Characterisation of a plasma membrane-associated phospholipase A(2) activity increased in response to cold acclimation

We here demonstrate the presence of a plasma membrane-associated phospholipase A(2) (EC 3.1.1.4; PLA(2)) activity in spinach (Spinacia oleracea) leaves. The pH profile of the spinach plasma membrane PLA(2) activity revealed two peaks, one at pH 4.4 and one at pH 5.5. The activity at pH 5.5 had an absolute requirement of Ca2+, with full enzyme activity at 10mumol/L Ca2+. The Ca2+-dependent PLA(2) activity was both heat sensitive and stimulated by diacylglycerol, whereas ATP completely inhibited the activity. Thus, the spinach plasma membrane contains a Ca2+-dependent PLA(2) activity, which has not previously been characterised in plants. Cold acclimation of spinach resulted in a 2.2-fold higher plasma membrane PLA(2) activity whereas the plasma membrane phospholipase D activity remained unaffected. Taken together, our data suggest a role of PLA(2) in cold acclimation in plants.