Shining
the light on shade responses in arabidopsis
One of the current buzz-words in biology is
‘systems’. Behind this term lies an approach that many of us have espoused for
a long time. We may study molecular or cellular aspects of biology in isolation
but there must be a realization that these events are integrated into
regulatory and developmental networks that contribute to the life of the whole
organism. This is nicely illustrated by the work of
Cookson and Granier (Montpellier, France, pp. 443–452) on the
development of rosette leaves in
Arabidopsis
thaliana (ecotype Landsberg
erecta).
Seedlings were kept in either fully lighted or shaded conditions with all other
conditions being identical. The authors then compared the initiation, growth
and development of the rosette leaves and the time to bolting under the two
conditions. The effects of the shading were seen at several levels. First,
leaves were initiated less frequently in shaded than in well-lit plants, an
effect that goes right back to the dynamics of the apical meristem. Secondly,
the phase of rosette leaf initiation was shorter and this was associated with
the timing of the floral transition in the apical meristem, which occurred 3
days earlier in shaded than in fully illuminated plants. Further, those rosette
leaves that were formed in shaded plants had significantly less area than those
of the fully illuminated plants. This was caused by a reduction in the rates of
both cell division and cell expansion, which were only partly compensated for
by increases in duration of both these phases. These effects on rosette leaf
number and on the area of individual rosette leaves also dramatically reduced
carbon gain via photosynthesis, the absolute of rate of which was already
reduced by the shade treatment. One wonders how much this factor contributed to
the signalling network in this set of responses.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
