Pertanika 13(1), 1-8(1990)

Comparative Micromorphology of the Seed Surface of Solariummelongena L. (eggplant) and Allied Species

SAYED MOHAMED ZAIN HASAN1 and RICHARD N. LESTER2

1 Department of Agronomy and Horticulture,Faculty of Agriculture

Universiti Pertanian Malaysia,43400 UPM Serdang, Selangor Darul Ehsan, Malaysia.

^School of Biological Science,The University of Birmingham,

P.O.Box 363, Birmingham, B15 2TT, U.K.

Keywords: Seed coat, SEM, enzyme etching, Solarium, S. melongena, S. incanum.

ABSTRAKMikrostrukturpermukaan biji Solanum melongena L.} S. incanum L. dan beberapa spesisyang lain diteliti denganmenggunakan SEM. Biji-biji telah diberi rawatan pelelasan enzim (Driselase) sebelum diteliti untuk mengikis lapisanluar biji yang mengaburkan penglihatan. Kebanyakan biji mempunyai struktur yang kelihatan seperti rerambut ataufibril mengelilingi setiap sel} yang mana merupakan tunjulan daripada penebalan dinding-dinding sisi epidermis luar seltesta. Struktur kulit biji S. melongena dan S. incanum telah ditemui sebagai seragam dalam keseluruhan masukanyang digunakan, menunjukkan hubungan yang rapat di antara dua takson ini. Bentuk kulit biji S.torvum Sw.}S.tomentosum L., S.aethiopicum L., S.kwebense Br. and Wr. dan S.cinereum R. Br. adalah sangat berbezabukan sahaja dengan S. melongena dan S. incanum tetapijuga di antara mereka, menunjukkan perbezaan di antaratakson-iekso)) ini.

ABSTRACTThe seed surface micro structure of Solanum melongena L., S. incanum L. and some other species were examinedusing SEM. Seeds were given enzyme (Driselase) etching treatment prior to examination to sweep off the outer layer ofcells which obscured observation. Most seeds were characterised by hair-like structures or fibrils which surrounded eachcell and which are strands of thickening in the lateral walls of the outer epidermal cells of the testa. Seed coat structure ofS.melongena and S.incanum was found to be highly uniform in the samples examined indicating a close relationshipbetween them. The seed coat patterns of 'S.torvum Sw.} S.tomentosum L.} S.aethiopicum L., S.kwebense Br. andWr. and S.cinereum R.Br. were considerably different not only from S. melongena andS. incanum but also betweenthemselves which supports the distinctness of these taxa.

INTRODUCTIONSolanum melongena L. (eggplant or brinjal) is avariable species and its taxonomic relationshipwith other taxa is still under discussion. Someexperimental taxonomic techniques includingmorphology, seed protein and isozyme electro-phoresis, crossability studies, etc. indicate that themost closely related taxon to S.melongena isS.incanum L. (Bhaduri 1951; Pearce 1975;

Narasimha Rao 1979; Reayat Khan 1979; Pearceand Lester 1979; Zohary 1983; Choudhury, 1984;Hasan and Lester 1988). S.incanum shows greatmorphological diversity which is distributed overa wide area in southern Asia and eastern Africa(Bitter 1923; Jaeger 1986; Jaeger and Hepper1986). This variability causes taxonomicconfusion in identification and classification ofthese two taxa as well as of closely related species.

SAYED MOHAMED ZAIN HASAN AND RICHARD N. LESTER

In this study, surface characters of the seedcoat were examined by scanning electronmicroscopy (SEM) to distinguish between severalecotypes S.melongena, S.incanum, and some otherspecies. The morphology of seed coat is usuallystable and is little influenced by externalenvironmental conditions whilst the seeds developand ripen within the fruit (Heywood 1971; Coleand Behnke 1975; Barthlottt 1981). Thereforeseed characters can provide valuable informationin the delimitation and identification of species.

Various workers have utilised seed coatstructures in comparative surveys of members ofthe genus Solarium. Some of them have also carriedout studies on embryo and seed development(Edmonds 1983; Morris 1986; Gunn and Gaffrey1974; Whallen 1979 and 1984). In most species ofSolarium, the epidermal surface of the seed coat isrelatively smooth and featureless due to thepresence of the flat tangential wall of the epidermis,or even if these have come off, the inner details maybe obscured by a covering of hair-like processesderived from secondary thickening of the radialwalls, which have been variously called hairs,spinous hair, pseudohairs, fibrils, or rod-likefibrous thickenings (Edmonds 1983; Lester andDurands 1984). Therefore, any attempt todescribe seed coat characters for taxonomicpurposes is confounded. However, by breakingdown or swepping off the outer layer, the hiddenintricate structures beneath are revealed.

