50(//11 African Journal o( Botany 2001 6 7 371- 375 Ponied III South Afnca - All nghrs res€lYed

Copynghr ~ NISC Pry Ltd

SOUTH AFRICAN JOURNAL OF BOTANY ISSN 0254-6299

Short Communication

A survey of the polysaccharide reserves in geophytes native to the winter­rainfall region of South Africa

B Orthen

Institut fOr Okologie der Pflanzen, Westfiilische Wilhelms-Universitiit, Hindenburgplatz 55,48143 Munster, Germany e ·mail: ot1hen@uni-muenster.de

Received 11 January 2000, accepted in revised form 5 June 2000

Underground organs of 63 geophytic species, repre­senting eight families of Monocotyledonae and five fam­ilies of Dicotyledonae, native to the w inter-rainfall region of South Africa, were analysed for their polysac­charide storage components, With respect to type of polysaccharide accumulated in the storage organs the species tested can be divided into three groups: I) geo­phytes storing starch, II) geophytes storing fructan, III) geophytes storing both , fructan and starch, Most of the geophytes tested showed a capacity for storing large to massive amounts of polysaccharides. Starch andlor fructan contribute more than 40% to total dry mass of the underground storage organs, Within a family or a genus, species cannot naturally be placed in one group, e,g, members of the genus Omithogalum or Lachenalia

The winter-rainfall region of South Africa comprises one of the richest geophytic floras of the world (Cowling et al. 1999); the geophytic life-form can contribute up to 40% of the totat flora (Snijman and Perry 1987). According to Raunkiaer (1907) the characteristic feature of the geophyte life-form is being able to evade unfavourable environmental conditions in the form of underground storage organs. For the geophytes under investigation these unfavou rable envi­ronmental conditions are the high temperatures and drought during the summer months. The seasonal cycles of geo­phytes are synchronised with the climate in such a way that these plants are actively growing only when temperature and moisture regimes offer comparatively favourable condi­tions during winter and spring. Thereafter the aerial parts die-back and the plants remain as underground storage organs unti l the next growing season (Du Plessis and Duncan t 989).

Such a growth strategy must be based on a large supply of reselVe materials in the storage organs of the plants, Only with the help of these reselVes is the initiation of growth fol­lowing seasonal dormancy possible. The possession of a storage organ also allows plants some independence from the periodicity of its habitat. Flowering, for example, can be achieved earl ier than in an annual which has to germinate

store either fructan or a combination of fructan and starch in the underground storage organs. However, all geophytes belonging to group III are members of the Monocotyledonae. In underground storage organs fruc­tan was previously considered to be one alternative to starch: species rich in fructan do not accumulate more than traces of starch and vice versa. This survey demonstrates that this assumption can not be con­firmed in the results for the underground storage organs of the South African geophytes, The majority of geophytes belonging to group III accumulated more than 20% of the total amount of polysaccharides as the minor component. In these geophytes fructan is accu­mulated in addition to and not as an alternative to starch ,

and pass through a juvenile phase with a bui ld-up of vege­tative structure to support Ihe demand of flowering and sub­sequent seed maturation . Alternatively it can be completely separated from above ground vegetative development (hys­teranlhous or proteranthous species) due to the availability of food reserves (Rees 1992).

There are few studies on the polysaccharide fraction of South African geophytes. Data on carbohydrate reselVes of geophytes nalive to the winter-rainfall reg ion are available for two species only. 80th species - one bulbous species in the Amaryllidaceae (Haemanthus pubescens) and one cor­mous species in the Iridaceae (Sparaxis grandiflora) - con­tain starch as the reserve polysaccharide in the underground storage organ (Ruiters et ai, 1993, Ruiters and McKenzie 1994), The bulbs of Nerine bowdenii, a geophyte native to the summer-rainfall region of South Africa, also store starch as the predominant polysaccharide (Theron and Jacobs 1996). Fructan, the reselVe polysaccharide of approximate­ly 15% of the angiosperm flora (Hendry 1993), was not pres­ent (Haemanthus pubescens, Ruilers et al. 1993; Sparaxis grandiflora, Ruiters and McKenzie 1994) or detectable as traces only (Nerine bowdenii, Theron and Jacobs 1996),

