AOBPreview originally published online on February 23, 2004
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Annals of Botany 93: 415-421, 2004
© 2004 Annals of Botany Company
Raphides in Palm Embryos and their Systematic Distribution
Fairchild Tropical Garden, 11935 Old Cutler Road, Coral Gables (Miami), FL 33156-4242, USA
* For correspondence. Fax 305-665-8032, e-mail szona{at}fairchildgarden.org
Received: 25 July 2003; Returned for revision: 25 November 2003; Accepted: 18 December 2003; Published electronically: 23 February 2004
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
• Background and Aims Raphides are ubiquitous in the palms (Arecaceae), where they are found in roots, stems, leaves, flowers and fruits. Their occasional presence in embryos, first noticed over 100 years ago, has gone largely unexamined.
• Methods Embryos from 148 taxa of palms, the largest survey of palm embryos to date, were examined using light microscopy of squashed preparations under non-polarized and crossed polarized light.
• Key Results Raphides were found in embryos of species from the three subfamilies Coryphoideae, Ceroxyloideae and Arecoideae. Raphides were not observed in the embryos of species of Calamoideae or Phytelephantoideae. The remaining subfamily, the monospecific Nypoideae, was not available for study.
• Conclusions Within the Coryphoideae and Ceroxyloideae, embryos with raphides were rare, but within the Arecoideae, they were a common feature of the tribes Areceae and Caryoteae.
Key words: Anatomy, Arecaceae, calcium oxalate, embryology, embryos, Palmae, raphides.
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Raphides, bundles of needle-shaped crystals of calcium oxalate monohydrate in specialized cells, are found throughout the Monocotyledonae (Franceschi and Horner, 1980; Prychid and Rudall, 1999) and are ubiquitous in the palms (Arecaceae). They are known from roots, stems, leaves, flowers and fruits (Uhl and Dransfield, 1987; Tomlinson, 1961, 1990) but occasionally turn up in unusual sites, such as anther tissue (Henderson and Rodríguez, 1999), the pseudopedicel epidermis (Barfod and Uhl, 2001) and epidermal trichome ‘sacs’ (Robertson, 1978). They were first noticed in palm embryos by Micheels (1891).
Examining material supplied by M. Treub from the Buitenzorg (now Bogor) Botanic Garden, Micheels (1891) reported the presence of raphides in the embryos of Caryota sp. and Archontophoenix alexandrae (F. Muell.) H. Wendl. (as Ptychosperma alexandra). Osenbrüg (1894) surveyed 35 taxa from throughout the family and found raphides in the embryos of 11 species. More recent embryological accounts pay little attention to raphides. Their absence was not specifically mentioned in accounts on the embryos of coconut (Haccius and Philip, 1979), Chamaerops humilis L. (Guignard, 1961), Elaeis guineensis Jacq. (Vallade, 1966) and Livistona chinensis (Jacq.) R. Br. ex Mart. (Kulkarni and Mahabale, 1974). Rao (1955) made no mention of raphides in the embryo of Areca catechu L. Shirke and Mahabale (1972) illustrated raphides in their drawings of Caryota urens L. embryos but did not remark on their significance.
Nevertheless, examining Osenbrüg’s work (Osenbrüg, 1894), one finds that the presence or absence of raphides in embryos seems to follow certain presumed evolutionary lineages within the palm family. The purpose of this survey was to determine if raphides are confined to certain lineages and if they could be used as additional evidence of phylogenetic relationships.
|
METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Palm seeds were harvested from fruits that were mature and ready to be dispersed. Most material for this study was collected as fresh seeds from Fairchild Tropical Garden (FTG). Some seeds were collected from wild or cultivated plants elsewhere in the Miami area (see Table 1); vouchers for these samples are deposited in the herbarium of FTG. Two samples of African rattans were supplied as living seeds for propagation by Dr T. Sunderland from wild plants in Cameroon (voucher at K, the herbarium of the Royal Botanic Gardens, Kew). Some samples were collected as mature seeds preserved in glycerine–alcohol (in the spirit collection at FTG); the appearance of raphides in pickled and fresh materials was the same.
|
Seeds were dissected, and the embryos were removed. The embryo usually came away from the endosperm with little effort. It was placed in a drop of toluidine blue, squashed under a coverslip, and examined in polarized and non-polarized light at x100 and x250. Raphides, when present, were usually visible in normal light, but became highly visible in polarized light. Images were captured electronically using a Pixera Professional® (Los Gatos, California) digital image capture system, using polarized light. Post-capture processing consisted of converting RGB colour mode to greyscale (half-tone), increasing resolution to 300 dpi, and enhancing contrast.
