Datta, N. M.

Szegletes, Zsolt

Tóth-Soma, László T.

English

Tóth-Soma László T.

Datta N. M.

Szegletes Zsolt

University of Szeged

ACTA BIOL. SZEGED. 41, pp. 37-44 ( 1995/1096) G E N E R A L C O N N E C T I O N S B E T W E E N L A T E X A N D N E C T A R S E C R E T I O N A L S Y S T E M S OF ASCLEPIAS SYRIACA L. L . T . T Ó T H - S O M A 1 , N . M . D A T T A 2 and Z s . SZEGLETES3 'Department of Botany. József Atlila University, 11-6701 Szeged, P.O.B. 657, Hungary Department of Botany, City College, Calcutta, Raja Rammohan Sarani 101/1, Calcutta, India 1 Institute of Biophysics, Biological Research Center. /1-6701 Szeged. POR 5? I, Hungary (Received: May 22,1995 ) Abstract The intracellular latex secretion and the extracellular nectar secretion are anatomically connected to each other in Asclepias syriaca L. The whole gynostemium is interwoven by the non-articulated laticifers, and they can also be found in the tissues of the epimorph nectary. The latex system is divided into several branches in the gland parenchyma, and the epithelial glandular tissues of the nectary. The question as to whether there is also a functional connection as a consequence of the anatomical connection (or whether it is possible that certain materials of the latex are sccrcted into the nectar and arc finally mixed into the honey) between the two secretional systems was answered by TLC and GC-MSD analyses of the latex and the honey. By means of TLC analyses at 254 nm and reactions with general alkaloid reagents (Dragendorff re-agent, Meyer reagent and 1% Cc(S04 ) . solution in I M H,S04 ) , several compounds were detected both in the latex and in the honey of Asclepias. Due to the lack of TLC standards, these compounds were not identified, and only the degree of compositional identity of the latex and the honey was established. By means o f GC-MSD (a gas chromatograph coupled with a mass selective detector) analyses, the fol-lowing compounds which can also be found in the latex were identified in the honey o f Asclepias syriaca: 2-propcnoic acid 6-methylheptyl ester (retention lime: 6.95 min). pentadecane (ret. time: 10.80 min), diethyl phthalate (ret. time: 11.43 min), hexadecane (ret. time: 12.05 min), heptadecane (ret. time: 13.20 min), 2.6,10,14-tetramethyl pentadecane (ret. time: 13.30 min), octadccane (ret. time: 14.32 min). 2-tetradecanoic acid methyl ethyl ester (ret. time: 14.45 min), phthalic acid butyl 2-mcthylpropyl ester (ret. time: 15.56 min), I -eicosene (ret. time: 17.15 min), docosane (ret. time 18.30 min) and his (2-cthylhexyl) phthalate (ret. time: 20.94 min) The functional connection between the two secretional systems consequent from their anatomical con-nection is strongly suggested by the partial compositional identity of the latex and the honey, and the direct connection of the latex-system with the glandular tissue of the nectary Key words', secretion, nectary, honey, Asclepias. Introduction In the past few decades, a number o f data have been obtained regarding the nectar production o f melliferous plants, the quantity o f honey produced and its composition. The chemical composition o f the nectar produced, and finally the honey, is an important medical question. In the case o f plants that produce latex, it can be influenced consider-38 I. T TOIH-SOMA. N M DATtA and Zs SZEGLETES ably by the connection o f intracellular and extracellular secretion. This paper examines the anatomical and functional connection o f the intracellular latex secretion and the extracellular nectar secretion o f Asclepias syriaca, which is an important plant in bee-farming. It is a wel l -known fact that the common mi lkweed is a plant that contains latex. The latex can be found in long, expanded, non-articulated laticifers as the product o f intracellular secretion (METCALFE, 1985). In fact, the latex can be regarded as the cell fluid o f laticifers (FREY-WYSSLING, 1933; ESAU, 1953). which may contain several biological ly active compounds such as organic acids, terpenoids (ADAMS. 