The aim of th is survey was to determine the major poly­saccharide reserves of the underground storage organs of

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various geophytes from different taxonomic families (Amaryllidaceae, Anthericaceae , Asphodelaceae , Colchicaceae, Eriospermaceae, Hyacinthaceae, lridaceae, Tecophilaceae , Asclepiadaceae . Asteraceae, Campanulaceae, Droseraceae, Oxalidaceae) native to the winter-rainfall region of South Africa.

The underground storage organs were collected in the field (South Africa, Kalkgat, 31°0S'S, 18°SS'E) or in the glasshouse (University of Munster, Germany) where plants were raised from seeds obtained from the National Botanical Garden, Kirstenbosch, Cape Town.

Sampling was carried out at the end of the growing sea­son. After harvesting , storage organs were thoroughly cleaned. Fresh weight was determined immediately and the material was killed in a microwave for 3- 10 seconds. Samples were then dried at BO°C to constant mass , weighed, ground and extracted with water (10mg dry mass per ml a, dest.) for 1 hour. After centrifugation the super­natants were used for a modified fructan assay obtained from Megazyme (I reland) and the determination of water soluble starch (as hexose units after breakdown with amy­loglucosidase). The insoluble residue was subjected to starch determination. After threefold extraction with 80% ethanol the starch was degraded by a-amylase (EC 3.2.1.1) and amyloglucosidase (EC 3.2.1.2) into its monomer glu­cose which was determined enzymatically according to Bergmeyer (1970).

The type of polysaccharide accumulated within the stor­age organs of the 63 species tested, representing eight fam­ilies of Monocotyledonae and five families of Dicotyledonae, can be divided into three groups: I) geophytes storing starch, II) geophytes storing fructan and III) geophytes storing both, fructan and starch.

Group I

Twenty four species - Monocotyledonae as well as Dicotyledonae - stored starch as the only polysaccharide reserve in the underground organs (Table 1). Within this group four species (Androcymbium sp., Ferraria crispa, Fockea sp., Drosera cistiflora) stored starch in a range from 90-100g kg ' dry mass and can be regarded as low starch storing species . Twelve species accumulated between 20 and 40% dry mass as starch. Eight species showed the capacity to accumulate more than 40% dry mass as starch and can be regarded as high starch storers (Babiana cedar­bergensis, Babiana nana, Babiana truncata, Freesia viridis, Lapeirousia pyramidalis, Moraea nana, Moraea serpentina, Cyanella hyacinthoides). Within one familiy (Inidaceae) there was a range in the storage of starch from high amounts (743g kg" dry mass Babiana truncata) to low amounts (99g kg" dry mass Ferraria crispa). The capacity to store starch is shown by geophytes with tubers (e.g. Drosera cistillora) , corms (e.g. Moraea serpentina) or bulbs (e.g. Oxalis f/ava) as underground storage organs. Starch is also used as a reserve polysaccharide by geophytes possessing a perennial storage organ (e.g. Fockea sp.) as well as by those which replace the storage organ annually (e.g. Moraea serpentina).

Orthen

Table 1: Geophytes storing starch (g kg' dry mass) as the only reserve polysaccharide in the underground organs (group I) . Samples were taken at the end of the growing season

Fami l}l: Species Starch Colchicaceae Androcymbium cillOlalum Sch tr.

and K. Krause 90 Iridaceae Babiana cedarbergensis GJ.l ewis 843

Babiana nana (Andr.) Spreng. 552 Babiana truncata GJ .Lewls 743 Babiana sp. 330 Ferraria crispa Burm. 99 Ferraria divaricata Sweet 204 Ferraria sp. 167 Freesia viridiS (AiL) Goldbl and Manning 711 Gladiolus sp. 184 Ixia sp. 301 Lapeirousia anceps (l. f.) Ker-Gawl . 349 Lapeirousla pyramidalis (l am.) Goldbl. 751 Moraea fugax (de la Roche) Jac. 129 Moraea nana Goldbl. and Manning 4t2 Moraea serpentma Baker 633 Romulea f/ava (lam.) De Vas 250 Romulea atrandra GJ. Lewis 198 Romulea setifolia N. E. Br. 312

