Peroxidase activity and ATP-dependent Ca 2+ transport in subeellular fractions of embryogenic and non-embryogenic Daucus carota cell suspensions

Abstract

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 Ca 2+ transport and peroxidase in isolated plasma membranes (PM) and intracellular membranes (ICM). The primary ATP-dependent Ca 2+ 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 peroxidase's. Using Spearman rank correlation a negative correlation was found between PM-bound Ca 2+ transport and ICM-bound peroxidase, in agreement with the fact that increases in cytosolic Ca 2+ activates the secretion and the activity of the peroxidase. The Ca 2+ 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 Ca 2+ transport are already obtained before embryo development takes place.