Comparative karyological investigation of four economically important ornamental Jasminum species from Bangladesh

Abstract

Jasmine (Jasminum spp.) is a flowering plant cultivated commercially in Bangladesh, India, and other Southeast Asian nations like Singapore, Malaysia, and the Middle East. Despite being an economically important genus, reports on karyotypes of these species have been scarce due to the small and sticky chromosomes. Here, four economically important ornamental Jasminum species, namely, J. auriculatum, J. grandiflorum, J. multiflorum, and J. sambac, were cytogenetically studied to evaluate the karyological relationship. J. auriculatum, J. grandiflorum, and J. multiflorum were found to possess 2n=2x=26 (diploid) whereas 2n=3x=39 (triploid) somatic chromosome number was found in J. sambac. These four Jasminum species differed in karyotype formulae such as 24m + 2sm in J. auriculatum, 22m + 4sm in J. grandiflorum, 26m in J. multiflorum and 39m in J. sambac. Based on Stebbins classification, J. auriculatum was positioned in 1A karyotype whereas J. grandiflorum, J. multiflorum, and J. sambac were placed in 1B karyotype. Considering different karyotypic asymmetric parameters, J. sambac and J. auriculatum could be suggested as more primitive over J. grandiflorum and J. multiflorum. The cluster analysis revealed that these four Jasminum species could be grouped into two main clusters and J. sambac was comparatively more distantly related to the others. The above findings could be an important tool for characterization and effective for evaluating karyotype diversity among four Jasminum species.

Floriculture is a key component of Bangladesh's agriculture, known for its profitability and popularity among farmers (Rakibuzzaman et al. 2018). Jasminum L., a prominent genus in the floral industry, is a member of the Oleaceae family (Ahmed et al. 2009). The Oleaceae family encompasses 25 genera and around 688 species, found in temperate and tropical regions (Manoj and Aiyer 2022). With almost 200 species, the Jasminum genus is the largest in the family (Green 1969, Green and Miller 2010). Twelve species of Jasminum have been reported in Bangladesh so far, namely, J. anstomonzans Wall. ex DC., J. attenuatum Roxb. ex G. Don., J. auriculatum Vahl., J. coarctatum Roxb., J. grandiflorum L., J. lanceolaria Roxb., J. laurifolium Roxb., J. listeria King ex Gage, J. multiflorum Burm. f., J. sambac (L.) Aiton, J. scandens Vahl., and J. subtriplinerve Blume (Ahmed et al. 2009). Among these species J. auriculatum, J. grandiflorum, J. multiflorum, and J. sambac, are common and cultivated for commercial purposes in Bangladesh.

The Jasminum is beneficial for treating conditions like stomach distension, gastric ulcers, amenorrhea, ringworm, leprosy and as a component in herbal remedies that enhance immunity, improve blood circulation, and remove blood clotting (Warrier et al. 1995, Panda 2000, Mourya et al. 2017). Among all the species of this genus, J. sambac is most favored in cultivation because of its wide demand (Sharma and Sharma 1958). Jasmine oil can be used in perfumery, soaps, flavorings, and the cosmetic industry due to their sweet and elegant fragrance impact (Lawless 1995). Jasmine oil is widely recognized for its ability to treat sensitive, dry, greasy, and irritated skin. Additionally, it is used to treat sprains, ease muscle discomfort, and calm irritating coughs (Prabuseenivasan et al. 2006).

The Jasminum comprises species with a common set of 13 chromosomes and most species have 26 somatic chromosomes (Table 1). The chromosomal size in the species is extremely short, and the position of centromere and secondary constriction on chromosomes is not clearly visible in conventional staining (Raman 1955). Moreover, chromosome stickiness poses challenges for detailed analysis. Previous attempts to characterize Jasminum species using cytological methods have been limited, mainly focusing on chromosome count. The somatic chromosome number ranges from 26 to 52, always being a multiple of 13 (Taylor 1945, Krishnaswamy and Raman 1948, Dutt 1952, Raman 1955, Sharma and Sharma 1958, Wang et al. 2022). Unfortunately, there is a lack of detailed karyotype information, which could shed light on the speciation mechanism in this genetically diverse genus (Sharma and Sharma 1958). Given the importance of Jasminum species as both ornamental and medicinal plants, it is crucial to investigate the species using cytogenetical approaches. Karyotyping can serve as a valuable tool for assessing genetic variations as it represents a stable characteristic unique to each species. In addition, by using karyological data in taxonomy, it is possible to evaluate the genetic relationships between taxa (species or populations) and make more accurate assumptions about how they separated from one another and about their common ancestor (Guerra 2008). Characterization with karyotype is also required for optimal conservation, management, and breeding efforts. Therefore, in this investigation, a comparative cytogenetical analysis was carried out to evaluate the karyotypic diversity among four economically important ornamental Jasminum species, viz., J. auriculatum, J. grandiflorum, J. multiflorum, and J. sambac.