Tecophilaeaceae Cyanefla hyacinthoides l . 620 Asclepiadaceae Fockea sp. 98 Droseraceae Drosera cistiflora l . 94 Oxalidaceae Oxalis f/ava L. 250

Oxalis sp. 191

Group /I

From the 63 geophytes surveyed 24 species accumulated fructan as the only polysaccharide in the storage organs (Table 2). These species belong to six families, four Monocotyledonae (Amaryllidaceae , Asphodeleaceae, Eriospermaceae, Hyacinthaceae) and two Dicotyledonae (Asteraceae, Campanulaceae) . Total Iructose polymers var­ied from 20Sg kg ' dry mass in Gethyl/is vil/osa to 729g kg , dry mass in Lachenalia mathewsii. Thirteen geophytes accu­mulated more than 40% dry mass as fructan and can be regarded as high fructan storing species. Among the species tested, fructan is found as the only polysacchanide reserve in perennial organs, bulbs (e.g. Urginia physodes) or stem tubers (e.g. Othonna hederilo/ia).

Group 11/

The underground storage organs of fifteen species out of the 63 geophytes tested were fructan and starch positive (Table 3), all these species belong to the Monocotyledonae. Except for Ch/orophytum undu/atum where the underground stor­age organ is a modified root these geophytes are charac­terised by the possession of bulbs. The total polysaccharide content varied between 176g kg ' dry mass (Ch/orophytum undu/atum) and 784g kg ' dry mass (Lachena/ia a/aides). Storage organs of 12 geophytes contained more than 40% dry mass as fructan and starch. In the bulbs of Brunsvigia sp., Crossyne flava, Massonia depressa and A/buca sp.

South African Journal of Botany 2001. 67 37-375

Table 2: Geophytes storing fructan (g kg 1 dry mass) as the only reserve polysaccharide in the underground organs (group II ). Samples were taken at the end of the growing season

Family Species Fructan AmarylJidaceae Gethyllis villosa (Thumb.) Thumb. 205

GethylJis sp. 267 Asphodeleaceae Bulbine mesembryanthemOldes Haw. 367

Bu/bine torta N. E. Br 520 Bu/bine sediflo/fa Schhltr. ex. V. Poelln. 632 Bu/bine sp. 460 Traeheandra falcala (U.) Kunth 312 Tracheandra kaooriea Oberm. 206 Traeheandra tortillis (Bak.) Oberm. 484

Eriospermaceae Eriospermum sp. I 244 Eriospermum sp. II 295

Hyacinthaceae Albuca spiralis L.f. 583 A/buea sp. 478 Laehenalia trichophylla Bak. 560 Laehenalia mathewsii W.F. Barker 729 Lachena/ia vio/aeeae Jacq. 287

Ornithogalum Omithoga/um mUIti/oHum Jacq. 378 Ornithoga/um cf. nanodes F.M. Leight 682 Omithogafum unifolium Retz. 614 Rhadamanlhus platyphyflus B. Nord. 310 Urginia physodes (Jacq.) Baker 419

Asleraceae Othonna hederifolia B. Nord. 630 Othonna eaelioides L.f 378

Campanu!aceae Cyphia oligotrieha Schllr. 484

starch content was higher than fructan content, whereas in the other species fructan content was higher. The fructan~ slarch ratio demonstrates that it is possible to distinguish between organs where either starch (e.g. Brunsvigia sp.) or fructan (e.g. Ornithoga/um pruinosurn) is the predominant polysaccharide and those where both carbohydrates are stored to similar amounts (e .g. Lachena/ia minima).

Most 01 the geophytes tested, showed a capacity to store large to massive amounts of polysaccharides: Where starch and/or fructan contribute more than 40% of total dry mass of the underground storage organs.

