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

Carrot (Daucus carota L.) cell suspensions with different embryo-forming capacity were used here for subcellular studies on processes that may be linked to embryogenesis, e.g. active Ca2+ transport and peroxidase in isolated plasma membranes (PM) and intracellular membranes (ICM). The primary ATP-dependent Ca2+ transport activity was mainly located in the PM, and was lower in PM from embryogenic compared to non-embryogenic cells. The major part of the peroxidase was soluble with about three times lower specific activity in embryogenic cells compared to non-embryogenic cells. However, there was also a membrane-bound peroxidase. This activity was enriched in the ICM fraction, and, interestingly, higher in preparations from embryogenic cells than from non-embryogenic cells, i.e. a behaviour opposite to the soluble peroxidaseʹs. Using Spearman rank correlation a negative correlation was found between PM-bound Ca2+ transport and ICM-bound peroxidase, in agreement with the fact that 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 data suggest that alterations in peroxidase activity and Ca2+ transport are already obtained before embryo development takes place.