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.