STRUCTURE OF PLASMODESMATA (INTERCELLULAR PLANT JUNCTIONS)

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We are studying the 3-dimensional structure of plant intercellular connections, the plasmodesmata (PD). Dr. Civotsky's laboratory sent Dr. Sosinsky grids containing thick and thin sections cut from embedded and sectioned material. These samples are 1) leaf tissue 2) purfied cell walls with plasmodesmata (PD) and 3) purified cell walls with PD treated with the detergent chaps. Dr. Sosinsky has collected 3 tilt series of sample 2. The first reconstruction just contained cell walls, so Dr. Sosinsky will collect more tilt series. She is presently examining the PD's in leaf tissue to compare with isolated, biochemically characterized PD's. In the past year, we have acquired five tilt series from preparations of purified cell walls containing plasmodesmota proteins. Three of the tilt series were from CHAPS (a detergent) treated cell walls while the other two tilt series were from preparations which were not detergent treated. Tomograms of each of the five tilt series were computed. Surprisingly, the plasmodesmota in all five tomograms did not look like models based on projection images. In models based on thin section images from both isolated plasmodesmota and ones found in leaf tissue, the plasmodesmota should resemble a barrel-shaped structure analogous to nuclear pore complexes. In the tomograpms, we found two elipsoidal elongated structures that span the cell wall longitudinally, but not radially. We will be recording tilt series from intact leaf tissue and consequently computing tomograms from these tilt series in order to assess if the plasmodesmota structure is barrel-shaped and a significant loss of pro teins in the structure have been lost during isolation (coordinating with the biochemistry of the project) or that the model based on thin section is incorrect and indeed, the plasmodesmota structure is not a solid cylinder.