Cytomorphological and biochemical changes in dwarf pea shoots induced by gibberellic acid

Treatment of 8-day-old pea plants for 15 and 24 hr with gibberellic acid resulted in: 1. 2-3 Fold increase of the cell length. 2. About 20% increase of the nuclei and nucleoli size in meristematic zone of plant shoots. 3. Increase of endomitotic and mitotic synthesis of DNA. 4. Increased ability of the cells to bind [3H]Actinomycin D. 5. Higher rate of RNA synthesis. 6. Increase of the fresh weight of apical parts of the green pea shoots. 7. These results indicated that gibberellic acid accelerates the growth and differentiation of plant cells.     

Activities of DNA polymerases and RNA polymerases detected in situ in growing and differentiating cells of root cortex.

Activities of DNA polymerases and RNA polymerases were studied by autoradiographic methods in growing and differentiating root cortex cells of Zea mays - a species in which endomitosis occurs - and Tulipa kaufmanniana - in which this process does not occur. In Tulipa kaufmanniana, the highest activity of DNA polymerase appears in the nuclei of meristematic zone during the S phase of the cell cycle. In Zea mays, endomitotic replication of DNA occurs in all growth and differentiation zones and the activity of DNA polymerase in the nuclei is similar to that in the meristematic zone. In both species, nuclear RNA synthesis, measured with 3H uridine incorporation, is highest in the meristematic zone and declines steadily with development. Activity of nuclear RNA polymerase is present in all developmental zones in both species and is similar to that in the meristematic zone. 3H uridine incorporation into nucleoli decreases markedly in both species, whereas the activity of nucleolar RNA polymerase remains at a high level in all root segments in Zea mays and decreases slightly in Tulipa kaufmanniana. It is argued that the differences between the incorporation of 3H uridine and that or 3H UMP may be caused by a reduction of the pool of endogenous ribonucleoside triphosphates. Marked activities of DNA polymerase and RNA polymerase in cytoplasm are possibly related to the growth and division of plastids and mitochondria.