Factors, affecting in vitro activation of potato phospholipase A 2

Abstract

In potato infected with an incompatible race of Phytophthora infestans, the late blight fungus, or treated with fungal elicitor hyphal wall components (HWC), there is possible involvement of phospholipase A 2 (PLA 2) in induction of resistance reactions. Activation of soluble PLA 2 in a partially purified PLA 2 preparation in vitro required Ca 2+, Mg 2+, diacylglycerol (DG), ATP and calmodulin. The optimal activity of PLA 2 in the presence of Ca 2+ was at a pH of 8.5. CaCl 2 or DG stimulated the activity directly. Increased activity with Ca 2+, Mg 2+, DG and ATP together suggests the involvement of a protein kinase in PLA 2 activation. The activity of PLA 2 was inhibited by straurosporine, a protein kinase inhibitor, and ophiobolin, a calmodulin inhibitor, in the presence of exogeneous Ca 2+ and calmodulin. Because straurosporine, but not ophiobolin, prevented activation by exogeneous Ca 2+, Mg 2+, DG and ATP, inhibition appears to result from an indirect effect of calmodulin on PLA 2. The activity of PLA 2 measured in the presence of Ca 2+, Mg 2+, DG and ATP increased to peak at 2–3 h following treatment of potato tuber discs with HWC. Modulation of PLA 2 activity by Ca 2+, DG and protein kinase(s) seems to be involved in signal transduction during the initiation of defence responses in potato tubers.