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induces the flowering of L. paucicostata plants. A weak flowering response was
detected after 2 weeks of stress treatment in strains 151 and 6746, and an apparent
flowering response was detected after 3 weeks of stress treatment in all of the
strains.
7.2 PAL-Inhibitor Inhibition of the Flowering Induced
by Poor Nutrition
SA has long been implicated in the regulation of flowering in Lemna spp. How-
ever, the current supporting evidence merely shows that exogenously applied SA
can induce flowering. Therefore, we attempted to reduce the endogenous SA level
by inhibiting its biosynthesis to ascertain whether this effect inhibits flowering.
Strain 6746, which is highly sensitive to poor-nutrition stress, was cultured in tap
water under LD conditions to induce flowering, and PAL inhibitors were added to
the tap water to examine their effects on poor-nutrition stress-induced flowering.
The flowering was completely inhibited with AOA at 10
-5
M and AOPP at
10
-4
M (Shimakawa et al.
2012
). The number of fronds per flask was decreased
with AOA at 10
-5
M, whereas the multiplication of fronds was not suppressed
with AOPP at 10
-4
M.
7.3 Endogenous SA Contents
Strain 6746 was cultured in tap water for 3 weeks to induce flowering, and SA was
extracted from the fronds for quantification using LC-MS. Significantly higher
amounts of SA were detected in fronds that flowered under the poor-nutrition
conditions when compared with the vegetative fronds cultured under nutrient
conditions (Shimakawa et al.
2012
). This is the first evidence showing that the SA
content increases when flowering is induced in Lemnaceous species.
7.4 Promotion of Flowering by Exogenously Applied SA
Strain 6746 was cultured in tap water containing SA and grown under non-
inductive LD conditions for 3 weeks. The addition of SA at 3 9 10
-5
M promoted
flowering (Shimakawa et al.
2012
). Taken together, the results suggest that
endogenous SA plays a role in the promotion of stress-induced flowering. Cleland
and his colleagues previously observed that SA induces flowering in many Lem-
naceous species in the study regarding photoperiodic flowering. It is now apparent
that SA regulates stress-induced flowering but not photoperiodic flowering.
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