ABSTRACT
Pollen grains of nine taxa of five genera of the tribe Trifolieae of subfamily Papilionoideae, including Ononis serrata and O. vagineiles have been investigated. Using both Light Microscope (LM) and Scanning Electron Microscope (SEM) to evaluate the comparative morphology of the pollen in the tribe. The morphology of the pollen grains shows that they are radially symmetrical, isopolar trizonocolporate, with perforate tectum and varying shape and sculpture. Based on tectum structure, four distinct pollen types viz., Melilotus sp. (tectate perforate, reticulate and pore distinct), Trigonella sp. and Medicago sp. (tectate imperforate, reticulate, verrucate and pore indistinct), Trifolium sp. (semi-tectate, reticulate and pore indistinct) and Ononis sp. (tectate perforate, regulate and pore distinct) are distinguished. The pollen morphology of these taxa shows that Trifolieae is eurypalynous tribe. These data may be support the earlier separation of the genus Ononis from the tribe Trifolieae in a separate tribe Ononideae. Furthermore, these results helps establish the taxonomic position of the species within the tribe.
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DOI: 10.3923/ijb.2006.270.277
URL: https://scialert.net/abstract/?doi=ijb.2006.270.277
INTRODUCTION
Fabaceae comprises three subfamilies namely; Caesalpiniodeae, Mimosoideae and Papilionoideae. The last is split into 10 tribes including Trifolieae (Randle, 1952; Willis, 1967). However, Polhill (1981) reported that the Papilionoideae is subdivided into 31 tribes including the Trifolieae. Lersten and Gunn (1982) reported that the tribe Trifolieae contains 7 genera including Factorovskya Eig, Medicago L., Melilotus Mill., Ononis L., Parochetus Buch. Ham. ex D. Don., Trifolium L. and Trigonella L. Except for Parochetus the remaining six genera are among the Egyptian flora (Montasir and Hassib, 1956; Taeckholm, 1974). The delineation of the tribe Trifolieae is largely disputed in the literature (Zohary and Heller, 1984). Schulz (1901) divided the tribe Trifolieae into two subtribes: the Trifolieae comprising Ononis, Parochetus and Trifolium and the Trigonelleae with Trigonella, Melilotus and Medicago. Heyn (1981) argued that the Ononis and Parochetus are distinct and that their inclusion in the Trifolieae is doubtful. Ascherson and Graebner (1908) also divided the tribe Trifolieae into two subtribes: the Ononidnae with the stamens all united, comprising only Ononis and the Trifoliinae with diadelphous stamens comprising the genera Trifolium, Melilotus, Medicago and Trigonella. Melchier (1964) grouped the genus Trifolium with, Parochetus, Trigonella, Medicago and Melilotus within the tribe Trifolieae but excluded Ononis from the tribe. Melchier (1964) and Gupta (1980) supported the placement of the genus Ononis in a separate tribe, Ononideae, depending upon the presence of the dimorphic anthers and moniliform staminal tube in the flowers of Ononis repens and O. spinosa. The recent floristical accounts tend to accept the tribe Trifolieae without Ononis (Davis, 1970; Zohary, 1972; Townsend, 1974). George and Hussein (2002) supported also the placement of Ononis in separated tribe, due to the presence of dissimilarity among the studied of species Ononis from those of the other genera of the Trifolieae depending upon the seed proteins analysis and or the chromosome number. Ferguson and Skvarla (1983) reported that pollen grains of Papilionoideae have wide range of transition forms of granular interstitial. Gautam and Vijayaraghavan (1991) described the cohesion of the pollen grains through exinal connection in Melilotus indica. Ming-Jau and Tseng-Chieng (1999) studied the pollen morphology and seed of Trigonella hamosa by SEM that represents as new record to the flora of Taiwan. Gillett et al. (1973) described the pollen grains of 45 American Trifolium species with aid of LM and SEM and provided a key of their identification. Kamel (1992) studied the macr-and micro- morphology of genus Trifolium in Egypt. The revision revealed the presence of 18 species. A comparative study on the Egyptian species of genus Trigonella showed the presence of 10 species belonging to five sections (Hassan, 1992). Gazar (2003) studied the pollen morphology of 28 species belonging to three genera (Melilotus, Trifolium and Trigonella) of subfamily Papilionoideae in Egypt to establish the taxonomic position of the species within their genera. Furthermore, the value of comparative studies of pollen grain morphology in solving many taxonomic and phylogenetic problems has been demonstrated by some workers (El-Ghazaly, 1981; El- Ghazaly and Chaudhary, 1993; Vinckier et al., 2000; Lashin, 2003). No attempts have been made earlier to examine the range of morphological variation in the pollen of Trifolieae in Egypt except Gazar (2003). The SEM of pollen grains has been used in many of systematic studies. Here we analyze the variability of pollen grains using SEM and LM to reassess species relationships among genera of the subfamily Papilionoideae. The present study aims to investigates the ultra-structure and comparative morphology of the pollen grains in nine taxa, of tribe Trifolieae including Ononis. Also to use these data to clarify their taxonomic position within the tribe. Furthermore to evaluate the exclusion of genus Ononis from the tribe Trifolieae.
