Outlook: From the cell culture to the vineyard – routes towards application.
The induction of oxidative burst (Figure 7C ), transcripts for MYB14 and RS (Figure 7A ), and accumulation of the bioactive phytoalexin, trans -resveratrol (Figure 7B ) by Al3+ in leaf discs of grapevine indicates that the signalling chain discussed above is active not only in suspension cells but in planta as well. Even genotype-dependent differences in the response amplitude between the more responsive sylvestrisgenotype Hö29 and the less responsive vinifera genotype Augster Weiss seen in earlier studies (Duan et al. , 2015; 2016) are preserved. The differences seen on the level of phytoalexins synthesis transcripts (RS ) or the specific transcription factor triggering these genes (MYB14 ) are preceded by corresponding differences in the abundance of MDA. This indicates that the differential response of the two genotypes, which is also seen for UVC or the Oomycete pathogenPlasmopara viticola (Duan et al. , 2015) is caused far upstream, possibly at the abundance or activation of RboH. Our findings also opens a new interpretation for the mode of action of Al-based compounds acting against Oomycete pathogens (Dercks & Buchenauer, 1987). Rather than acting through interfering with the pathogen itself, such compounds might act to stimulate or prime the immunity of the host. Especially for P. viticola, the causative agent of Downy Mildew of Grapevine, this would open new avenues for plant protection. Rather than the need to rely on the very short time window, where the infecting zoospore still has not entered the stoma (leading to the excessive fungicide load characteristic for viticulture), a prophylactic treatment would be feasible, where the host, rather the pathogen is addressed.