Egg-shell calcium and the hatching of Globodera rostochiensis

The Ca²⁺ content of Globodera rostochiensis egg-shells was investigated by X-ray microanalysis. When intact eggs were treated with 5 mM sodium 1, 2-di (2-aminoethoxy) ethane-N,N,N',N',-tetra-acetate (EGTA) only part of the egg-shell Ca²⁺ was removed. Similarly treated opened egg-shells lost almost all their Ca²⁺. We think that Ca²⁺ of intact egg-shells which is accessible to EGTA is in the outer part of the shell and that the inaccessible Ca²⁺ is in the inner lipoprotein layer. Much Ca²⁺ was removed from opened egg-shells by the hatching agents Zn²⁺, La³⁺ and decationised potato-root exudate, but none by dilute acetic acid or Mg²⁺. Hatching agents, by binding to or replacing Ca²⁺, may change lipoprotein membrane structure. Eggshells treated with potato-root exudate contained about 3 times as much Ca²⁺ as untreated shells, because the treatment makes additional binding sites available. Our results suggest that three types of Ca²⁺ -binding sites occur in the egg-shell.