Journal Article

Light-Induced Degradation of Starch Granules in Turions of <i>Spirodela polyrhiza</i> Studied by Electron Microscopy

Klaus-J. Appenroth, Aron Keresztes, Ewa Krzysztofowicz and Halina Gabrys

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 52, issue 2, pages 384-391
Published in print February 2011 | ISSN: 0032-0781
Published online January 2011 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq199
Light-Induced Degradation of Starch Granules in Turions of Spirodela polyrhiza Studied by Electron Microscopy

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  • Biochemistry
  • Molecular and Cell Biology
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Spirodela polyrhiza forms turions, starch-storing perennial organs. The light-induced process of starch degradation starts with an erosion of the surface of starch grains. The grain size decreases over a period of red irradiation and the surface becomes rougher. The existence of funnel-shaped erosion structures demonstrates that starch degradation is also possible inside the grains. Neither etioplasts nor clues as to their transition into chloroplasts were found in the storage tissue by transmission electron microscopy. Juvenile chloroplasts always contained the starch grains which remained from amyloplasts. No chloroplasts were found which developed independently of starch grains. Amyloplasts are therefore the only source of chloroplasts in the cells of irradiated turions. The intactness of amyloplast envelope membranes could not be directly proved by electron microscopy. However, the light-induced transition of amyloplasts into chloroplasts provides indirect evidence for the integrity of the envelope membranes throughout the whole process. The starch grains are sequestered from the cytosolic enzymes, and only plastid-localized enzymes, which have access to the starch grains, can carry out starch degradation. In this respect the turion system resembles transitory starch degradation as known from Arabidopsis leaves. On the other hand, with α-amylase playing the dominant role, it resembles the mechanism operating in the endosperm of cereals. Thus, turions appear to possess a unique system of starch degradation in plants combining elements from both known starch-storing systems.

Keywords: Electron microscopy; Spirodela polyrhiza; Starch degradation; Starch grains; Storage starch; Turion

Journal Article.  4765 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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