POLLEN MORPHOLOGICAL STUDIES ON TWO SOLANACEOUS GENERA: BRUGMANSIA PERS

Dhanya C 1 and Devipriya V 2 . 1. Post Graduate & Research Department of Botany, Sree Narayana College, Kollam, Kerala. 2. Department of Botany, Sree Narayana College, Chempazhanthy, Thiruvananthapuram, Kerala. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


ISSN: 2320-5407
Int. J. Adv. Res. 4 (9), 1879-1887 1880 America, and comprises of 10-12 species distributed in the tropical and temperate regions of the world, of which four have been reported from South India (Sasidharan, 2004). The genus includes several medicinal plants and some weedy species. BrugmansiaPers. (formerly included under Datura and later given a generic status by Lockwood, 1973), is native to South America and includes six to nine species of small ornamental trees, of which only one has so far been reported from South India.
The earlier palynological literaturelargely focuses on the economically more valuable genus -Datura, and includes the study on the pollen grains of eleven taxa of Chinese Datura by Guang-Fang et al. (1985), Daturastramoniumfrom Jordhanby Al-Quran (2004),three species of Datura from Pakistanby PerveenandQaiser (2007)and Datura metel from Nigeria (Adedeji and Akinniyi, 2015). Although Persoonet al. (1999) compared the pollen morphology of five species of Brugmansia and eight species of Datura from America,palynological studies on the taxa recorded from India are scanty. The present study focuses on the comparative evaluation of the fine exomorphological features of the pollen of six taxa of Brugmanisaand five taxa of Daturafrom Kerala and Tamil Nadu, India using Light Microscopy and Scanning Electron Microscopy.

Materials and Methods:-
The details regarding the taxa selected for the present study from Kerala and Tamil Nadu are furnished below in Table -1. Polliniferous materials were collected from live plants and fixed in glacial acetic acid, followed by acetolysisafterErdtman (1952) and Nair (1970). Morphological features relating to the pollen aperture, exine ornamentation, pollen size and shape were studied from LM and SEM observations. Pollen measurements were made using an ocular micrometer, from a random sample of 30 pollen grains from each taxon studied. The terminologies suggested by Punt etal. (1994) have been usedto describe aperture types and exine ornamentation pattern.

Results and Discussion:-
The pollen were 3-zonocolporate and large (B. suaveolens and D.inoxia) or medium in size. Brugmansiapollen were in general medium or large-sized, prolate-spheroidal or oblate-spheroidal to suboblate, 3-zonocolporate and striate (Table-2; Fig. 2), while those of Datura were mostly medium-sized, 3-zonocolporate, striato-reticulate, sometimes rugulateand possessing variable forms (Table-3; Fig. 15). Endocingulum was a common feature in both genera. Acolpate and monocolpate pollen and thin exine were observed in the three varieties of D. metel. The polar outline was rounded with apertures in the obtuse angles,while the equatorial outline was rounded or elliptic, and occasionallyslightly rectangular as in some members of Brugmansia (Fig.1).  The members of Brugmansia had striateor striato-reticulate exines, the latter observed only in the two varieties of B. suaveolens (Figs. 10 & 12). The exine was striato-reticulate inDatura except for striato-rugulate pattern in D. metel var. fastuosa and rugulate-reticulate exine inD. stramonium. The tectum showed slight variation in exine ornamentation at the apocolpium in some members, eg.rugulatein two members of Brugmansiaandrugulatereticulate in all five taxa ofDatura studied.
The lumina were not visible in the striate pollenof Brugmansiadue to the close packing of the long parallel muri (Fig.2), except inthe two varieties of B. suaveolenswhere it was reticulate. In Datura, the lumina were mostly reticulate (Fig.14), except for the granular lumina in D. metel var. fastuosa (Fig.17). B. suaveolenswas similar to Datura in pollen exine thickness, ornamentation and lumina nature (Tables 2 & 3).
The long muri or liraewere parallelly aligned and distinctly raised in mostmembers (Figs.6 &8), being broaderand more closely packed in Brugmansia.InD. stramonium, they were short, irregular and loosely packed (Figs.19 & 23). The mural subunits were distinct or less distinct, thin or very thin, cylindrical, transverse and closely packed, perpendicular to the muri in Brugmansia (Fig. 3). In B. sanguinea, they were occasionally diagonally and/or vertically oriented (Figs.7& 9).On the other hand, the subunits were striate, thin and longitudinally arranged, parallel to the muri in Datura (Fig. 15),sometimes very feeble and not clearly visible as in D. metel (Figs.17& 21). Large and nodular microscabrae were denselyarranged in single or occasionally two or more rows inBrugmansia, in contrast to the small granular ones in Datura which were sparsely present and irregularly scattered (Figs. 7 &21).

