The activity of Balbiani rings 1 and 2 in salivary glands of Chironomus tentans larvae under different modes of development and after pilocarpine treatment.

The activity of the Balbiani rings 1 and 2 (BR1 and BR2) in the salivary gland was followed during development of fourth instar larvae of Chironomus tentans under different modes of development, with or without a previous pilocarpine treatment. The activity was determined in parallel by two different methods, by incorporation of [3H]uridine into BR-RNA (75 S) and by morphometry of BR1 and of BR2. In glands of untreated larvae BR2 does not change dramatically except for a depression of activity during oligopause (resting phase). BR1 is completely inactive during this phase but exhibits a pronounced activity maximum in the middle of the prepupal period, in subitaneously developing (i.e., uninterrupted) as well as in postoligopause cultures. After pilocarpine treatment the activity of BR2 (rather than of BR1) is generally increased. The extent of this stimulation, however, is strongly development dependent. A most striking activity difference is observed in postoligopause between animals of stage 5 and of stage 6. The relationship between BR2 activity and degree of emptying of the salivary gland lumen was investigated. A model is proposed in which BR2 activity is conceived as being regulated by two parameters: by the degree of filling of the gland lumen and by the stage and mode of development of the larva.