International Journal of Botany

Year: 2007 | Volume: 3 | Issue: 3 | Page No.: 276-282
DOI: 10.3923/ijb.2007.276.282

Foliar Epidermal Studies, Organographic Distribution and Taxonomic Importance of Trichomes in the Family Solanaceae

O. Adedeji, O. Y. Ajuwon and O. O. Babawale

Abstract: The leaf epidermal and organographic distribution of trichomes studies were carried out on nine species in four genera in the family Solanaceae. Distinctive anatomical characters which indicate close inter-relationship amongst the genera and species include presence of trichomes on leaf epidermal surfaces, petiole, stem, pedicel, sepal and petal surfaces, amphistomatic leaf surfaces, anisocytic to anomocytic stomatal types, polygonal, occasionally irregular epidermal cell shape on the adaxial epidermal surfaces and generally lower number of stomata on the adaxial surface. Some characters can be used to separate the genera within the family and also the species within each genus. These include anticlinal walls on the adaxial and abaxial epidermal surfaces, stomatal types in addition to the basic anisocytic to anomocytic stomatal complex types. S. nigrum in the genus Solanum has the highest number of stomatal types. Noteworthy is the presence of protrusions on the stomata of the species in the genus Lycopersicon which is absent in the species of the other genera. The different trichome types have differing organographic distributions within the same species and within the same genus in the family. This can be useful in the identification of the species and even their corresponding organs such as leaf, stem, petiole, etc. which would be of interest to pharmacognosists, archaeobotanists, palaeobotanists and agronomists. Capsicum annuum can be separated from C. frutescens and C. chinense on the basis of the organographic distribution of the trichomes. Solanum torvum is the only species in the genus Solanum and in the species of the family Solanaceae studied with stellate non-glandular trichomes on the adaxial and abaxial epidermal surfaces. The spine-like non-glandular trichome type observed in Lycopersicon pimpinellifolium was completely absent in all the plant parts of Lycopersicon lycopersicum cv Roma VF. This can be used to delimit the two species in the genus. The unique bicellular to multicellular stalk glandular trichomes of Nicotiana tabacum, a mono-species genus in Nigeria are reported. They are believed to be responsible for the unique smell that emanates from N. tabacum. The genus Nicotiana is the only genus in the family with multicellular stalk glandular trichomes.

Keywords: multicellular stalk, Trichomes, stomatal types, Solanaceae and Lycopersicon

INTRODUCTION

Only eight genera of the family Solanaceae are reported in West Africa and in Nigeria (Hutchinson and Dalziel, 1958). Generally, the family is herbaceous or woody. Many plants in the family are economically important. Products include potato and eggplant (Solanum sp.) and tomato (Lycopersicon lycopersicum Linn.). Edible fruits can be found in the genus Physalis (Cape gooseberry, Jamberry, Sugar cherry, Chinese lantern etc., according to the species and variety), Capsicum (sweet and chilli peppers), etc. Most produce poisonous alkaloids and some are commercially important in this connection (Nicotiana, Datura).

The taxonomic value of epidermal morphology is well documented in botanical literature, Dilcher (1974), Jayeola et al. (2001), Adedeji and Faluyi (2001), Adedeji (2004) and Adedeji and Illoh (2004). Metcalfe and Chalk (1950) gave some description of the general anatomy of the family Solanaceae. Since then there has been no additional anatomical work on the family in Nigeria.

Trichomes have long been of considerable importance in comparative investigations in angiosperms. They are frequently present, easily observable and have often been found to have variation patterns which correlate with other features of the taxa under investigation (Cutler, 1969). Rao and Ramayya (1977) used the structure and distribution of trichomes to separate two species of Malvastrum in India. Inamdar et al. (1990) also reported the structure, ontogeny, organographic distribution and taxonomic significance of trichomes in the family Cucurbitaceae. There is no report on the organographic study of trichomes in the family Solanaceae.

To redress the scanty information available, the observations on the foliar epidermal anatomy and organographic trichome distribution of the family Solanaceae are reported.

