Cytochemical localization of phosphatase in barley aleurone cells: The pathway of gibberellic-acid-induced enzyme release

Abstract

Acid phosphatase has been localized by cytochemical techniques in aleurone layers of dry barley (Hordeum vulgare L.) grains, in imbibed half-grains and in isolated layers treated with and without gibberellic acid (GA₃). A major fraction of the enzyme activity is located in the cell walls. During imbibition and incubation of layers without GA₃ a steady increase of enzyme activity in the inner wall region indicates a continued release of enzyme into the walls, but there is no essential change in the distribution of wall-enzyme sites. On the other hand, when GA₃ is present enzyme activity is found for the first time in regions of the wall that become digested during GA₃ treatment. These results indicate that the digested wall channels act as preferential routes through which acid phosphatase is released from the aleurone layer. No digested wall channels are formed in the absence of GA₃ and, there being no route for release of the enzyme, it accumulates in the inner regions of the wall around aleurone cells. Assays of enzyme activity in vitro support the conclusions based on the histochemical data. They indicate that release of acid phosphatase from aleurone layers is under strict GA₃ control, but that some of the increase in acid phosphatase activity in the isolated during incubation is not GA₃ dependent. Acid phosphatase is present in the protein matrix of aleurone grains in all stages except the dry grain. Enzyme activity persists in aleurone grains throughout GA₃ treatment when enlargement of the grains and mobilization of reserves takes place. It is suggested that this phosphatase hydrolyses phosphate reserves within the aleurone grains.