Exaggerated root respiration accounts for growth retardation in a starchless mutant of Arabidopsis thaliana.
The knock-out mutation of plastidial phosphoglucomutase (pgm) causes a starchless phenotype in Arabidopsis thaliana, and results in a severe growth reduction of plants cultivated under diurnal conditions. It has been speculated that high soluble sugar levels accumulating during the light phase in leaf mesophyll might cause a reduction of photosynthetic activity or that shortage of reduced carbon during the night is the reason for the slow biomass gain of pgm. Separate simultaneous measurements of leaf net photosynthesis and root respiration demonstrate that photosynthetic activity per unit fresh weight is not reduced in pgm, whereas root respiration is strongly elevated. Comparison with a mutant defective in the dominating vacuolar invertase (AtβFruct4) revealed that high sucrose concentration in the cytosol, but not in the vacuole, of leaf cells is responsible for elevated assimilate transport to the root. Increased sugar supply to the root, as observed in pgm mutants, forces substantial respiratory losses. Because root respiration accounts for 80% of total plant respiration under long-day conditions, this gives rise to retarded biomass formation. In contrast, reduced vacuolar invertase activity leads to reduced net photosynthesis in the shoot and lowered root respiration, and affords an increased root/shoot ratio. The results demonstrate that roots have very limited capacity for carbon storage but exert rigid control of supply for their maintenance metabolism.
['Brauner|Katrin|K|', 'Hörmiller|Imke|I|', 'Nägele|Thomas|T|', 'Heyer|Arnd G|AG|']
D017360:Arabidopsis D029681:Arabidopsis Proteins D001692:Biological Transport D018533:Biomass D050260:Carbohydrate Metabolism D002245:Carbon Dioxide D019069:Cell Respiration D002940:Circadian Rhythm D055786:Gene Knockout Techniques D018527:Hydroponics D008027:Light D009154:Mutation D010733:Phosphoglucomutase D017440:Photoperiod D010788:Photosynthesis D018515:Plant Leaves D018517:Plant Roots D018520:Plant Shoots D018087:Plastids D013213:Starch D043324:beta-Fructofuranosidase
root respiration Arabidopsis thaliana assimilate transport root/shoot ratio carbohydrate compartmentation phosphoglucomutase mutant sink source relation