Table 1. Previous records of chromosome count four studied Jasminum species.

Name of the species	Chromosome number	References
J. auriculatum	2n=26	Krishnaswamy and Raman (1948, 1949), Raman (1955), Sharma and Sharma (1958)
J. grandiflorum	2n=26	Bowden (1940), Krishnaswamy and Raman (1948), Dutt (1952), Raman (1955), Sharma and Sharma (1958)
J. multiflorum	2n=26	Taylor (1945)
J. sambac	2n=26	Krishnaswamy and Raman (1948), Wang et al. (2022)
	2n=39	Bowden (1940), Krishnaswamy and Raman (1948), Dutt (1952), Raman (1955), Sharma and Sharma (1958)

Materials and methods

To conduct this investigation, J. auriculatum, J. grandilorum, J. multiflorum, and J. sambac were collected from Azimpur, Dhaka University Campus, different nurseries of Dhaka city, National tree fairs-2021, Dhaka, Bangladesh.

The roots of the specimen were harvested from experimental plots and the collected root tips (RTs) were put on filter paper to remove external water before being treated with 0.002 M 8-hydroxyquinoline for 2 h at room temperature (28–30°C). Carnoy’s solution (absolute alcohol : Glacial acetic acid=3 : 1) was used to fixation and preserve the fixed RTs at 4°C. The pretreated RTs were hydrolyzed for 5 min at 65°C in a mixture of 1M HCl and 45% acetic acid (2 : 1). The hydrolyzed RTs were then soaked in filter paper and transferred to a clean slide. The hydrolyzed roots’ meristematic areas were taken apart and a drop of 1% aceto-orcein was added. The sample was then put in an acetic acid chamber for 2 h 30 min. The slides were then prepared by the orcein squash technique. The slides were observed under a Euromax Axion microscope and photographs were taken by using a Euromex microscopic camera CMEX-18Pro (18 megapixels) in auto mode. Chromosomes were measured from five metaphase plates in order to acquire precise length measurements. The Karyotype formula was analyzed according to Levan et al. (1964). KaryoType software (Altinordu et al. 2016) was used to generate the idiograms by inputting the chromosomal measurements. Karyotype asymmetry assessment was carried out by using KaryoType software. Karyotypes were categorized based on Stebbins’s classification (1971). We utilized the UPGMA technique implemented in the online software DendroUPGMA, http://genomes.urv.cat/UPGMA, for cluster analysis.

Results

J. auriculatum has 2n=26 chromosomes (Figs. 1A, 2A, Table 2). In this species, the total chromosome length (TCL) was 33.12 µm. The relative length (RL) ranged from 2.92 to 5.31%. Individual chromosomal lengths ranged between 0.97 and 1.76 µm. For this species, the karyotype formula (KF) was 24m + 2sm.

Fig. 1. Mitotic metaphase chromosomes of four Jasminum species.

(A) J. auriculatum, (B) J. grandiflorum, (C) J. multiflorum, and (D) J. sambac. Scale bar=10 µm.

Fig. 2. Idiogram of four Jasminum species.

(A) J. auriculatum, (B) J. grandiflorum, (C) J. multiflorum, and (D) J. sambac. Scale bar=1 µm.

Table 2. Comparative karyotype analysis of four Jasminum species.

Karyotype features	J. auriculatum	J. grandiflorum	J. multiflorum	J. sambac
2n	26	26	26	39
KF	24m + 2sm	22m + 4sm	26m	39m
TCL (µm)	33.12	34.43	32.35	44.88
ACL (µm)	1.27	1.32	1.24	1.15
RL (%)	2.92 to 5.31	2.26 to 5.15	2.04 to 5.03	2.15 to 3.82
CVCI	8.58	8.9	6.27	3.49
CVCL	15.99	23.12	23.84	18.41
MCA	9.21	10.51	6.24	6.20
AsK%	54.47	54.55	53.42	53.18
TF%	45.53	45.45	46.58	46.82
Syi%	83.6	83.33	87.21	88.02
Rec%	72.42	74.82	76.8	66.94
A1	0.16	0.18	0.11	0.12
A2	0.16	0.23	0.24	0.18
A	0.09	0.11	0.06	0.06
AI	1.37	2.06	1.5	0.64
DI	7.09	9.85	11.83	8.25
Category	1A	1B	1B	1B

2n=Somatic chromosome number, KF=Karyotype formula, TCL=Total chromosome length, ACL=Average chromosome length, RL=Relative length, CV_CI=Coefficient of variation of centromeric index, CV_CL=Coefficient of variation of chromosome length, M_CA=Mean centromeric asymmetry, AsK%=Karyotype asymmetry index (%), TF%=Total form value (%), Syi%=Karyotype symmetry index (%), Rec%=The index of chromosomal size resemblance, A₁=Intrachromosomal asymmetry index, A₂=Interchromosomal asymmetry index, A=Degree of asymmetry of karyotypes, AI=The asymmetry index, DI=The dispersion index.

