Planta

, Volume 178, Issue 1, pp 110–122

Reduced-activity mutants of phosphoglucose isomerase in the cytosol and chloroplast of Clarkia xantiana

II. Study of the mechanisms which regulate photosynthate partitioning
  • H. Ekkehard Neuhaus
  • Arthur L. Kruckeberg
  • Regina Feil
  • Mark Stitt
Article

DOI: 10.1007/BF00392534

Cite this article as:
Neuhaus, H.E., Kruckeberg, A.L., Feil, R. et al. Planta (1989) 178: 110. doi:10.1007/BF00392534

Abstract

(i) We have studied the influence of reduced phosphoglucose-isomerase (PGI) activity on photosynthetic carbon metabolism in mutants of Clarkia xantiana Gray (Onagraceae). The mutants had reduced plastid (75% or 50% of wildtype) or reduced cytosolic (64%, 36% or 18% of wildtype) PGI activity. (ii) Reduced plastid PGI had no significant effect on metabolism in low light. In high light, starch synthesis decreased by 50%. There was no corresponding increase of sucrose synthesis. Instead glycerate-3-phosphate, ribulose-1,5-bisphosphate, reduction of QA (the acceptor for photosystem II) and energy-dependent chlorophyll-fluorescence quenching increased, and O2 evolution was inhibited by 25%. (iii) Decreased cytosolic PGI led to lower rates of sucrose synthesis, increased fructose-2,6-bisphosphate, glycerate-3-phosphate and ribulose-1,5-bisphosphate, and a stimulation of starch synthesis, but without a significant inhibition of O2 evolution. Partitioning was most affected in low light, while the metabolite levels changed more at saturating irradiances. (iv) These results provide decisive evidence that fructose-2,6-bisphosphate can mediate a feedback inhibition of sucrose synthesis in response to accumulating hexose phosphates. They also provide evidence that the ensuing stimulation of starch synthesis is due to activation of ADP-glucose pyrophosphorylase by a rising glycerate-3-phosphate: inorganic phosphate ratio, and that this can occur without any loss of photosynthetic rate. However the effectiveness of these mechanisms varies, depending on the conditions. (v) These results are analysed using the approach of Kacser and Burns (1973, Trends Biochem. Sci. 7, 1149–1161) to provide estimates for the elasticities and flux-control coefficient of the cytosolic fructose-1,6-bisphosphatase, and to estimate the gain in the fructose-2,6-bisphosphate regulator cycle during feedback inhibition of sucrose synthesis.

Key words

Clarkia Fructose-2,6-bisphosphate Mutant (phosphoglucose isomerase) Phosphoglucose isomerase Photosynthate partitioning Sucrose synthesis 

Abbreviations and symbols

Chl

chlorophyll

Fru6P

fructose-6-phosphate

Frul,6bisP

fructose-1,6-bisphosphate

Fru-1,6Pase

fructose-1,6-bisphosphatase

Fru2,6bisP

fructose-2,6-bisphosphate

Fru2,6Pase

fructose-2,6-bisphosphatase

Glc6P

glucose-6-phosphate

PGI

phosphoglucose isomerase

Pi

inorganic phosphate

QA

acceptor for photosystem II

Ru1,5bisP

ributose-1,5-bisphosphate

SPS

sucrose-phosphate synthase

Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • H. Ekkehard Neuhaus
    • 1
  • Arthur L. Kruckeberg
    • 2
  • Regina Feil
    • 1
  • Mark Stitt
    • 1
  1. 1.Lehrstuhl für PflanzenphysiologieUniversität BayreuthBayreuthFederal Republic of Germany
  2. 2.Department of GeneticsUniversity of CaliforniaDavisUSA

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