Raphide presence was further qualified as ‘sparse’ when fewer than ten raphide bundles were seen in the embryo. It was called ‘abundant’ when more than 25 bundles were observed in the embryo preparation. No other mineral inclusions, such as silica bodies or styloids, were observed in palm embryos.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
The results of this survey of 148 taxa are presented in Table 1, organized by taxonomic tribes (Uhl and Dransfield, 1999), which are more likely to represent monophyletic groups. To present a more complete picture, the 35 observations of Osenbrüg (1894) are also included in Table 1, alongside 127 new observations. The new observations overlap with those of Osenbrüg for only six taxa, but in each case the new results agree with those presented by Osenbrüg (1894). Eight taxa were sampled from two different accessions, but in each case the results were concordant.
Raphides were observed in the embryos of palms from only six tribes, the Corypheae, Hyophorbeae, Caryoteae, Areceae, Cocoeae and Geonomeae. These tribes are presently classified in three subfamilies: Coryphoideae, Ceroxyloideae and Arecoideae (Uhl and Dransfield, 1999). Raphides were not observed in the following groups: Calameae and Lepidocaryeae (which together comprise the Calamoideae), Phoeniceae, Borasseae, Cyclospatheae, Ceroxyleae and Phytelephantoideae. Embryos of the Nypoideae, Iriarteeae and Podococeae were not available for examination.
Within the Corypheae, Rhapis excelsa, one species of Livistona and the monotypic genus Zombia were observed to have raphides present in their embryos. Many species of Livistona remain to be sampled, as do several recognized species of Rhapis, but the data show the trait of raphides in embryos to be variable within the genus Livistona.
Only one member of the Hyophorbeae, Chamaedorea tepejilote, was found to have raphides in its embryos, although two other species were lacking raphides.
The three genera of the Caryoteae, well known for their raphide-rich fruits, were surprisingly diverse in the raphide content of their embryos. Most species of Arenga lacked raphides, while Caryota and Wallichia had raphides in their embryos.
Raphides were present in the embryos of 19 genera from the Areceae, including members of the subtribes Ptychospermatinae (Fig. 1), Dypsidinae, Linospadicineae, Arecinae (Fig. 2), Euterpeinae, Cyrtostachydinae, Onco spermatinae and Archontophoenicinae. One noteworthy sample from among these genera is Solfia samoensis, the sole member of its genus. Although the sizes of raphide bundles were not recorded, Solfia was unique in having small bundles, less than half the size of bundles in other palms and difficult to see without polarized light.
|
|
Only one sample of Cocoeae was observed to have raphides in its embryo: Desmoncus orthocanthos (as D. chinatlensis Leibm. ex Mart) had approximately five raphide bundles in the embryo examined. Likewise, of the two Geonomeae sampled, one, Geonoma interrupta var. interrupta, was found to have raphides in its embryos.
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
Within the palm family, the systematic value of calcium oxalate crystals was thought to be nil, as raphides are ubiquitous in the vegetative organs of palms (Tomlinson, 1961, 1990); however, Osenbrüg (1894) demonstrated that raphide presence in embryos is a variable trait. The results presented here give a clearer picture of the systematic distribution of raphides in palm embryos, which are neither randomly nor evenly distributed among the 148 taxa surveyed.
Raphides were observed in three out of 42 Coryphoideae samples, an occurrence rate of 7 %. Osenbrüg (1894) did not report raphides among any of the eight genera from the Coryphoideae examined by him. Among the three tribes that comprise the Coryphoideae, only the Corypheae has members with raphides in their embryos. The three samples in which raphides were observed are from three genera – Livistona, Rhapis and Zombia – that are not believed to be closely related (Hahn, 2002).
The subfamily Ceroxyloideae—comprising the Ceroxyleae, Hyophorbeae and Cyclospatheae—is surely not monophyletic; however, its three tribes taken individually show evidence of monophyly (Lewis and Doyle, 2001; Hahn, 2002). No raphides were observed by Osenbrüg in one member of the Ceroxyleae, nor did this study find raphides in the embryos of Cyclospatheae. Raphides were found in one Chamaedorea of the Hyophorbeae; however, as the genus Chamaedorea is large and diverse additional sampling is needed before one can draw meaningful conclusions about the rate of occurrence of raphides in embryos in this Hyophorbeae.
The subfamily Arecoideae comprises six tribes, four of which were sampled in the present study. In the tribe Caryoteae, which comprises three genera, only Caryota and Wallichia appear to have abundant raphides in their embryos, and this character may help set these two genera apart from the remaining genus, Arenga. The presence of raphides in the embryos of Arenga tremula, however, is a caution flag to an otherwise clear distinction between Arenga and the other genera.