Lester and Durands (1984) developed atechnique involving the enzyme Driselase toremove the outer tangential epidermal cell walland/or excessive hair-like processes in the radialwalls prior to observation. Using this technique,they were able to show that the wild species,S.anguivi, was distinct from S.violceum , the taxa ofwhich had been treated previously as a singlespecies under the name S.indicum.

This technique was used to evaluate thepossible use of seed surface microstructure in theidentification and classification of S. melongena,S.incanum and some others species.

MATERIALS AND METHODS

Seeds from several accessions of S. melongenaand S.incanum in section Andromonoecum and someallied species in sections Oliganthes and Torvariawere used (Table 1).

About 10 clean, dry seeds of each accessionwere soaked and washed thoroughly in distilledwater in 10 cm3 vials for about 1.5 hr. They werethen subjected to surface sterilisation by soakingthe seeds in 5% (v/v) Domestos solution (sodiumhypochlorite) for about 10 min. The seeds werethoroughly sterilised to prevent contamination bybacteria which would digest the enzyme and thusreduce enzyme activity during the digestionperiod. The seeds were then thoroughly washedwith distilled water before being soaked with 1.0ml of 2% Driselase enzyme (Fluka AG) inSorensons phosphate buffer pH 5.5 (5 parts 1/15M Na2HPO4 + 95 parts 1/15 M KH2PO4) in thevials.

The vials were kept in a waterbath at 30°Cfor about 24 hr, with mixer blades providinggentle agitatjon of the vials and their contents.Where appropriate, the seeds were washed andsterilised again, and treated with fresh enzyme fora further 24 hr. The seeds were subsequentlythoroughly rinsed in distilled water and were leftto dry, by allowing them to stick inside the wallof open vials, at room temperature.

The dry seeds were carefully mounted onSEM stubs dagged with silver conductive paintand were sputter-coated with gold. The seedswere observed under a Cambridge Stereocsan 600Scanning Electron Microscope. For eachaccession a standard photograph ( X 4 0 J I ) of theflank away from the hilum of the seed was taken.Subjective comparisons of the seed surfacebetween accessions were made both directly fromthe SEM screen and from the photographsproduced later.

RESULTS AND DISCUSSION

SEM micrograph of seeds of S. melongena, S.incanum and related species are shown in Figures 1~3.

In general, seed coat pattern within S.melongena and S. incanum is fairly uniform betweenaccession. However, there were some differencesin size, shape, convolution, fibril shape, and depthof the lumen or pore of the cell. In general, theshape of the cell was more elongated near and atthe edges of the seeds. In some accessions such asS.1501, these cells were relatively larger than theothers (Figure 2). In a few accessions, i. e. S.0859,S.2052 and S.2024 (Figure 2), convolutions

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COMPARATIVE MICROMORPHOLOGY OF SEED SURFACE OF S. MELONGENA L.

TABLE 1Species used for the micromorphology of seed

surface examination under SEM

Sections

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Andromonoecum

Oliganthes

Oliganthes

Otiganthes

Oliganlhes

Torvaria

Species

S.melongena L.

S.melongena L.

S.melongena L.

S.melongena L.

S.melongena L.

S.melongena L.

S.incanum L.

S.incanum L.

S.incanum L.

S.incanum L.

S. if/can urn L.

S.incanum L.

S.incanum L.

S.incanum L.

S.aelhiopicum L.

S.lomenlosum L.

S.cinereum R.Br.

S.kwebense Br. & Wr.

S.torvum Sw.

