Amylopectin-like Starch is Present in the Cell Walls of Kiwifruit Pericarp Tissues during Development

The contents of cell wall polysaccharides in pericarp tissues of immature Hayward kiwifruit were determined during development. Two methods employed to remove starch from the crude cell wall preparations were enzymatic digestion (porcine pancreatic α-amylase and Pseudomonas iso-amylase, Method 1) and dimethyl sulfoxide extraction (DMSO, Method 2). Method 2 was more effective in removing starch than Method 1. After extensive removal of starch, cell wall materials were successively extracted with 50 mM EDTA, followed by 4% and 24% KOH. The hot EDTAsoluble (pectic) and alkaline-soluble (hemicellulosic I and -II) polysaccharides were further treated with enzymatic digestion. In subsequent amylase digestions of fractions derived from cell walls previously subjected to the two methods the glucose content was further depleted by 28-77% (Method 1) and 85-91% (Method 2) in the pectin fraction, and 51- 86% (Method 1) and 45-91% (Method 2) in the hemicellulose fractions, suggesting starch in the crude cell walls was not released by initial enzymatic treatment or DMSO extraction. Moreover, the crude cell walls yielded α-amylase activity upon extraction by 1 M NaCl, further suggesting that starch is present in the cell walls. Methylation analysis of the starch fraction revealed a molar ratio of 0.2∼0.6:3.8∼11.6:1 for T-Glc, 4-Glc and 4,6-Glc. The red-violet starch-iodine complex had an absorption maximum of 550∼565 nm. These results provide evidence for an amylopectin-type starch present in the cell walls of immature kiwifruit.