and the perennial habit. It had long been specu-
lated that starch stored in roots and stolons of
perennial legumes provides an important source
of carbon for their regrowth after dormancy or
cutting back. However, attempts to test this idea
experimentally had led to contradictory conclu-
sions (Vriet et al. 2013 ). By comparing wild-type
and starchless mutant plants of L. japonicus,
Vriet et al. ( 2013 ) showed unambiguously that
under at least some growth conditions, starch
storage in roots is essential for regrowth fol-
lowing removal of all shoots. A survey of root
starch content and the response to cutting back in
24 species ofLotussimilarly revealed a general
correlation between vigorous regrowth and root
starch content. Furthermore, species with high
root starch and vigorous regrowth were mostly
perennials, while species with little root starch
and poor regrowth were mostly annuals. Thus,
although the capacity to store starch in roots is
unlikely to be a primary determinant of the
perennial habit, it may well confer advantages on
perennial species subject to grazing and/or winter
dormancy (Vriet et al. 2013 ).
10.7 Conclusions:Lotus japonicus
Resources Provide New
Insights into the Relationship
Between Growth, and Starch
and Sucrose Metabolism
The collection ofL. japonicusmutants defective
in starch and sucrose metabolism is one of the
most extensive available, arguably second only
to Arabidopsis. While comparative genomic
analysis reveals that the components of pathways
of starch and sucrose metabolism are largely
conserved betweenL. japonicusandArabidopsis
(Table10.1), mutant analyses show that their
importance for plant growth and development
differs substantially between the two species. At
least, part of these differences may be attributed
to the fact thatArabidopsisis an annual, whereas
L. japonicus is a perennial. For example, in
contrast toArabidopsis, loss of starch has little
consequence for normal growth inL. japonicus.
However, starch stored in the roots is important
for regrowth following cutting back in this
perennial plant. The substantial accumulation of
starch in plants approachingflowering also sug-
gests that stored starch may be important for
continued vegetative growth post-flowering
under at least some conditions. The genetic
resources available inL. japonicus have also
given new insights into the way in which carbon
is supplied for nitrogenfixation and subsequent
ammonia assimilation in root nodules. The
resources may well prove to be of great impor-
tance in understanding the engineering of carbon
storage and partitioning that will be required in
the future to enable non-leguminous crop plants
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