MATERIALS AND METHODS
Polliniferous material from the species listed in Table 1 was prepared for examination with both light and scanning electron microscope as follows:
Light Microscope (LM): Polliniferous material were placed in glacial acetic acid for three minutes and then acetolysed according the method of Erdtman (1960) and Faegri and Iverson (1975), resdue was mounted in glycerin jelly and examined using a CH2 Olympus microscope.
Scanning Electron Microscope (SEM): Dried polliniferous material was attached to stubs with double-faced selotape. The stubs were gold coated in B sputter coater for one minute and examined representative pollen grains were photographed at various magnifications in a Jeol T 100 SEM operated at an accelerating voltage of 15 kv. The investigated taxa are shows in Fig. 1-15 and Table 2. The material and the slides were stored in the department of Botany, Faculty of Sciences, Zagazig University.
RESULTS
A summary of pollen dimensions, exine structure, apertures and sculpture is provided at Table 2. Measurements are based on examination of ten specimens. Descriptive terminology of the pollen grains follows Erdtman (1966, 1969) and Erdtman et al. (1961).
Table 1: | The collections of the investigated species of Trifolieae between March and June (1999-2000) from Egypt |
Table 2: | Pollen morphology: Dimensions, shape class and shape (by using LM and SEM) among the examined species (the main size and range for each characters are present) |
POLLEN GRAINS DESCRIPTION
All pollen grains of the studied taxa are tricolporate.
1-Medicago sativa, x2000 (Fig. 1)
English name: Maina, Lucerne or Alfalfa.
Arabic name: Barseem Hegazi
LM
Pollen grain is subsphaeroidal to subprolate, rounded and semi-angular amb. Colpi irregular with slightly tapering ends in equatorially constricted, pore indistinct.
Exine: 1.3 μm thick. Sexine thicker than nexine, faintly perforate, microreticulate, columlla regularly distributed. Reticulum homobrochate.
SEM
Apertures: Colpus margin irregular, thick in the Os region.
Pore indistinct, due to the presence of equatorial constrictions of ectoaperture and slightly sunken (non-leveled).
Exine: Sexine tectate, nanoverrucae scattered over the surface of the grains densely spaced minute faint unevenly distributed perforation.
Comment: A common animal food plant in Egypt. The pollen grains are distinguished by their comparatively long polar axis (27.5 μm), rounded ends, exine tectate-verrucate (psilate) with large mesocolpia and sexine protruding over ora and in some cases fused to form a bridge.
2-Melilotus indicus, x2000 and x3500. (Fig. 2 and 3)
English name: Ban Methi or Sweet clover.
Arabic name: Nafal, Handakouk or Etrah.
LM
Pollen grain is subsphaeroidal to subprolate pollen with circular amb. Colpi with tapering ends equatorially constricted, tectate perforate, columella regular distribution, pore distinct and lalongate (4x5 μm).
Exine: 1.5 μm thick. Sexine thicker than nexine, microreticulate.
Reticulum homobrochate.
