Tapping into
carbon supply
The developmental
plasticity and capacity for regeneration after damage in plants are things that
botanists tend to take for granted. These features are of course
adaptations to a lifestyle in which running away is
impossible, but nonetheless they are remarkable. One interesting example that
we have discussed previously in these pages is the resprouting ability of
Quercus
crispula seedlings following decapitation. The tap-root acts as a storage
organ and supplies the nutrients to support the outgrowth of previously dormant
buds until the new shoots become photosynthetic. In the present study,
Kabeya
and Sakai, Sendai,
Japan (pp.
479–488) have evaluated the roles of the carbon and nitrogen components of
the stored material in the resprouting process. Prior to clipping the
seedlings, the carbon content of the tap-roots was manipulated by maintaining
seedlings at different light levels (thus influencing photosynthetic carbon
fixation) and N-content was manipulated via nutrient-feeding regimes. These
treatments gave a range of combinations of carbohydrate and N-contents.
Interestingly, the level of light, as well as positively influencing the
carbohydrate content of the tap-roots, also negatively affected the N-content (high
light levels led to lower N-contents). After clipping, it was clear that
resprouting ability was directly correlated with the stored carbohydrate
content of the roots and not with their N-content. Indeed, it was the carbohydrate
content and not the N-content of the tap-root that was depleted during
resprouting. However, there was some influence of N: the mass of the resprouted
shoots was directly correlated with the N-content of the tap-root. In this
situation, then, release from apical dormancy is not on its own enough to
ensure outgrowth of the dormant buds: the available carbohydrate must also be
adequate, presumably to supply energy and carbon skeletons. Only if these needs
are met does N have any influence on the process.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
