Involvement of phospholipase A2 in the response of Solanum species to an elicitor from Phytophthora infestans

Changes in activity of phospholipase A(2) (PLA(2)), a key enzyme in lipid metabolism and signal network in defence mechanisms, were investigated in Solanum species and Phytophthora infestans interaction. We have compared PLA(2) activity in response to an elicitor, a culture filtrate (CF) derived from P. infestans, in non-host resistant Solanum nigrum var. gigantea, field resistant S. tuberosum cv Bzura and susceptible S. tuberosum clone H-8105. To elucidate the contribution of specific forms of PLA(2) to plant defence mechanism reasonably selective PLA(2) inhibitors, haloenol lactone suicide substrate (HELSS) and p-bromophenacyl bromide (BPB), which discriminate between Ca+2-independent PLA(2) (iPLA(2)) and Ca+2-dependent secretory PLA(2) (sPLA(2)), were used. The in vivo and in vitro effects of the inhibitors on PLA(2) activity and on generation of reactive oxygen species (ROS) induced by CF in the studied plants were assayed. We found that PLA(2) activity increased in response to CF treatment, displaying various kinetics and intensity depending on the resistance status of a given genotype. Differences among the genotypes in the effects of each inhibitor on CF-induced PLA(2) activity and on ROS production may reflect the diversity of PLA(2) isoforms in plants. Contrary to BPB, the inhibitory effect of HELSS was observable mainly on CF-induced PLA(2) activity, which suggests that iPLA(2) participates in signal transduction in defence reactions. Various effects of the two inhibitors on PLA(2) activity and ROS production suggest different contribution of sPLA(2) and iPLA(2) to modulation of defence reactions in the interaction between Solanum genotypes and P. infestans.