SEM
Apertures: Colpus margin regular, thick in the Os region and the membrane of endoaperture is indistinct.
Exine: Sexine tectate, perforate. Perforation, irregular in shape. Lumina vary in shape and size decreasing in size towards the colpi margin.
Comment: A common weed plant in Egypt. The pollen grains are distinguished by their comparatively short polar axis (22 μm), tapering ends and sexine tectate-erforates.
3-M. messanensis, x3500 (Fig. 4 and 5)
Sy. M. siculus
Arabic name: Nafal or Etrath
LM
Subprolate pollen, rounded triangular to trilete amb. Colpi with tapering ends equatorially constricted.
Exine: 1.6 μm thick. Sexine thicker than nexine, microreticulate, tectate-perforate columella more regular and pore indistinct.
Reticulum homobrochate.
SEM
Apertures: Colpus margin slightly irregular, thick in the Os region; colpus membrane covered with granular of varying size and shape.
Exine: Sexine tectate, perforate. Perforation irregular shape, membrane towards the colpus become psilate or verrucate.
Comment: It's common weed plants in Egypt. The pollen grains are distinguished by their comparatively long polar axis (43.75 μm) tapering ends and colpi margin granulate of varying size and shape.
4-Ononis serrata, x5000 (Fig. 6)
Arabic name: Zetab
LM
Pollen grain subprolate and irregular rounded amb. Colpi with tapering ends Equatorially constricted and tectate perforate and columellae are regular distributed, pore rounded or lalongate (3.5x4 μm).
Exine: 1.5 μm thick. Sexine thicker than nexine, microreticulate.
Ornamentation heterobrochate.
SEM
Apertures: Colpus margin irregular, thick in the Os region; membrane of endoapertures indistinct.
Exine: Sexine tectate, regulate. Perforation faintly minute, circular, beset of minute spinulose varying size.
Comment: A rare plant of the flora of the Northern Coast of Egypt. The pollen grains are distinguished by their comparatively short polar axis (21.75 μm) and perforation minute and shallow.
5-O. vagineiles, x5000 (Fig. 7 and 8)
Arabic name: Zetab
LM
Pollen grains prolate and rounded or triangular amb. Colpus with tapering end, equatorially constricted. Pore lalongate or circular (3x4 μm).
Exine: 1.5 μm thick. Sexine thicker than nexine, tectate faintly perforate and microreticulate. columella faintly more or less distinct regularly distributed.
Reticulum homobrochate.
SEM
Apertures: Colpus margin slightly irregular, thick in the Os region; the membrane of endoaperture is covered with grana of varying size and shape.
Exine: Sexine tectate, perforate. Perforation minute, narrow or indistinct.
Comment: A common plant of the flora of the Northern Coast of Egypt (Montasir and Hassib, 1956; Taeckholm, 1974). The pollen grains are distinguished by their comparatively long polar axis (40 μm), sexine tectate and microreticulate.
Fig. 1: | Medicago sativa L. distal polar view, x 2000 |
Fig. 2 and 3: | Melilotus indicus L. distal polar view, All x 2000 and x 3500 |
Fig. 4 and 5: | M. messanensis L. equatorial view, all x 3500 |
Fig. 6: | Ononis serrata forssk, distal polar view, x 5000 |
Fig. 7: | O. vagineiles Vahl. polar view, x 5000 |
Fig. 8: | O. vagineiles Vahl. distal polar view, x 5000 |
Fig. 9-11: | Trifolium alexandrinum L. distal polar view, All x 2000, 3500 |
Fig. 12: | T. resupinatum L. equatorial view, x 3500 |
Fig. 13 and 14: | Trigonella foenum graecum L. distal polar view, All x 2000, 3500 |
Fig. 15: | Trigonella stellata L. equatorial view, x 3500 |
6-Trifolium alexandrinum, x2000 (Fig. 9-11)
Arabic name: Barseem Messqawi.
LM
Pollen grain prolate/subprolate and rounded amb. Colpus with tapering ends, equatorially constricted and pore indistinct.
Exine: 1.5 μm thick. Sexine thicker than nexine, microreticulate, columella indistinct and semi-tectate.
