Normal growth of Arabidopsis requires cytosolic invertase but not sucrose synthase.
The entry of carbon from sucrose into cellular metabolism in plants can potentially be catalyzed by either sucrose synthase (SUS) or invertase (INV). These 2 routes have different implications for cellular metabolism in general and for the production of key metabolites, including the cell-wall precursor UDPglucose. To examine the importance of these 2 routes of sucrose catabolism in Arabidopsis thaliana (L.), we generated mutant plants that lack 4 of the 6 isoforms of SUS. These mutants (sus1/sus2/sus3/sus4 mutants) lack SUS activity in all cell types except the phloem. Surprisingly, the mutant plants are normal with respect to starch and sugar content, seed weight and lipid content, cellulose content, and cell-wall structure. Plants lacking the remaining 2 isoforms of SUS (sus5/sus6 mutants), which are expressed specifically in the phloem, have reduced amounts of callose in the sieve plates of the sieve elements. To discover whether sucrose catabolism in Arabidopsis requires INVs rather than SUSs, we further generated plants deficient in 2 closely related isoforms of neutral INV predicted to be the main cytosolic forms in the root (cinv1/cinv2 mutants). The mutant plants have severely reduced growth rates. We discuss the implications of these findings for our understanding of carbon supply to the nonphotosynthetic cells of plants.
Barratt
D H Paul
DH
John Innes Centre and Institute of Food Research, Norwich Research Park, Norwich NR4 7UH, United Kingdom.
Derbyshire
Paul
P
Findlay
Kim
K
Pike
Marilyn
M
Wellner
Nikolaus
N
Lunn
John
J
Feil
Regina
R
Simpson
Clare
C
Maule
Andrew J
AJ
Smith
Alison M
AM
D017360:Arabidopsis / Q000201:enzymology / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000502:physiology*; D002482:Cellulose / Q000096:biosynthesis; D003600:Cytosol / Q000201:enzymology; D005964:Glucosyltransferases / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D007527:Isoenzymes / Q000032:analysis; D010641:Phenotype; D043324:beta-Fructofuranosidase / Q000502:physiology*
D029681:Arabidopsis Proteins; D007527:Isoenzymes; D002482:Cellulose; D005964:Glucosyltransferases; C022699:sucrose synthase; D043324:beta-Fructofuranosidase