1885
The most extensive pollen morphological study comparing Brugmansia and Datura was made by Knapp and Persoon (1999). They recognized two pollen types on the basis of the thickness of exine, height of muri and alignment of mural subunits viz. Datura inoxia type and Brugmansia sanguinea type. Here the major focus seems to be on the alignment of the mural subunits, a feature distinct to each group being transverse in Brugmansia and longitudinal in Datura (Figs. 3 &15). But in the present study, B. sanguinea 'MishaTora' showed a combination of both longitudinal and transverse alignment of mural subunits occasionally, even though the major pattern was the transverse type characteristic of the Brugmansia type (Fig.7). Similarly, B. sanguinea 'Oroverde' showed diagonally 1886 oriented mural subunits (Fig.9). Hence mural subunit alignment cannot be considered aunique or major distinguishing character between the two genera. Moreover,Persoonetal.observed microscabrae in only some species of both genera and did not consider them significant in distinguishing between the two groups. But in the present study, microscabrae were present in all the eleven members and showed clear distinction in their size, form, occurrence and distribution between the two genera. They were large, nodular and dense in single or more rows in Brugmansia in contrast to being small, granular, sparse and irregularly scattered in members of Datura (Figs 5 &  21). Interestingly, they did not observe these bodies in the American taxa of B. candida and B. sanguinea, while the Indian taxa showed very distinct large, nodular microscabrae in large numbers on the pollen muri (Figs. 3 & 7). Hence microscabrae may also be considered as distinctive markers for comparison between the two genera.
In the light of the above discussion, the pollen of the two groups may be classified into Brugmansia -type and Datura -type as follows : 1. Brugmansia-type : Exine thick, striate or striato-reticulate, apocolpium same as mesocolpium in ornamentation; muri or lirae long and closely packed; mural subunits cylindrical, distinct and transverse -rarely diagonal and/or longitudinal; microscabrae large, nodular, dense and arranged almost regularly in one or occasionally more rows.

Conclusions:-
The exine sculpturing viewed under the Scanning Electron Microscope opens up a treasure trove of pollen microstructural features. These 'micro' traits are most often specific to plant groups and are increasingly used as 'micro' palynological markers in systematic studies and phylogenetic evaluations. The pollen of Datura and its closely related genus Brugmansia are similar being3-zonocolporate,large or medium andstriateor striato-reticulate, occasionally rugulate. Despite these overall similarities, the two genera have been palynologically distinguished largely based on the transverse or longitudinal alignment of the mural subunits in the exine. But longitudinal and/or diagonal orientation of mural subunits have been observed in two varieties of B. sanguineapresently studied. Hence mural subunit alignment cannot be depended upon as a unique distinguishing character between pollen of the two genera.In addition, microscabrae on the muri also showed distinction between the two genera, being large, nodular and dense in single or more rows in Brugmansia and small, granular, sparse and irregularly scattered in members of Datura. On the basis of the present observations, two pollen types are proposed here for the two genera studied viz. Brugmansia -type and Datura-type.