MATERIALS AND METHODS

For the purpose of this research, nine species in four genera in the family Solanaceae were collected. Capsicum frutescens Linn., Lycopersicon pimpinellifolium (Jusl.) Mill., Solanum macrocarpon Linn., Solanum torvum Sw., Solanum nigrum Linn. and Nicotiana tabacum Linn. were collected from the wild in Ile-Ife, Osun State, Nigeria. The cultivated species Capsicum chinense Jacq., Capsicum annuum Linn. and Lycopersicon lycopersicum cv. Roma VF Linn. were collected from Nigeria Horticultural Institute (NIHORT), Ibadan, Oyo State, Nigeria.

Fresh specimens of all the species were used. The epidermal layers were isolated by maceration of leaf segments in Jeffrey’s maceration mixture (10% chromic acid and bench concentrated hydrochloric acid). The isolated layers were rinsed in water, stained in 1% aqueous Safranin and mounted in glycerine for microscopic study.

Mature trichomes were studied in epidermal peels of different plant parts, stained with safranin and mounted in 70% glycerine.

RESULTS

Capsicum chinense Jacq.: Epidermal cells polygonal to irregular in shape with undulating anticlinal walls on adaxial surface (Fig. 1A), irregular with sinuous anticlinal walls on the abaxial surface (Fig. 2A). Amphistomatic leaf surfaces, stomata largely anisocytic to anomocytic, occasionally brachy-paracytic (Fig. 3A, B and D), circular, occasionally elliptic in shape; stomatal size-adaxial 437.50-687.50 μm², abaxial 450.10-675.75 μm²; stomatal index-adaxial 3.96-15.81%, abaxial 16.25-32.29%.

Trichomes: (Table 1; Fig. 4B, C, F, H and J, Fig. 6S₅): Epidermal surfaces-unicellular, bicellular non-glandular, stalked glandular; petiole-non-glandular bicellular, multicellular; stem- non-glandular bicellular, multicellular; pedicel-non-glandular multicellular; sepal-largely non-glandular bicellular, multicellular, stalked glandular; petal-largely unicellular and bicellular non-glandular.

Capsicum annuum Linn.: Epidermal cells polygonal to irregular in shape with straight to wavy anticlinal walls on the adaxial surface (Fig. 1B), irregular with wavy to slightly undulating walls 33.60-61.60 μmlong and 22.40-42.00 μm wide on the abaxial surface (Fig. 2B).

Amphistomatic, stomata anisocytic to anomocytic, occasionally brachy-paracytic (Fig. 3A, B and D), circular to elliptic in shape; stomatal size-adaxial 400.20-675.50 μm², abaxial 350.50-618.75 μm²; stomatal index-adaxial 13.19-19.41%, abaxial 25.35-31.32%.

Trichomes: (Table 1; Fig. 4F, H and J, Fig. 6S_4-6,9): Epidermal surfaces- non-glandular trichomes absent, only stalked glandular trichomes with long unicellular stalks present; petiole-non-glandular bicellular, multicellular; stem-largely non-glandular multicellular; pedicel-non-glandular multicellular; sepal-stalked glandular largely, occasionally, non-glandular bicellular; petal-non-glandular bicellular, multicellular.

Capsicum frutescens Linn.: Epidermal cells polygonal to irregular with sinuous anticlinal walls on the adaxial surface (Fig. 1C), irregular with sinuous anticlinal walls on the abaxial surface (Fig. 2C).

Leaf surfaces amphistomatic, stomata largely anisocytic, occasionally anomocytic, (Fig. 3A and B), circular in shape; stomatal size-adaxial 405.20-902.41 μm², abaxial 505.21-812.50 μm², stomatal index-adaxial 9.09-20.26%, abaxial 23.33-37.30%.

Trichomes: (Table 1; Fig. 4B, C, F, H, J, K, M and N; Fig. 6S_3-5): Epidermal surfaces-non-glandular unicellular and multicellular, stalked glandular with long unicellular stalks; petiole- non-glandular multicellular; stem- non-glandular multicellular, stalked glandular occasionally; pedicel- non-glandular multicellular; sepal- non-glandular bicellular, multicellular; petal- non-glandular- bicellular, multicellular present.