J. grandiflorum possessed somatic chromosome number 2n=26 (Figs. 1B, 2B, Table 2). The TCL was 34.43 µm. The RL ranges from 2.26 to 5.15%, while the individual length ranges from 0.78 to 1.77 µm. This species' KF was 22m + 4sm.

In the case of J. multiflorum, 2n=26 chromosomes were found (Figs. 1C, 2C, Table 2). The TCL was 32.35 µm. The RL ranged from 2.04 to 5.03%. The lengths of the individual chromosomes ranged from 0.66 to 1.63 µm. This species’ KF was 26m.

J. sambac was found to possess 2n=39 chromosomes (Figs. 1D, 2D, Table 2). The TCL was 44.88 µm. The RL of chromosomes was ranged from 2.15 to 3.82%. Individual chromosome length ranged from 0.79–1.71 µm. The KF was recorded as 39m for this species. No satellite was observed in these four studied species during orcein staining.

According to KaryoType software analysis, CV_CI value ranged from 3.49 (J. sambac) to 8.90 (J. grandiflorum). J. auriculatum had the lowest value for CV_CL (15.99) and J. grandiflorum had the lowest value for TF% (45.45). M_CA value was the highest (10.51) in J. grandiflorum and the lowest (6.20) in J. sambac. In the case of AsK%, the highest value (54.55) was observed in J. grandiflorum and the lowest (53.18) in J. sambac. Variation was observed in all studied species regarding A₁ and A₂ values which ranged from 0.11–0.18 and 0.16–0.24, respectively. A₁ value was the highest in J. grandiflorum (0.18) and the lowest in J. multiflorum (0.11). On the other hand, A₂ value was the highest in J. multiflorum (0.24) and the lowest in J. auriculatum (0.11). The value of degree of asymmetry of karyotypes (A) in J. grandiflorum was maximum (0.11) and in J. multiflorum and J. sambac were minimum (0.06). On the basis of Stebbins’s classification (1971), 1A karyotype was found in J. auriculatum and 1B karyotype in the other three species (Table 2).

Discussion

The present investigation shows that J. auriculatum, J. grandiflorum, and J. multiflorum had 2n=26 somatic chromosomes. Previously, different scientists reported the same chromosome count (2n=26) for these three species (Table 1). On the other hand, J. sambac was found to possess 2n=39 somatic chromosomes in this study, which was similar to the findings of Taylor (1945), Krishnaswamy and Raman (1948), Dutt (1952), Raman (1955) and Sharma and Sharma (1958). In addition, 2n=26 chromosome was also reported for this species by Bowden (1945) and Raman (1955). Different Jasminum species such as J. angustifolium, J. azoricum, J. calophyllum, and J. nudiflorum were found to possess 2n=52 chromosomes (Kumar and Subramaniam 1987). The above reports indicated that the genus Jasminum has a strict basic chromosome number x=13. Therefore, J. auriculatum, J. grandiflorum and J. multiflorum are diploid (2n=2x=26) and J. sambac is triploid (2n=3x=39) which are investigated in the present study (Fig. 1). However, Verma et al. (2018) reported different basic chromosome number x=19+1 (2n=39) for J. sambac, which suggested this species as an aneuploidy. Generally, aneuploidy tends to show less vegetative growth due to non-disjunction at the anaphase stage. A polyploid series of 2n=26, 39, 52, 65, and 78 have been reported for the Jasminum, with diploids dominating (51.5%), followed by tetraploids (11%), triploids (3%), pentaploids and hexaploids (2.65% each) (George and Geethamma 1992). Earlier findings and the current analysis suggest that the Jasminum is dibasic, with x=12 and 13 (Darlington and Wylie 1955). In the family Oleaceae, the Menodora was reported to have n=x=11 which was the lowest basic chromosome number reported so far (Darlington and Wylie 1955). George and Geethamma (1992) hypothesized that the basic chromosome numbers x=12 and 13 might have originated via aneuploidy from the ancestor with the basic number x=11. Therefore, polyploidy significantly contributed to speciation in the Jasminum. According to Deng et al. (2016), in J. sambac, failure of fertilization occurred due to restricted pollen viability and poor seed-setting caused by abnormal growth of embryo sacs. However, J. sambac which was studied in the present investigation showed normal growth and regular segregation revealing its euploidy nature. Moreover, probably triploidy doesn’t affect its vegetative growth because it usually propagates by stem cutting (Ahmed et al. 2009). According to Sharma and Sharma (1958), the sexual sterility of J. sambac is probably due to gene mutation or structural chromosome aberration rather due to triploidy.

