Soluble and particulate lysophospholipase in the aleurone and endosperm of germinating barley

Lysophospholipase was measured in extracts of germinating barley by determining the amount of free [¹⁴C]palmitate released from [1-¹⁴C] 1-palmitoyl-lysophosphatidylcholine (LPC). Soluble and particulate lysophospholipase activity was measured at 1-day intervals in extracts from the aleurone and endosperm of barley seeds germinated for 8 days. The soluble and particulate activities of the aleurone increase approximately in parallel with one another and after 8 days of germination have 20–30 times more activity than at day 1. The activity profiles and the distribution of the activity between the soluble and particulate forms of lysophospholipase in the endosperm are markedly different. With the exception of the first 2 days when the aleurone activity is low, the endosperm activity is less than that associated with the aleurone. The soluble activity increases during the first 3 days and is more active than that of the aleurone. Thereafter it diminishes and remains low. The particulate enzyme, however, increases dramatically between days 4 and 5 and remains moderately high. The fourth and fifth day represent that stage of germination when starch-bound LPC is released in concert with the increase in amylase activity. It is proposed that it is this particulate form of the endosperm activity which may be responsible for maintaining the level of free LPC low in the endosperm of the germinating seed.