Intracellular distribution of lipolytic activity in the female gametophyte of germinating Douglas fir seeds.

Acid (pH 5.2) and neutral (pH 7.1) lipase activity was studied in order to localize the sites of lipolysis in cellular fractions of catabolic organ of Douglas fir seed. Cellular particles were separated by differential centrifugation of the tissue homogenate and identified by electron microscopy. Emulsified native neutral lipids were provided as a substrate to protein body, mitochondrial, microsomal and soluble fractions, and endogenous lipids were used as a substrate for light and heavy fat body fractions. Little difference was observed in average specific activity of the two enzyme systems in dry seeds, but acid lipase activity increased sevenfold and neutral lipase activity fourfold during germination. Highest specific activity of both enzyme systems was found to be associated with the heavy fat bodies and the soluble fraction. Heavy fat bodies contained an ample quantity of endogenous substrate while the soluble fraction consisted of little substrate. Experimental data indicated that the soluble fraction was the source of lipases, and the heavy fat bodies were the site of in situ lipolysis.