The Nectary Exudate of Lycium cestroides (Solanaceae)

Abstract

The floral nectary exudate of Lycium cestroides Schlecht.-a psychophilous and ornithophilous South American shrub-indudes amino acids, proteins, reducing acids, and sugars. It is hexose dominant with 57.38 percent glucose, 34.39 percent fructose, and 8.21 percent saccharose. Lipids, phenols, and alkaloids are not present, although vegetative parts produce alkaloids. This is the first complete report of nectar composition for a species of this genus. ALTHOUGH MUCH WORK has been done on nectars, our knowledge of the chemical constituents of solanaceous nectar is meager. Lycium has been incidentally studied (Bonnier 1879, Knuth 1906-1909, Percival 1961), but no species has been analyzed in detail. I have observed that Argentine species of Lycium secrete floral nectar through a circular nectariferous tissue located in the ovary base (Bernardello 1986). Some shrubs with short, infundibuliform corolla tubes (like Lycium chilense Bert. and Lycium ciliatum Schlecht.) produce little exudate compared with others showing long tubulose corolla tubes (for instance, Lycium gilliesianum Miers and L. cestroides). Nevertheless, nectar production is not only affected by such internal factors as flower size and shape and nectary surface, but also by a number of external ones, soil and atmospheric humidity and temperature, among others (Percival 1969, Maurizio 1976, Fahn 1979, Cruden et al. 1983). Lycium cestroides is a spiny shrub which occurs from southern Bolivia to Uruguay. Butterflies and hummingbirds seek its nectar and act as pollinators (Bernardello 1983). In this paper I describe the nectar constituents, induding qualitative and quantitative analyses of sugars, with the objective of contributing to understanding the pollinator-plant relationship. MATERIAL AND METHODS Nectar was collected during the day in fair weather from a population of 14 shrubs growing in Cordoba (Argentina, Prov. Cordoba, Dept. Capital, Bernardello 346, 3 Dec. 1980, CORD). Two ml samples of freshly produced floral nectar were taken by finely drawn micropipettes. Maximum caution was taken to avoid pollen contamination and evaporation. Nectar drops were placed on sterile Whatman No. 1 chromatography paper and quickly I Received 29 April 1985, revision accepted 24 August 1985. dried; the remainder was immediately frozen and stored at -25?C until use (2-4 wk). Additionally, part of the nectar was lyophilized for further use. The analyses for amino acids, proteins, lipids, phenols, and reducing acids followed the procedures of Baker and Baker (1975). Dragendorff's reagent (Krebs et al. 1969) was employed to detect alkaloids. All these tests were done on nectar spots. Sugar concentration of fresh nectar was measured in sucrose equivalents with a Goldenberg T/C pocket refractometer. Separation of the sugars was obtained by thin-layer chromatography on microcrystalline cellulose (Lewis & Smith 1969) and by paper chromatography on Whatman No. 3 paper with n-Butanol : acetic acid: water (3:1:1) as a solvent. They were visualized with aniline diphenylamine or aniline phtalate. Sugar identification has also been attempted by gas chromatography. Nectar was previously silylated as indicated by Sweeley et al. (1963), and the derivatives were injected into a chromatograph equipped with a flame ionization detector and a SE-30 column, 3 percent on Chromosorb W DMCS net 80-100. Operating conditions were as follows: nitrogen as the carrier gas and a temperature of 200-250'C. Sugar standards were prepared under the same procedure. Quantitative analyses for sugar were done by gas chromatography with a Varian aerograph 9600 data processor. RESULTS AND DISCUSSION Amino acids, proteins, and reducing acids were present in the nectar drops; alkaloids, lipids, and phenols were not. The application of bromphenol blue on nectar drops developed a blue-green color, indicating proteins, and ninhydrin yielded the usual violet color for amino acids. The test for reducing acids was performed with 2,6 dichlorophenol indophenol; the rapid development of a dark red color indicated organic and ketoacids, and subsequent lightening of the color to gray, reducing acids. BIOTROPICA 18(3): 241-243 1986 241 This content downloaded from 207.46.13.111 on Sun, 22 May 2016 06:34:17 UTC All use subject to http://about.jstor.org/terms Of particular interest is the absence of alkaloids in L. cestroides nectar, despite their presence in the vegetative parts (Cabrera & Juliani 1981, Chiale et a-l. 1984). A similar pattern occurs in Nicotiana sylvestris Speg. and Comes (Solanaceae) (Baker et a-l. 1973). Baker and Baker (1975) stated that butterflies and moths do not tolerate alkaloids in the nectar they drink; supporting this assumption is the fact that L. cestroides is psychophilous and has no alkaloids. Furthermore, L. cestroides, like other examined Solanaceae (Voss et agl. 1980, Hernandez 1981, Gottsberger et agl. 1984) has amino acids. According to Baker and Baker (1973a, b, 1975, 1983), nectary exudates possess detectable amounts of amino acids and are important rewards for insects that have no other source of proteinbuilding materials. Notwithstanding, Gottsberger et a-l. (1984) pointed out that apparently nectars are not rich enough in amino acids for the insect's nutritional require-