Lipid acyl-hydrolase in leaves of different kidney bean (Phaseolus vulgaris L.) cultivars: Purification and characterization of a kidney bean lipid acyl-hydrolase, and foliar lipid changes in the cultivars with ozone exposure

Levels of acyl-hydrolase (EC 3.1.1.26) activity toward monogalactosyldiacylglycerol (MGDG) varied greatly not only in leaves of 12 plant species but also in those of 11 cultivars of kidney bean (Phaseolus vulgaris L.). The activity was detected in soluble and particulate fractions from kidney bean leaves, and the specific activity in both fractions was higher in young premature leaves than in the old in Koshu Shakugosun, a cultivar exhibiting the highest specific activity among kidney bean plants tested. The enzyme was purified 868-fold with a yield of 8.2% from the particulate fractions of leaf homogenate of this cultivar. The purified enzyme showed a single band on native polyacrylamide gel electrophoresis and a native molecular mass of 74 kDa. The enzyme had broad substrate specificity toward classes of glycolipids, phospholipids, and monoacylglycerol, but was inactive to triacylglycerol, indicating that the enzyme belongs to non-specific lipid acyl-hydrolases. Distinct from other lipid acyl-hydrolases previously reported, however, the enzyme showed preferential hydrolysis at sn-1 position of MGDG. Antiserum prepared against the purified enzyme completely inhibited not only the purified enzyme activity but also the activity in the soluble fraction of leaf homogenate. Exposure to ozone, a stress to stimulate endogenous acyl hydrolysis of MGDG, of kidney bean cultivars with different acyl-hydrolase activity resulted in essentially the same changes in leaf lipids of all cultivars.