TY  - JOUR
A1  - Fettke, Jörg
A1  - Malinova, Irina
A1  - Albrecht, Tanja
A1  - Hejazi, Mahdi
A1  - Steup, Martin
T1  - Glucose-1-Phosphate transport into protoplasts and chloroplasts from leaves of arabidopsis
JF  - Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants
N2  - Almost all glucosyl transfer reactions rely on glucose-1-phosphate (Glc-1-P) that either immediately acts as glucosyl donor or as substrate for the synthesis of the more widely used Glc dinucleotides, ADPglucose or UDPglucose. In this communication, we have analyzed two Glc-1-P-related processes: the carbon flux from externally supplied Glc-1-P to starch by either mesophyll protoplasts or intact chloroplasts from Arabidopsis (Arabidopsis thaliana). When intact protoplasts or chloroplasts are incubated with [U-C-14]Glc-1-P, starch is rapidly labeled. Incorporation into starch is unaffected by the addition of unlabeled Glc-6-P or Glc, indicating a selective flux from Glc-1-P to starch. However, illuminated protoplasts incorporate less C-14 into starch when unlabeled bicarbonate is supplied in addition to the C-14-labeled Glc-1-P. Mesophyll protoplasts incubated with [U-C-14] Glc-1-P incorporate C-14 into the plastidial pool of adenosine diphosphoglucose. Protoplasts prepared from leaves of mutants of Arabidopsis that lack either the plastidial phosphorylase or the phosphoglucomutase isozyme incorporate C-14 derived from external Glc-1-P into starch, but incorporation into starch is insignificant when protoplasts from a mutant possessing a highly reduced ADPglucose pyrophosphorylase activity are studied. Thus, the path of assimilatory starch biosynthesis initiated by extraplastidial Glc-1-P leads to the plastidial pool of adenosine diphosphoglucose, and at this intermediate it is fused with the Calvin cycle-driven route. Mutants lacking the plastidial phosphoglucomutase contain a small yet significant amount of transitory starch.
Y1  - 2011
U6  - https://doi.org/10.1104/pp.110.168716
SN  - 0032-0889
VL  - 155
IS  - 4
SP  - 1723
EP  - 1734
PB  - American Society of Plant Physiologists
CY  - Rockville
ER  - 
TY  - JOUR
A1  - Malinova, Irina
A1  - Steup, Martin
A1  - Fettke, Jörg
T1  - Starch-related cytosolic heteroglycans in roots from Arabidopsis thaliana
JF  - Journal of plant physiology : biochemistry, physiology, molecular biology and biotechnology of plants
N2  - Both photoautotrophic and heterotrophic plant cells are capable of accumulating starch inside the plastid. However, depending on the metabolic state of the respective cell the starch-related carbon fluxes are different. The vast majority of the transitory starch biosynthesis relies on the hexose phosphate pools derived from the reductive pentose phosphate cycle and, therefore, is restricted to ongoing photosynthesis. Transitory starch is usually degraded in the subsequent dark period and mainly results in the formation of neutral sugars, such as glucose and maltose, that both are exported into the cytosol. The cytosolic metabolism of the two carbohydrates includes reversible glucosyl transfer reactions to a heteroglycan that are mediated by two glucosyl transferases. DPE2 and PHS2 (or, in all other species, Pho2).
 In heterotrophic cells, accumulation of starch mostly depends on the long distance transport of reduced carbon compounds from source to sink organs and, therefore, includes as an essential step the import of carbohydrates from the cytosol into the starch forming plastids.
 In this communication, we focus on starch metabolism in heterotrophic tissues from Arabidopsis thaliana wild type plants (and in various starch-related mutants as well). By using hydroponically grown A. thaliana plants, we were able to analyse starch-related biochemical processes in leaves and roots from the same plants. Within the roots we determined starch levels and the morphology of native starch granules. Cytosolic and apoplastic heteroglycans were analysed in roots and compared with those from leaves of the same plants. A. thaliana mutants lacking functional enzymes either inside the plastid (such as phosphoglucomutase) or in the cytosol (disproportionating isoenzyme 2 or the phosphorylase isozyme, PHS2) were included in this study. In roots and leaves from the three mutants (and from the respective wild type organ as well), starch and heteroglycans as well as enzyme patterns were analysed.
KW  - Cytosolic heteroglycans
KW  - Cytosolic glucosyl transferases
KW  - Photoautotrophic tissues
KW  - Heterotrophic tissues
KW  - Starch metabolism
Y1  - 2011
U6  - https://doi.org/10.1016/j.jplph.2010.12.008
SN  - 0176-1617
VL  - 168
IS  - 12
SP  - 1406
EP  - 1414
PB  - Elsevier
CY  - Jena
ER  -