Properties, synthesis, and accumulation of storage proteins in Pieris rapae L.

Abstract

AbstractTwo kinds of storage proteins (SP‐1, SP‐2) were confirmed in hemolymph and fat body of Pieris rapae during metamorphosis. Both proteins were present in high concentrations in the hemolymph during the last larval instar. Hemolymph concentrations of SP‐1 and SP‐2 dropped after pupation as the proteins were being deposited in fat bodies. SP‐2 is present in a larger amount than SP‐1. Detailed studies on storage proteins determined their properties, mode of synthesis, and accumulation in the fat body.SP‐1 has a molecular weight of 500,000 and consists of one type of subunit (Mr 77,000), while SP‐2 has a molecular weight of 460,000 and is composed of two types of subunits (Mr 80,000 and 69,000). The pl values of SP‐1 and SP‐2 were determined to be 6.97 and 7.06, respectively.Fat body cells from 1‐day‐old fifth instar larvae synthesized storage proteins in large amounts, whereas those from late prepupae exhibited high protein sequestration. Proteins taken up in fat body accumulated in dense granules during the pupal stage but sharply decreased at the adult stage.Morphological changes in the fat body tissues were observed during the larval‐pupal transformation; the nuclei of fat body cells became irregularly shaped, and the boundaries between cells seemed to be obscure. Synthesis, storage, or degradation of storage proteins in fat body during development is closely associated with morphological changes in the tissues.