ONTOGENY AND CYTOCHEMISTRY OF ALKALOIDAL VESICLES IN LATICIFERS OF PAPAVER SOMNIFERUM L. (PAPAVERACEAE)

Development of alkaloidal vesicles in laticifers of opium poppy, Papaver somniferum L., was investigated at the ultrastructural level. Laticifer initials possessed abundant endoplasmic reticulum throughout their dense cytoplasm. During differentiation the endoplasmic reticulum organized into long, folded sheets that were parallel to the longitudinal walls along the periphery of the cell. Vesicles appeared to be derived from dilation of endoplasmic reticulum. This relationship was confirmed through cytochemical data obtained with zinc iodide-osmium tetroxide and osmium tetroxide impregnation. Alkaloidal vesicles had electron-dense regions or caps that occurred early in laticifer differentiation, but these caps became less conspicuous in mature cells. Caps appeared to be derived from small particles which condensed along the inner surface of the vesicle membrane and subsequently accumulated at one or two positions along the membrane of the vesicle. LATICIFERS in opium poppy, Papaver somniferum L., can be distinguished from other cell types at the ultrastructural level by the large, irregularly shaped vesicles that fill the mature cell. Origin of these vesicles from endoplasmic reticulum was first suggested by Sarkany et al. (1964) in an abstract unaccompanied by micrographs. In a more detailed report, Thureson-Klein (1970) described abundant, elongated profiles of endoplasmic reticulum in undifferentiated poppy laticifers that appeared to give rise to vesicles through local distension. The bottom fraction of ultracentrifuged latex from P. somniferum has been shown to consist of vesicles that contained alkaloids within their vacuolar plasm (Fairbairn, Hakim, and El Kheir, 1974). Dickenson and Fairbairn (1975) investigated the ultrastructure of these "alkaloidal vesicles" in both ultracentrifuged latex and intact plants. In the present investigation the ontogeny of alkaloidal vesicles in laticifers of Papaver somniferum is described and cytochemical evidence is presented for their origin from endoplasmic reticulum. MATERIALS AND METHODS-Plants of Papaver somniferum L. cv. "Neuga" were grown from seed in the greenhouse. Seeds were also germinated in glass jars on cheese cloth discs supported by filter paper cylinders to obtain straight radicles that were uncontaminated with soil particles. 'Received for publication 9 September 1976; revision accepted 2 February 1977. This research was supported by a grant from the United Nations, UN 444-75, and the Indiana University Foundation. D. E. A. Registration No. PM0084537. Tissue processing for general electron microscopy-For general electron microscopy, tissues from various portions of plant axes and seedlings were fixed for 8-12 h at room temperature in one of the following fixatives: 1) 2% glutaraldehyde in 0.1 M phosphate buffer, pH 7.2; 2) 1% glutaraldehyde, 3 % paraformaldehyde in 0.1 M phosphate buffer, pH 7.2 (Karnovsky, 1965); or 3) 4% glutaraldehyde, 0.7 % picric acid in 0.1 M sodium cacodylate buffer, pH 7.0 (Turner, 1970). After several rinses with 0.05 M sodium cacodylate, pH 7.0, tissues were post-fixed by immersion in 1 % osmium tetroxide in 0.05 M sodium cacodylate, pH 7.0, for 2 h, rinsed with glassdistilled water and prestained in 1 % aqueous uranyl acetate at 4 C for 6-12 h. Tissues were then rinsed with glass-distilled water, dehydrated through an ethanol-acetone series and embedded in Spurr's (1969) low-viscosity resin. Some tissues were fixed in 1 % osmium tetroxide in 0.1 M phosphate buffer, pH 7.2, for 2 h and dehydrated and embedded as described above. Tissue processing for cytochemical electron microscopy-Procedures described above were modified for cytochemical electron microscopic investigations as follows: 1) Zinc iodide-osmium tetroxide (ZIO) impregnation. Tissues were fixed in the dark for 24 h in a zinc iodide-osmium tetroxide solution as described by Niebauer et al. (1969). ZIO fixed tissues were rinsed with glass-distilled water, prestained with uranyl acetate, dehydrated and embedded as above. A modification of this procedure consisted of treating tissues with Turner (1970) fixative for 8-16 h before ZIO impregnation.