Lycopersicon pimpinellifolium (Jusl.) Mill: Epidermal cells polygonal to irregular in shape with undulating anticlinal walls on adaxial surface (Fig. 1D), irregular with sinuous anticlinal walls on the abaxial surface (Fig. 2D). Amphistomatic leaf surfaces, stomata anomocytic to anisocytic (Fig. 3A and B); elliptic to circular in shape with small protrusions at both ends; stomatal size-adaxial 670.80-996.41 μm², abaxial 485.65-1,005.74 μm²; stomatal index-adaxial 2.04-10.62%, abaxial 16.06-19.64%.

Trichomes: (Table 1; Fig. 4A, C, D, F, G, H, I and J; Fig. 6S_1-5): Epidermal surfaces- non-glandular spine-like, unicellular hooked and bicellular, stalked glandular; petiole- non-glandular bicellular, multicellular; stem- non-glandular bicellular, multicellular; pedicel- non-glandular multicellular largely, occasionally stalked glandular; sepal- short prickle-like, bicellular and multicellular non-glandular; petal- largely bicellular non-glandular and stalked glandular.

Lycopersicon lycopersicum cv. Roma VF. Linn.: Epidermal cells polygonal to occasionally rectangular with wavy to undulating anticlinal walls on the adaxial surface (Fig. 1E), irregular with sinuous anticlinal walls on the abaxial surface (Fig. 2E). Leaf surfaces amphistomatic, stomata complex types anomocytic to anisocytic (Fig. 3A and B), elliptic to circular in shape with small protrusions; stomatal size-adaxial 702.12-1,408.02 μm², abaxial 565.10-1,578.09 μm²; stomatal index-adaxial 8.57-14.81%, abaxial 17.19-28.87%.

Trichomes: (Table 1; Fig. 4B-H and J; Fig. 6S_3,5,8): Epidermal surfaces- non-glandular unicellular, unicellular hooked, bicellular, multicellular and stalked glandular; petiole- unicellular, multicellular non-glandular, stalked glandular occasionally; stem- non-glandular unicellular, bicellular, multicellular and stalked glandular; pedicel- non-glandular bicellular, multicellular occasionally stalked glandular; sepal- non-glandular, bicellular, multicellular occasionally stalked glandular; petal-non-glandular unicellular, bicellular and multicellular.

Solanum macrocarpon Linn.: Epidermal cells polygonal in shape with straight to slightly wavy anticlinal walls on the adaxial surface (Fig. 1F), irregular with undulating to sinuous anticlinal walls on the abaxial surface (Fig. 2F). Amphistomatic leaf surfaces, stomatal type anisocytic to anomocytic, occasionally brachy-paracytic (Fig. 3A, B and D), largely circular in shape, occasionally elliptic; stomatal size-adaxial 393.73-520.50 μm², abaxial 394.50-500.65 μm²; stomatal index-adaxial 13.53-16.23%, abaxial 22.57-30.20%.

Trichomes: (Table 1; Fig. 4B, C, H and J; Fig. 6S_3,5): Epidermal surfaces- stalked glandular only; petiole- stalked glandular largely, occasionally non-glandular unicellular; stem-unicellular non-glandular largely, stalked glandular occasionally present; pedicel- unicellular and multicellular non-glandular; sepal-unicellular, non-glandular and stalked glandular; petal-bicellular non-glandular and stalked glandular occasionally present.

Solanum torvum Sw.: Epidermal cells polygonal to rectangular in shape with straight to wavy anticlinal walls on the adaxial surface (Fig. 1G), irregular with sinuous anticlinal walls on the abaxial surface (Fig. 2G). Amphistomatic; stomatal type largely anisocytic, occasionally anomocytic and brachy-paracytic (Fig. 3A, B and D), elliptic to occasionally circular in shape; stomatal size-adaxial 301.10-481.25 μm², abaxial 295.67-458.25 μm²; stomatal index-adaxial 2.01-7.40%, abaxial 4.88-18.63%.