Reticulum heterobrochate.
SEM
Apertures: Colpus margin irregular, thick in the Os region; the membrane of endoaperture is covered with grana of varying size and shape.
Exine: Sexine semi-tectate reticulates. Perforation indistinct.
Comment: A common cultivated plant in Egypt. The pollen grains are distinguished by their comparatively long polar axis (26.25 μm) rounded ends and sexine semi-tactate and perforation indistinct.
7-T. resupinatum, x3500 (Fig. 12)
Arabic name: Barseem- Shaftala-or Shatalah
LM
Pollen grain prolate and rounded, triangular amb. Colpi with tapering ends, equatorially constricted and pore indistinct.
Exine: 1.5 μm thick. Sexine thicker than nexine, tectate, perforates and columella more regular distribution.
Reticulum heterobrochate.
SEM
Apertures: Colpus margin irregular, thick in the Os region; membrane pislate.
Exine: Sexine tectate, perforate. Perforation large, scattered, beset in shallow, slit-like concavities or circular of varying size.
Comment: A common cultivated plant in Egypt. The pollen grains are distinguished by their comparatively short polar axis (20.50 μm), rounded ends and perforation large and irregular.
8-Trigonella foenum graecum, x2000, 3500 (Fig. 13 and 14)
English name: Methi or Funm greek.
Arabic name: Helbaa.
LM
Pollen grain prolate and rounded triangular amb. Colpi with tapering ends, equatorially constricted. Pore indistinct.
Exine: 1.5 μm thick. Sexine thicker than nexine, microreticulate, tectate perforate, columella irregular distributed.
Reticulum heterobrochate.
SEM
Apertures: Colpus margin irregular, thick in the Os region; membrane covered with grana of varying size and shape.
Exine: Sexine tectate, perforate. Perforation minute, circular, slit-like concavities of varying size rare in mesocolpium.
Comment: A common human food plant in Egypt. The pollen grains are distinguished by their comparatively long polar axis (30.0 μm) and rounded ends.
9-Trigonella stellata, x3500 (Fig. 15)
Arabic name: Helbaa.
LM
Pollen grain prolate and rounded amb. Colpi with more tapering ends equatorially constricted and pore less distinct.
Exine: 1.5 μm thick. Sexine thicker than nexine, tectate perforate and columella regularly distributed.
Reticulum homobrochate.
SEM
Apertures: Colpus margin regular, thick in the Os region; membrane covered with grana elements (granules).
Exine: Sexine tectate, perforate. Perforation minute, circular, narrow slit-like concavities of varying size absent near colpi margin.
Comment: A common weed plants in Egypt. The pollen grains are distinguished by their comparatively long polar axis (21.10 μm) and rounded ends.
DISCUSSION AND CONCLUSION
Ferguson and Skvarla (1983) were studied the pollen morphology of many Papilionoideae tribes. The Papilionoideae have a wide range of granular types in genera and tripes. The subfamily Papilionoideae have highly advanced in general macromorphology and other cryptic characters, as for example, chromosome number and distribution of concavanine. The pollen of these subfamily also show a wide range of specialized characters including trend from spheroidal in shape to breviax increase in aperture number in some cases, increase in relative thinking of the endexine and reduction to loss of the foot layer (Ferguson and Skvarla, 1983). Gazar (2003) was studied the genera Trifolium, Trigonella and Melilotus from Egypt. Ononis has been many pollen morphology and macromorphology differences form another taxa in this tripe (Ascherson and Graebner, 1908). Cytologically its different in chromosome number from the other members of the tribe (George and Hussein, 2002). The results obtained from the present work, sheds light on the taxonomic status among the taxa of tribeTrifolieae based on their pollen characters attributes. On the basis of pollen shape class (P/E ratio), there are three distinct pollen types viz., Type 1 (1.33 subprolate-prolate) Trigonella sp., Type 2 (1.22 subprolate) Melilotus, Medicago and Trifolium sp. Type 3 (1.11 prolate-spheroidal) Ononis sp. is recognized. The pollen morphology is closely