Bathellier et al. (2008)
• Substantial evidence has been published in recent years
demonstrating that postphotosynthetic fractionations occur in plants,
leading to 13C-enrichment in heterotrophic (as compared with
autotrophic) organs. However, less is known about the mechanism
responsible for changes in these responses during plant development.
•
The isotopic signature of both organic matter and respired CO2 for
different organs of French bean (Phaseolus vulgaris) was investigated
during early ontogeny, in order to identify the developmental stage at
which isotopic changes occur.
Isotopic analyses of metabolites and mass balance calculations helped to constrain the metabolic processes involved.
•
At the plant scale, apparent respiratory fractionation was constantly
positive in the heterotrophic phase (c. 1‰) and turned negative with
autotrophy acquisition (down to –3.08‰). Initially very close to that
of the dry seed (–26.83 ± 0.69‰), isotopic signatures of organic matter
and respired CO2 diverged (in opposite directions) in leaves and roots
after onset of photosynthesis. Respired CO2 reached values up to –20‰
in leaves and became 13C-depleted down to –29‰ in roots.
• It was
concluded that isotopic differences between organs occurred subsequent
to metabolic changes in the seedling during the transition from
heterotrophy to autotrophy. They were especially related to respiration
and respiratory fractionation.
autotrophy, carbon isotope, dark respiration, discrimination, germination, heterotrophy, Phaseolus
