ABSTRACT
The research work was conducted to investigate the pollen morphology of twenty-two taxa of Origanum L., which had been described in accordance with their external-morphological characteristics and comparatively examined through the light and scanning electron microscopes (SEM). Each taxons had also been described palynologically. According to palynological data the pollens of Origanum L. showed reticulate and suprareticulate ornamentation. Chilocalyx section, that showed reticulate ornamentation, contained the taxons of O. bilgeri P. H. Davis, O. minutiflorum O. Schwarz and P. H. Davis and O. micranthum Vogel. O. husnucan-baserii Duman and AytaƧ was one of the taxons in Brevifilamentum section and this taxon also exhibited reticulate ornamentation, Suprareticulate ornamentation had been found in other taxons.
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DOI: 10.3923/ajps.2003.28.41
URL: https://scialert.net/abstract/?doi=ajps.2003.28.41
INTRODUCTION
The genus Origanum L. is a member of Labiatae family which has forty-one different species in the world, whereas in Turkey there are eight sections that include twenty-six taxa (O. calcaratum juss. and O. symes A. Carlstrom are excluded) (Heywood, 1985; Cronquist, 1982; Davis, 1982; Davis, 1982; Davis et al., 1988; Duman et al., 1995). The endemism is 57%.
There are limited number of studies in pollen morphology of Origanum L. Husain and Heywood (1982) have studied the pollen morphology of Origanum L. species. Varghese and Verma (1968) shortly mention about the light microscopic features of Origanum vulgare L. pollen grains. In this study, thirty different kinds of Origanum L., six of which grow in Turkey, are examined and their similar species are separated according to their pollen characteristic.
This study aims at contributing to the systematic problems of Origanum L. species, which are widely used in medicinal and aromatic plants.
MATERIALS AND METHODS
The pollens used in this study were obtained from the herbarium species as well as living species. Twenty-two taxa were examined in the years of 1997-1999; the number of herbarium collection used in this study and the locality of each species are given in Table 1. At least 30 pollen species from each taxon are scrutinized on light microscope. The pollen slides were made with the techniques of Erdtman (1960, 1969) and SEM. On the light microscope, pollen grains of each taxons per P, E, Clg and Clt were measured until the gausse curve is reached. The average, variations and the standard deviations of these measurements were calculated separately. SEM jeol JX A -840, which was used throughout this study, belongs to Gebze Tübitak Marmara Research Center. The photographs of pollen samples, which revealed the detailed surface ornamentations on their general appearance, were developed by the dimension ranging from 2200 and 11000. On these microphotographs, the supratectal structure, lumen and perforation diameter and the thickness of muri on the reticulation were measured. On the 2 μ2 area of the microphotographs, the lumen number on the mezocolpium area, the perforation numbers and diameters were calculated separately for the pollen grains of each species. The terminology of Erdtman (1960, 1969), Faegri and Iverson (1975) and Walker and Doyle (1975) was followed.
RESULTS AND DISCUSSION
The pollen grains of Origanum were 4-6-8 colpate, subprolate, prolate sferoid, oblate sferoid, suboblate (Table 1). The colpi were elongated, narrowing at the poles. The colpus membrane was covered by small granules or big granules (Fig. 1-10). The ectexine was thicker than the endexine. Tectum was subtectate. The ornamentation was reticulate or suprareticulate, the lumina different in shape and size in Origanum (Table 3-4, Fig. 1-10). In polar view they were circular or circular-elliptically.
Based on polen size, shape in equatorial view and ornamentation, pollen type could be recognized:
Pollen type I: Pollar diameter less than 30 μm, ornamentation suprareticulate, rarely reticulate.
Pollen grains suboblate (O. acutidens (Hand-Mazz.) Ietswaart, O. minutiflorum Schwarz and P.H. Davis, O. majorana L. (Antalya), O. onites L. and O. vulgare L. ssp. gracile (C. Koch.) Ietswaart), P/E = 0.82-0.88, dimensions PxE= 22.87-28.49 X 29.16-32.76 μm (Table 2).