Trichomes: (Table 1; Fig. 4B, C and F; Fig. 5O-R; Fig. 6S₃): Epidermal surfaces- stellate non-glandular (triradiate, tetraradiate or H-shaped and multiradiate types), short stalked glandular; petiole- stellate non-glandular; stem- stellate non-glandular, occasionally stalked glandular; pedicel-stellate non-glandular; sepal- unicellular, bicellular non-glandular occasionally, largely stellate; petal- largely stellate, occasionally unicellular, bicellular non-glandular.

Solanum nigrum Linn.: Epidermal cells polygonal with undulating anticlinal walls on the adaxial surface (Fig. 1H), irregular with sinuous anticlinal walls on the abaxial surface (Fig. 2H). Amphistomatic; stomatal type largely anisocytic occasionally paracytic, diacytic, hemi-paracytic and anomocytic (Fig. 3A, B, C and F), largely elliptic occasionally circular in shape; stomatal size-adaxial 700.50-937.60 μm², abaxial 375.50-787.50 μm²; stomatal index-adaxial 12.16-22.51%, abaxial 24.48-33.54%.

Trichomes: (Table 1; Fig. 4B, C, F, H and J; Fig. 6S_5-7): Epidermal surfaces- largely stalked glandular; petiole- unicellular, bicellular and multicellular non-glandular, occasionally stalked glandular; stem- unicellular, bicellular, multicellular non-glandular and stalked glandular; pedicel- unicellular, bicellular, multicellular non-glandular and stalked glandular occasionally; sepal- unicellular, bicellular, multicellular non-glandular and stalked glandular; petal- largely unicellular and bicellular non-glandular trichome types.

Nicotiana tabacum Linn.: Epidermal cells polygonal to irregular with straight to undulating anticlinal walls on the adaxial surface (Fig. 1I), irregular with sinuous anticlinal walls on the abaxial surface (Fig. 2I). Amphistomatic; stomatal type anisocytic to anomocytic (Fig. 3A and B), largely circular occasionally elliptic in shape; stomatal size-adaxial 675.00-962.50 μm², abaxial 624.20-897.65 μm²; stomatal index-adaxial 7.41-11.68%, abaxial 10.38-20.68%.

Trichomes: (Table 1; Fig. 4F, H and J; Fig. 6T_1-6): Epidermal surfaces- multicellular non-glandular and special type of long bicellular to multicellular stalk glandular trichomes; petiole- multicellular non-glandular and stalked glandular; stem- multicellular non-glandular present largely, very occasionally stalk glandular; pedicel- bicellular to multicellular stalk glandular trichome present in abundance; sepal- multicellular stalk glandular trichome present; petal- bicellular non-glandular and long stalked multicellular trichome types present.

DISCUSSION

Metcalfe and Chalk (1950) gave sparse report on the foliar epidermal anatomy of the family Solanaceae. Since then, there has been no additional study on the foliar anatomy of the family and none also on the organographic distribution of trichomes. This study is aimed at redressing the aforementioned knowledge gaps.

On the adaxial surface, the epidermal cell shape is generally polygonal, occasionally irregular to rectangular in all the species studied. Anticlinal cell wall pattern on the adaxial surface can be used to separate the species within each genus studied. Within the genus Capsicum, it is undulating in C. chinense, straight to wavy in C. cannuum and sinuous in C. frutescens. In the genus Lycopersicon, while it is undulating in L. pimpinellifolium, it is wavy to undulating in L. lycopersicum cv. Roma VF. Within the genus Solanum, it is straight to wavy in S. macrocarpon and S. torvum while it is undulating in S. nigrum. The anticlinal wall of the epidermal cells of Nicotiana tabacum a mono-species genus in Nigeria, is straight to slightly undulating. However, on the abaxial surface, the epidermal cells are generally irregular with sinuous anticlinal walls except in C. annuum where the anticlincal wall is wavy to undulating.