1987), alka-loids (SOKOLOV, 1952), saturated and aromatic hydrocarbons (CAMPBELL, 1983; SlMiONESCU, 1987), steroids and alcohols (BlSBOAR, 1983), in the form o f either solu-tion or colloidal suspension. The chemical compounds o f the Asclepias genus are also mentioned by HEGNAIJER (1966). In contradiction with the statements o f SPRENGEL (1793) , STADLER (1886), KNUTII (1909) , FITTING (1930) and RENDLE (1953 ) regarding the nectar-secretional system o f the common milkweed, GALLIL and ZI ROM (1965) and KEVAN et al. (1989) provided information on the anatomy and tissue structure o f the nectar-secretional system o f Asclepias species, and the epithelial position o f the glandular tissue, which is so important here. The composition o f the nectar produced by extracellular secretion, and finally the composit ion o f the honey are extremely diversif ied. Besides the most important com-pounds, which are different types o f carbohydrates (SOUTHWICK, 1981, 1983a,b), the nectar may contain vitamins (WEBER, 1942), other organic acids (MAURIZIO, 1960), antimicrobial compounds (KEVAN et al., 1989), etc. The toxic compounds o f the nectar were submitted to detailed examinations by SCHULTZ-LANGER (1966, 1967) among others. In the wor ld o f plants there also occur honeys which have a harmful, toxic e f f ec t on the human organism. The honey o f some tropical Euphorbia species has a strong, irritant e f fect (JURl l'Z, 1925). Compounds with the same physiological e f fect were also detected in the latex o f these plants (Ul'ADMYAY and HECKER, 1975; SOSATII, 1988). The common origin o f certain compounds o f nectar and latex, and the connection between extracellular and intracellular secretion in the Euphorbia genus, have already been emphasized in previous publications (TOTH-SOMA and GUI.YAS, 1991; TOTII-SOMA et al., 1993). In the present paper, the fo l l owing questions are examined: is the latex system o f Asclepias syriaca anatomically connected to its nectar-secreting system, and if it is, is there also a functional connection between them due to their anatomical connection? May certain compounds o f the latex be secreted into the nectar, and finally into the honey? General connections between latex antl nectar sccretional systems o f Asclepias syriaca L 39 Materials and methods Anatomical examinations on the nectary. The tissue structure o f the nectaries in the stigmatic chambers of the gynostemium of Asclepias syriaca was examined; this is an excellent melliferous plant found all over Europe. To examine the gynostemium derived from its petals, we used the celloidin embedding method described by KISSER (1920) and ROmeis (1932), as modified by GlILYAs (1968) We made 20 to 30 ц т thick cross-sections with sledge-microtome. For better examination of the gland, the cross-sections were stained with Erlich's hacmatoxylin and conserved in Canada balsam I he slides were examined under an NU-2 light microscope. Chemical detections The comprehensive analyses o f milkweed latex and honey were performed by analytical techniques. By means of thin-layer chromatography, alkaloids and other compounds were detected which gave a positive reaction with alkaloid reagents. Other organic compounds were detected by the GC-MSD method. From the latex and honey, a chloroform extract was made according to the method applied b^SzAsz (1979) and ТйТН-SOMA et al. (1993). These extracts were examined on Kieselgel 60F 254 (MERCK ) thin-layer plates, by developing the chromatograms in an 85:15 (v/v) mixture o f benzene and methanol. Preliminary examination of the plates was performed under 254 nm light. They were then developed with three general alkaloid reagents: a 1% solution of Ce (SOj ) , iu I M l l :S( ) 4 , the Meyer reagent and the DragendorfTreagent (IIAIS and МЛСЕК, 1961; MUNIER and MACHEBOEUF. 1949). The extracts were further examined with a Hewlett Packard GC-MS l ) system (an HP 5890A G C coupled to an HP 5970 MSD, 70 eV El), using a 12 m » 0.2 mm * 0.5 (im HP-1 capillary column (OV- I compatible), and He as carrier gas. Results During the anatomical examinations o f the nectaries, their structure (already predicted in the literature) was observed. In the light microscopical pictures, the differentially stained gland-parenchyma and Ihe epithelial glandular tissue could be clearly observed (Fig. I, panel A ) . The whole gynostemium and both layers o f the parenchyma o f the epimorph nectary situated in the stigmatic chamber are interwoven by the inarticulate system of laticifers which is characteristic of the plant (Fig. 1, panels A , B, C) . The nectar stored in the stigmatic chamber is responsible for the germination o f the pollinium that comes from outside (Fig. I, panel