Table 1: | List of Origanum L. collections used in this study |
Pollen grains oblate sferoid (O. bilgeri P.H. Davis, O. majorana L. (Balikesir), O. syriacum L. var. bevani (Holmes) Ietswaart and O. vulgare L. ssp. hirtum (Link) Ietswaart), P/E= 0.88-1.00, dimensions PxE= 23.73-29.35 X 26.44-33.07 μm (Table 2). Reticulate ornamentation shown by O. bilgeri P.H. Davis and O. minutiflorum Schwarz and P.H. Davis (Fig. 6, 7)
Pollen type II: Pollar diameter less than 40 μm, ornamentation suprareticulate, rarely reticulate.
Pollen grains oblate-sferoid (O. saccatum P.H. Davis, O. sipyleum L. (Ankara-Kizilcahamam, Isparta), O. rotundifolium Boiss., O. leptocladum Boiss. and O. laevigatum Boiss.), P/E = 0.88-1.00, dimensions PxE = 32.99-39.15 X 32.07-41.02 μm (Table 2). Pollen grains prolate sferoid (O. hypericifolium O. schwarz and P.H. Davis, O. sipyleum L. (Manisa, Balikesir and Ankara-Beypazari) and O. bargyli Mouterde) P/E =1.00-1.14, dimensions PxE = 31.72-37.91 X 32.07-33.97, subprolate (O. micranthum Vogel, O. vulgare L. ssp. viride (Boiss.) Hayek and O. vulgare L. ssp. vulgare), P/E = 1.14-1.33, dimensions PxE = 32.17-39.29 X 27.33-33.44 μm (Table 2). Reticulate ornamentation shown only by O. micranthum Vogel (Fig. 6).
Pollen type III: Pollar diameter less than 45 μm, ornamentation suprareticulate and rarely reticulate.
Pollen grains subprolate (O. boissieri Ietswaart, O. solymicum P.H. Davis and O. haussknechtii Boiss.), P/E= 1.14-1.33, dimensions PxE = 40.73-46.02 X 35.18-38.00, Prolate (O. hüsnücan-baserii Duman and Aytac), P/E = 2-1.14, dimensions PxE = 40.99 X 31.98 (Table 2). Reticulate ornamentation shown only by O. hüsnücan-baserii Duman and Aytac (Fig. 6).
The results of these investigation show that pollen morphology of the Türkiye representatives of Origanum L. is comparatively homogenous. Nevertheless, based on pollen size, shape in polar view and ornamentation, three pollen types can be distinguished (Table 2).
The maximum P value was observed in O. solymicum P. H. Davis with values 46.02 μm and maximum E values in O. rotundifolium Boiss. with values in 41.2 μm (Table 2). The minimum P values was observed in O. vulgare L. ssp. gracile (C. Koch) Ietswaart with values in 22.87 μm. The minimum E values was observed in O. vulgare L. ssp. viride (Boiss.) Hayek. with values in 27.33 μm. The highest value of P/E was found in O. hüsnücan-baserii Duman and Aytac (Table 2) and the minimum P/E value in O. vulgare L. ssp. gracile (C. Koch) Ietswaart (Table 2). Besides in the taxa subprolate, oblate sferoid, prolate sferoid, suboblate, prolate grains were found. There is little variation in the size of pollen grains (Table 2). In Hussain and Heywoods (1982) study, the polar and equatorial axis confirm aproximately the same numerical values of this investigation.
The ectexin in apocolpial areas of O. hypericifolium O. Schwarz and P. H. Davis, O. sipyleum L., O. rotundifolium Boiss., O. leptocladum Boiss. and O. micranthum Vogel was thicker than the area in mesocolpium. In Hussain and Heywoods (1982) study confirm this results except for O. micranthum Vogel. Some pollen grains demonstrate differences in the aperture system of which O. majorana L., O. onites L. (4-6-8) , O. syriacum L. var. bevanii (Holmes) Ietswaart, O. solymicum P.H. Davis, O. hüsnücan-baserii Duman and Aytac (6-8) and O. sipyleum L. (Balikesir) O. vulgare L. ssp. hirtum (Link) Ietswaart. (4-6) have been shown aperture number variations (Table 2). These taxons have heteromorpic characteristics in terms of the number of their aperture (Aytug, 1967; Inceoglu, 1973).
