Developmental- physiological investigations on the embryonic mycetoma of Euscelis plebejus : Elimination and abnormal combination of various components of the symbiontic system
Develop Biol 17(1): 16-38
The egg of the leafhopper E. plebejus encloses a ball-shaped mass of symbiontic bacteria near its posterior pole. The bacteria belong to types a and t (Buchner, 1965). The a-type symbionts are taken up by a1-mycetocytes during anatrepsis; immediately before katatrepsis they are taken over by another cell type, the a2-mycetocytes. Shortly before this, the t-type symbionts become lodged in t-mycetocytes. The egg can be divided by ligation into 2 fragments of varying sizes. The mass of symbionts may be shifted experimentally within the posterior 2/3 of the egg. By combining these techniques it is possible to eliminate either symbionts or germ anlage from an egg fragment, to prevent the contact of symbionts and germ band contained in the same fragment, and to combine the symbionts with atypical regions of yolk system and germ band. In egg fragments deprived of the bacterial mass, no a1-mycetocytes are found unless the posterior part of the abdomen is present, but even then these cells may be lacking. The t- and a2-types of mycetocytes are produced by certain abdominal segments regardless of presence or absence of symbionts. Symbionts shifted experimentally within the egg are unable to induce the formation of t- and a2 -mycetocytes in their new positions. They may, however, be able to divert cleavage cells of different prospective fates into a1 -mycetocytes. Symbiont masses isolated in the yolk system show signs of decay on or before day 8, although as a rule they are supplied with a1-mycetocytes. These mycetocytes degenerate even if the germ band within the same egg fragment has not yet reached the stage corresponding to their decay in normal development. This decay may be prevented by contact of the symbiont mass with any part of the germ band; in this position the a1 -mycetocytes may stay intact beyond the germ band stage normally correlated with their destruction.