Plant and Cell Physiology Advance Access originally published online on April 8, 2005
Plant and Cell Physiology 2005 46(6):858-869; doi:10.1093/pcp/pci091
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Involvement of 
-Amylase I-1 in Starch Degradation in Rice Chloroplasts
1 Laboratories of Plant and Microbial Genome Control, Graduate School of Science and Technology, Niigata University, Niigata, 950-2181 Japan
2 Department of Applied Biological Chemistry, Niigata University, Niigata, 950-2181 Japan
3 Corresponding author: E-mail, t.mitsui{at}agr.niigata-u.ac.jp; Fax, +81-25-262-6641.
To determine the role of 
-amylase isoform I-1 in the degradation of starch in rice leaf chloroplasts, we generated a series of transgenic rice plants with suppressed expression or overexpression of -amylase I-1. In the lines with suppressed expression of -amylase I-1 at both the mRNA and protein levels, seed germination and seedling growth were markedly delayed in comparison with those in the wild-type plants. However, the growth retardation was overcome by supplementation of sugars. Interestingly, a significant increase of starch accumulation in the young leaf tissues was observed under a sugar-supplemented condition. In contrast, the starch content of leaves was reduced in the plants overexpressing -amylase I-1. In immunocytochemical analysis with specific anti--amylase I-1 antiserum, immuno-gold particles deposited in the chloroplasts and extracellular space in young leaf cells. We further examined the expression and targeting of -amylase I-1 fused with the green fluorescent protein in re-differentiated green cells, and showed that the fluorescence of the expressed fusion protein co-localized with the chlorophyll autofluorescence in the transgenic cells. In addition, mature protein species of -amylase I-1 bearing an oligosaccharide side chain were detected in the isolated chloroplasts. Based on these results, we concluded that -amylase I-1 targets the chloroplasts through the endoplasmic reticulum–Golgi system and plays a significant role in the starch degradation in rice leaves.
(Received December 9, 2004; Accepted March 18, 2005)
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