Cell structure of Lacandonia schismatica visualized by atomic force microscopy R. Fragoso-Soriano (l),C. Falcony (l),C. Vazquez-Lopez (l),L.F. Jimenez-Garcia (2) (1) Centro de Investigacibn y Estudios Avanzados, IPN, Mexico D.F., Mexico. (2) Facultad de Ciencias, UNAM, Mexico D.F., Mexico. Lacandonia schismatica E. Martinez & C.H. Ramos is the only known flowering plant where the reproductive organs are spatially inverted (l-2). Several studies have been made to better understand its biology. We have previously studied the cell nucleus and the cytoplasm of the species by transmission electron microscopy (TEM) (3-5). In the cell nucleus we described an abundant 32 nm in diameter ribonucleoprotein particle. The nucleus is reticulated, because the chromatin is arranged as thick strands, similar to other plants as AZZium cepa. In the cytoplasm, .plastids, mitochondria, rough endoplasmic reticulum, Golgi apparatus, and large vacuoles are present. The aim of this study was to probe whether the atomic force microscope (AFM) can be used to analyze plant cell structure in order to eventually obtain for example, higher resolution than that offered by TEM. If the microscope gives information about the surface of samples, we reasoned that sectioning a biological sample, each section can be analyzed as an individual surface . In addition, roughness of the sections would correspond to the different cell structures. Samples of L. schismatica were prepared for standard TEM including glutaraldehyde fixation and epon embedding. Semitbin section were mounted on glass slides and scanned with an Autoprobe CP AFM equipped with a scanner of either 100 or 10 urn, operating in environment conditions in the contact mode at1 0 nN of contact force, a scan rate of l-2 Htz and a gain of 0.3-0.5 arb. units. Images were processed with the Proscan version 3.1 software. Pictures were printed with a high resolution Codonics dye sublimation printer. Cell walls defined the boundaries of each cell. Vacuoles were seen as large spaces in the cell. Cell nuclei were observed as large rounded structures. A reticulated pattern for chromatin was similar to that produced by TEM. One or two nucleoli were also observed. In the cytoplasm we have been able to detect mitochondria and plastids. For comparison we also observed cell structure of the plant Ginkgo biluba, where chloroplast are abundant. L. schismatica has no chloroplasts due to its saprophytic habit. With the AFM, chloroplast were observed, including the starch within. Our results indicate that plant cell structure can be analyzed with atomic force microscopy from semithin sections of material prepared for standard electron microscopy. References 1. Martinez E. and Rasnos C.H., Ann. MO Bat. Gurd., 76 (1989) 128. 2. Marquez-Guzman J. et al., AnnMO Bat. Gard., 76 (1989) 124. 3. Jimenez-Garcia L.F. ef al., Biol. Cell 75 (1992) 101. 4. Agredano-Moreno L.T. et al., Biol. Cell 82 (1994) 177. 5. R&ynoso-Robles R. Tesis Biologia, Fac.d e Ciencias UNAM, Mkxico (1996). 600 MO 400 200 J Fig. 1. Atomic force microscope image of Lacandonia schisma~icu ovary ceils. N, nucleus; n, nucleolus; v, vacuole; m, mitochondria; w, cell wall. .