The role of serine endopeptidase in cu-cumber leaf senescence was studied by using the inhibitor of serine endopeptidase and plant growth regulators(6-BA and ABA)on darkness-induced cucumber leaves.

Endopeptidase, BAPA, from sterile line at trinucleate stage showed cysteine- and serine types, and also part of type with metalloprotease, but it was the serine type only in maintainer line.