ORGANIZATION OF MICROTUBULES AND MICROFILAMENTS IN PROTOPLASTS FROM SUSPENSION CELLS OF NICOTIANA-PLUMBAGINIFOLIA - A QUANTITATIVE-ANALYSIS

The cortical cytoskeleton of suspension cells and protoplasts of Nicotiana plumbaginifolia was studied by means of fluorescent probes by a light microscope and by means of dry-cleaved preparations by an electron microscope. No differences in the organization of the cortical cytoskeleton of the suspension cells and protoplasts were observed. Generally, the cytoskeleton showed highly organized domains within superficially random-like patterns. Microtubules formed extensive bundles with up to 10 elements per cross-linked bundle. About 65 cross-bridges occurred per micrometre. The cross-links were 25-50 nm long and 5-20 nm in diameter. On average, 56% of the entire microtubular length was present in the cross-linked bundles. The length and abundance of microtubules ranged between 0.8 and 14.28-mu-m and 0.93-4.29-mu-m mu-m-2, respectively. Microtubules were regularly aligned with microfilaments, either as parallel or as 'stitched' filaments. These alignments did not occur over distances longer than 1.46-mu-m. The distribution of the coated pits appeared to depend on microtubular distribution. Coated pits were often connected with the microtubules by means of putative actin filaments.