## 3 Results and Discussion
### Effect of Allicin on Auxin Distribution  
Based on the observation that allicin destroyed the localization of PIN proteins, and because PIN proteins are essential for the directional transport of auxin, the final aim was to investigate whether the aberrant localization of auxin occurred after allicin treatment. Two independent methods based on fluorescent proteins were used to check the localization of allicin. The DR5-GFP reporter system was based on the fact that auxin induced the activity  
Figure 5: Influence of alicin on the localization of PIN1 and PIN3 proteins and on auxin distribution in the root tip. (**A**) While the localization of PIN1 in the control was restricted to the central cylinder, a diffuse localization of PIN1 is seen in (**B**) alicin-exposed plants. (**C**) The localization of PIN3 in the control is seen in the central cylinder and in the meristematic zone of the root tip, but under allicin exposure (**D**) the localization of PIN 3 protein was also diffuse. This was also reflected in the localization of auxin. In control plants, where GFP expression was under the auxin-responsive DR5 promoter, a typical distribution of auxin is seen in the root tip, meristematic and quiescent zone (**E**), whereas this clear localization was abolished under allicin exposure (**F**). The detection of auxin distribution in the root by means of DII-VENUS indicated in a complementary way that no auxin was present where the fluorescent protein was observed, because auxin led to the degradation of the protein. Accordingly, in the control (**G**), fluorescence is seen in the marginal areas of the root, but not in the meristematic and quiescent zone, whereas under allicin exposure, fluorescence is observed everywhere in the cells (**H**). All treated samples were exposed to 2 mM alicin for 24 h.  
of the DR5 promoter and thus drove GFP expression. GFP fluorescence thus indexed the presence of auxin.  
Untreated _Arabidopsis thaliana_ roots showed a clear localization of auxin around the quiescent zone of the root apical meristem, in the central cylinder and in the epidermal layers of the root (Figure 5E). Treatment with allicin resulted in the localization of GFP fluorescence being restricted to the root apex; auxin-dependent expression of GFP was no longer found in the quiescent and division zone of the root apex (Figure 5F). This showed that allicin caused a clear redistribution of auxin localization at the root tip.  
As an alternative method to detect the localization of auxin at the tissue level, the DII-VENUS construct was used, in which a \"fast maturing\" form of yellow-fluorescent protein (YFP) was expressed in frame with an IAA protein under the control of a constitutive promoter. Because IAA proteins are degraded in the presence of auxin, a lack of fluorescence of the VENUS protein would indicate a high concentration of auxin, whereas a strong fluorescence of the protein would indicate a low concentration of auxin. The results obtained by means of DII-VENUS corresponded to the statements we also perceived with DR5-GFP. While the control showed that auxin was present in the root meristem area, the distribution was diffuse after allicin exposure (Figure 5G).