expression in the apex (Vanneste et al, 2009). In SD soybean (Glycine max) indole-3-
acetic acid (IAA) was shown to accumulate in the SAM during a short photoperiod,
which is associated with an activation of GmAP1 gene involved in floral primordia
formation (Wong CE. et al., 2013). Abscisic acid (ABA) is mostly described as an
inhibitor of flowering processes because in LD plants (incl. Arabidopsis) ABA
specifically binds to FCA (Flowering time control protein A) that leads to late
flowering (Razem et al., 2006). However, some SD plants accumulate ABA in the
shoot apex during inductive conditions that affects the activity of ABA-sensitive genes
and their transcripts responsible for a floral morphogenesis and flower development
(Wong CE. et al., 2009).
We have previously shown that soybean lines isogenic for E loci accumulated
ABA in the leaves and especially in the shoot apexes during a short-day condition
regardless their genotype (Yukhno et al., 2016). At the same time, we still poorly
understand a role of photoperiodic control genes in a hormonal regulation of the
transition of plants to flowering. The E genes are a series of loci with two alleles at
each locus identified in soybean. They determine a sensitivity to photoperiod,
flowering time, late or early maturity etc. Nearly isogenic lines of soybean may be used
to study effects of E genes for they have no significant differences in the genotype
(Mao et al., 2017), except for allelic versions at the E loci – dominant and/or recessive
(Wang Y., 2008).
Some E genes participate in both signaling pathways of flowering initiation,
growth process regulation and the transition to flowering by interacting with plant
hormonal networks (Abe et al., 2003; Price, 2012). Based on the foregoing analysis,
the purpose of the research was to study a relationship between the alleles
(dominant/recessive) of the E genes and the contents of plant hormones (IAA, ABA,
GA) as well as their ratio in the leaves and shoot apical meristems of isogenic soybean
lines under different daylength condition (photoperiod).
Plant materials used in this research were soybean lines of Clark cultivar isogenic
for E genes (Glycine max (L.) Merr.), which were kindly provided by National Centre
for Plant Genetic Resources of Ukraine. These lines differ in a photoperiodic
sensitivity, which depends on allelic versions of E genes (E1/е1, E2/е2 and E3/е3),
whereas the genotype of Clark cultivar is common for all these lines. Soybean lines
were grown under field conditions during growing seasons of 2010-2012 years.
Planting trials were carried out manually within the optimal planting dates for soybean
in Eastern Ukraine. Experimental plant groups were artificially darkened at 5 node
stage (the third true leaf stage) reducing the daylength to 9 hours by means of the
opaque boxes. Control plant groups were grown under a long photoperiod (about 16
hours at the latitude of Kharkiv) during the experiment. The contents of gibberellins
(GAs), auxins (IAA) and abscisic acid (ABA) were measured in fixed dry plant
materials. The second leaf and SAM were collected and fixed at the beginning of the
experiment (long day conditions for all lines), and on the 7th and 14th days after
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