Accessionsno

S.2458

S.2444

S.2426

S.2424

S.2310

S.1554

S.0931

S.1518

S.1501

RNL 336

S.2024

S.2052

S.0859

S.1782

S.2339

S.1040

S.0202

S.1789

S.2415

Status/group

advanced cultivar;large fruit.

primitive cultivar,small round fruit.

wild /weedy; prickly.

primitive cultivar;small round fruit.

wild/weedy ;prickly.

weeds; hairy-prickly,low atid stranggiinghabit.

truly wi ld ; ovate

broad-leaved.

truly wild; lanceolatebroad-leaved.

truly wild; elongated.narrow leaved.

truly wild; elongated.broad leaved.

truly wild; broad-lanceolate, narrowleaved

truly wild; broad-lanceolate, narrowleaved

truly wild; broad-lanceolate, narrowleaved.

truly wild; broad-lanceolate, narrowleaved.

truly wild

truly wild

truly wild

truly wild

wild/weedy

Country of origin

United Kingdom

Thiland

Malaysia

Malaysia

Malagasay

India

Israel

South Africa

Zambia

Zimbabwe

Kenya

Kenya

Uganda

Tanzania

Upper Volta

Bostwana

South Australia

South Africa

Malaysia

surrounding the lumen were more invaginated shallow and narrow which might be due to morethan in others. For some accessions, such as extensive secondary cell wall thickening.S.1782, S.1518 and RNL336 (Figure 2), the cell The fibrils surrounding each cell werelumen or pore was relatively deep, but in some strands of lignified thickening in the radial walls ofothers such as S.2052 (Figure 2) the lumens were the epidermal cell (Edmonds 1983), which arise

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SAVED MOHAMED ZAIN HASAN AND RICHARD N. LESTER

S.2426 S. 2444

S.2424 S. 2458

S. 2310 S. 1554

Figure 1: Seed surface micrographs for several accessions of S. me 1 ongvna

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COMPARATIVE MICROMORPHOLOGY OF SEED SURFACE OF S. MELONGENA L.

S. 1518

mmm&P3Z

S. 0931

S.1782

S. 2024

Figure 2: Seed surface micrographs for several accessions ofS. incanum

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SAVED MOHAMKD ZAIN HASAN AND RICHARD N. LESTER

Solatium at (hio/ticum Solo Hum hunt h

Solatium (///tit urn kwfbense

•

1 : ^

Solatium torvum

figure J: Seed surface micrographs for several others species in genus Sola num.

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COMPARATIVE MICROMORPHOLOGY OF SEED SURFACE OF S. MELONGENA L.

from pyramid-shaped bases. These structuresshowed considerable variation both between andwithin S. melongena, S. incanum and the otherspecies.

The fibrils of some accessions extend asthickenings of the outer tangential wall, giving anet-like structure, such as those found in S.2426,S.2458 and S.2310 {Figure 1). In some otheraccessions, including S.2024 and RNL336 [Figure2), the fibrils were long, curved and irregularlyspread, Accessions S.1501, S.0931, S.0859 [Figure2), S.2424 and S.2444 (Figure 1) have short ormedium-length fibrils which were mostly upright.However, variation in fibril structure was alsoaffected by the efficiency of the etching treatmentby the enzyme. Careful and detailed observationsof the fibril structures of the seed coat failed todistinguish consistently between seed of S. me-longena and S. incanum nor between them and theother species examined, confirming that there wasgeneral similarity between them.

This uniformity in seed coat characters notonly indicates the coherence of these species, butthat these characters are of little taxonomic valuein discriminating within this species complex,Edmonds (1983) came to a similar conclusionbased on the results of her study on seed surfacestructure in taxa belonging to Solanum sectionSolarium, where again many morphologically-distinct species had similar seed surface features.

Nevertheless, seed coat structure may yetprovide useful taxonomic characters at thesectional and generic levels. This study indicatesthat the seed surface structure of S. torvum Sw.[Figure 3) in section Torvaria is completelydifferent from the other species surveyed, havingconvoluted cells walls with a sinuous pattern. Celllumens and fibril are also lacking.

S.kwebense Br. & VVr. and S.cinereum R.Br.(Figure 3) in section Oliganthes are also distinguish-able from the other species examined. But they aresomewhat similar to each other in size and shapealthough the convolutions are more invaginatedin S.cinereum .

The seed coats of S.aethiopicum L. andS.tomentosum L. (section Oliganthes) [Figure 5), arerather different from those of S. melongena-S.incanum complex, although they are similar insome aspects such as cell size.

CONCLUSIONThe micromorphological variation in seedsurfaces failed to distinguish S. melongena fromS.incanum indicating that these highly variabletaxa belong to the same closely-knit group.However, from the small sample examined, seedcoat microstructure may be useful in theidentification and classification of the sectionaland generic levels in the Solanaceae .

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( Received 6 September, ig8g)

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