Differential activation of stilbene synthesis in different
sylvestris chemovars
We wondered, whether the pathway responsible for aluminium-induced
activation of phytoalexin synthesis is active in planta . In our
previous work (Duan et al. , 2015), we could characterise two
chemovars in the Wild European Grape (V. sylvestris ) that
differed with respect to stilbene inducibility (triggered by UV light)
correlated with respective differences in the steady-state transcript
levels of RS and STS (Duan et al. , 2015), as well
as for transcript levels of their activator MYB14 (Duan et
al. , 2016). We selected two genotypes representing those
chemovars: The V. vinifera variety ‘Augster Weiss’ was selected
as representative for the low stilbene chemovar, while the V.
sylvestris genotype ‘Hö29’ belonged to the high-stilbene chemovar.
First, we tested, whether induction by aluminium would reproduce the
differences in transcript levels seen in the past for UV-C as trigger.
This was indeed the case (Figure 7A ): both, the transcripts forMYB14 as well as those for RS were induced more vigorously
in Hö29 as compared to Augster Weiss. For MYB14 , this difference
appeared earlier (highly significant from 30 min after application of
aluminium) as compared to RS (highly significant only at 60 min
after application of aluminium). We asked next, whether these
differences in transcript levels would lead to a corresponding
difference in the accumulation of the active stilbenetrans -resveratrol. We determined the trans -resveratrol
content by HPLC 24 h after treatment with aluminium, and found that Hö29
accumulated more than twice of trans -resveratrol as compared to
Augster Weiss (Figure 7B ). Since the induction of
phytoalexins-synthesis related transcripts by aluminium had been found
to depend on activation of RboH (Figure 3 ), we wondered,
whether footprints of this oxidative burst could be detected in real
plant tissues. Since reactive oxygen species will react, among other
targets, with membrane lipids, an oxidative burst should lead to a
transient increase of lipoxygenation, which can be detected through
measuring the abundance of malone dialdehyde (MDA). In fact, we were
able to detect a rapid (from 15 min after addition of aluminium), and
transient (dissipating from 45 min after addition aluminium) increase of
MDA levels by around 30% in Hö29, while in Augster Weiss, the MDA
levels did not show any increase (Figure 7C ). Thus, aluminium
triggers, in the two chemovar representatives, a differential response
of MDA (indicative of oxidative burst), transcripts for the stilbene
regulator MYB14 , the phytoalexin synthesis gene RS , and
eventually, accumulation of the active stilbenetrans -resveratrol.