Starch, the most common storage carbohydrate in vascu~

373

lar plants, was detected in the underground storage organs of 38 out 01 the 63 geophytes sUNeyed (Table 1, Table 3). The amount 01 starch accumulated in the bulbs, corms and tubers differs considerably (from 90-843g kg ' dry mass, Table 1). The maximum value 01 84% dry mass in the corms of Babiana cedarbergensis was in the same range as the starch content of plants commercially used as starch sources (e.g. potato tubers: 86% dry mass, Paul and Southgate 1978).

Fructan, the reserve carbohydrate of approximately 15% 01 the angiosperm flora (Hendry 1993), was stored by 38 species, representing 6 monocotyledonae and two dicotyle­donae families (Table 2, Table 3). Within this group of Iruc­tan storing species maximum values of up to 73% dry mass have been obseNed (Table 2). Again, these amounts are similar to those detected in commercially used species (Cichorium inlybus, Helianlhus luberosus, Incoll and Bonnett 1996).

It has been suggested that the occurrence of fructan may be related to phylogenetic relationship (Pollard and Amuti 1981, Smouter and Simpson 1989, Tertuliano and Figueiredo-Ribeiro 1993). Pollard (1982) reports a sUNey 01 Monocotyledons. It was demonstrated that Iructan is restricted; within a given family fructan occurred consjstent~

Iy in every representative plant. Within the monocotyledonae under investigation all species belonging to the Amaryllidaceae, Anthenicaceae, Asphodelaceae, Eriospermaceae and Hyacinthaceae were fructan positive (Table 2) . Interestingly, all species tested belonging to the Iri­daceae (Babiana, Ferrar;a, Lapeirousia, Moraea, Romubea, Ixia) - a family known for Iructan storing species (e.g. Meier and Reid 1982, Hendry and Wallace 1993) - were Iructan negative and stored starch (Table 1).

Except for the Asteraceae Olhonna hederifolia, Olhonna cacalioides and the Campanulaceae Cyphia oligolricha, which are Iructan storers (Table 2) , the other Dicotyledonae species tested accumulated starch as polysaccharide reseNes (Table 1).

In 15 species starch as well as fructan was present in bulbs and root tubers (e.g. Lachenalia a/oides, Ch/orophylum undu/alum, Table 3) . Except for the bulbs of

Table 3: Geophytes storing fructan as weI! as starch (g kg 1 dry mass) in the underground organs (group III) and the fruclan to starch ratio. Samples were taken at the end of the growing season

Family Species Fructan Starch F.lSt. AmarylUdaceae Brunsvlgia radula (Jacq.) Ail. 128 542 0.2

Brunsvigia sp. 101 657 0.2 Crossyne flava (Snijman) D. and U. MII~Doblies 189 336 0.6

Anthericaceae Chlorophytum undulatum (Jacq.) Oberm. 125 51 2.5 Hyacinthaceae Laehenalia aloldes (l.t.) Asch. and Graebner 592 192 3.1

Laehenalia eontaminata Ail. 515 100 5.2 Laehenafia minima W.F Barker 408 304 1.3 Laehenafia undufata Masson ex Bak. 260 147 1.8 Laehena/ia zebrina W.F Barker 357 99 3.6 Massonia echinata L.f 250 183 1.4 Massonia depressa Houtt. 306 450 0.7 Ornithogalum dilueulum Oberm. 250 150 1.7 Ornithogalum ova tum Thunb. 397 96 4.1 Ornithogalum pruinosum Leighton 300 50 6.0 Albuea sp. 203 251 0.8

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Brunsvigia sp., Crossyne flava, Massonia depressa and Albuca sp. fructan content was higher than starch content. The fruetan/starch ratio differed considerably: in some species starch content was much lower than truetan content (Lachenalia contaminata, Ornithogalum pruinosum) , in oth­ers the accumulation of starch nearly equaled that of truetan (Lachenalia minima, Massonia echinata) .

