Annals of Botany 81 : 157–162, 1998 SHORT COMMUNICATION Secretory Structures and Localization of Alkaloids in Conium maculatum L. (Apiaceae) GABRIELLA CORSI and DAVID BIASCI Dipartimento di Scienze Botaniche dell’ Uniersita  , Via Luca Ghini 5, 56126 Pisa, Italy Received : 23 June 1997 Returned for revision : 21 July 1997 Accepted : 22 September 1997 In this paper histochemical investigations of the secretory structures of Conium maculatum L., are described that discriminated between ducts and vittae. The localization of alkaloids in seedlings, vegetative organs, flowers, and in the mericarp (during its development from ovary to full maturity), was achieved using specific histochemical tests.  1998 Annals of Botany Company Key words : Conium maculatum L., poison hemlock, secretory structures, alkaloids, histochemistry. INTRODUCTION It is well known that the majority of the Apiaceae produce volatile oils in clearly-delimited tissues of the fruits, known as vittae, which also appear to be the sites of synthesis andor storage of biologically-active secondary products, such as flavonoids and coumarins (Crowden, Harborne and Heywood, 1969 ; Hegnauer, 1971). In contrast, Conium maculatum L. produces alkaloids, although linear furano- coumarins have been isolated from the plant (Nielsen, 1971), and synthesis andor accumulation sites have not yet been unequivocally identified (Cromwell, 1956 ; Fairbairn and Challen, 1959). It is uncertain whether vittae are actually present (Moynier de Villepoix, 1878 ; Bentley and Trimen, 1880 ; Tanfani, 1891 ; Planchon and Collin, 1895 ; Tschirch and Oesterlie, 1900 ; Moll and Janssonius, 1923 ; Fairbairn and Challen, 1959 ; Wallis, 1960 ; Clapham, Tutin and Warburg, 1962 ; Fairbairn, 1971). The most recent work on the subject (Fairbairn, 1971) refers to ‘ provittae ’, i.e. small, anomalous, secreting structures, present in the ovary in the early stages of the ripening process ; when the fruit was fully ripe, these structures were very compressed tangentially, becoming nearly invisible. Accordingly, it was proposed that ‘ at an even earlier stage volatile oil is produced in these ducts but later there is a switch to alkaloid production ’ (Fairbairn, 1971). Many members of the Apiaceae also have secretory ducts, producing volatile oils, in vegetative organs and in fruits (Corsi and Pagni, 1983 ; Coassini Lokar and Corsi, 1986 ; Pagni, Corsi and Cappelletti, 1986 ; Maffei et al., 1987 ; Innocenti, Pagni and Corsi, 1990). There is no information on such structures in C. maculatum, although early workers (Moynier de Villepoix, 1878 ; Tanfani, 1891) pointed out the presence of secretory ducts, discerning them from vittae only by their location. The present research, based mainly on histochemical studies of C. maculatum, has three aims: (1) to identify and locate secretory structures, discriminating between vittae and secretory ducts (Corsi and Pagni, 1983) at different stages of development from seedling to fruit ; (2) to test for the presence of essential oils in these structures ; and (3) to establish the distribution of alkaloids. MATERIALS AND METHODS Plant material The plant material used in this investigation originated from a natural population of Conium maculatum L., collected from the Coltano Estate, near Pisa (NW Tuscany) and maintained by seed in the Botanic Garden of the University, Pisa. Tissues studied included seedlings germinated in Petri dishes on blotting paper and sampled at three stages : 1S (seedling length 3 to 4 mm); 2S (seedling length 5 to 10 mm) ; and 3S (seedling length more than 10 mm). Freehand cross- and longitudinal sections were also pre- pared from the following tissues of garden plants : root, stem, first to third order rachis, leaf blade, ovary and mericarp. The latter two tissues were studied at the following seven stages of the ripening process : 0 (immature ovary in buds—not fertilized) ; 1 (swollen ovary, all petals attached— fertilization had just occurred) ; 2 (swollen ovary, petals starting to abscise—about 1 week after fertilization) ; 3 (green mericarp, all petals had abscissed—about 10 d after fertilization) ; 4 (growing mericarp, still green—about 2 weeks after fertilization) ; 5 (mericarp turning brown, almost fully ripened—about 3 weeks after fertilization) ; 6 (brown mericarp, fully ripened—more than 3 weeks after fertiliza- tion). Methods Ten–25 μm cross- and longitudinal sections of each tissue were prepared using a Leitz-1720 Digital Cryostate, at 14–18 C. Semi-thin (2 μm) sections of each tissue were prepared using a Leica 2055 Autocut Automatic Microtome, fixed in FAA for 24 h (Sass, 1958), and embedded in epoxy 0305-73649801015706 $25.000 bo970547  1998 Annals of Botany Company