The pollen grains of Origanum L. taxons show similar features under light microscope; however when SEM is used, the number of lumen in 2 μ2 per section, the number of perforation in each lumen and the muri thickening show different features (Table 3 and 4).
In this study, number of lumen per 2 μ2 averaged between 3 and 8, whereas the perforation number had an average ranging from 5 to 33. Pollen grains showed suprareticulate ornamentation (Fig. 1, 2, 3, 4, 5, 7 C and 8, 9, 10 D)
Table 2: | Morphological observations of the pollens of Origanum L. |
Fig. 1: | SEM micrograms of (A, C, E ) view of whole pollen grain in equatorial view, (B, D, F ) magnified view showing sculpturing of the tectum. A. O. boissieri x2200. B.O. boissieri x8500. C. O. saccatum x3000. D. O. saccatum x9000. E. O. solymicum x2500. F. O. solymicum x8500. Scale bars: A-C-E 10 m, B-D-F μm |
Fig. 2: | SEM micrograms of (A, E )view of whole pollen grain in equatorial view, (C ) whole pollen grain showing the polar region, (B, D, F) magnified view showing sculpturing of the tectum. A. O. hypericifolium x2700. B.O. hypericifolium x11000. C. O. sipyleum (Manisa) x3000. D. O. sipyleum (Manisa) x8000. E. O. sipyleum (Balikesir) x2500. F. O. sipyleum (Balikesir) x8500. Scale bars: A-C-E 10 m, B-D-F μm. |
Fig. 3: | SEM micrograms of (A, C ) view of whole pollen grain in equatorial view, (E ) whole pollen grain showing the polar region, (B, D, F ) magnified view showing sculpturing of the tectum. A. O. sipyleum (Ankara-Kizilcahamam) x2700. O. sipyleum (Ankara-Kizilcahamam) x9000. C. O. sipyleum (Ankara-Beypazari) x2200. D. O. sipyleum (Ankara-Beypazari) x8000. E. O. sipyleum (Isparta-Sütçüler) x3300. F. O. sipyleum (Isparta-Sütçüler) x9000. Scale bars: A-C-E 10 m, B-D-F μm. |
Fig. 4: | SEM micrograms of (A, C ) view of whole pollen grain showing the polar region, (E ) whole pollen grain in equatorial view, (B, D, F ) magnified view showing sculpturing of the tectum. A. O. acutidens x3000. B.O. acutidens x8000. C. O. haussknechtii x2700. D. O. haussknechtii x7500. E. O. bargyli x2300. F. O. bargyli x8000. Scale bars: A-C-E 10 m, B-D-F μm. |
Fig. 5: | SEM micrograms of (A, C )view of whole pollen grain in equatorial view, (B, D) magnified view showing sculpturing of the tectum. A. O. rotundifolium x2200. B.O. rotundifolium x11000. C. O. leptocladum x3000. D. O. leptocladum x9000. Scale bars: A-C-E 10 m, B-D-F μm. |
The perforations differed in size and shape and have had an irregular structure (Table 3, Fig. 1, 2, 3, 4, 5, 7 C-D, 8, 9, 10). According to Hussain and Heywood (1982), perforation number per was lumina found between 1 and 7 and ornamentation in this species was only reticulate. Howewer, in this investigation, all species in chilocalyx section and O. husnucan-baserii Duman and Aytac in brevifilamentum section showed reticulate ornamentation (Table 4, Fig. 6, 7 A, B).