related to its function. Most wind pollinated angiosperms produce pollen grains size ranging from 20-40 μm (White, 1969). Size differences were noticed but no comments were made because size can and dose varies between different geographical localities of the same species (Rao and Tian,1974) or under different environmental conditions (Jones and Newell, 1942). On the basis of shape in equatorial view four distinct types viz., Type 1: oval-elliptic (Melilotus and Medicago sp.). Type 2: oblong (Trigonella sp.). Type 3: subcircular (Trifolium sp.). Type 4: elliptic (Ononis sp.) are recognized. The generally oblong shape (breviax) and smooth exine surface of pollen of anemophlious angiosperms are adaptations best suited to wind pollination (Muller, 1979). On the basis of tectum perforation, three distinct pollen types viz., Type 1: tectate perforates (Melilotus and Trigonella sp.). Type 2: tectate (Ononis and Medicago sp.), this agrees with earlier finds concerning Ononis (Moore et al., 1991), Type 3: Semi-tectate with few minute perforates (Trifolium sp.) are distinguished. The data support earlier studies on Trifolieae by Zohary and Heller (1984) and Gazar (2003). On the basis of the exine sculpturing types, three distinct pollen types viz. Type1: sculpturing reticulates, (Melilotus, Trifolium and Trigonella). Type 2: verrucates (Medicago). Type 3: regulates (Ononis) are recognized. The output of the present study could be outlined as follows: The correlation of pollen morphology in these taxa show that the genus Onoins supports the utility of the pollen evidence that largely accords to the earlier separation of the genus Ononis from the tribe Trifolieae (Ascherson and Graebner, 1908; Gupta, 1980). Furthermore, the pollen characters proved their value for delimitation of the examined taxa at the specific levels respectively. Eventually, it could be concluded that the pollen characters attributes of the species relationships in the tribe. However, there is much scope for more experimental work encompassing the rate of the pollen in total biological system (Ferguson and Skvarla, 1983).
Key of the Investigated Taxa
1- | Tectat minute perforate and exine regulate sculptures.............Ononis. |
• | Tectat perforate and exine not regulate sculptures...............2 |
2- | Exine reticulate sculptures and equatorial axis less than or equal 21.25 μm...............Trigonella. |
• | Exine reticulate sculptures and equatorial axis more than 21.25 μm...............3. |
3- | Pollen shape in E.v. is subcircular...............Trifolium. |
• | Pollen shape in E.v. is not as above...............4. |
4- | Exine verrucate and equatorial axis less than or equal 22.5 μm...............Medicago. |
• | Exine not as above...............5. |
5- | Colpi margin regulate, pore distinct and homobrocate reticulation...............Melilotus. |
ACKNOWLEDGMENTS
My grateful thanks to Prof. A. Badawi and Ass. Prof. M. Murad Department of Botany, Faculty of Sciences, Ain Shams University for reviewing the initial draft of this contribution also for their many valuable suggestions in her thorough and perceptive reviews. I wish also to thank Dr. Hussein A. Hussein Department of Botany, Faculty of Sciences, Zagazig University, Egypt for the identification of field specimens and his constant interest in the present study.
REFERENCES
- Erdtman, G., 1960. The acetolysis method: A revised description. Svenok. Bot. Tidskr, 54: 561-564.
Direct Link - Erdtman, G., 1966. Pollen Morphology and Plant Taxonomy: Angiosperms. Hafner Publication Company, New York.
Direct Link - Ferguson, I.K. and J.J. Skvarla, 1983. The granular interstitium in the pollen of subfamily Papilionoideae (leguminosae). Am. J. Bot., 70: 1401-1408.
Direct Link - Gautam, N.S. and M.R. Vijayaraghavan, 1991. Aggregation of pollen grains in Melilotus indica. Proceeded. Indian Nat. Sci. Acad., Part B, Biolog. Sci., 57: 413-416.
Direct Link - Ming-jou, W. and H. Tseng-Ching, 1999. Notes on the flora of Taiwan. (34) Trigonella hamosa forssk. (Leguminosae). Taiwania, 44: 376-383.
Direct Link