HCl Treatment for Preventing Diapause Causes Ca2+ Efflux in Bombyx mori Eggs.

Abstract

To elucidate the mechanism for preventing entry into embryonic diapause or breakdown of diapause in Bombyx mori by HCl and dimethyl sulfoxide (DMSO) treatment or a combination of cold and HCl treatment, we performed quantitative analysis of Ca2+ and Mg2+ in the chorion and egg content using inductively coupled plasma atomic emission spectrometry (ICP-AES). When diapause eggs that had been incubated at 25°C for 2 days from oviposition and at 4°C for an additional six days were treated with HCl solution, the amount of Ca2+ in the chorion and egg content after HCl treatment was reduced to one-seventh, as compared with the amount before treatment. In contrast, there was no change in the amount of Mg2+ with HCl treatment. The amount of Ca2+ in the HCl solution after the diapause eggs were treated increased 7.5-fold, as compared with that of eggs treated with water. Even when 17-day-old diapausing eggs were treated with HCl, which did not break diapause, the amount of Ca2+ in the chorion and egg content was reduced to one-fifth, as compared with the control. Meanwhile, changes in Ca2+ and Mg2+ contents were not observed in 12-hr-old diapause-destined eggs before or after treatment with DMSO, which effectively prevents diapause. These data may suggest that Ca2+ efflux from diapause eggs by HCl is not directly associated with preventing entry into diapause or breaking of diapause. In addition, we discovered that the amount of Ca2+ in diapause-destined eggs was more than 2.4-fold larger than in non-diapause-destined eggs.