Acylhydrolase that catalyzes the hydrolysis of phosphatidylcholine (PC) at the sn-1 position. High activity toward PC, medium activity toward monogalactosyldiacylglycerol (MGDG) and low activity toward triacylglycerol (TAG). Confers sensitivity to UV-B radiation probably by deesterifying membrane phospholipids. Expressed in leaves, stems, flowers and siliques, and, at low levels, in seeds and roots (at protein level). Strongly induced in response to sublethal levels of UV-B radiation. Down-regulated as the leaves senesce. Enhanced tolerance to UV-B stress but not osmotic stress. Impaired PR-1 accumulation in response to UV-B. Belongs to the AB hydrolase superfamily. Lipase family.