THE KINETICS OF EMBRYO DRYING IN DROSOPHILA-MELANOGASTER AS A FUNCTION OF THE STEPS IN PERMEABILIZATION - THEORETICAL

Previously, we gravimetrically examined the Drosophila embryos' rate o f air drying after each step in their permeabilization; namely, (1) de chorionation, (2) isopropanol exposure, and (3) heptane/butanol exposu re. Here we describe a physical model characterizing the dehydration a nd compare the theory with the experimental kinetics. The model is bas ed on those of Eyring. It treats the net flux (J(net)) through the mem brane as the sum of two opposing fluxes (air --> embryo {a} and embryo --> air {i}). Each flux is the product of a kinetic constant (k), the number of embryos in the sample (n), and the water concentration (C). Thus, J(net)=k(a)nC(a)-k(i)nC(i). The relationship between k(i) and k (a), for embryos in steady state with room humidity, is k(i)/k(a)=Ca/C -i. Determining the k values requires the mass and density of the embr yo solids, n, C-i as a function of drying time, and the steady-state v alue of C-i. Following integration of the flux equation, linear regres sion was used to determine k(i). k(a) was computed using the previous equation. The resulting values for k(a) are 3.96, 26.70, 17.40, and 25 8.00 mm(3)/embryo . h for untreated embryos and embryos treated with, (1), (1)+(2), (1)+(2)+(3), respectively. The corresponding values for k(i) (x10(6)) are 484, 3680, 2800, and 47,300 mm(3)/embryo . h. Publis hed by Elsevier Science Ltd