Contact:
Dr Nikolaus Wellner
T: +44 (0)1603 255012
E: wellner@ifr.ac.uk

Sucrose synthase mutants

Effects of localised gene knockouts on the cell wall biosynthesis in Arabidopsis

To examine the routes of sucrose catabolism in Arabidopsis, we investigated mutant plants prepared by or Alison Smith at JIC that lack one of the two classes of sucrose-degrading enzymes, sucrose synthase, in all cell types except the phloem. Surprisingly, these plants are normal with respect to starch and sugar content, seed weight and lipid content, and cellulose content. The results reveal the extreme plasticity of primary carbohydrate metabolism in Arabidopsis, in contrast to the situation in the storage organs of crop plants.

Primary cell walls of leaves of the quadruple mutant retained lamellar and fibrillar structure and were indistinguishable by SEM from those of wild-type plants. The stem xylem was also indistinguishable in cross section from that of wild-type plants, indicating that secondary cell wall synthesis is not seriously disrupted. Mutants deficient in cellulose and other components of the secondary cell wall display a collapsed xylem phenotype. FTIR microspectroscopy on wall preparations of roots of seedlings revealed no major differences in the carbohydrate region of the spectrum between quadruple mutant and wild-type plants. The ratio of absorbances at 1056 and 1100 cm-1 can be used as a measure of the pectin to cellulose ratio of cell wall material. This ratio was 0.72 ± 0.02 and 0.68 ± 0.02 for preparations of cell walls from roots of wild-type and quadruple mutant seedlings respectively, indicating that cell wall composition is not radically altered in the quadruple mutant (mean ± SD from 20 scans of preparations of roots from 40 five-day-old seedlings grown on agarose; very similar results were obtained from a further, independent experiment). To check the distribution of cellulose in primary and secondary walls, we used FTIR array microscopy on stem sections. At a wavelength at which the IR spectrum of plant cell walls is dominated by cellulose, there was no difference between quadruple mutant and wild-type plants in the vasculature and surrounding regions. This was confirmed by chemical measurements of cellulose in cell wall fractions from stems which showed that the cellulose contents of quadruple mutant and wild-type plants were the same.

Further details can be found in:

D.H.P. Barratt, P. Derbyshire, K. Findlay, M. Pike, N. Wellner, J. Lunn, R. Feil, C. Simpson, A.J. Maule & A.M. Smith, Normal growth of Arabidopsis requires cytosolic invertase but not sucrose synthase, PNAS 2009, 106, 13124-13129.