Carbon transitions from either Calvin cycle or transitory starch to heteroglycans as revealed by 14C‐labeling experiments using protoplasts from Arabidopsis. Issue 1 (25th March 2013)

• Record Type: Journal Article
• Authors: Malinova, Irina; Steup, Martin; Fettke, Joerg
• Is Part Of: Physiologia plantarum. Volume 149:Issue 1(2013:Sep.)
• Page Start: 25
• Page End: 44
• Publication Date: 2013-03-25
• Subjects: Plant physiology -- Periodicals; 571.2
• DOI: 10.1111/ppl.12033
• Languages: English
• ISSNs: 0031-9317

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>Plants metabolize transitory starch by precisely coordinated plastidial and cytosolic processes. The latter appear to include the action of water‐soluble heteroglycans (SHG<sub>in</sub>) whose monosaccharide pattern is similar to that of apoplastic glycans (SHG<sub>ex</sub>) but, unlike SHG<sub>ex</sub>, SHG<sub>in</sub> strongly interacts with glucosyl transferases. In this study, we analyzed starch metabolism using mesophyll protoplasts from wild‐type plants and two knock‐out mutants [deficient in the cytosolic transglucosidase, disproportionating isoenzyme 2 (DPE2) or the plastidial phosphoglucomutase (PGM1)] from <italic>Arabidopsis thaliana</italic>. Protoplasts prelabeled by photosynthetic <sup>14</sup>CO<sub>2</sub> fixation were transferred to an unlabeled medium and were darkened or illuminated. Carbon transitions from the Calvin cycle or from starch to both SHG<sub>in</sub> and SHG<sub>ex</sub> were analyzed. In illuminated protoplasts, starch turn‐over was undetectable but darkened protoplasts continuously degraded starch. During illumination, neither the total <sup>14</sup>C content nor the labeling patterns of the sugar residues of SHG<sub>in</sub> were significantly altered but both the total amount and the labeling of the constituents of SHG<sub>ex</sub> increased with time. In darkened protoplasts, the <sup>14</sup>C‐content of most of the sugar residues of SHG<sub>in</sub> transiently and strongly increased and then declined. This effect was not observed in any SHG<sub>ex</sub> constituent. In darkened DPE2‐deficient protoplasts, none of the SHG<sub>in</sub> constituents exhibited an essential transient increase in labeling. In contrast, some residues of SHG<sub>in</sub> from the PGM1 mutant exhibited a transient increase in label but this effect significantly differed from that of the wild type. Two conclusions are reached: first, SHG<sub>in</sub> and SHG<sub>ex</sub> exert different metabolic functions and second, SHG<sub>in</sub> is directly involved in starch degradation.</p> </abstract>