PARENT SESSION

Symposium S8C C4 and CAM
Friday September 3rd, 2004 8:30 AM-10:30 AM Room 510B
Chair: Rowan Sage
Co-Chair: Howard Griffiths

Role of the cytoskeleton in organelle compartmentalization in chlorenchyma of single cell C₄ plants (Chenopodiaceae). Simon Choung¹, Gerald Edwards^*,1, Vincent Franceschi¹, ¹ School of Biological Sciences, Pullman, WA, USA

ABSTRACT- Recently, Bienertia cycloptera and Borszczowia aralocaspica (Chenopodiaceae) were shown to possess a novel mechanism of C₄ photosynthesis generated through spatial compartmentation of organelles and enzymes into distinct regions within a single chlorechyma cell. Previous anatomical, histochemical and biochemical studies (Voznesenskaya et al., 2001, Nature; Vosnesenskaya et al., 2002, Plant J) have shown that these species utilize two different and unique patterns of compartmentation of organelles and enzymes to achieve the spatial separation, analogous to that in Kranz anatomy, within a single chlorenchyma cell. To better understand the mechanism maintaining compartmentation of organelles, we examined the distribution of microtubules and actin filaments and their spatial relationship with the dimorphic chloroplasts in the two compartments. Immunofluorescence and confocal microscopy of chlorenchyma cells showed that the distribution of chloroplasts to distinct cellular compartments correlates to patterns of both microtubule and actin filament networks. These cytoskeletal systems appear to be associated with the surface of the chloroplasts as extensive arrays of microtubules and actin filaments in the cell cortex and in the form of a cage surrounding the chloroplasts in both species. Furthermore, experiments using inhibitors of actin filaments and microtubules also showed that both cytoskeletal components are required for positioning and maintaining chloroplasts to distinct cellular compartments. We showed that, in Bienertia, disruption of microtubules and actin filaments induced an abnormal arrangement of chloroplasts in the central cytoplasmic compartment. These results provide evidence for the involvement of the cytoskeleton in maintaining the positioning of chloroplasts in the chlorenchyma cells of Bienertia and Borszczowia.

KEY WORDS: chloroplasts, development, C₄ photosynthesis, cytoskeleton