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The measurement of chromomycin A3/DAPI fluorescence ratios is shown to allow base content determinations in eu- and heterochromatic regions of interphase cell nuclei. The base content values obtained in chromocenters and euchromatin of Scilla sibirica agree with those measured earlier [12] on the band and non-band areas of the chromosomes of this species. In Sinapis alba three different heterochromatin types, with regard to base content, can be discerned. The heterochromatin amplification observed in the polyploid nuclei of Sinapis roots and hypocotyl involves either all three heterochromatin types, with little resulting change of the total nuclear base content, or only one or the other of them, with a measurable shift of the base content.

The product of cauliflower mosaic virus (CaMV) gene I has been characterized from extracts of infected plants. Two size classes of this protein can be identified by the use of specific antiserum. The antiserum was induced against a chimeric protein produced in E. coli from a gene fusion between a fragment of the CaMV genome and the beta-galactosidase gene. A 36-kDa form of the gene I product is associated with virus particles. A 45-kDa form of this product was found only in the insoluble fraction of tissue homogenates. This insoluble fraction, the only fraction found to contain the product of viral gene VI, contains the virally induced inclusion bodies.

Phloem sieve elements in small nodules of callus tissue have open sieve pores and scattered P-protein when the tissue is fixed intact. Intentionally slicing the nodules prior to fixation results in the formation of wound responses, including an alteration in P-protein distribution and the formation of plugged sieve pores. Freeze-fracture replicas show well-preserved P-protein as randomly oriented filaments in intact sieve elements. Wounded sieve elements, however, demonstrate dense bundles of oriented P-protein filaments in freeze-fracture replicas. Open pores with few P-protein filaments are seen in replicas of undamaged sieve elements. These callus nodules can be used as a model system to investigate phloem structure, function, and wounding.