ศูนย์นวัตกรรมเทคโนโลยีหลังการเก็บเกี่ยว

Calcium-stimulated protein kinase activity of the hypodermal-mesocarp plasma membrane from preharvest-mature and postharvest muskmelon.

Gene E. Lester, Victor M. Baizabal-Aguirre, Luis E. Gonzalez de la Vara, and Wolfgang Michalke

Journal of Agricultural and Food Chemistry. Volume 46, Number 4, 1998. Pages 1242 -1246.

1998

บทคัดย่อ

Vanadate-sensitive H(+)-ATPase and calcium-dependent protein kinase (kinase) activities of hypodermalmesocarp plasma membrane (PM) vesicles isolated from preharvest mature, harvested, and stored muskmelons (Cucumis melo L. var. reticulatus Naud.) decreased following harvest. Kinase activity is markedly stimulated by Ca2+ and is responsible for phosphorylation of many melon PM proteins. Specifically, a PM protein band at 97 kDa, immunodetected as H(+)-ATPase, appeared phosphorylated in mature fruits, but phosphorylation and the sodium dodecyl sulfate (SDS) gel protein band were not detected in PM from harvested or stored fruit. Kinase peptide, immunodetected at 63 kDa, was present in all PM tissues, but kinase phosphorylation activity decreased with fruit harvest and storage. However, PM kinase activity in the presence of exogenous Ca2+ and histone III-S was greatly increased in harvested, and stored fruit, indicating both a stimulatory effect of Ca2+ and a loss of a suitable endogenous kinase substrate in postharvest melons. Washing PM vesicles with EGTA to remove Ca2+ and Ca2+ from Ca(2+)-binding proteins, e.g. calmodulin, or adding brain calmodulin affected kinase activity only in preharvest mature melon tissue. Our data indicate that the loss in kinase phosphorylation activity after harvest in melon PM is most likely due to the decrease in H(+)-ATPase peptide, a known kinase substrate, and that the decrease in H(+)-ATPase activity in postharvest fruit PM is most likely due to a loss in peptide content rather than its phosphorylation status by kinase.