The occurrence of all metacentric chromosomes in the karyotype of an organism suggests the symmetric nature of that karyotype (Stebbins 1971). In this study, four chromosomes in J. grandiflorum and two chromosomes in J. auriculatum were submetacentric, and the remaining two Jasminum species possessed all metacentric chromosomes (Fig. 2, Table 2). In these four species, the distance between small and large chromosomes was about 1 µm. The above finding suggested the symmetric nature of chromosomes in these species. According to Stebbins classification (1971), J. auriculatum was assigned to 1A karyotype, whereas J. grandiflorum, J. multiflorum, and J. sambac were assigned to 1B karyotype. Datta (1960) reported total chromosomal lengths of 40.4, 38.4, and 38.2 µm for J. auriculatum, J. grandiflorum, and diploid J. sambac species, respectively. In this study, the total somatic chromosomal lengths were 33.12, 34.43, and 44.88 µm for J. auriculatum, J. grandiflorum, and triploid J. sambac species, respectively, which was different from the previous report. The influence of the pretreatment agent and treatment duration may be the reason for the differences in chromosomal length.

The degree of asymmetry is not entirely represented by the karyotype formula. Even though there is clear morphological distinction between the species, it is occasionally probable that closely related species will not display substantial variations in karyotypes. To prove the phylogenetic resemblance between the closely related species in these situations, it is still important to distinguish between closely related karyotypes belonging to the same class of karyotype based on supplementary asymmetry analysis (Vimala et al. 2021). The evaluation of karyological diversity across closely related karyotypes has led to the development of a number of karyotypic symmetric and asymmetric indexes. Assessment of karyotype asymmetry was analyzed with conventional and ‘KaryoType’ software data. After analysis in both cases, M_CA, AsK%, CV_CI, A₁, A, and AI were the highest in J. grandiflorum (Table 2). All the above values were lowest in J. sambac except A₁ and DI values (Table 2). The lowest value of the above parameter considered as a primitive character and the highest as an advanced character contrary to the highest TF% and Syi% considered as primitive nature and the lowest value considered as advance nature (Huziwara 1962, Arano 1963, Greilhuber and Speta 1976, Zarco 1986, Lavania and Srivastava 1992, Watanabe et al. 1999, Paszko 2006, Peruzzi and Eroğlu 2013, Altinordu et al. 2016, Akter et al. 2023). Considering these parameter J. grandiflorum and J. auriculatum could be suggested as more advance over J. sambac and J. multiflorum. The boxplot shows the range and divergence in chromosomal length among the four species that were examined (Fig. 3). Although the average chromosomal length of these four studied species was more or less similar, the individual chromosomal length of J. grandiflorum and J. multiflorum showed wider diversity than the other two species (Fig. 3). The median was about in the center position of the interquartile ranges in case of J. auriculatum, indicating that all of the chromosomes are around the same length. The wider dispersion between the median and the 1st quartile in the case of J. grandiflorum and J. multiflorum represents broader diversity comparatively among smaller chromosomes of these species. The cluster analysis by UPGMA on the basis of the Pearson correlation coefficient of the karyotypic parameters revealed that these four Jasminum species could be grouped into two main clusters and J. sambac was comparatively more distantly related to the others (Fig. 4). The highest distance was between J. sambac and J. grandiflorum (0.580) whereas the lowest in between J. grandiflorum and J. multiflorum (0.155).

Fig. 3. Boxplot representing the chromosome length diversity among four Jasminum species.

The horizontal dashed line represents the mean and the solid line indicates the median.

Fig. 4. Cluster analysis by UPGMA on the basis of the Pearson correlation coefficient of the karyotype parameters among four Jasminum species.

The cytological information provided for the Jasminum species demonstrated significant diversity and distinctiveness. The occurrence of karyotype diversity in this genus suggested that chromosomal reshuffling likely happened at various stages of evolution. This study is an initial investigation of four species of Jasminum; additional study is required on other species under this genus as well as other genera within the family.

Acknowledgments

The first author has done this research work under the NST fellowship program of the Ministry of Science and Technology, Peoples Republic of Bangladesh.

Author contributions

Ifrat Jahan: investigation, methodology, data analysis, original draft (writing), review and editing (writing). Chandan Kumar Dash: validation, image preparation, data analysis, original draft (writing), review and editing (writing). Syeda Sharmeen Sultana: conceptualization, review, and editing (writing), supervision. All authors have read and approved the final version of the manuscript.

Supplementary information

Supplementary information including Tables S1–S4 is available online.

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