In leaves the co-occurrence of starch and fructan is a well­known phenomenon (e.g. Chatlerton et al. 1989, Housley and Pollock 1993, Kelly and van Staden 1994, Wang and Tillberg 1997). As a reserve carbohydrate in underground storage organs fruetan was considered as one alternative to starch - species rich in fructan do not accumulate more than traces of starch (Pale and Dixon 1982, Brocklebank and Hendry 1989, Tertuliano and Figueiredo-Ribeiro 1993). This survey demonstrates that this assumption cannot be confirmed in the results for the underground storage organs of Ihe South African geophyles. The majorily of geophyles belonging to group III accumulated more than 20% of the total amount of polysaccharides as the minor component. In these geophytes fructan was accumulated in addilion to and not as an alternative to starch.

The queslion of whether the slorage of fructan instead of starch is of any benefit fo r the planl is still a matter of debale. Atlempts have been made to establ ish a function of fructan beyond its role as a reserve carbohydrate , two additional functions have received much attention in the literature in its role as an osmoregulator and as a solute in stress - cold or drought - adaptation (e.g. Pontis 1989, Pollock and Crains 1991 , Hendry 1993; Pilon-Smits et al. 1999).

A survey on Ihe reserve carbohydrales of 20 species of the Sheffield tlora (UK) led Brocklebank and Hendry (1989) to the conclusion that fructan storage is associated with rel­atively restricled phenologies, whereas Ihe slorage of starch is associaled with the broadesl variation in phenological pat­terns. The phenologies related to the storage of fructan were early and low lemperalure growth (Brocklebank and Hendry, 1989). Phenological data for the South African geophytes are limited; a study by Van Rooyen et al. (1979) conducted on plants in the Goegap Nature Reserve (17"57'E, 29"34'S) includes 7 geophytes which are part of this survey as well. Neilher the species storing only fruclan (Bu/bine sedilolia, Trachenadra fa/cata) nor the species storing both fructan and starch (Massonia depressa, Ornithogalum pruinosum) showed significant differences in phenology when compared with the starch storing species (Babiana truncata, Cyanella hyacinthoides). Personal observations of the liming of regrowth following dormancy in the natural habilat as well as in the glasshouse revealed no significant differences between starch and/or fructan storing species.

Another aspeci with respect to phenology is Ihat fructan remobilisation is associated with rapid inflorescence devel­opment (Solhaug and Aares 1994) and rapid petal expan­sion (Bieleski 1993). The utilisation of fructan for rapid repro­duction might be an advantage especially for hysteranlhous and proteranthous geophytes. In bOlh these groups flower­ing is completely separated from above ground vegelative development and occurs during the dry period.

The occurrence of bolh fructan and starch as reserve poly­saccharides in subterranean organs has received little atten-

Orthen

tion. Histological studies on HeNanthus tuberosus showed that low amounts of starch are detectable in the tuber during tuber development, fructan synthesis and the beginning of sprouling, but not during dormancy (Ernst 1991). A compa­rable result was obtained for onion bulbs (Ernst and Butler 1994). Fructan, Ihe principle carbohydrate reserve is found Ih roughout the bulb (Darbyshire and Henry 1978), whereas Ihe occurrence of slarch is restricted to Ihe siems (= basal plate). Starch can be detected in its primary thickening meristem du ring sprouting but not during dormancy (Ernst and Bufler 1994).

These results allow for speculalion thai these two reserve carbohydrates fulfil different roles during specific phenologi­cal phases (e.g. resprout ing , reproduction, dormancy). For the geophytes with a similar fructan and starch content in the storage organs (Table 3) in particular, a differenlial use of fructans and starch seems possible and would ensure that there is always carbon available should adverse conditions prevai l.

Acknowledgements - Thanks are due 10 Ihe owner (Prof. Dr Kuhlmann) and the scientific administrator (prof Dr von Willert) of Kalkgat as well as to Cape Nature Conservation for gettmg the per­mission to remove the geophytes. Thanks go to the staff of the Compton Herbarium for the help with the plant identification. The technical assistance of H. Schwltle is gratefully acknowledged.

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