Ietswaart (1980,1982) has collected similar species according to their external morphological characteristics (Amaracus, anatolicon, breviflamentum, chilocalyx, majorana, origanum, prolaticorolla). The species in the sections have been found differences in essential oil chemistry (Baser et al., 1991; 1992; 1993; 1994; 1996; 1998; Sezik et al., 1993; Tumen and Baser, 1993; Tumen et al., 1994; 1995a,b). The samples collected from different localities studied in Anatolicon and majorana sections (Table 1). In this study, little variations have been observed for pollen grains of the samples (Table 3). However, their palynological features exhibit no significant difference. Irene et al. (1994) have also noted that these species demonstrate no difference as far as palynological term are concerned, but different geographically, ecologically, macromorphologically, phytochemically and caryologically.
Fig. 6: | SEM micrograms of (A, E ) view of whole pollen grain showing the polar region, (C ) whole pollen grain in equatorial view, (B, D, F ) magnified view showing sculpturing of the tectum. A. O. hüsnücan-baserii x3000. B.O. hüsnücan-baserii x9000. C. O. bilgeri x2500. D. O. bilgeri x8000. E. O. micranthum x3300. F. O. micranthum x7000. Scale bars: A-C-E 10 m, B-D-F μm. |
Fig. 7: | SEM micrograms of (A, C ) view of whole pollen grain in equatorial view, (E ) whole pollen grain showing the polar region, (B, D, F ) magnified view showing sculpturing of the tectum. A. O. minutiflorum x3300. B.O. minutiflorum x8500. C. O. majorana (Balikesir) x3300. D. O. majorana (Balikesir) x10000. E. O. majorana (Antalya) x4000. F. O. majorana (Antalya) x8500. Scale bars: A-C 10 m, E-B-D-F μm. |
Fig. 8: | SEM micrograms of (A, C ) view of whole pollen grain in equatorial view, (E ) whole pollen grain showing the polar region, (B, D, F ) magnified view showing sculpturing of the tectum. A. O. onites x3500. B.O. onites x11000. C. O. syriacum var. bevani x3500. D. O. syriacum var. bevani x8000. E. O. vulgare ssp. gracile x3500. F. O. vulgare ssp. gracile x10000. Scale bars: A-C-E 10 m, B-D-F μm. |
Fig. 9: | SEM micrograms of (A, C ) view of whole pollen grain in equatorial view, (B, D ) magnified view showing sculpturing of the tectum. A. O. vulgare ssp. hirtum x3500. B. O. vulgare ssp. hirtum x13000. C. O. vulgare ssp. viride x3700. D. O. vulgare ssp. viride x11000. Scale bars: A-C-E 10 m, B-D-F μm. |
Fig. 10: | SEM micrograms of (A, C ) view of whole pollen grain in equatorial view, (B, D ) magnified view showing sculpturing of the tectum. A. O. vulgare ssp. vulgare x3000. B.O. vulgare ssp. vulgare x9000.C. O. laevigatum x2000. D.O. laevigatum x8500. Scale bars: A-C-E 10 m, B-D-F μm. |
Table 3: | The palynological features of the pollens that have suprareticulate ornamentation on SEM microphotagraphs |
The species are put in order in terms of their average peforation diameter in their palynological features |
Table 4: | Palynological features of the pollen species having reticulate ornamentation on SEM microphotographs |
As a conclusion, the pollen grains of the species from section chilocalyx and only in O. husnucan-baserii Duman and Aytac of brevifilamentum section show distinct ornamentation (Reticulate) from the others.
ACKNOWLEDGMENT
This study has been supported by the Research Foundation of Balikesir University as a Ph. D. Dissertation. I would like to thank Prof. Ö. INCEOGLU from the Faculty of Science at Ankara University, Prof. G. TUMEN from the Faculty of Science and Art at Balikesir University, and Prof. B. YILDIZ from the Faculty of Science and Art at Balikesir University, who generously helped me. I am greatly indebted to Prof. K.H.C. BASER, the TBAM director at Anadolu University who kindly allowed me to take pollen samples from their valuable specimens. I am also grateful to Dr. N.M. PINAR for her generous support in my study and the specialist Z. MISIRLI, who helped me in Electron Microscope work at Tübitak MAM.
REFERENCES
- Walker, J.W. and J.A. Doyle, 1975. The bases of angiosperm phylogeny: Embryology. Ann. Missouri Bot. Garden, 62: 621-646.
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