Eggshell calcium and the hatching of globodera-rostochiensis

Abstract - no further text Juveniles of Globodera rostochiensis hatch in response to potato root diffusate which is thought to initiate a permeability change in the inner lipoprotein membrane of the egg-shell. The existence of the lipoprotein membrane has now been shown using electron microscopy. The presence of Ca2+ in the egg-shell suggested that Ca2+ might be involved in maintaining egg-shell impermeability. We therefore examined the Ca2+ content of egg-shells using X-ray microanalysis. When intact eggs were treated with 5 miti EGTA only part of the Ca2+ present in the egg-shell was removed. However, when opened egg-shells were similarly treated almost all of the Ca2+ was lost. The Ca2+ of intact egg-shells which is accessible to EGTA is thought to be present in the outer chitinous layer of the shell and the inaccessible Ca2+ in the inner lipoprotein membrane. The Ca2+ in the inner layer was not removed when opened egg-shells were treated with dilute acids. We have confirmed previous work that egg-shells treated with potato root diffusate bind additional Ca2+, but as hatching can be initiated even if there is little free Ca2+ in the medium, it is unlikely that Ca2+ has a messenger role. Opened egg-shells treated with hatching agents (e.g. Zn2+, La3+) lost Ca2+ from the lipoprotein membrane. The near absence of Ca2+ in the egg-shell shows itself in a loss of structure in the ashed egg-shell. Our results show that the tightly bound Ca2+ present in the lipoprotein membrane is removed by the action of hatching agents. We suggest that hatching agents, by binding to or replacing Ca2+, induce structural change in the membrane and hence alter egg-shell permeability.