The kinetics of embryo drying in Drosophila melanogaster as a function of the steps in permeabilization: Experimental

The Drosophila embryo is surrounded by an outer chorion and an inner vitelline membrane that are an effective barrier to the movement of water. The chorion can be removed by 2.5% hypochlorite (1). If surface water is then removed by isopropanol (2), the vitelline membrane can be rendered permeable to water by heptane containing 0.3% 1-butanol (3). Here, we determined quantitatively the effects of these three steps on the permeability of the embryo to water. Permeability was assessed by exposing embryos to air at 22–23 °C and approx. 56% r.h. and determining weight loss with time. We also determined the effect of the three permeabilization steps on the water and solids contents of the embryos initially, after equilibration with air, and after complete drying. The intact embryo contains 76% ( w w ) water and 24% solids. The successive permeabilization steps produce small increases in the former and small decreases in the latter. Intact embryos require 5–12h to lose half their water, the longer times being applicable to older embryos. After permeabilization steps (1), (1) + (2), and (1) + (2) + (3) the times for 50% water loss decrease to 1.6, 1.9, and 0.1 h, respectively.