The tribe Areceae has the most species with raphides in their embryos. Of 55 taxa of Areceae reported in Table 1, 34 were found to have at least some raphides in their embryos, which is an occurrence rate of 62 %. Only two genera, Ptychosperma and Veitchia, both members of the Ptychospermatinae, had species with and without raphides in their embryos, an observation suggesting that the raphide presence might be taxonomically useful at the species level. The tribe Cocoeae, as reported by Osenbrüg (1894), lacked raphides in the embryos of its species. However, this survey found one member, Desmoncus orthocanthos, that has raphides in its embryos, albeit sparsely. One species out of 19 Cocoeae reported in Table 1 is an occurrence rate of 5 %. Only two species of Geonomeae were sampled, and one species of Geonoma was found to have raphides in its embryos. Additional sampling is desired.
There is no correlation between the presence of raphides in anthers (Henderson and Rodríguez, 1999) and raphides in embryos (this study). Thirty-three taxa were sampled in both studies. The results of a Fisher Exact Probability test show no positive or negative association for the two conditions (P one-tailed = 0·36773; P two-tailed = 0·69422).
The function of raphides in embryos has not been addressed experimentally; however, there are several hypotheses for the function of raphides in plant cells, and these provide a useful framework in which to address the question in regard to palm embryos. Raphides may serve as a calcium storage depot, to be tapped as needed (Franceschi, 1989; Ilarsan et al., 1996; Ilarsan et al., 2001), and certainly, rapid seedling development and growth require an adequate supply of calcium. Raphides may also serve as a source of oxalate, which some plants secrete from their root tips to detoxify aluminium ions in the soil (Ma and Miyasaka, 1998; Ma et al., 2001). Oxalate can be broken down by oxalate oxidase into carbon dioxide and hydrogen peroxide; the latter is critical in cross-linking cell wall polymers during cell wall extension (Lane, 1994), another process that is common in rapidly growing and developing seedlings. Raphides may also play a role in sequestering excess calcium (Franceschi, 1989; Fink, 1991; Webb, 1999), although one imagines that an embryo would be an unlikely sink for excess minerals. Finally, raphides have a known function as an anti-herbivory defence (Ward et al., 1997; Finley, 1999; Molano-Flores, 2001). As herbivores are deterred only after they initiate chewing and as embryos are very small and could be fatally damaged by even minor herbivory, investing embryos with raphides hardly seems like an effective defensive strategy. Palm seeds are, in general, well protected by fibres, tannins, raphides and silica bodies in the tissues of the ovary (Uhl and Moore, 1973). The most likely—but as yet untested—function for raphides in palm embryos is as storage depots for calcium, oxalate and/or hydrogen peroxide.
Regarding those embryos lacking raphides, a question that remains unanswered by this survey is, when do seedlings acquire raphides in their vegetative tissues? At some point, presumably during or immediately after germination, raphides are formed in the seedlings, where they have a presumed defensive function (Tomlinson, 1990).
Given their scattered occurrence in the family, raphides in embryos must have evolved and/or been lost many times. The presence of raphides in palm embryos follows certain phylogenetic trends and most likely has some utility as an indicator of relationships at the subtribe level or below. In certain genera within which the trait is polymorphic, such as Livistona and Ptychosperma, the presence of raphides may be a useful taxonomic character as well. The function of raphides in embryos is a topic deserving further study.
|
ACKNOWLEDGEMENTS |
|---|
I am grateful to Angela Rosario for assistance in translating the original Osenbrüg paper. Jean-Christophe Pintaud kindly supplied a copy of the Micheels reference. I thank Dr Jack Fisher, Dr Sawsan Khuri, Dr C. Prychid and an anonymous reviewer for their helpful comments on this paper. Dr Carl Lewis assisted in collected many of the samples and made useful comments on an early draft of this paper.
|
LITERATURE CITED |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONLITERATURE CITED |
|---|
-
Barfod AS, Uhl NW. 2001. Floral development in Aphandra (Arecaceae). American Journal of Botany 88: 185–195.
Fink S. 1991. The micromorphological distribution of bound calcium in needles of Norway spruce [Picea abies (L.) Karst.]. New Phytologist 119: 33–40.[CrossRef]
Finley DS. 1999. Patterns of calcium oxalate crystals in young tropical leaves: a possible role as an anti-herbivore defense. Revista de Biología Tropical 47: 27–31.
Franceschi VR. 1989. Calcium oxalate formation is a rapid and reversible process in Lemna minor L. Protoplasma 148: 130–137.[CrossRef]
Franceschi VR, Horner HT Jr. 1980. Calcium oxalate crystals in plants. Botanical Review 46: 361–427.
Guignard J-L. 1961. Embryogénie des Palmiers. Développement de l’embryon chez le Chamaerops humilis. Comptes Rendus de l’Académie de Sciences sér. D. 253: 1834–1836.