D). The laticifers closer to the epithelial glandular tissue are parallel with the secretional layer o f the nectary (Fig. I, panel F.), and their final ramifications end on the border between the subepithelial parenchyma and the epithelial tissue, directly touching the secretional tissue (Fig. I, panel F). It is clear, therefore, that the intracellular latex secretion and the extracellular nectar secretion are anatomically connected to each other. The functional connection resulting from the anatomical connection was verified by T L C examinations. These examinations revealed that several compounds that are present in the latex are also present in the honey (Fig. 2). On the chromatograms examined under 254 nm light, four compounds were found which were present in the extracts o f both honey and latex (Fig. 2, spots a-d, plate I ). On the plate developed with Meyer reagent, there were five compounds (Fig. 2, spots a-e, plate II), the plate 40 L I Trtm-SOMA. N VI DATTA and Zs. SZEGLETES Fig. I Cross-section o f the floral nectaries of Axclepinx xyriaca L. Enlargement: panel A 80» . B 125*. C 265«, D 125*. E 500», F 530». epithelial glandular tissue (egt), subepithelial parenchyma (sep), gland-parenchyma (glp). laticifers (I), stigmatic chamber (sc). pollinary (p). See explanation in text General connections between latex antl nectar sccretional systems o f Asclepias syriaca L 41 I II I I I IV Ce(S0J, Meyer Dragendorff s a • m e * • a » • a * * b » • b • • b « • c » * c « * c & m 0 * « b » * 0 • « c ® * d « * 1 8 * d 9 * * • s h A a e * •L 1 » • t i » i a 1 t Fig. 2. T L C of latex ( I ) and honey (2) extracts o f Asclepias syriaca L. The distances o f the spots from the front from a to h. 1-2: numbers of samples, f: front, s: start. developed with Ce (S0 4 ) 2 revealed eight compounds (Fig. 2, spots a-h, plate I I I ) , and on the plate developed with Dragendorf f reagent, there were four compounds (Fig . 2, spots a-d, plate I V ) that could be found in both extracts. Due to the lack o f T L C standards, w e did not investigate these compounds qualitatively, but the compositional identity o f the latex and the honey was thus clearly demonstrated. In the GC ' -MSD examinations, several identical compounds could be observed (F ig . 3). The mass spectra (with the help o f the N B S mass spectrum library) permitted identification o f the fo l lowing compounds in the honey extract (Fig. 3, B ) : 2-propenoic acid 6-methylheptyl ester (ret. time: 6.95 min), pentadecane (ret. time: 10.80 min), diethyl phthalate (ret. time: 11.43 min), hexadecane (ret. time: 12.05 min), heptadecane (ret. time: 13.20 min), 2,6,10,14-tetramethyl pentadecane (ret. time: 13.30 min), octa-decane (ret. time: 14.32 min), 2-tetradecanoic acid methyl-ethyl ester (ret. time: 14.45 min), phthalic acid butyl 2-methylpropyl ester (ret. time: 15.56 min), i-eicosene (ret. time: 17.15 min) , docosane (ret. time: 18.30 min) and bis (2-ethylhexyI ) phthalate (ret. time: 20.94 min). The peaks o f these compounds can also be seen on the gas chromatogram o f the latex extract (F ig . 3, A ) . As these peaks appeared at the same retention times with the same mass spectra for both extracts, they are considered to relate to identical compounds. 42 I I TCfTH-SOMA, N \1 DATTA and Zs SZEGLETES Time (nun) l-'ig. Gas chromatograms of latex ( A ) and honey ( I t ) extracts of Asctepias syriaca I. Discussion Our anatomical examinations o f the gynostemium and the nectary ver i fy that the intracellular latex-secretional and the extracellular nectar-secretional systems o f Asclepias syriaca L. are anatomically connected to one another. The parenchyma layer o f the nectary is richly interwoven by inarticulated laticifers which arc also present in the gynostemium and are characteristic of the whole plant. After several ramifications, the laticifers end on the border between the epithelial glandular tissue and the gland-parenchyma of the nectary. Therefore, a functional connection between the two secretional system is anatomically possible. 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General connections between latex and nectar secretional systems of Asclepias syriaca L.

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General connections between latex and nectar secretional systems of Asclepias syriaca L.

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