Sucrose-Controlled Transport and Turnover of -Amylase in Rice (Oryza sativa L.) Cells

Abstract

We studied the sucrose-controlled intracellular transport and turnover of α-amylase molecules in suspension-cultured cells of rice (Oryza sativa L.) employing pulse labeling techniques with [35S] amino acids. The secretion of two classes of α-amylase isoforms, α-amylase I-1 (encoded by RAmy1A) and II-4 (encoded by RAmy3D) was differentially controlled by sucrose. In rice cells labeled with [35S] amino acids under different sucrose-supplemented conditions, sucrose preferentially prevented the extracellular liberation of [35S]-labeled α-amylase II-4 molecules from rice cells at around 2 mM, whereas the de novo protein synthesis still occurred at this concentration. Pulse-chase experiments showed that sucrose regulates the intracellular transport of [35S]α-amylase II-4 molecules and stimulates the protein turnover. However, cycloheximide, a protein synthesis inhibitor, was induced the extracellular liberation and reduced the turnover of [35S]α-amylase II-4 molecules in the presence of sucrose. These results strongly suggested that newly synthesized sucrose-induced proteins are involved in the posttranslational regulation on sucrose-controlled α-amylase secretion in rice cells.