The leaves are amphistomatic. Generally the stomata are more on the abaxial surface than on the adaxial surface. Stomatal complex types are generally anisocytic to anomocytic, though more anisocytic to anomocytic in the species within the genera Solanum and Nicotiana. In addition to these two stomatal types, some other stomatal types were observed occasionally. Brachy-paracytic stomatal complex type was observed occasionally in C. chinense, C. annuum and S. macrocarpon, paracytic in S. torvum and S. nigrum only. Diacytic and hemi-paracytic stomatal types were observed in S. nigrum which happens to be the species with the highest number of stomatal types. Stomatal size, although quantitative is quite diagnostic. On the adaxial and abaxial surfaces, it is highest in the species within the genus Lycopersicon and lowest in Solanum torvum. Stomatal index is highly constant for a certain species and can be used for species delimitation (Olatunji, 1983). This may be due to the presence of a high density of stellate trichomes. Stomatal index is lowest on the adaxial and abaxial surfaces of S. torvum. Stomatal shape is also of diagnostic importance. It is largely circular, occasionally elliptic in the Capsicum genus, largely elliptic, often circular too in the Lycopersicon genus, circular to occasionally elliptic in the genus Nicotiana. In the genus Solanum, it is largely elliptic, occasionally circular in S. torvum and S. nigrum while it is largely circular, occasionally elliptic in S. macrocarpon. Small protrusions on the stomata of the species in the genus Lycopersicon separate the genus from the other genera in the family.

Trichomes are found in all the species of the family Solanaceae studied. They have been of considerable importance in comparative investigations in angiosperms. They are frequently present, easily observable and have often been found to have variation patterns which correlate with other features of the taxa under investigation (Cutler, 1969). Isawumi (1992) in his study on the genus Hibiscus used the structure and distribution of trichomes to classify the West African species of Hibiscus. Rao and Ramayya (1977) studied the organographic distribution of trichomes in two Indian species of the genus Malvastrum and used this to separate the two species.

In this study, a study of the organographic distribution of the trichomes of the species of the family Solanaceae show that both the types of trichomes and their distribution vary in the species within each genus. Basically two types occur, the stalked glandular and the non-glandular trichome types. The different types of trichomes have differing organographic distributions within the same species and within the genera in the family.

All the three species in the genus Capsicum are included in this study. In the genus, Capsicum annuum can be separated from Capsicum frutescens and Capsicum chinense on the basis of the organographic distribution of the trichomes. Whereas C. frutescens and C. chinense have both non-glandular and glandular trichome types on the adaxial and abaxial epidermal surfaces, Capsicum annuum has largely only the glandular trichome types.

In the genus Solanum, Solanum torvum is the only species with stellate non-glandular trichomes on the leaf adaxial and abaxial epidermal surfaces. Infact, it is the only species in the family that has stellate non-glandular trichomes on the adaxial, abaxial epidermal surfaces and other plant parts. Within the genus, S. macrocarpon and S. nigrum leaf epidermal surfaces are also characterized by presence of stalked glandular trichome largely. In the genus Lycopersicon on the other hand, L. lycopersicum cv. Roma VF and L. pimpinellifolium can be separated from each other on the basis of the type of and organographic distribution of the trichomes found in them. On the adaxial and abaxial leaf epidermal surfaces of L. pimpinellifolium, for the non-glandular trichome type, only the spine-like, unicellular and bicellular types can be found, multicellular non-glandular trichomes were completely absent whereas the multicellular non-glandular trichome type was found occurring in L. lycopersicum cv. Roma VF leaf epidermal surfaces. On the other hand, the organographic study of trichomes on other plant parts revealed that the multicellular non-glandular trichome type absent on the leaf epidermal surfaces of L. pimpinellifolium were found occurring in other parts like the petiole, stem, pedicel, sepal and petal. The spine-like non-glandular trichome type was completely absent in all the plant parts of Lycopersicon lycopersicum cv. Roma VF.

The trichome types of the species within each genus as noticed from their distribution are useful in distinguishing the species and even their corresponding organs such as leaf, stem etc. which would be of interest to pharmacognosists, archaeobotanists, palaebotanists and agronomists. Unique abundant bicellular to multicellular stalk glandular trichomes were observed in N. tabacum, a mono-species genus in Nigeria. They are believed to be responsible for the unique smell of N. tabacum.

REFERENCES