SCANNING ELECTRON-MICROSCOPY OF HETEROCHROMATIN IN CHROMOSOME SPREADSOF MALE GERM-CELLS IN SCHISTOCERCA-GREGARIA (ACRIDIDAE, ORTHOPTERA) AFTER TRYPSINIZATION

Chromosome spreads, prepared from testes of the desert locust Schistoc erca gregaria, were analyzed using scanning electron microscopy (SEM) after varying periods of preincubation in trypsin. The emphasis of the study was on the appearance of heterochromatin. A trypsin pretreatmen t of 5 sec resulted in a smooth surface on the chromatin throughout an d the heterochromatin was highly electron-emissive. The facultatively heterochromatic X chromosome was clearly visible in interphase spermat ogonia and in pachytene and late prophase I spermatocytes. Chromomeres of autosomal bivalents could be recognized in pachytene cells. Centro meric heterochromatin segments were very prominent in autosomes of lat e prophase I spermatocytes and some chromosomes showed interstitial an d telomeric bands, Longer trypsin treatment (10 sec) resulted in a fin e globular surface on the chromatin; however, the electron emission of heterochromatic chromosome segments was lower under these conditions. The result of trypsin pretreatment of euchromatin differed only sligh tly from that of the heterochromatin. Extensive trypsin treatment (20 sec) did not alter further the relative electron emission of heterochr omatin and euchromatin, but the regular globular appearance was lost, apparently owing to damage on the chromatin surface, The loss of elect ron emission from the centromeric heterochromatin of the autosomes and the facultatively heterochromatic X chromosome after extended trypsin treatment suggests a central role of proteins in mediating the hetero chromatic status in meiotic chromosomes of the locust. Information obt ained using scanning electron microscopy of chromosome spreads is comp lementary to that obtained by C-banding in that facultative heterochro matin is visualized with particular clarity.