Haccius B, Philip VJ. 1979. Embryo development in Cocos nucifera L. A critical contribution to the general understanding of palm embryogenesis. Plant Systematics and Evolution 132: 91–106.[CrossRef]
Hahn WJ. 2002. A molecular phylogenetic study of the Palmae (Arecaceae) based on atpB, rbcL, and 18S nrDNA sequences. Systematic Biology 51: 92–112.[CrossRef][Web of Science][Medline]
Henderson A. 1995. The palms of the Amazon. New York: Oxford University Press.
Henderson A, Rodríguez D. 1999. Raphides in palm anthers. Acta Botanica Venezuelica 22: 45–55.
Henderson A, Galeano G, Bernal R. 1995. Field guide to the palms of the Americas. Princeton, NJ: Princeton University Press.
Ilarsan H, Palmer RG, Horner HT. 1996. Presence of calcium oxalate crystals in developing ovules of normal soybean (Glycine max (L.) Merr.). American Journal of Botany 83 (6 Suppl): 41–42.
Ilarsan H., Palmer RG, Horner HT. 2001. Calcium oxalate crystals in developing seeds of soybean. Annals of Botany 88: 243–257.
Kulkarni KM, Mahabale TS. 1974. Studies on palms: embryology of Livistona chinensis R. Br. Proceedings of the Indian Academy of Science B 80: 1–17.
Lane BG. 1994. Oxalate, germin, and the extracellular matrix of higher plants. FASEB Journal 8: 294–301.[Abstract]
Lewis CE, Doyle JJ. 2001. Phylogenetic utility of the nuclear gene malate synthase in the palm family (Arecaceae). Molecular Phylogenetics and Evolution 19: 409–420.[CrossRef][Web of Science][Medline]
Ma JF, Miyasaka SC. 1998. Oxalate exudation by taro in response to Al. Plant Physiology 118: 861–865.
Ma JF, Ryan PR, Delhaize E. 2001. Aluminium tolerance in plants and the complexing role of organic acids. Trends in Plant Science 6: 273–278.[CrossRef][Web of Science][Medline]
Micheels H. 1891. De la présence de raphides dans l’embryon de certains palmiers. Bulletins de l’Académie Royale des Sciences, des Lettres et des Beaux Arts de Belgique, sér. 3. 22(11): 391–392.
Molano-Flores B. 2001. Herbivory and calcium concentrations affect calcium oxalate crystal formation in leaves of Sida (Malvaceae). Annals of Botany 88: 387–391.
Moore HE Jr. 1963. An annotated checklist of cultivated palms. Principes 7: 119–182.
Osenbrüg T. 1894. Ueber die Entwicklung des Samens der Areca catechu L. und die Bedeutung der Ruminationen. Inaugural Dissertation, Marburg, Germany.
Prychid CJ, Rudall PJ. 1999. Calcium oxalate crystals in Monocotyledons: a review of their structure and systematics. Annals of Botany 84: 725–739.
Rao CV. 1955. Embryo development in Areca-nut. Nature 175: 432–433.
Robertson BL. 1978. Raphide-sacs as epidermal appendages in Jubaeopsis caffra Becc. (Palmae). Annals of Botany 42: 489–490.
Shirke NS, Mahabale TS. 1972. Studies on palms: Embryology of Caryota urens L. In: Murty YS, Johri BM, Mohan Ram HY, Varghese TM, eds. Advances in plant morphology. Meerut: Sarita Prakashan, 218–232.
Tomlinson PB. 1961. Anatomy of the monocotyledons. II. Palmae. Oxford: Clarendon Press.
Tomlinson PB. 1990. The structural biology of palms. Oxford: Clarendon Press.
Uhl NW, Dransfield J. 1987. Genera Palmarum: a classification based on the work of H. E. Moore, Jr. Lawrence, KS: International Palm Society and L. H. Bailey Hortorium.
Uhl NW, Dransfield J. 1999. Genera Palmarum after ten years. Memoirs of the New York Botanical Garden 83: 245–253.
Uhl NW, Moore HE Jr. 1973. The protection of pollen and ovules in palms. Principes 17: 111–149.
Vallade J. 1966. Aspect morphologique et cytologique de l’embryon quiescent d’Elaeis guineensis Jacq. Comptes Rendus de l’Académie de Sciences 262: 856–859.
Ward D, Spiegel M, Saltz D. 1997. Gazelle herbivory and interpopulation differences in calcium oxalate content of leaves of a desert lily. Journal of Chemical Ecology 23: 333–346.[CrossRef]
Webb MA. 1999. Cell-mediated crystallization of calcium oxalate in plants. Plant Cell 11: 751–761.
CiteULike 
Connotea 
Del.icio.us What's this?
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||