Enhancement by gibberellic acid and asymmetric distribution of lysophospholipase in germinating barley

Abstract

Germination of whole barley seeds for 4 and 6 days followed by measurement of lysophospholipase (lysolecithin acyl hydrolase, LAH) in the embryo-containing and embryo-free halves revealed a gradient of activity between the two halves of the seed. Most of the activity appeared in the embryo-containing half. This gradient decreased slightly in the aleurone and dramatically in the starchy endosperm during the 2 day germination interval. Embryo-containing and embryo-free half seeds of surface sterilized barley were placed separately on sterile agar plates. After 4 and 6 days LAH was observed in both the aleurone and starchy endosperm of the embryo-containing halves. In the embryo-free halves, LAH appeared at low levels in the aleurone and was virtually absent in the starchy endosperm. The scutellum of germinating seeds contains LAH activity. Exposure of embryo-free half seeds to GA 3 for 24 hr showed enhancement of acidic and alkaline LAH activities in the aleurone fraction and in the GA 3-medium in which the half seeds were treated. The LAH activity of the starchy endosperm of these half seeds was little changed by GA 3 treatment. Exposure of isolated aleurones to GA 3 for 24 hr resulted in substantial enhancement of acidic and alkaline LAH activities in the bathing medium and in fractions prepared from the aleurone. The physiological significance of the influence of GA 3 on LAH activity during barley germination is discussed.