investigated ratios in the leaves of ND lines at both the 9h and 16h photoperiods were
the same as that in the leaves of SD lines at the 9h photoperiod.
There was the decrease of IAA/ABA ratio, that led to the growth delay and
retracting apical dominance. At the same time, an increase in the GAs/ABA ratio (as
well as the GAs/IAA ratio) is consistent with the fact, that GAs induce flowering via
FT or its paralogue, TSF (Wong et al, 2013). It has been shown that GAs stimulate
phloem loading and can regulate the expression of FT in the leaves (Conti, 2017).
The effect of photoperiodic conditions on level and ratio of phytohormones in
the SAM of soybean E-isolines. Plants are able to integrate all internal and external
cusses in the general floral stimulus, such as FT, that is phloem-borne in the SAM and
affects the transcription of floral integrators (Davis, 2009). At the same time, a certain
hormonal status of SAM, level and ratio of different hormones may indicate their role
as components of this stimulus and / or their participation in the autonomous (age)
regulation of development (Conti, 2017). It can be supposed that similar mechanisms
can occur in ND plants, as well, that allows them to flower in the same time, regardless
of the length of the photoperiod.
Different experimental data argue in favor for a positive role for endogenous ABA
in flowering via potentiation of florigen-like genes in a photoperiodic manner (Cheng
et al. 2002; Kohli et al., 2013 Riboni et al. 2013). But it is still unclear how ABA might
affect photoperiodic signaling. Auxin (IAA) is critical for flowering process too as it
defines the site of flower initiation, controls floral organ growth and patterning as well
as subsequent events determining reproductive fitness (Vanneste et al., 2009).
Therefore, delineating a dynamic of ABA and IAA levels (and their ratio) in the
SAM during photoperiodic induction is an important goal if we are to understand the
role of these hormones in transition to flowering.
The IAA/ABA ratio in the soybean SAM is shown on the Figure 3. This ratio at
the beginning of the experiment was 2-3-fold lower in SAM than that in the leaves of
all soybean lines, but all the same, the content of IAA prevailed over the content of
ABA (Table 2). The further IAA/ABA dynamics was different in various daylength
conditions so as it depends on E genes.
This ratio was significantly decreased in the SAM of all soybean lines under 16-
hour photoperiod during the first week of the experiment, especially in the ND lines –
3-3,5 times (Fig. 3, A). It is explained by a decrease of IAA content in the SAM against
an accumulation of ABA (Tab.2). However, there were differences in the level of
IAA/ABA ratio on 16h photoperiod towards the end of experiment, depending of
dominant E alleles presents.
This ratio was decrease in SAM of the lines carrying E1 and E3 dominant alleles
(Е1е2е3, е1е2еЕ3), whereas the lines carrying e1 and e3 recessive alleles (е1е2е3 and
е1Е2е3) showed the inverse dynamics of this ratio by the 14th day of the experiment
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