Peroxidase activity and ATP-dependent Ca2+ transport in subcellular fractions of embryogenic and non-embryogenic Daucus carota cell suspensions

摘要

The primary ATP-dependent Ca2+ transport activity was mainly located in the plasma membranes (PM) of carrot cell suspensions, and was lower in PM from embryogenic than non-embryogenic cells. The majority of the peroxidase was soluble with about three times lower specific activity in embryogenic cells than in non-embryogenic cells. However, there was also a membrane-bound peroxidase. This activity was enriched in the intracellular membrane (ICM) fraction, and was higher in preparations from embryogenic cells than from non-embryogenic cells, i.e. a behaviour opposite to that of the soluble peroxidase. Using Spearman rank correlation a negative correlation was found between PM-bound Ca2+ transport and ICM-bound peroxidase, in agreement with the factthat increases in cytosolic Ca2+ activates the secretion and the activity of the peroxidase. The Ca2+ transport was inhibited by calmodulin, probably due to a very high endogenous calmodulin concentration, especially in non-embryogenic cells. These datasuggest that alterations in peroxidase activity and Ca2+ transport occur before embryo development takes place.