of winter bud of Pteridophyllum racemosum showing curving young leaves and a curving inflorescence. a. Bud scales were cut off to show a young inflorescence covered by curving young leaves. b. Bud scales and two outer young leaves were cut off to show a curving young leaf. c. Bud scales, young leaves, and several basal flower buds were cut off to show a curving young inflorescence. d. Bud scales were cut off to show a young leaf with circinate vernation. a—c, collected at Mt. Ontake-san, Gifu Prefecture in Oct. 29, 2009 (Endo 3640, TUS). d, collected at Mt. Taihei-zan, Akita Prefecture in Aug. 11, 2007 (Endo 3569, TUS). f. Flower bud. i. Inflorescence. y. Young leaf. Scale bar = 1 mm. leaves and an inflorescence curved from the the families related to Pteridophyllaceae. tips downward in the winter buds (Figs. 7a–c). The young leaves showed circinate vernation Anatomical features (Fig. 7d). Such vernation has been reported in Scale tissues of Pteridophyllum racemosum Droceraceae in angiosperms (Kenneth et al. were composed of an epidermis, a cortex, and a 2002), and may be rare in angiosperms. To know vascular bundle (Figs. 2a, 3). whether circinate vernation is an apomorphy or The scale cortex was composed of a plesiomorphy for Pteridophyllaceae, we need parenchymatous cells, with intercellular spaces to know distribution of the vernation type among (Fig. 4). The cortex of the petiole also had October 2011 Journal of Japanese Botany Vol. 86 No. 5 301 intercellular spaces (Fig. 5). The intercellular (Thymelaeaceae). Am. J. Bot. 92: 1350–1358. spaces might help intercellular freezing of water Kenneth M. C., Kenneth J. W. and Jobson R. W. 2002. Molecular evidence for the common origin of snap- and prevent intracellular freezing, which destroys traps among carnivorous plants. Am. J. Bot. 89: 1503– intracellular structures (Sakai and Larcher 1987). 1509. Therefore, the presence of intercellular spaces in Kimura M. 1970a. Analysis of production processes of an winter buds may be a mechanism for resisting undergrowth of subalpine Abies forest, Pteridophyllum racemosum population 1 growth, carbohydrate lower temperatures during the winter. In further economy and net production. Bot. Mag. (Tokyo) 83: examination, the mechanism has to be confirmed 99–108. experimentally in P. racemosum. Kimura M. 1970b. Analysis of production processes of an Each scale had only one vascular bundle undergrowth of subalpine Abies forest, Pteridophyllum (Fig. 2a), but the leaf petiole had three vascular racemosum population 2 respiration, gross production and economy of dry matter. Bot. Mag. (Tokyo) 83: bundles, i.e., one mid-vein and two lateral 304–311. veins (Figs. 2a, 5a). Therefore, scales could Kumazawa M. 1960. Analytical studies on the anodic and be distinguished from leaf petioles based on cathodic positions of prophylls in some dicotyledonous their internal structures. We suggest that the plants I. Indtroductory remarks. Bot. Mag. (Tokyo) 73: 487–493 (in Japanese with English summary). winter bud of P. racemosum would be classified Kumazawa M. 1963a. Analytical studies on the anodic and as a type C winter bud, i.e., having perfectly cathodic positions of prophylls in some dicotyledonous differentiated scales, as described by Yoshie and plants II. Xamtium canadense. Bot. Mag. (Tokyo) 76: Yoshida (1989). 225–233 (in Japanese with English summary). The cortex of bud scales contained starch Kumazawa M. 1963b. Analytical studies on the anodic and cathodic positions of prophylls in some dicotyledonous grains (Fig. 4). Furthermore, the leaves of P. plants III. Erigeron sumatrensis. Bot. Mag. (Tokyo) 76: racemosum also contain starch grains in winter 299–308 (in Japanese with English summary). and are considered to act as storage organs Kumazawa M. 1967. Analytical studies on the anodic and (Kimura 1970a). Thus, bud scales would share a cathodic positions of prophylls in some dicotyledonous plants IV. Impatiens balsamina and Kochia scoparia. storage function with the winter leaves. Bot. Mag. (Tokyo) 80: 404–412 (in Japanese with English summary). The authors thank Dr. Hiroko Murata Kumazawa M. 1979. Plant Organography. 408 pp. (Setsunan University, Japan) for providing Shokabo, Tokyo (in Japanese). information on the locality of Pteridophyllum Kumazawa M. and Kumazawa M.1970. Analytical studies on the anodic and cathodic positions of prophylls in racemosum. The authors also thank two some dicotyledonous plants V. Periodic variation of the reviewers for their comments. This study was prophyll position. Bot. Mag. (Tokyo) 83: 242–248 (in supported by Grants-in-Aid for Scientific Japanese with English summary). Research (C) (21570087) to Y. E. from the Japan Mizuno M., Tanaka T., Kouya T., Hukuhara H., Suzuki T. and Oouti Y. 1975. About the vegetation for the habitat Society for the Promotion of Science. of Pteridophyllum racemosum Sieb. et Zucc. in Mt. Ontake. Ann. Proc. Gifu Pharm. Univ. 24: 21–38 (in References Japanese with English summary). Akiyama S. 2006. Papaveraceae. In: Iwatsuki K., Boufford Ohwi J. 1965. Flora of Japan, 1067 pp. Smithsonian D. E., and Ohba H. 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Ecological Studies 62. 321 pp. Springer Verlag, Yoshie F. and Yoshida S. 1989. Wintering forms of Heiderberg. perennial herbs in the cool temperate regions of Japan. Tucker S. C. 1963. Development and phyllotaxis of the Can. J. Bot. 67: 3563–3569. vegetative axillary buds of Michelia fuscata. Am. J. 遠藤泰彦a，斉藤　潤a，大野啓一b：オサバグサの冬芽 の形態と構造 　日本固有で，山地帯から亜高山帯に生育する常緑草本 前葉と呼ばれる2枚の葉をつけることが知られている． オサバグサPteridophyllum racemosum（オサバグサ科） この2枚の葉は，蓋葉の左右の方向に着くことから， は地表面に冬芽を形成する．冬芽の最も外側には,葉柄 側生前葉と呼ばれ，対生する（開度1/2）．一方，本研 から分化したと考えられる3枚から4枚の芽鱗がある． 究での冬芽の観察結果，オサバグサの側枝では側生前葉 芽鱗は表皮，皮層，そして1本の維管束より成り，3本 に相当する2枚の葉の開度は3/8であり，この点で特徴 の維管束が認められる葉柄とは明確に異なっている．芽 的である． 鱗の内側に，渦巻き状をした幼葉と湾曲した花序が配置 　本研究で認められた被子植物でも稀なオサバグサの されている．このような渦巻き状の幼葉重畳法は被子植 特徴，つまり(1)渦巻き状の幼葉重畳法，(2)開度3/8 物では稀である．芽鱗の皮層は比較的広い細胞間隙と細 の前葉，の分類学的意義については，オサバグサに近縁 胞内のデンプン粒によって特徴づけられる．ここで見ら な分類群の相当する特徴と比較検討することにより明 れる広い細胞間隙は，冬期の低温による細胞内凍結を避 らかにする必要がある． ける構造と考えられる．花序は頂芽由来であり，茎は仮 （a茨城大学理学部， 軸分枝している．葉序は螺旋葉序で，開度は3/8である． b千葉県立中央博物館） 　一般に単子葉類を除く種子植物では，側枝最基部に